Rear caliper rebuild

[charlie_pank]

After an incident that was entirely my fault, I obtained a caliper seals kit and a reconditioned sierra piston. Everything went fine transferring the piston internals across from the old one to the new one, the seal was easy to get in to the cylinder, I obtained the correct (red) grease and even managed to get the boot into the groove at the top even though the guy at the local motor factor said it was impossible (smug). I used my improvised rewind tool to get the piston all the way down then I filled the caliper via the bleed nipple using a syringe while I had it in the vice.

 

Once I get it back on the car though, it just pisses fluid from around the seal whenever I apply any pressure to the brake pedal. Is there some magic I'm not doing, or did I get sold a dud piston that has been ground down too far and won't make a good seal with the rubber ring in the cylinder?

[c7trp]

When I rebuilt my calipers I did as you described and had no problems getting them to seal (or to fit the boots 😬 )

 

I'm guessing you've checked the bore for wear and scoring, so unless the seal has been dislodged during assembly, it may be time to compare the diameter of the new pistons with the old one.

 

Edit to say, it may be worth removing the boot, seal and check the fit / rotation of the piston in the bore. IIRC it was a close fit without the seals in place

 

 

Edited by - c7trp on 21 Jul 2012 19:34:52

[DJ.]

When rebuilding the calipers on my Elan, I remember the main seal around the piston had to go in a particular way as it was slightly thicker on the edge furthest into the caliper. I haven't had a Sierra caliper apart, so I'm no expert.

 

I hope you get it fixed soon

 

Duncan

[charlie_pank]

Saga continues...

 

Spoke to the guys who sold me the piston. They assure me that the seals are 'square cut' so it doesn't matter which way around it goes in. This means that I must have nicked the seal, so I ordered a re-con caliper...

 

Caliper arrives, I put it on, bleed everything, get the wheel back on take it off the axle stands, find that I've overtightened the bearing nut . Loosen it off... jack it up... take wheel off... borrow 200lbft torque wrench... remove caliper and slider to allow bearings to free-up again... find slider spacer and de-dion ear have been damaged by the pad that parted company... order replacements from CC... wait for them to arrive... remove bearing from old DD ear whilst being careful not to damage speedo sensor attached to bearing... file down new spacer to same depth as old one (was .6mm thicker) ... remove DD ear and put on new one... attach bearing to new ear and ear to axle... attach hub and torque correctly to 200ftlb...attach caliper slider... attach caliper... note that brake fluid is weeping ever so slowly from bleed screw threads of new caliper ... try PTFE tape on threads to no effect ... call supplier who says it has been pressure tested and he's happy for me to tighten it further even though I'm concerned I'll strip the threads... strip threads from bore of bleed screw ... supplier sending me another caliper FOC, won't arrive til at least Tuesday

 

What next?!!

 

Edited by - charlie_pank on 28 Jul 2012 11:52:10

[Myles]

What next?

 

Ah! I know this one!

 

What you then find is that the recon caliper is everso slightly different to the one originally fitted by Caterham. I my case, the saddle height was a few mm lower and I didn't notice that it fouled the outer edge of the disc (I.e. the disc was effectively too large a diameter). One quick abortive test drive later and I was off to B&Q for my first angle-grinder.

 

So it ended happily in the end 😬

[charlie_pank]

Yeah, saw your writeup on that, I already have the angle-grinder sitting in waiting!