R90S ATE caliper rebuild

[craydds]

Time to remove the master cylinder and brake lines.


Master cylinder appears in good condition externally. Will disassemble completely, clean and inspect.


All the parts appear to be in good condition, just dirty, and the grease is all dried up. Time for cleaning and fresh grease. It is amazing that all the parts are such high quality. These old BMW's are great machines, very well made, and it's easy to work on them. Looks like I will have to buy some expensive pistons, but most of the work is just cleaning and lubrication.

[oz_airhead]

Some stuff I wrote recently to the airlist, might be useful..

Firstly, watch any parts you get particularly the Caliper Dust Seals. I
destroyed four Caliper dust seals, all purchased aftermarket – from the
U.K. I read everything I could, searched archives, and just could NOT
get them on without destroying the seal, particularly on the outer edge
where it bonds to the metal stiffening ring. In the end after No.4, I
worked out (I'm pretty quick on the uptake, eh?) I had Buckley's of
getting one on without destroying it..

In the end I pressed one on using a mates press. Even then it still was
slightly damaged. I had to be doing something wrong....

So I got my measuring stuff out. I measured. After I measured some OEM
ATE seals I found out that they (aftermarket seals ) are approximately
~0.05mm bigger in diameter! Needless to say the OEM dust seals just
pushed in with thumb pressure. The actual fluid seal (aftermarket & OEM)
seemed to work fine. But as far as I know you cannot get OEM seals
without a piston – and that's how I got mine.

The pistons themselves. One was cactus, the other had corrosion in a
non-
travel part of it's body. In other words it was corroded no where near
the fluid side of the piston. So I reused that one. The other was crook,
so I stumped up and bought a new one, OEM of course – ouch!

Another thing for me was that I stripped the Caliper body bleeder
screw thread. I thought about a repair kit you can apparently get,
(mate said they were pretty dodgy at beast) but ended up with a good
second hand unit. Interesting was that the wrecker had only one 38mm
caliper left (mine are 38mm) but heaps of 40mm – so keep that in mind
if you need one.

Bleeding was relatively easy. I bled holding the caliper up as high as I
could with a wedge of timber holding the pads apart. Air came through
easily, did the other side, and I got a good lever feel quickly. Thanks
to whomever posted that tip on to the Airlist!

The brakes themselves are fantastic! Gone is the constant dragging of
the pads on the disk that I had before. After 36 years you would reckon
that the rubber seal would have had it! Performance seems to me to be
much better, I reckon I could lock the front wheel easily now – still
not two finger – it ain't a S1000RR either!

Finally, I think this job should be high up the list as a thing to do
sooner rather that later. Our bikes are getting on and well brakes are
Important!

HTH

OZ

[JonnyCash]

Now would be the time to go with a handlebar mounted MC! I put one one my single ATE front end, and I swear it has more usable stopping power than when I was running the stock ATE dual disks like you are. I used a general fitment Magura MC and it looks good and works great. This being an R90S you might be wanting to keep it all stock, but it's all bolt on stuff, so you could always go back if you wanted, but I bet you never would.

[craydds]

Originally Posted by oz_airhead

Some stuff I wrote recently to the airlist, might be useful..

Firstly, watch any parts you get particularly the Caliper Dust Seals. I
destroyed four Caliper dust seals, all purchased aftermarket – from the
U.K. I read everything I could, searched archives, and just could NOT
get them on without destroying the seal, particularly on the outer edge
where it bonds to the metal stiffening ring. In the end after No.4, I
worked out (I'm pretty quick on the uptake, eh?) I had Buckley's of
getting one on without destroying it..

In the end I pressed one on using a mates press. Even then it still was
slightly damaged. I had to be doing something wrong....

So I got my measuring stuff out. I measured. After I measured some OEM
ATE seals I found out that they (aftermarket seals ) are approximately
~0.05mm bigger in diameter! Needless to say the OEM dust seals just
pushed in with thumb pressure. The actual fluid seal (aftermarket & OEM)
seemed to work fine. But as far as I know you cannot get OEM seals
without a piston – and that's how I got mine.

The pistons themselves. One was cactus, the other had corrosion in a
non-
travel part of it's body. In other words it was corroded no where near
the fluid side of the piston. So I reused that one. The other was crook,
so I stumped up and bought a new one, OEM of course – ouch!

Another thing for me was that I stripped the Caliper body bleeder
screw thread. I thought about a repair kit you can apparently get,
(mate said they were pretty dodgy at beast) but ended up with a good
second hand unit. Interesting was that the wrecker had only one 38mm
caliper left (mine are 38mm) but heaps of 40mm – so keep that in mind
if you need one.

Bleeding was relatively easy. I bled holding the caliper up as high as I
could with a wedge of timber holding the pads apart. Air came through
easily, did the other side, and I got a good lever feel quickly. Thanks
to whomever posted that tip on to the Airlist!

The brakes themselves are fantastic! Gone is the constant dragging of
the pads on the disk that I had before. After 36 years you would reckon
that the rubber seal would have had it! Performance seems to me to be
much better, I reckon I could lock the front wheel easily now – still
not two finger – it ain't a S1000RR either!

Finally, I think this job should be high up the list as a thing to do
sooner rather that later. Our bikes are getting on and well brakes are
Important!

HTH

OZ

The stock, original outer seals look good.

I will re-install them.

[craydds]

Originally Posted by JonnyCash

Now would be the time to go with a handlebar mounted MC! I put one one my single ATE front end, and I swear it has more usable stopping power than when I was running the stock ATE dual disks like you are. I used a general fitment Magura MC and it looks good and works great. This being an R90S you might be wanting to keep it all stock, but it's all bolt on stuff, so you could always go back if you wanted, but I bet you never would.

I might consider that master cylinder. I am not going for a show bike or a trailer queen, I want to RIDE this bike, so keeping it all original is not too important. Yes, it will still look like an R90S, but I am going with some basic upgrades - I want it to STOP!

[oz_airhead]

Originally Posted by craydds

The stock, original outer seals look good.

I will re-install them.

My outer seal has swelled up considerably, so I had no choice.

Cheers

OZ.

[H96669]

Originally Posted by oz_airhead

My outer seal has swelled up considerably, so I had no choice.

Cheers

OZ.

Warning warning.....don't use any type of petroleum based cleaners on them seals, they will swell up. They "may" shrink back after a couple days of drying and washing with methyl hydrate but, considerably slows down them caliper rebuilt jobs.

[craydds]

Got it. Thanks!

[oz_airhead]

Originally Posted by H96669

Warning warning.....don't use any type of petroleum based cleaners on them seals, they will swell up. They "may" shrink back after a couple days of drying and washing with methyl hydrate but, considerably slows down them caliper rebuilt jobs.

Yep! Got it. Mine were old, split and had swelled. I have never put any sort of that type of cleaner on them.

Thanks.

[craydds]

Waiting on parts for the brakes. Noticed the fork seals are leaking. Good time to fix 'em.

Got this Fork Drain Tool from Joes Tools. http://www.culayer.com/Joes_tools.htm


Socket welded to a wrench. Allen wrench goes into damper rod, allows you to keep the damper rod from turning as you loosen the nut. Loosen and remove the damper rod nut/washer before proceeding.

[craydds]

Good time to loosen the ends with the axle in place. Note: the nut on the end of the damper rod is loosened FIRST. see above.

The fork legs are off.

All in good condition, just need a thorough cleaning.

[surtees]

thanks craydds for a great post. I have just gotten some parts (lower sliders, dual disk MC, caliper, etc) from a 79 R100 rt to add the right brake to my 75 R90 and this is very helpful. Will do some careful cleaning and looking at the shape of the individual pieces this weekend and if it is ok to jump on your thread post some pics and maybe questions here as well? One quick question - what are good cleaners/solvents for these metal and rubber parts?
thanks.

[craydds]

Originally Posted by surtees

thanks craydds for a great post. I have just gotten some parts (lower sliders, dual disk MC, caliper, etc) from a 79 R100 rt to add the right brake to my 75 R90 and this is very helpful. Will do some careful cleaning and looking at the shape of the individual pieces this weekend and if it is ok to jump on your thread post some pics and maybe questions here as well? One quick question - what are good cleaners/solvents for these metal and rubber parts?
thanks.

Glad to have you join in. Yes, post your pics. We always learn from each other. Be careful with the solvents, some eat plastic/rubber parts. Be safe, use detergents (Dawn, S100, etc.) and elbow grease, scrub with tooth brush, scotchbrite, fine steel wool, gently but thoroughly. Many of the old parts are no longer available, and if you can clean up your machine, lube and reinstall, then you'll have a good result. What amazes me is the hight quality of the original parts. My ol' bike is dirty, dried out grease, but in disassembly, then clean-up, everything is looking good as new. But, as an example, rusted caliper pistons, could have been polished, rust treatment (Ospho,etc.), then reinstalled and it could possibly work alright; as was previously noted, they could rust again. So, in this case I am going with new pistons (freakin' expensive) because as Snowbum told me (personal email), we don't want to experiment with our brakes. Keep us posted on your project. Good luck, and stay tuned.

[surtees]

Here are the lowers and calipers as received:

Externally looked pretty good but lots of muddy sludge in the piston and caliper body:

Also a little pitting of piston, not very deep but through to coating:

So does this look like it is salvageable with some polishing (I have the second one to do as well)? And does polishing mean using a fine wet sandpaper or something else (I do have a bench grinder).
Also probably a really noob question but when I took out the dust cover it left this hard ring - I think it is part of the dust cover but before moving it just wanted to make sure...
Thanks for any help.

[oz_airhead]

Originally Posted by surtees

Here are the lowers and calipers as received:

Externally looked pretty good but lots of muddy sludge in the piston and caliper body:

Also a little pitting of piston, not very deep but through to coating:

So does this look like it is salvageable with some polishing (I have the second one to do as well)? And does polishing mean using a fine wet sandpaper or something else (I do have a bench grinder).
Also probably a really noob question but when I took out the dust cover it left this hard ring - I think it is part of the dust cover but before moving it just wanted to make sure...
Thanks for any help.

Steel ring is part of the dust cover. I don't know about polishing up that piston. Up to you. But mine (dual disc) had one of the pistons just as bad - I replaced it. I couldn't find a aftermarket replacement. I bought OEM...($$) OEM comes with a seal kit (both fluid and dust)


Read my post #17 above about after market dust seals.

Good luck!

OZ