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1Back to top Go down    Front brakes pulsating on Sat Sep 15, 2018 7:25 pm

TIV

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Hi all.
I have had this rather annoying problem on my K75RT all the time Iíve had it. Front brakes are OK when brake pads are brand new. After a short time, maybe 1 or 2000 km, they begin to pulsate when applied. Worst at relatively low speed and when not braking hard. I seem to remember having heard that this problem is fairly common on these bikes. Anyone found a way to cure this?


__________________________________________________
1936 Harley Davidsson 750 (sold), 1964 BMW R69S (sold), 1973 Suzuki RM400 (sold), 1972 Triumph Bonneville (sold), 1971 BSA Thunderbolt (sold), 1972 BSA Lightning (sold), 1977 Yamaha XS650 (sold), 1971, BMW R75/5 (sold), 1973 BMW R75/6 (sold), 1984 BMW R100RT 1992 Yamaha FJ1200 ABS (sold), 1990 Harley Davidson Electra Glide (sold)
1990 BMW K75RT Ex-Police (owned now)
2004 BMW R1150RT iABS (owned now)

Cheers TIV
    

2Back to top Go down    Re: Front brakes pulsating on Sat Sep 15, 2018 8:46 pm

RicK G

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VIP
I had a similar problem on the K100 and ended up replacing the calipers because the alloy had worn where the caliper fitted.† It fixed the problem but to me it just didn't make sense as to why it would stop the pulsating because I would expect that the pads would be pulled up against the caliper when the pressure was applied and then should not be able to pulse but it worked.


__________________________________________________
"Every normal man must be tempted, at times, to spit upon his hands, hoist the black flag, and begin slitting throats."† from Mencken's 1919 Prejudices

Bikes 1993 K1100 LT, 1998 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 for now
    

3Back to top Go down    Re: Front brakes pulsating on Sat Sep 15, 2018 8:52 pm

yamaguzzi

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@TIV wrote:Hi all.
I have had this rather annoying problem on my K75RT all the time Iíve had it. Front brakes are OK when brake pads are brand new. After a short time, maybe 1 or 2000 km, they begin to pulsate when applied. Worst at relatively low speed and when not braking hard. I seem to remember having heard that this problem is fairly common on these bikes. Anyone found a way to cure this?
My 1988 K100rs does the same .I replaced the pads,put on new steel braided lines cleaned everything well,did a proper bleed and they are worse than ever.I replaced the fork seals at the same time so I went back and realigned the tubes so the axle just slides thru both legs with no interference .It did this ever so slightly before I did the brakes and† seals now it's terrible.Tomorrow or the next day I am going to rebuild the master.I have a new rebuild BMW kit to use.I'm thinking it might be something in there causing the pressure to be unstable .Going to try another bleed first but I think it's in the master for some unknown reason.Just a gut feeling .Like you,when I brake real hard it's fine but stopping normally it terrible and the brake lever action isn't as smooth as I feel it should be.It's kind of jerky which is making me suspect the master


__________________________________________________
1988 K 100RS ,1975 Moto Guzzi 850-T , 1971 BMW R60/5 , 1971 Yamaha R5B,1969 Yamaha DS6C ,1966 Yamaha YM1 , 1965 Yamaha YDS3
https://facebkfugitive.blogspot.com/
    

4Back to top Go down    Re: Front brakes pulsating on Sat Sep 15, 2018 9:08 pm

TIV

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Me to. I have done everything I can think of to eliminate this, but in vain. Overhauled and cleaned the calipers. New pads, steel braided lines, new master cylender, bleed the brakes once a year. Aligned the the tubes, the axle slides in and out with a push of a finger, just like you did. My brake lever does not feel jerky though, I canít feel the pulsing in the lever.
My 1988 K100rs does the same.........


__________________________________________________
1936 Harley Davidsson 750 (sold), 1964 BMW R69S (sold), 1973 Suzuki RM400 (sold), 1972 Triumph Bonneville (sold), 1971 BSA Thunderbolt (sold), 1972 BSA Lightning (sold), 1977 Yamaha XS650 (sold), 1971, BMW R75/5 (sold), 1973 BMW R75/6 (sold), 1984 BMW R100RT 1992 Yamaha FJ1200 ABS (sold), 1990 Harley Davidson Electra Glide (sold)
1990 BMW K75RT Ex-Police (owned now)
2004 BMW R1150RT iABS (owned now)

Cheers TIV
    

5Back to top Go down    Re: Front brakes pulsating on Sat Sep 15, 2018 9:34 pm

yamaguzzi

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I'll let you know how mine turns out after I rebuild the master.I plan on taking the bike on a 2000 mile trip the end of next week for 2 and a half weeks so I'm motivated to solve this mystery.Either way,I'm going.The bike stops so it's not a a reason to ride something else.Could take 'ol faithfull my 75 Moto Guzzi† but I really want to ride the K some more and get the feel for it traveling.


__________________________________________________
1988 K 100RS ,1975 Moto Guzzi 850-T , 1971 BMW R60/5 , 1971 Yamaha R5B,1969 Yamaha DS6C ,1966 Yamaha YM1 , 1965 Yamaha YDS3
https://facebkfugitive.blogspot.com/
    

6Back to top Go down    Re: Front brakes pulsating on Sat Sep 15, 2018 9:37 pm

MarcS

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Yep mine has the same problem. I have replaced everything except the calipers (no rebuild either, just a clean out). I even went as far as to sand the new disks that I have just installed in case I had† contaminated them some how. It will be interesting to see what the collective brain comes up with.


__________________________________________________
K100rt ex plod bike 5/1990.



I have no problem with authority. Just some of the morons that are paid to enforce it.
    

7Back to top Go down    Re: Front brakes pulsating on Sat Sep 15, 2018 9:52 pm

TIV

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This seems to be fairly common. It will be interesting to see if the master rebuild will do something. One possibility could be air bubble/bubbles trapped in the system? I draw the fluid through with vacuum brake bleeding tool. It would be very nice to find a remedy for this annoying problem!


__________________________________________________
1936 Harley Davidsson 750 (sold), 1964 BMW R69S (sold), 1973 Suzuki RM400 (sold), 1972 Triumph Bonneville (sold), 1971 BSA Thunderbolt (sold), 1972 BSA Lightning (sold), 1977 Yamaha XS650 (sold), 1971, BMW R75/5 (sold), 1973 BMW R75/6 (sold), 1984 BMW R100RT 1992 Yamaha FJ1200 ABS (sold), 1990 Harley Davidson Electra Glide (sold)
1990 BMW K75RT Ex-Police (owned now)
2004 BMW R1150RT iABS (owned now)

Cheers TIV
    

8Back to top Go down    Re: Front brakes pulsating on Sat Sep 15, 2018 10:00 pm

yamaguzzi

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My money is on some sort of problem in the fluid system either mechanical or trapped air someplace causing the pressure to fluctuate .Now I'm reading that front wheel bearings can be the cause of this problem. Well,we will see soon enough



Last edited by yamaguzzi on Sat Sep 15, 2018 10:14 pm; edited 1 time in total


__________________________________________________
1988 K 100RS ,1975 Moto Guzzi 850-T , 1971 BMW R60/5 , 1971 Yamaha R5B,1969 Yamaha DS6C ,1966 Yamaha YM1 , 1965 Yamaha YDS3
https://facebkfugitive.blogspot.com/
    

9Back to top Go down    Re: Front brakes pulsating on Sat Sep 15, 2018 10:04 pm

RicK G

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VIP
I went through everything just like you guys are doing. First was the steering head bearings then fork legs and seals etc.
I will be interested to hear what you find.
The first thing I noticed was that the pads were rattling at slow speed then the pulsating started.
Oh by the way have you got the spring loading on top of the pads where the pins go through that may prevent the wear that causes the problem.


__________________________________________________
"Every normal man must be tempted, at times, to spit upon his hands, hoist the black flag, and begin slitting throats."† from Mencken's 1919 Prejudices

Bikes 1993 K1100 LT, 1998 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 for now
    

10Back to top Go down    Re: Front brakes pulsating on Sat Sep 15, 2018 11:14 pm

Gaz

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Hi All, my experience may not be relevant to this discussion but here goes.

My 1990 K75 had a shudder in the front when I first applied the brakes under moderate braking but did not do it when I had to brake hard. A friend of mine had a K75 also that exhibited the same behaviour. Both these bikes were fitted with ABS.

After a fair bit of head scratching and research I noted that the non-ABS bikes are fitted with pads that are approximately 55.5mm across the backing plate (FA18 in EBC speak) and the ABS bikes are fitted with pads that are approximately 57mm across the backing plate (FA171 in EBC speak).

I had fitted the FA18 pads which seemed to fit well into the callipers. Once I changed to the FA171 pads the shudder disappeared. This change also eliminated the problem on my friends bike.


__________________________________________________
Gaz
95 K1100LT 0232224; 90 K75 6427509; 87 R80G/S PD 6292136
    

11Back to top Go down    Re: Front brakes pulsating on Sun Sep 16, 2018 12:51 am

TIV

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Yes Rick, Iíve got the springs right. Gaz, you may have hit the nail square on the head! Mine is ABS bike. I canít remember which size I bought last time, I thought there was only one size for these bikes, with or without ABS. If the smaller once are in, itís logical that they might rock a little in the calipers and cause this problem! I will go measure mine tomorrow!


__________________________________________________
1936 Harley Davidsson 750 (sold), 1964 BMW R69S (sold), 1973 Suzuki RM400 (sold), 1972 Triumph Bonneville (sold), 1971 BSA Thunderbolt (sold), 1972 BSA Lightning (sold), 1977 Yamaha XS650 (sold), 1971, BMW R75/5 (sold), 1973 BMW R75/6 (sold), 1984 BMW R100RT 1992 Yamaha FJ1200 ABS (sold), 1990 Harley Davidson Electra Glide (sold)
1990 BMW K75RT Ex-Police (owned now)
2004 BMW R1150RT iABS (owned now)

Cheers TIV
    

12Back to top Go down    Re: Front brakes pulsating on Sun Sep 16, 2018 2:03 am

MartinW

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I had shuddering front brakes so I removed the calipers and attached a dial gauge indicator to the top caliper bolt with a cobbled up bracket. I ran the DGI on a smooth track on the outer edge of the disc. The DGI indicated it had a warp in one spot on the disc on both sides. If you have non floating discs it is possible to straighten minor warps. If you are heavy handed and have no patience forget it. Mark the high or low spot on the disc and swing the DGI out of the way. Then using a 10-12" piece of broom handle and a nylon hammer gently tap the alloy carrier in the opposite direction. Reattach the DGI and get another reading if it has not moved enough tap again. Avoid tapping it back and forth, go gently it is better to sneak up on it. I learnt this from a mate when I used to race Karts. The discs aren't much smaller than the wheel and kerbing happens, patience and practice give you a feel for it. The above method works with minor warps not major buckles. If you are about to buy new discs you have nothing to loose in giving it a go.

Regards Martin.

Special tools are subject to copy write.


__________________________________________________
K75s Hybrid
    

13Back to top Go down    Re: Front brakes pulsating on Sun Sep 16, 2018 2:23 am

nobbylon

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My money is on warped discs. My rear disc on the RS does it. It also did it on the Dakar until I replaced the disc. Slow speed and gentle stopping is where itís noticed most.


__________________________________________________
R1100GS Feb 1995
K100RS July 1989
K100 Dec 1983†
R90s June 1975
R75/6 Feb 1976
F650GD May 2001
    

14Back to top Go down    Front brakes pulsating on Sun Sep 16, 2018 5:29 am

audibob

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I agree with Nobbylon

my original front discs would pulsate at low speeds which I found really annoying, especially coming to a stop.

I overhauled the calipers but no difference.

I found slight run out on both so,† new discs .

Have done 20,000 miles on them and still smooth.

I wish I had tried the special tools of Martin W on my originals first........

Bob


__________________________________________________
Yamaha 90
Honda CD 175
Honda CB 360†
Triumph T 140V Bonneville
Triumph T150 Trident
Honda CB750 F1
Cz 175
Yamaha XS 750
R 100/7
R 80
K100 LT
K100 LT current bike
    

15Back to top Go down    Re: Front brakes pulsating on Sun Sep 16, 2018 6:24 am

TIV

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I put on new discs 20.000 kilometers ago. The pulsing has been there since I installed these discs. Just gets worse as the pads wear. Last time I bought pads I must have bought the 57mm because on Motorworks website the 55.5 pads are marked pre 09/88 and the 57mm are marked post 09/88. I will check anyway and measure the discs for runout. Winter is closing in here in middle of nowhere, so Iíll have plenty of time to fiddle around. But please keep info and possible causes coming in.
idea2


__________________________________________________
1936 Harley Davidsson 750 (sold), 1964 BMW R69S (sold), 1973 Suzuki RM400 (sold), 1972 Triumph Bonneville (sold), 1971 BSA Thunderbolt (sold), 1972 BSA Lightning (sold), 1977 Yamaha XS650 (sold), 1971, BMW R75/5 (sold), 1973 BMW R75/6 (sold), 1984 BMW R100RT 1992 Yamaha FJ1200 ABS (sold), 1990 Harley Davidson Electra Glide (sold)
1990 BMW K75RT Ex-Police (owned now)
2004 BMW R1150RT iABS (owned now)

Cheers TIV
    

16Back to top Go down    Re: Front brakes pulsating on Sun Sep 16, 2018 6:29 am

nobbylon

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Just because they were new doesnít mean they were true. Get them checked and skimmed before anything else. Check the run after installation also.


__________________________________________________
R1100GS Feb 1995
K100RS July 1989
K100 Dec 1983†
R90s June 1975
R75/6 Feb 1976
F650GD May 2001
    

17Back to top Go down    Re: Front brakes pulsating on Sun Sep 16, 2018 6:32 am

TIV

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I have sometimes considered running a line from the master cylender to a T-junction, and from there separate lines to each cylender. Anybody done this?


__________________________________________________
1936 Harley Davidsson 750 (sold), 1964 BMW R69S (sold), 1973 Suzuki RM400 (sold), 1972 Triumph Bonneville (sold), 1971 BSA Thunderbolt (sold), 1972 BSA Lightning (sold), 1977 Yamaha XS650 (sold), 1971, BMW R75/5 (sold), 1973 BMW R75/6 (sold), 1984 BMW R100RT 1992 Yamaha FJ1200 ABS (sold), 1990 Harley Davidson Electra Glide (sold)
1990 BMW K75RT Ex-Police (owned now)
2004 BMW R1150RT iABS (owned now)

Cheers TIV
    

18Back to top Go down    Re: Front brakes pulsating on Sun Sep 16, 2018 6:33 am

TIV

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@nobbylon wrote:Just because they were new doesnít mean they were true. Get them checked and skimmed before anything else. Check the run after installation also.
Youre right there of course nobbylon.


__________________________________________________
1936 Harley Davidsson 750 (sold), 1964 BMW R69S (sold), 1973 Suzuki RM400 (sold), 1972 Triumph Bonneville (sold), 1971 BSA Thunderbolt (sold), 1972 BSA Lightning (sold), 1977 Yamaha XS650 (sold), 1971, BMW R75/5 (sold), 1973 BMW R75/6 (sold), 1984 BMW R100RT 1992 Yamaha FJ1200 ABS (sold), 1990 Harley Davidson Electra Glide (sold)
1990 BMW K75RT Ex-Police (owned now)
2004 BMW R1150RT iABS (owned now)

Cheers TIV
    

19Back to top Go down    Re: Front brakes pulsating on Sun Sep 16, 2018 6:55 am

Dai

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Just y'all bear in mind one thing: the caliper relies on minor imperfections in the disc to knock the pads back in. If the pads aren't pushed back properly i.e the disc is absolutely flat, you can get a build up of road shite behind the pads which will eventually cause them to make permanent contact with the discs. Mind you, depending on what country you're in, some of you will never suffer from that. Very Happy


__________________________________________________
'83 K100 upgraded to K100RS spec
Others...
'78 Moto Guzzi 850-T3, '79 Moto Guzzi 850-T3 California,'93 Moto Guzzi 1100ie California,
'03 Suzuki Blandit GSF600SK3 (NFS any more because wifey has claimed it)
    

20Back to top Go down    Re: Front brakes pulsating on Sun Sep 16, 2018 7:08 am

Corkboy

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Also worth a try before consigning the existing disks to the metal recycling bin.

Sometimes (as happens to me) if the bike is lying idle for a while, the pads deposit material on the part of the disk they are contacting. This causes pulsing when in use, due to the different friction now being obtained from different parts of the disk.†

The fix, and I'd recommend it be tried before anything else (cause its free† bounce†), is to find a vacant car park and do some serious emergency braking.† Bring the bike up to speed and really heat those pads and disks up (I take no responsibility blah, blah, blah etc. ).

This can burn off any residue on the disks and bring the surface back to uniform friction again.

Worked for me.


__________________________________________________
Regards,

Corkboy '87 K100RS SE (The black one - one of the two bikes I'm sorry I sold)
† † † † † † †'87 K100RS 0140995 (Gone)
†††††††††††† '97 K1100LT 0188024 (Gone)
† † † † † † †'08 K1200GT Wedge - but still a K
†††††††††††† '08 Transalp 700
    

21Back to top Go down    Re: Front brakes pulsating on Sun Sep 16, 2018 7:24 am

MartinW

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Due to the fact that I've had new discs with runout, I check them after they are mounted. I've had to perform minor adjustments on brand new discs. The discs were locally sourced, I will be using EBC next time as I picked a new floating set cheap. Twenty years ago a mate had to have the mounting surfaces on his wheel machined due to runout.
Regards Martin.


__________________________________________________
K75s Hybrid
    

22Back to top Go down    Re: Front brakes pulsating on Sun Sep 16, 2018 8:11 am

nobbylon

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@Dai wrote:Just y'all bear in mind one thing: the caliper relies on minor imperfections in the disc to knock the pads back in. If the pads aren't pushed back properly i.e the disc is absolutely flat, you can get a build up of road shite behind the pads which will eventually cause them to make permanent contact with the discs. Mind you, depending on what country you're in, some of you will never suffer from that. Very Happy
This is not my understanding of how a disc set up works. The master cylinder is designed to pull fluid back in when pressure on lever is released thereby pulling the pistons slightly back to release pressure from the disc. This is probably the effect seen of fluid spurting in the master cylinder as pressure is released. †Using square edge seals helps this process thus no return springs required.
On the old airhead master cylinders it was necessary to set up with a feeler blade so that the relief hole lined up correctly with the piston. Failure to do this could result in wheel lock up as the calipers would not release. Discs should be true.


__________________________________________________
R1100GS Feb 1995
K100RS July 1989
K100 Dec 1983†
R90s June 1975
R75/6 Feb 1976
F650GD May 2001
    

23Back to top Go down    Re: Front brakes pulsating on Sun Sep 16, 2018 9:26 am

Laitch

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@TIV wrote:I have sometimes considered running a line from the master cylender to a T-junction, and from there separate lines to each cylender. Anybody done this?
If you mean as illustrated below, BMW used this configuration on some K models.
From the Haynes manual.


__________________________________________________
1995 K75T 68,000 miles
    

24Back to top Go down    Re: Front brakes pulsating on Sun Sep 16, 2018 2:15 pm

yamaguzzi

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Well,this morning I took off the brake lever and saw some debris around the piston shaft that the lever pushes on† .Looked like some sort of rubber packing material.I was going to change out the piston so I started picking at it to find the cir clip described in the service manual but couldn't find it.This rubber is thick.So,after reading the procedure to take the master off I decided to try to lubricate the shaft with some brembo assembly lube that came in the caliper rebuild kit for my Moto Guzzi calipers.I cleaned everything up real good with brake cleaning solvent then lubed it moving the piston in & out a few timed and putting more lube on ..After doing this I sucked out the fluid from the master and put new fluid in then bleed the brakes until all the fluid had been changed.Lubed the lever well as I put it back on and took the bike out to test. It is much better than yesterday ! But,there is still a slight pulse. It is good enough to travel with now so after lunch I'm taking her out for a 100 mile ride to see. The next thing I'm going to try is taking off the front wheel and removing the rotors and reinstalling them torquing all the bolts to the same value to see if that helps.


__________________________________________________
1988 K 100RS ,1975 Moto Guzzi 850-T , 1971 BMW R60/5 , 1971 Yamaha R5B,1969 Yamaha DS6C ,1966 Yamaha YM1 , 1965 Yamaha YDS3
https://facebkfugitive.blogspot.com/
    

25Back to top Go down    Re: Front brakes pulsating on Sun Sep 16, 2018 3:24 pm

TIV

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Good man!


__________________________________________________
1936 Harley Davidsson 750 (sold), 1964 BMW R69S (sold), 1973 Suzuki RM400 (sold), 1972 Triumph Bonneville (sold), 1971 BSA Thunderbolt (sold), 1972 BSA Lightning (sold), 1977 Yamaha XS650 (sold), 1971, BMW R75/5 (sold), 1973 BMW R75/6 (sold), 1984 BMW R100RT 1992 Yamaha FJ1200 ABS (sold), 1990 Harley Davidson Electra Glide (sold)
1990 BMW K75RT Ex-Police (owned now)
2004 BMW R1150RT iABS (owned now)

Cheers TIV
    

26Back to top Go down    Re: Front brakes pulsating on Sun Sep 16, 2018 6:01 pm

MartinW

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YG a dial gauge indicator complete with magnetic base can be had for around $20.00. The brackets to attach it to the top caliper bolt do require a bit of wrangling.
Regards Martin.


__________________________________________________
K75s Hybrid
    

27Back to top Go down    Re: Front brakes pulsating on Sun Sep 16, 2018 6:09 pm

TIV

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@MartinW wrote:YG a dial gauge indicator complete with magnetic base can be had for around $20.00. The brackets to attach it to the top caliper bolt do require a bit of wrangling.
Regards Martin.


__________________________________________________
1936 Harley Davidsson 750 (sold), 1964 BMW R69S (sold), 1973 Suzuki RM400 (sold), 1972 Triumph Bonneville (sold), 1971 BSA Thunderbolt (sold), 1972 BSA Lightning (sold), 1977 Yamaha XS650 (sold), 1971, BMW R75/5 (sold), 1973 BMW R75/6 (sold), 1984 BMW R100RT 1992 Yamaha FJ1200 ABS (sold), 1990 Harley Davidson Electra Glide (sold)
1990 BMW K75RT Ex-Police (owned now)
2004 BMW R1150RT iABS (owned now)

Cheers TIV
    

28Back to top Go down    Re: Front brakes pulsating on Sun Sep 16, 2018 6:57 pm

yamaguzzi

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Oh I have a dial indicator and a mag base that reads in 100th mm . I use it to set the timing on all my Yamaha Two Stroke twins. ! I'm going to see if they are true before I dis mount the wheel.Gonna be a rainy day Tuesday so I'll do it then.Just returned from a 120 mile ride and the brakes stayed the same as they were after I did the lever and piston push rod work this morning which is good news for me.I can travel with it this way no problem so Thursday I head north to the Adirondack Mountains in northern New York for a couple weeks of riding and camping.


__________________________________________________
1988 K 100RS ,1975 Moto Guzzi 850-T , 1971 BMW R60/5 , 1971 Yamaha R5B,1969 Yamaha DS6C ,1966 Yamaha YM1 , 1965 Yamaha YDS3
https://facebkfugitive.blogspot.com/
    

29Back to top Go down    Re: Front brakes pulsating on Sun Sep 16, 2018 8:37 pm

Dai

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@nobbylon wrote:
@Dai wrote:Just y'all bear in mind one thing: the caliper relies on minor imperfections in the disc to knock the pads back in. If the pads aren't pushed back properly i.e the disc is absolutely flat, you can get a build up of road shite behind the pads which will eventually cause them to make permanent contact with the discs. Mind you, depending on what country you're in, some of you will never suffer from that. Very Happy
This is not my understanding of how a disc set up works. The master cylinder is designed to pull fluid back in when pressure on lever is released thereby pulling the pistons slightly back to release pressure from the disc. This is probably the effect seen of fluid spurting in the master cylinder as pressure is released. †Using square edge seals helps this process thus no return springs required.
On the old airhead master cylinders it was necessary to set up with a feeler blade so that the relief hole lined up correctly with the piston. Failure to do this could result in wheel lock up as the calipers would not release. Discs should be true.
We're talking about the same process. Once the hydraulic pressure is off, the disc knocks the pads back.

And yes; I've screwed up setting up the rear caliper on my Cali 1100ie by hiding the relief hole. Only did it once...


__________________________________________________
'83 K100 upgraded to K100RS spec
Others...
'78 Moto Guzzi 850-T3, '79 Moto Guzzi 850-T3 California,'93 Moto Guzzi 1100ie California,
'03 Suzuki Blandit GSF600SK3 (NFS any more because wifey has claimed it)
    

30Back to top Go down    Re: Front brakes pulsating on Sun Sep 16, 2018 8:48 pm

RicK G

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VIP
VIP
@nobbylon wrote:
@Dai wrote:Just y'all bear in mind one thing: the caliper relies on minor imperfections in the disc to knock the pads back in. If the pads aren't pushed back properly i.e the disc is absolutely flat, you can get a build up of road shite behind the pads which will eventually cause them to make permanent contact with the discs. Mind you, depending on what country you're in, some of you will never suffer from that. Very Happy
This is not my understanding of how a disc set up works. The master cylinder is designed to pull fluid back in when pressure on lever is released thereby pulling the pistons slightly back to release pressure from the disc. This is probably the effect seen of fluid spurting in the master cylinder as pressure is released. †Using square edge seals helps this process thus no return springs required.
On the old airhead master cylinders it was necessary to set up with a feeler blade so that the relief hole lined up correctly with the piston. Failure to do this could result in wheel lock up as the calipers would not release. Discs should be true.
When the pressure is released the seal in the caliper returns to it's normal shape and in doing this pulls the piston back about 3-4 thousandths and then the disc will push the pads clear.


__________________________________________________
"Every normal man must be tempted, at times, to spit upon his hands, hoist the black flag, and begin slitting throats."† from Mencken's 1919 Prejudices

Bikes 1993 K1100 LT, 1998 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 for now
    

31Back to top Go down    Re: Front brakes pulsating on Mon Sep 17, 2018 12:36 am

nobbylon

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Silver member
I think weíll have to agree to disagree on this one fellas. The disc plays zero part in pushing pistons back into calipers.†
In an ideal set up, the pistons retract and the pads float between piston and disc. There may be some friction between pad and disc remaining but itís minimal. The square edge seals may not be symetrical and need to be fitted the correct way in the caliper to aid this retraction process. Some seals are symetrical and the caliper is machined to force the piston side edge of the square seal slightly proud. The machined true disc merely acts as a stop for the pistons movement and theresfter deformatiom of one edge of the seal. It plays no part in Ďpushingí anything as it has theoretically and ideally no lateral movement.
Relying on an imperfect disc to push calipers back would result in severly over heating brakes and rapidly diminishing performance from them plus very low pad and disc life.
Iíll add to the above by saying, do a static test ie bike stationary, pull the brake lever, bike will not move, release brake lever, bike will move. The disc wasnít rotating so therefore played no part in this process and indeed if you watch a caliper piston when brake pressure is released it retracts into the caliper itself.†
Iíve spent a lot of time over the years watching this occur while getting old airhead ate calipers running parallel to the discs.


__________________________________________________
R1100GS Feb 1995
K100RS July 1989
K100 Dec 1983†
R90s June 1975
R75/6 Feb 1976
F650GD May 2001
    

32Back to top Go down    Re: Front brakes pulsating on Mon Sep 17, 2018 6:42 am

Dai

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@nobbylon wrote:I think weíll have to agree to disagree on this one fellas.
No problem. Very Happy


__________________________________________________
'83 K100 upgraded to K100RS spec
Others...
'78 Moto Guzzi 850-T3, '79 Moto Guzzi 850-T3 California,'93 Moto Guzzi 1100ie California,
'03 Suzuki Blandit GSF600SK3 (NFS any more because wifey has claimed it)
    

33Back to top Go down    Re: Front brakes pulsating on Tue Sep 18, 2018 6:22 am

TIV

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Silver member
Silver member
I personally think that the discs have nothing to do with pushing/pulling the pads back when you release the lever (if everything is normal). This is done by the master cylender/fluid. I am going to take everything apart this winter, measure the discs and get this sorted. I will fit a quality rear shock as well.†


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1936 Harley Davidsson 750 (sold), 1964 BMW R69S (sold), 1973 Suzuki RM400 (sold), 1972 Triumph Bonneville (sold), 1971 BSA Thunderbolt (sold), 1972 BSA Lightning (sold), 1977 Yamaha XS650 (sold), 1971, BMW R75/5 (sold), 1973 BMW R75/6 (sold), 1984 BMW R100RT 1992 Yamaha FJ1200 ABS (sold), 1990 Harley Davidson Electra Glide (sold)
1990 BMW K75RT Ex-Police (owned now)
2004 BMW R1150RT iABS (owned now)

Cheers TIV
    

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