R90S Caliper Service

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San Arthur
Posts: 475
Joined: Sun Apr 22, 2007 2:08 pm

R90S Caliper Service

Post by San Arthur »

HI everyone

I’m going to service the brakes on my R90S.
I need ATE’ front brake caliper O-rings, which is sandwiched in-between the caliper halves.

I only need two and before I order a pack of 100 McMaster-Carr EPDM O-ring 9557K72 do you have a couple to spare. It's only $8.07 for a pack of 100, but I hate to be wasteful.

Thanks
San Arthur in San Antonio, Texas
'58 R26 '76 R90S '94 R100GS/PD

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schrader7032
Posts: 7256
Joined: Fri Oct 27, 2006 3:00 am

What do you mean by "caliper

Post by schrader7032 »

What do you mean by "caliper halves"? I've heard people talk about splitting Brembo brakes, though.

For the ATE brakes, I can think of the large squarish o-ring that goes around the piston, then there's the o-ring that goes around the eccentric bolt...there's also a dust cover. There's a very small o-ring that holds the pad in place with the spring clip.

BMW Hucky has some individual parts.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

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San Arthur
Posts: 475
Joined: Sun Apr 22, 2007 2:08 pm

Hi Kurt!

Post by San Arthur »

Hmmm, I think I got confused with my latter model ATE caliper, which I'm restoring too.

Going back to my R90S, let me tell you what is going on.

My front brake is beyond pulsating, is graving each turn before it stops, to the point I can feel the suspension diving with each turn.

Some time ago I check the axel, bearings and spacers and the rotors using shims for alignment. Pulsation is less, not totally away, but now it got very hard to stop.

Someone suggested to change the rotors for EBC floating rotors, but before I do the $400 plus investment I want to double check all breaking components.

1. Hub, axle and bearings
2. Wheel alignment
3. ATE calipers, service or refurbish
4. Brake pads
5. Master Cylinder
6. Brake lines
7 Suspension

M I missing something?

Thanks

Arturo
San Arthur in San Antonio, Texas
'58 R26 '76 R90S '94 R100GS/PD

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San Arthur
Posts: 475
Joined: Sun Apr 22, 2007 2:08 pm

What I have done so far

Post by San Arthur »

First I dismount the wheel. I'll bring it to the museum to check alignment of the rotors.
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The caliper pistons have some rust.
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I empty the gas and remove the tank.
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I checked the master cylinder for leaks and looks good.
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Break fluid will be flushed.
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From the bottom of the fork tube, remove the cover screw.
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With a big screw driver loosen the caliper alignment screw.
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I use a metric bolt to pull the screw.
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I couldn't remove the brake lines for the lack of a 11mm wrench. I'll do this at the museum.
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This are all the parts before I remove the pistons from the calipers.
Image

I'll continue next Tuesday.
San Arthur in San Antonio, Texas
'58 R26 '76 R90S '94 R100GS/PD

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San Arthur
Posts: 475
Joined: Sun Apr 22, 2007 2:08 pm

Caliper

Post by San Arthur »

I don´t know if this is the professional procedure, but his is what I did, I used a flare wrench to undo the lines. The nipples are very fragile.

Image

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Next I used compressed air through the brake line to blow the piston out of the caliper. I didn´t need a lot of pressure.

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Last I remove the bleeder screw.

Surprise, suprise...
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I have two different capacity pistons!! Would this be my pulsation problem? Would the difference in volume make one side grave more then the other, making one caliper stop harder then the other?

Cylinder 1 R=1.25cm H=1.8cm V=8.84 aprox.
Cylinder 2 R=1.55cm H=1.8cm V=13.59 aprox.

One piston brake fluid capacity is 65% larger then the other.

Any thoughts?
San Arthur in San Antonio, Texas
'58 R26 '76 R90S '94 R100GS/PD

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schrader7032
Posts: 7256
Joined: Fri Oct 27, 2006 3:00 am

I'm not sure that the

Post by schrader7032 »

I'm not sure that the different volumes would pulse like that. What if the disk was perfectly smooth? Wouldn't any hydraulic force you held the pistons result in a smooth running brake? Now if the disk had a warp in it or if there was some looseness in the bearings, than that could result in lateral forces which might be too much if the force was down on one side.

I wonder where the other piston came from. Original to the bike? I could see some differences on say a regular /6 when someone might have added the second disk and used what they could get their hands on. It would be interesting to see what the parts tables says for dimensions...if it's given.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

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San Arthur
Posts: 475
Joined: Sun Apr 22, 2007 2:08 pm

Is not exactly a pulse

Post by San Arthur »

Kurt is like it graves the wheel in every turn until it stops.
I don't know which one is the original. Lighter piston more volume or heavier piston less volume.

Any clues out there?
San Arthur in San Antonio, Texas
'58 R26 '76 R90S '94 R100GS/PD

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Randolph
Posts: 37
Joined: Tue Jan 13, 2015 11:31 pm

38mm and 40mm diameter pistons

Post by Randolph »

There are two types of ATE caliper, a 40mm dia. and a 38mm dia. The 40mm caliper is stamped "40" on the caliper body. I'm not sure if the 38mm caliper is stamped.
I'm not sure where you got the "R" dimension, but the piston itself should measure either 38mm dia.or 40mm dia.
You might as well make sure you have two 40mm calipers and see if that helps the problem.

Randy
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schrader7032
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Joined: Fri Oct 27, 2006 3:00 am

If the wheel grabs that much,

Post by schrader7032 »

If the wheel grabs that much, did you have a chance to measure the runout of the disks? My guess is it has a warp in it.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

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San Arthur
Posts: 475
Joined: Sun Apr 22, 2007 2:08 pm

At the museum

Post by San Arthur »

I used a dial gage to check alignment and I only have 0.006 of an inch in both rotors.
Image

Then I check thickens in different areas of each rotors and I have close to 0.20 millimeters difference in areas of the rotors.
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What do you think, is this the cause of my bad braking? Should I cut or replace?

I measure both pistons and both are exactly 40mm.

San Arthur in San Antonio, Texas
'58 R26 '76 R90S '94 R100GS/PD

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