Overhauling ATE brake Calipers

[Jeremy R65]

Good afternoon all.  I was wondering if there was a blow-by-blow guide to ATE caliper overhauling somewhere on the forum.  I tried searches, but with mixed results.  My calipers do not free off fully and the pads rub the discs. I was intending to buy overhaul kits from Motorworks.  Many thanks.

[mrclubike]

First dissemble them to see if the piston are bad and if they are you are better off just getting a brand new complete Brembo 38mm FO-8 caliper
You will get better braking with the larger 38mm piston over the stock 36mm piston
This is what I did
Here it is in the States but I  bet you could find it cheap in the UK also
And it comes with new pads
It is also easier and cheaper to find parts for
http://www.mgcycle.com/index.php?main_page=product_info&products_id=1034

[mrclubike]

Here is a link To FO8 over haul
Should be about the same as the ATE
http://www.bmbikes.org.uk/Forum/viewtopic.php?t=1604

The bolts holding the 2 half's together are tight
But I don't think their is a published torque for them

[Barry]

The Ate caliper pistons are prone to rusting and expensive to replace. If the pistons will clean up OK the secret to eliminating drag from the pads is use red rubber grease on reassembly. Without some protection, the area of the piston outside of the main seal will soon corrode and the pistons will become too stiff for the seals to retract them.  I caught mine in time and with the pistons properly lubed I have zero drag from the pads. I can spin the wheel by hand and it will keep turning for a long time.

If you do decide to overhaul  the Ate's  you are apparently not supposed to split the halves which is why there is no recommended torque value for reassembly.  That said I and many others have spilt them without problems.

[clonmore1]

What Barry says,

I have split mine, vapour blasted them, replaced all seals, cleaned up the pistons, changed to S/S brake lines, replaced the M/C ( the bike has been off the road for 17 years and it was as all gummed up, I didn't want to take a chance with the brakes..), new pads and all back together. Have around 30 miles of road testing and no problems so far[ch128077]

[Lucky_Lou]

If you do decide to overhaul  the Ate's  you are apparently not supposed to split the halves which is why there is no recommended torque value for reassembly.  That said I and many others have spilt them without problems.

I split mine and reassembled with no problems, there is an "O" ring between the two halves which you should replace its a stock item from Motorworks/Motobins.
A while back someone on this forum gave a link to replacement Stainless Steel pistons (not BMW parts) but the pistons do clean up but if you have any corrosion on the housing look for a replacement. The UK bikes are usually twin disc in which case the piston diameter is not an issue.
Lou

[Jeremy R65]

Thank you all for your help and advice.  Is it possible to extract the pistons without splitting the calipers and, if not, what torque do you suggest I use to do the halves up again with?

[Barry]

Yes you can get the pistons out without splitting the calipers.

1st thing I suggest is to exercise both pistons by holding one back at a time with a G clamp while pumping the other out and pressing it back in for a few cycles. Reason for doing this is while you can pump one all the way out the other one will need to be levered out and as they are not particularly easy to lever out you might as well try to reduce any existing stiction as far as possible.

As already mentioned there is no book torque figure but I'll try to find the setting I used.

OK I found the figure. In deference to the alloy threads of unknown tensile strength I used a very conservative 15ftlbs. This was many years ago and I haven't had the slightest leak from the calipers.  However much more recently there was a thread on ADVrider where someone used 50ftlbs without stripping the thread, which frankly astounded me.  I'll admit if I had to do it again I would use a little more torque perhaps 20 or 25 ftlbs but no way would I risk 50ftlbs.

For what it's worth here's the link to the ADVrider thread.
You won't find a consensus though as one guy was suggesting 50 inlbs and another used a figure 12 times higher at 50ftlbs.

http://advrider.com/index.php?threads/80-r65-ate-twin-piston-o-ring.998567/page-1

[Bob_Roller]

If you are considering splitting the calipers, I would suggest that you loosen the bolts that hold the calipers together when they are still bolted to the fork tubes .

I've  rebuilt two ATE and four Brembo calipers, those bolts are tight !!!!!!!!!!!!!!!!!!!!

They make a loud crack when they finally give way .

[Jeremy R65]

Thank you all for your excellent advice, the job is now done.  I loosened the set screws before removing the calipers (thanks Bob) but did not do a good enough job exercising the pistons before disconnecting the hydraulics (sorry Barry) so had to resort to a bit of brutality with a pipe wrench to pull them out.  I found a hint on line to boil the caliper halves for a few minutes in hot water to allow differential expansion to ease removal...seemed to work. Cleaned them up with brake fluid afterwards.  As it happened there was rust corrosion on the pistons anyway so I replaced them with anodised alloy ones from Motorworks.  The caliper bores were in good condition, happily. After a rebuild with new seals and some red rubber grease around the outer end of the piston inside the seal (thanks Barry), I reassembled the two halves and torqued them up to 30 ft-lb, which "felt" right.  All is now good and the brakes have a firm feel but completely free off when the lever is released - which they did not do before.  Thanks again, Jeremy

[Bob_Roller]

You can use compressed air to get the pistons out of the caliper .

Just make sure they are wrapped in shop rags to contain the fluid and the piston !!!!

[Jeremy R65]

Nice idea, but I have no compressed air.  Another one found on line was to use a pressure grease gun to force then out.

[Jakob Andresen]

Will Brembo F08 or F09 fit on my 1979 R65? It has ATE calipers mounted on each of the two discs, but they are leaking fluid and beyond repair I think.

[Barry]

Yes the F08 will fit. See the post by Mrclubike at the start of this thread.

[Jakob Andresen]

Thanks a lot. Just wanted to make sure!