Author Topic: Pulsing front brakes  (Read 29357 times)

Offline Filmcamera

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Re: Pulsing front brakes
« Reply #25 on: April 14, 2018, 11:01:38 AM »
I have not checked them no, but they have only maybe 500 miles on them so are still virtually new.  I will check them later and see.
  • San Jose, Costa Rica
  • 1991 K100RS 16v ABS1, 2018 Triumph Street Triple RS 765
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Offline beemuker

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Re: Pulsing front brakes
« Reply #26 on: April 14, 2018, 11:35:08 AM »
my left front rotor is warped and my brakes pulse. anyone have a good one they want to sell? There are a few on fleabay, but I don't want to get stuck with another warped one.
  • Panama City, FL
  • '00 R1100RT,’92 K75 RT,past tense:'83 R80ST, '93 K1100LT,,94 R1100RS K75s, Honda NC700, Suzuki Bandit 1200, bmw R75/5 Honda 750

Offline Martin

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Re: Pulsing front brakes
« Reply #27 on: April 14, 2018, 05:16:02 PM »
If you are heavy handed and tend to belt things with a sledge and have no patience read no further. As per Gryph remove the brake calipers and support them. Then jack up the front so the wheel spins clear of the ground. Set up a dial gauge indicator to run on the outer rim of disc on a smooth consistent track. You will have to manufacture brackets to mount the DGI off the caliper bolt.

Rotate the wheel 360 deg and mark the high or low spot with a suitable marker. Once you have found the spot you need to carefully correct it by tapping out the carrier not the disc. I use a 10" piece of broom handle and a nylon hammer to gently tap the carrier in or out to correct the warp. Use only light taps and check with the DGI after each tap, you will have to remove the DGI every time you adjust the carrier.

You don't want to be belting the carrier to and fro, you will just make things worse. You need to sneak up on it taping gently eventually you get a feel for it you may need to tap once or twice in the opposite direction if you overdo it. but this should be avoided if possible. This is a slow process but I have successfully straightened out minor warps on bikes and Karts. I learnt from a mate who was a master at staightening damaged Karts trackside.
Regards Martin.

* BMW rotor alignment tool.jpg (60.99 kB . 768x576 - viewed 456 times)

  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline Filmcamera

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Re: Pulsing front brakes
« Reply #28 on: May 08, 2018, 03:13:22 PM »
Having done everything I could think of to fix the brake pulsing issues I finally decided to put the old discs back on and see what happened.  All pulsing gone!  So I guess that means the new discs are either slightly twisted or that the bobbins are just so tight they do not let the disc float enough.  Either way I am going to send the new discs back to EBC who I have been in touch with via email and see what they say.
  • San Jose, Costa Rica
  • 1991 K100RS 16v ABS1, 2018 Triumph Street Triple RS 765
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Offline Martin

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Re: Pulsing front brakes
« Reply #29 on: May 08, 2018, 04:09:55 PM »
Did you check them for run out? :dunno
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline Filmcamera

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Re: Pulsing front brakes
« Reply #30 on: May 08, 2018, 04:13:33 PM »
I do not have the tools to do that but in my desperation I had taken the bike to a certified BMW mechanic and they did and said they were out, though they didn't give me exact measurements. 


I actually had a new set of bobbins which I fitted to my old discs so now there is not much movement in the old discs - maybe 0.25mm in either direction but it is enough it seems.


I was thinking about taking out the bobbins on the EBC discs and using the kit but they are not the replaceable type so it would mean cutting them off.  I would rather try the warranty route before going to that kind of extreme.
  • San Jose, Costa Rica
  • 1991 K100RS 16v ABS1, 2018 Triumph Street Triple RS 765
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Offline Martin

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Re: Pulsing front brakes
« Reply #31 on: May 08, 2018, 04:31:15 PM »
A DGI can be had from $10.00 up. The clamps to attach it too the brake caliper mounting bolt can be made up out of anything that is handy. A magnetic base with adjustable arms can be had for around $20.00. The magnetic base will not work but the arms will save you some manufacturing.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline Filmcamera

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Re: Pulsing front brakes
« Reply #32 on: May 08, 2018, 04:34:20 PM »
Something like this then?


DGI
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Offline Martin

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Re: Pulsing front brakes
« Reply #33 on: May 08, 2018, 05:32:22 PM »
 :2thumbup: However you will still have to rig something so you can attach it to the caliper mount. You need to get the indicator to run on a smooth track on the outer most edge of the disc. It is not rocket science but it can be a bit fiddly. It gets easier with practice, as do most things.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline beemuker

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Re: Pulsing front brakes
« Reply #34 on: May 09, 2018, 09:07:03 AM »
Having done everything I could think of to fix the brake pulsing issues I finally decided to put the old discs back on and see what happened.  All pulsing gone!  So I guess that means the new discs are either slightly twisted or that the bobbins are just so tight they do not let the disc float enough.  Either way I am going to send the new discs back to EBC who I have been in touch with via email and see what they say.
when you say disks, I assume you are referring to the rotors? are the bobbins the pads?
  • Panama City, FL
  • '00 R1100RT,’92 K75 RT,past tense:'83 R80ST, '93 K1100LT,,94 R1100RS K75s, Honda NC700, Suzuki Bandit 1200, bmw R75/5 Honda 750

Offline Laitch

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Re: Pulsing front brakes
« Reply #35 on: May 09, 2018, 09:17:41 AM »
when you say disks, I assume you are referring to the rotors? are the bobbins the pads?
Disks, discs = rotors   bobbins = the roller assemblies allowing floating disks to float.
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  • 1995 K75 89,000 miles
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Offline Filmcamera

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Re: Pulsing front brakes
« Reply #36 on: May 17, 2018, 05:12:01 PM »
I heard back from EBC today...


Great news - they are sending me two new discs/rotors under guarantee and a set of pads just because.


 :clap: :clap: :clap: :clap: :riding: :riding: :riding:


Once i get them I will install them and see how they feel - I have a plan B to take the first pair I brought and drill out the bobbins and use the new set I have from Motobins to see if that works better.


Watch this space.



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  • 1991 K100RS 16v ABS1, 2018 Triumph Street Triple RS 765
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Offline beemuker

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Re: Pulsing front brakes
« Reply #37 on: July 24, 2018, 05:22:26 PM »
my left front rotor is warped and my brakes pulse. anyone have a good one they want to sell? There are a few on fleabay, but I don't want to get stuck with another warped one.
well, replacing the left rotor didn't help. bucks like a bronco as you come to a stop. since I got a used left and right when I bought the replacement, I thought , what the heck, I'll replace the right one too. problem solved, it was the right that was warped. this was from a non abs bike, so now I've got the blinking light until I can source a rotor with a ring. 
  • Panama City, FL
  • '00 R1100RT,’92 K75 RT,past tense:'83 R80ST, '93 K1100LT,,94 R1100RS K75s, Honda NC700, Suzuki Bandit 1200, bmw R75/5 Honda 750

Offline Filmcamera

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Re: Pulsing front brakes
« Reply #38 on: July 24, 2018, 06:34:41 PM »
I got and installed the new rotors that I was sent by EBC - pulsing gone - great news.  The bad news is that they bind o muh I cannot spin the front wheel more than a quarter of a turn.  Right now I am being an ostrich and ignoring the issue in the hope that as the new pads wear a bit the problem fixes itself...
  • San Jose, Costa Rica
  • 1991 K100RS 16v ABS1, 2018 Triumph Street Triple RS 765
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Offline Martin

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Re: Pulsing front brakes
« Reply #39 on: July 24, 2018, 06:46:39 PM »
FC you need to fix it, binding discs will cause hot spots, that could cause warping. Then you will be back to square one. :musicboohoo:
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

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Re: Pulsing front brakes
« Reply #40 on: July 24, 2018, 07:34:08 PM »
I would love to fix it but have no idea how to, I have done everything I can think of and more.. actually the only thing I have not done is have the pads made thinner by a couple of mm to give more clearance but I am loathe to do that

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Offline Martin

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Re: Pulsing front brakes
« Reply #41 on: July 24, 2018, 08:18:19 PM »
Are you sure the pads are retracting properly after activation? Can you push the pads away from the discs or are they hard up against the calipers?
The seals in the calipers are designed so that after being activated they retract the pistons back into the caliper. If the pistons are retracting and every thing is free there should be a minute gap between the pads and disc and not between the pad and the piston. I know this might cause you pain but remove the calipers and see if the pads are free to slide in and out. I smear a very light coating of copper grease on my locating pins. Are the pins clean and free of pits marks corrosion? Are the pins free of bends? The pads must move smoothly in and out on the pin, check the holes in the pads to see that they are smooth. Alternatively ride over to my place and I will have a look. :dunno Remember the truth is out there.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

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Re: Pulsing front brakes
« Reply #42 on: July 24, 2018, 09:28:16 PM »
The pads retract but only so far, they remain just touching the discs. The inside pad in particular is pretty hard up against the disc. After pushing the pads all the way out there is room for the wheel to rotate freely so it is a retraction issue for sure. I just do not know how to fix it.  So far I have replaced the master cylinder, the pistons and the seals as well as new pads and new discs. I stripped and cleaned the calipers and made sure all passages are free and clear of gunk. I have also removed all old paint or powder coating from the caliper mounting points and even replaced the front axle that was all beaten up. Lastly I have done my best to align the forks on a few occasions. The pins are straight as far as I can see and I have used copper grease when reassembling everything. It seems to be about retaction at the very end of the pistons when they are close to the caliper body because if I remount the old discs there is no problem, hence why I was considering having the pads shaved back by a couple of mm.
  • San Jose, Costa Rica
  • 1991 K100RS 16v ABS1, 2018 Triumph Street Triple RS 765
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Offline Martin

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Re: Pulsing front brakes
« Reply #43 on: July 24, 2018, 09:34:05 PM »
Are the caliper bores pit, and mark free? Are the pistons mark free? Does the problem only appear to be on one piston not retracting fully.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

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Re: Pulsing front brakes
« Reply #44 on: July 24, 2018, 09:37:49 PM »
The pistons are new so yes they are pit free, the caliper bores seem good, I have also used 600 grit wet and dry to smooth them off and try and remove and pits.  It appears the issue is the same or more or less the same on both sides. The culprit is, I suspect, that when I had the calipers powder coated the idiot that did the job did BOTH sides of the calipers so I got them back and had to spend hours carefully removing it from the mating surfaces.  It seemed to go ok, they have never leaked etc but maybe it has caused this issue.  I may have to search or a pair of used brembo 4 pt calipers.
  • San Jose, Costa Rica
  • 1991 K100RS 16v ABS1, 2018 Triumph Street Triple RS 765
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Offline Martin

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Re: Pulsing front brakes
« Reply #45 on: July 24, 2018, 09:49:13 PM »
It is slightly possible that during the process of powder coating the calipers were slightly distorted. Have you checked the bores for ovality and are the bores parallel? Did you try the pistons in the bores lubricated with brake fluid? Did they move freely, if rotated in the bores are there any tight spots? You are on the right track, in OZ we have a local guy that sleeves master cylinders and calipers. Do you have a local brake expert who can check them for you if you don't have the equipment?
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline Martin

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Re: Pulsing front brakes
« Reply #46 on: July 24, 2018, 10:11:25 PM »
FC it's a long shot but if you find any pistons that are not freely moving in and out or when rotated try swapping piston and bores. But make sure you can go back to where you started from. Doing this may reveal where the source of the problem may lie.

Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline Filmcamera

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Re: Pulsing front brakes
« Reply #47 on: July 25, 2018, 08:42:10 AM »
Doing some research it seems to show that the calipers from a K1200 RS are the same as on my bike (a 1991 K100 RS 16v), can anyone confirm that?


I found a nice set of calipers from a 1999 K1200 RS for $99 the pair on eBay but want to try and make sure they are compatible before I buy them.
  • San Jose, Costa Rica
  • 1991 K100RS 16v ABS1, 2018 Triumph Street Triple RS 765
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Offline Laitch

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Re: Pulsing front brakes
« Reply #48 on: July 25, 2018, 09:39:58 AM »
Doing some research it seems to show that the calipers from a K1200 RS are the same as on my bike (a 1991 K100 RS 16v) . . .
I go by the BMW parts fiche numbers. At Max BMW, the caliper part numbers for the '90–'92 K100RS and the K1100RS are the same; the K1200's differs. Give us a link to where your research suggests these calipers are the same.
  • Along the Ridley in Vermont.
  • 1995 K75 89,000 miles
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Offline Filmcamera

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Re: Pulsing front brakes
« Reply #49 on: July 25, 2018, 09:44:04 AM »
One of the places I was looking at to potentially replace my calipers was beemerboneyard and they have this link


Calipers
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  • 1991 K100RS 16v ABS1, 2018 Triumph Street Triple RS 765
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