Ate brake calliper assembly

[Barry]

Because ATE don't approve splitting the caliper halves you won't find an official figure anywhere.  I used a relatively low figure of 15 ftlbs in sympathy for the alloy threads in the caliper body and have not had problems. Part of my thinking was I don't exceed 15 fts on the alloy spark plug threads which are much bigger in diameter.  There were differing views on  another forum recently which raised a whole range of torque values from 5ftlbs to 49 ftlbs.   Frankly common sense and experience suggests to me that both extremes there were wrong. Short of someone testing a scrap caliper to failure I don't know where we are going to get an optimum figure.

[Mike V]

Barry - I couldn't agree with you more, again.

I think this is another one of those use your own judgment calls since ATE does not obviously post torque values since they don't recommend splitting the caliper.  I find it interesting the momentum this issue has developed, as I continue to follow and listen closely.

Obviously there is a liability issue with ATE for not wanting to split the calipers.  Maybe they haven't exposed the true reasons, or feel they are responsible to do so by their no-split procedure recommendation.  I'm curious why Brembo doesn't follow the same protocol since the calipers and materials seem to be similar if not identical.  But I'm not a metallurgist, structural engineer or trying to start another debate accusing manufactures of anything slanted.  That would never happen.

I replaced my caliper half bolts with a set of SS bolts, their stretch and tinsel characteristics are unknown to me.  I torqued them in 2 stages to 15 Ft-lbs.  That was about 5 years and several hundred miles ago with the replacement EPDM round O-rings installed.  My ATE front brakes are working quite well with no failures, or leaks.  In fact - the brakes on my R65 are one of the things I am most impressed with.

Your mileage may vary.

Does this mean I've just ventured into the English Channel with only a Speedo and no life vest and chase boat?

-M  

[Bob_Roller]

 I agree with a 15 ft/lb torque value .

To be honest, I didn't use a torque wrench, when I  reassembled the calipers on my '82 LS .
 
This is a low pressure hydraulic system, I don't think it's much more than  200-300 psi maximum .

[arvo92]

ATE does not want you to open the caliper halves since they do not want you to know what is inside Common sense in me would put my money to that.

ATE brake pistons are chromed. Maybe they lasted pretty good straight out of the factory. If ATE would have reccommended to open the caliper halves, pistons could easily be contaminated by inexperienced home mechanic and then you can get horrible amount of corrosion.  By now the time has passed some 30  years and the weather has done its work anyway, the matter is only the amount of damage but I truly do not believe that anybody riding in wet weather can escape the piston corrosion. If you open the caliper now for the first time you may find unpleasant suprise as the pistons may be horribly corroded causing life-threatening situations on the road.

Probably everybody knows by now that I crashed my bike on my first ride when the brakes snapped on due to horrible amounts of corrosion inside the caliper halves (thing I do not see without opening the caliper halves). How can I not open the caliper halves if something like this happens?

[Luca]

To be honest, I didn't use a torque wrench, when I reassembled the calipers on my '82 LS .

nor did I... just put some German torque on it.  That's "gutentight."  IIRC the bolts were coarse thread, so the aluminum should be a bit more forgiving for over tightness than a finer thread application (like spark plugs).

Poking around on the internet I found this: http://mtsspecialservices.homestead.com/files/technical_data.pdf

Note that they recommend using 60-65% of the standard torque value when going into aluminum.  That puts 15 ftlbs in the ballpark.  If folks want to go much tighter, I'd recommend experimenting on the left hand caliper; they're cheaper and more plentiful [smiley=thumbsup.gif]

[Bob_Roller]

Just to add, I used anti-seize compound on the bolt threads .

I'm sure it will be a while before I remove the bolts again .

Steel bolt and aluminum threads, a good set up for corrosion, with a bit of water mixed in there .

[Mike V]

Just to add, I used anti-seize compound on the bolt threads .

As did I.

I also have become better about maintaining my brakes in a better scheduled manner. That's an admittance of guilt folks.  I try to replace seals and fluid annually - now, along with wheel bearing grease seals.  Let's not overlook the job these seals do and the relatively low cost it is to replace them.  It can get quite damp here in San Diego, and my R65 may go through periods of non use for extended periods of time.  Probably the worst abuse of all I could do to my bike(s).

[Barry]

At the time I settled on 15 ftlbs I made some estimated comparisons between torque values for steel bolts and what I thought would be suitable for alloy threads. As the consensus seems to be homing in on that value I've tried to put some numbers against that comparison if only to convince myself it's in the right ball park.

In the absence of torque values for alloy threads we have to estimate how much weaker the alloy is than the steel bolts that we do have published torque figures for.  The quality to look for is yield strength which is how much force is required to permanently deform the material. If we compare the yield strength of cast alloy with steel bolts and apply the same factor to torque values that should come up with a reasonable figure.

The typical high quality 8.8 bolts on a BMW have a yield strength of  93,000PSI

The yield strength of our calipers is difficult to determine as we don't know the exact material other than it's high quality cast alloy. The yield strength of cast alloy seems to vary enormously. Typically the best figures I saw were in the range 30-35,0000 PSI which is approximately 1/3 of our quality steel bolt. That feels about right as a maximum so my gut feel is I'd rather go down from that figure than up.


A 10mm 8.8 bolt has a typical torque value of 50 ftlbs

1/3rd of that is 16.7 ftlbs

So go down a bit for safety and torque wrench error and 15 ftlbs still looks reasonable.

[jamestnewsonr65]

Thanks for the info that's really helpful.
I will use the 15ft lbs and see how it goes.

The forum really is very helpful and I would not have got this far without all the help I have obtained.

[Luca]

Note that they recommend using 60-65% of the standard torque value when going into aluminum.  That puts 15 ftlbs in the ballpark.  

I was thinking the bolts were 8mm  

[Barry]

I was thinking the bolts were 8mmEmbarrassed

At one time I'd got in my head they were 8mm but when I looked at them again even by the size of the screw head they must be 10mm.

I wasn't sure what to make of the "60-65% of the standard torque value when going into aluminum".  The idea that aluminum has 2/3rds of the strength of steel and similar strength to cast iron doesn't hold up when you look at the yield strengths. I think they must have meant "whatever the rated torque for aluminium is for dry threads reduce it further to 60 -65% when the threads are lubricated".

[Tony Smith]

I think that ti is easy to get lost in fine detail in these matters. It never even occurred to me to worry about a set torque. The bolts are nicely sized and are clamping a relatively large mating surface - If memory serves they got a good 3/4 grunt based on the scientifically proved "TLAR"  method of torque calculation






"TLAR" (That Looks About Right)

[Luca]

You're right, Tony.  The beauty of these bikes is their simplicity.

The problem is that leaves a lot of spare time on our hands    Can we get away with just a good snugging up by feel?  Certainly a number of us have... but it never hurts to give it a little more consideration.  Might help somebody who hasn't developed a good feel for these things yet  [smiley=thumbup.gif]

...but don't do using a torque wrench on the fork drain bolts, transmission vent bolt, final drive check plug, etc  

[jamestnewsonr65]

So after rebuilding the calipers and replacing the o rings with some new EPDM ones they are all back together and looking good except the pads rub slightly on the disks now that they are all back together.

It is very slightly and I thought about maybe adding a shim on the caliper body to shift them over slightly, but they touch on the inside and cant move any further.

Has anyone else had this issue? I'm using all new parts from motorworks to rebuild them along with the pistons from http://www.etypeparts.com/ which seemed ok and went together just fine.

[Barry]

Are you saying the pistons won't push back far enough to provide room for the pads or is it that the pistons are not self retracting as they should. This tiny amount of self retraction can be observed if you get down close enough and look while operating and releasing the brake.