any special tricks in assembling caliper?

Pantdino

Pantdino

Low Mileage
CONTINUATION OF THE FRONT CALIPER SAGA-- I started a new thread because it is a different problem really.

Hi again,

Well, I got the new alloy part installed in the steel part with the spring-loaded pin in position as it should be.

But after hooking up the brake line and stepping on the brake pedal a few times to move the piston against the (nearly new) pads, I can't turn the rotor. Flushing the caliper did not yield any rusty fluid or other debris noticeable in the bleed line.

In my experience this means the piston is frozen and is in need of rebuilding or replacement, but this is a NEW caliper.

However, there was some dried powder like stuff beneath the protective cap thing in the hole where the banjo bolt goes, so if that was totally dried up assembly lube this caliper might have been made 20 yrs ago.

Taking out the shims that hold the caliper assembly to the carrier solves the problem 90%.

I can't depress the piston back into the caliper with my thumbs, but I was not able to open the bleed screw as I did so, so I'm not sure if that means anything.

Am I doing something wrong with the shims? Is there an upper and lower one, or are they the same?
If there is nothing special about the shims I guess I'll have to disassemble the whole thing and take the piston out of the new caliper.. Maybe it's bound up with that powdery stuff I saw in the brake line hole.

Thanks again,
Jim
 
Sounds like the NOS caliper is sticking in it's bore...common for a 25 year old part.

Remove it all again and remove the piston from it's bore... reassemble lubricating everything with fresh brake fluid (or rubber grease)

I would take the square section o ring out of it's groove and ensure there is no powdery buildup in the groove... square section O ring seal may need replacing, the dust boot should be fine.

Ideally you should do brake components in pairs too... the other side front caliper should at least have a new kit put thru it too..

SteveC
 
The piston and bore of the caliper I replaced looked perfect-- zero rust. I had to replace the caliper because the bleed screw seating area was deformed and wouldn't seal.

I figure I'll pull the other side apart if it pulls under braking.

The seal replacement is annoying-- the old $7 shipping for a 50 cent part and waiting a week for it to arrive story.
If the seal looks OK and there's an obvious reason for the piston binding I might reuse it.
 
Well... one thing I do is...

Remove the O rings, clean everything up... and BLOW them out with compressed air... Then I take the piston and caliper and use a fine Scotchbrite pad to remove any and all rough stuff and polish the surfaces.

Clean the parts again and trial fit them (without O rings) and then lube them with brake fluid. Insure that all pistons move very freely... now reinstall the O rings.

HTH...
 
I had the same problem

I had a sticky piston too. I had hard times getting the piston in. No way pushing it in with your thumbs. I did a test trial without the seal first to check if the piston glides smooth. This showed me that there was not much room to play with. Make shure that the groove for the seal is absolutly clean. I realized that after having 3 attempts that failed. Could get the piston in not even with a clamp. So I had to remove the piston again, cleaned the groove with help of q-tips and to be 100% sure I have placed the piston in my freezer. I finaly got it in with my thumbs and a lttle help of a clamp. :headbang:
Good luch and take your time. You don't wanna messaround with breaks. Oh forgot to mention I replaced the seals with new ones as the dust boot was falling appart.
 
update and solution

I took it all apart again and found there was unidentifiable matter in the cylinder but otherwise everything was perfect. I removed the matter and reinstalled the caliper, but it was no different-- the piston was not moving back in the cylinder to allow the rotor to move. I took it apart again and found that the new seal is visibly thicker than the old one -- several thousandths of an inch w caliper measurement. So I put the old seal in the new cylinder. The new piston did not want to go in, so I put the old one in and it felt good. After reinstallation the rotor turns fine now. So : new cylinder + old seal + old piston works. Other combinations yield a sticky piston.
 
hmm...

There must be a rear brake issue epidemic going around as I just heard from a friend here today with rears that are not coming together well.

Sounds like you pretty much re-built your caliper :)
 
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