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Author: Subject: HELP! Sierra rear calipers
gr8ging

posted on 20/9/07 at 04:02 PM Reply With Quote
HELP! Sierra rear calipers

Have been trying to rebuild my calipers today, what a pain in the arse!
Anyway managed to get one rear built back up (lost the hanbrake lever seal on the other, DOH!) Had quite a hard time winding the piston back in but it all went well until I tried the handbrake lever and NOTHING, the piston doesn't move? I guess it should, a little?
Anyone have any thoughts? Don't say I should have gone for recon ones, I know that now! Has anyone else had snags or is this right? I don't see anything I have done wrong





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worX

posted on 20/9/07 at 04:18 PM Reply With Quote
How did you "wind them" back in - it might be that you've simply gone a little too far and now the knurled (?) piston hasn't quite engaged.

Wind it back out slightly an try it again.

HTH
Steve

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gr8ging

posted on 20/9/07 at 04:31 PM Reply With Quote
What do you mean engaged? I wound them as far in as I could get them-not quite flush with the caliper.
thinking about it the handbrake lever can be lifted quite alot say 8-10mm is that normal?





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James

posted on 20/9/07 at 04:32 PM Reply With Quote
Even on my cheap-skate build car I bought the rear callipers.

If I'd spent the amount of money a Vortex costs I wouldn't hesitate to be on the phone to Brakesint to order some new ones!

Cheers,
James





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worX

posted on 20/9/07 at 04:41 PM Reply With Quote
My rear calipers had to be WOUND and PUSHED back in.
When I wound them in they were also pushed back and then they recessed back into the caliper.
When I'd wound them in as far as they could go they seemed to spin freely and therefore were not "engaged" on the thread.
So I wound them back out a little and then they "engaged" and could then travel in and out as normal.

quote:
Originally posted by gr8ging
What do you mean engaged? I wound them as far in as I could get them-not quite flush with the caliper.
thinking about it the handbrake lever can be lifted quite alot say 8-10mm is that normal?

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gr8ging

posted on 20/9/07 at 04:43 PM Reply With Quote
Even on my cheap-skate build car I bought the rear callipers.

yeah, but I've done it now, well nearly

I can't give in now, someone must have the answer?:





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Paul (Notts)

posted on 20/9/07 at 04:44 PM Reply With Quote
quick question - when you tried the handbrake had you fitted the brake lines back on and blead the brakes first ?

I seem to recall a warning about not touching the hand brake untill this had beed done!

Paul

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gr8ging

posted on 20/9/07 at 04:45 PM Reply With Quote
WORX-
Cheers I'll go and give it ago.
stand by for result





Weaseling out of things is what separates us from the animals.... except the weasel.
You couldn't fool your own mother on the foolingest day of your life with an electrified fooling machine!

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gr8ging

posted on 20/9/07 at 04:47 PM Reply With Quote
"quick question - when you tried the handbrake had you fitted the brake lines back on and blead the brakes first ?

I seem to recall a warning about not touching the hand brake untill this had beed done!"

They are off the car, so no fluid in them.

how do you post a quote in a reply?





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ed_crouch

posted on 20/9/07 at 04:53 PM Reply With Quote
You need to actually have some pressure on the piston for it to move.

In the piston (if its the same arrangement as an Audi A4, and i suspect strongly that it is) is a thrust bearing. The thrust bearing fits between a nut and the piston. When significant axial loads (i.e. braking/handbrake) are applied to this thrust bearing, it locks solid. If you do not have any significant resistance on place to stop the piston proceeding out of the caliper, it wont!

This sounds very counter intuitive, but it is true.

The handbrake is actuated by the axial movement of a threaded rod. You will have seen this rod when you removed the piston.

If theres no mechanical load on the piston when the rod is actuated, the axial movementof the rod will just rotate the nut inside the piston (because the bearing isnt locked cos theres not enough resistance).

Hence, the piston wont move. clamp the piston into the caliper with a G clamp, then have another go at the handbrake lever. You should find, if all is well, that the handbrake lever experiences much more resistance.

The reason this layout is used is because you get a hydraulic footbrake, a purely mechanical handbrake AND a reliable auto-adjuster all in one assembly.


HTH.

Ed.

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worX

posted on 20/9/07 at 04:56 PM Reply With Quote
The Sierra one does have the same Mech as the A4 Ed.

Gr8ging - What Ed said above is the same as I said, but he used all the correct terminology, so please don't let my hamfisted explanation confuse you!

Steve

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worX

posted on 20/9/07 at 04:58 PM Reply With Quote
how do you post a quote in a reply?

you click the "Quote" button just above the persons post that you want to quote and it takes you straight into your own posting screen...

Steve

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ed_crouch

posted on 20/9/07 at 05:03 PM Reply With Quote
If you followed that then you now know why you have to use a windback tool:

You need to lock the thrust bearing up to make the nut turn with the piston, hence threading it back down the rod to allow the piston to reced into the bore when you change the pads. I.e. you need to apply pressure at the same time as turning the piston.

This is why its a mugs game to spend all day with a pair of mole grips just turning the piston.





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John.Taylor

posted on 20/9/07 at 05:39 PM Reply With Quote
I had the same problem when rebuilding my first rear caliper.

If I remember correctly, there is a small 'liquorish torpedo' shaped bit of metal that sits into a groove at the bottom of the handbrake spindle within the caliper, and when the cable pulls the leaver to turn the spindle, it pushes the bit of metal out which in turn forces the piston out.

I didn't see this piece of metal when I stripped the caliper because of all the grease around the bottom of the spinde, but when I phoned Bigredd to query why their seal kit wasn't woking, they told me about it and I eventually found the offending piece of metal in the bottom of the container that I soaked the caliper in overnight!

Had to remove the spindle and new grease, insert the bit of metal, regrease, refit the splindle and hey presto - worked first time.

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gr8ging

posted on 21/9/07 at 01:11 PM Reply With Quote
Thanks John, but I know I put that bit in. When I had just the push rod in and no piston it seemed to move fine when I turned the handbrake lever. I tried applying pressure with a g-clamp this morning an it seems to work ok. So hopefully all will be well when the time comes to fit them.

Thank you all for your help





Weaseling out of things is what separates us from the animals.... except the weasel.
You couldn't fool your own mother on the foolingest day of your life with an electrified fooling machine!

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