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914World.com _ 914World Garage _ Alloy brake caliper rebuild ?

Posted by: Eddie Williams Oct 26 2003, 11:49 PM

When rebuilding Alloy S calipers, what is the trick to getting the piston back in the bore? I put the springs back in the SS pistons, but can only seem to get the piston 1/4 of the way in. I used a clamp to apply pressure and the piston goes in, but as soon as the clamp is removed, the spring back out. What am I doing wrong?

Posted by: Brad Roberts Oct 27 2003, 01:01 AM

I'm going to try and help you... but I dont use the S calipers (they flex ALOT). I *think* if you install the sealing rubber rings facing the wrong way.. it makes the pistons "pop" out. Does this make sense ?? Some of the seals are tapered and designed to be installed facing a certain direction.

You can also try twisting them into place while pushing on them.

Shoot some pics..

B

Posted by: Eddie Williams Oct 27 2003, 07:36 AM

I'll try the seal thing, but all 4 pistons are exibiting the same problem. I've read on this, i believe, and another forum, that the flexing issue is highly over-rated, and only under the most extreme conditions (i.e. big tires, high heat)

Posted by: KenH Oct 27 2003, 10:12 AM

Am I missing somthing here??

To the best of my knolwdge there ARE NO springs involved with the brake calipers??

Ken

Posted by: Brad Roberts Oct 27 2003, 11:05 AM

Eddie,

Lets put it this way about the flexing. Have someone sit in the car and pump the pedal 3 times while you watch the caliper. Then do this same thing with a steel caliper car. You wont run the alloy calipers when your done. It has nothing to do with heat or big tires. They flex big time. However.. I would run them without issues (Porsche did for years). They do flex big time compared to steel calipers.

Ken,

I *think* the S calipers had springs..

B

Posted by: Eddie Williams Oct 27 2003, 11:28 AM

here's a pic of how far I can get the pistons inserted

Attached image(s)

Posted by: Eddie Williams Oct 27 2003, 11:30 AM

A pic of the back side of a piston with springs installed.

Attached image(s)

Posted by: Brad Roberts Oct 27 2003, 11:30 AM

Eddie,

this is a real stupid question from me...

Do you have the bleeder screws loose ?? Are they free and clear of any junk ??

B

Posted by: Eddie Williams Oct 27 2003, 11:30 AM

just the spring

Attached image(s)

Posted by: Brad Roberts Oct 27 2003, 11:31 AM

The pins that those ride on... sand them down with something. I have seen this problem before..lube everything real good with brake fluid when you reassemble them.

B

Posted by: Eddie Williams Oct 27 2003, 11:32 AM

yes, they are no bleeders and no crossover pipe installed

Posted by: Brad Roberts Oct 27 2003, 11:33 AM

Damn it. There is a easy answer for this and I dont recall it.

Call me later this afternoon if you can.

415-884-9146

I'll call some of the elders (Bontempi) and see if he recalls the solution. This exact same thing has happened to me in the past.

B

Posted by: Eddie Williams Oct 27 2003, 11:34 AM

I cleaned the centering pins with a dremel wire brush, I was thinking of soaking the springs in fluid, I'll try that next

Posted by: J P Stein Oct 27 2003, 11:37 AM

They do flex.....dunno about "big time". I'll have to measure it some day.

The main result is a softer brake pedal. This actually has an advantage (or so it seems) during the quick paced action of AX when overexurberant braking can result in locking the front tires.....kind of an automatic "smoothly roll on the brakes" sort of thing...it's about the only thing I do smoothly

They ARE a bitch to bleed, tho.

Posted by: Eddie Williams Oct 27 2003, 02:37 PM

I thought I may have found the problem...
these little tubes, were in my bag of parts, I put the tubes in, but it still only goes that far...

Attached image(s)

Posted by: davep Oct 27 2003, 02:47 PM

I'm guessing it is hanging up on the seals. Mark & measure to find out. Sometimes you do have to rotate the pistons to get them into the seals. Did you put in new seals? If so, try putting in an old seal and force it in. Then you will get an idea of the force required. Most pistons are well rounded to help the transition. Haven't tried the stainless pistons yet.

One of my next tricks is to make a copy of the GT caliper I have so I can have a pair. I'm sure that they can be overbored enough. Then I'll need a new set of pistons for sure.

DaveP

Posted by: Brad Roberts Oct 28 2003, 03:18 AM

Eddie..

Force them in. I now recall what needed to be done. They are tough to get it but they willl "pop" and slide in.

I had to use a C clamp to get the last set in I did (last year). Once they "pop" your all good.

B