Front Brake Caliper Stuck

[davidr]

Next I clamped off the flexible brake hose and disconnected the hose.

I disconnected the ABS lead from inside the inner wing in the engine compartment.
Then there are 2 lock-wired bolts that hold the caliper to the hub carrier upright. Take care with these! As mentioned above, I managed to shear the longer one that goes through the steering arm as it had rusted in. This gave me a load of pain as getting it out meant stripping the entire hub down and applying serious heat!

Between the steering arm and the caliper are some shims. These were kept as they will need to be replaced.

[davidr]

This was the caliper as extracted. Not pretty!

Next thing was stripping the caliper down to get the pistons and seals out.
I used an airline to push the pistons out - with a 4 pot caliper like this its quite tricky to get them all out as they all need to come out at the same time or the pressure is lost and its not very easy to get a stuck piston out without the option of pressure behind. I make this sound simple but it took some time and persuasion to get there using a suitable thickness of wood to prevent the pistons pushing all the way out.

The seals were then pulled out using a small hook.

Surprisingly, the seals weren't cooked but will be replaced anyway.
I then sent the calipers off to be blasted and they came back like this

I'd made sure that the inside of the cylinders and the other openings were protected - I didn't want any blasting grit in there!
Next job was to paint them with a special high-temperature paint

[davidr]

So, I began to clean and rebuild the calipers. First was to clean the inside of the pistons. The area past the seal is clean so that's good. If it wasn't then the calipers would be scrap.
The most important area to clean is the groove that the seal fits into. If there is corrosion in there it pushes the seal outwards and that's what causes it to stick.

I used a bent over screwdriver to clean out the groove and then cleaned the outside with an abrasive pad. Its very important to make sure that's there's no debris left in there at all that could get stuck between the seal and the caliper and again cause it to seize.

The pistons were marked and slightly corroded on the outside but the crucial sealing faces were clean and smooth so I was happy to reuse them. If there was any corrosion behind the seal I would have replaced them.

Below is the rebuild kit

The seals were lubricated with rubber lube and fitted, then the pistons were pushed back in and the dust boots fitted.

The bleed screws were also replaced and then here it is ready to go back in.
Obviously this was done for both sides

[davidr]

Refitting the caliper is obviously the reverse of fitting.
Things to look out for are the shims between the caliper and the steering arm.
The correct procedure is to measure the gap as shown below and insert the required thickness of shims. As I was using all the same components I simply replaced what I'd taken out.

Bolts are tightened to the specified torque and then lock wired so they cannot shake loose.
Final checks were to measure end float on the hub and run out on the disc.

Checking end float on the hub bearings.

Checking the disc for run out. As it had all got so hot I was concerned that the disc may have warped but luckily it had not. As it was fairly new and not very worn I as happy to put it back on (with new pads).
All that was left to do was to bleed the brakes, refit the wheels and road test. I'm pleased to say that all was well. In fact, I had obviously had a slight problem for a while that I hadn't really noticed. What I did notice was that a slight vibration that I had thought was a slightly out of balance front wheel had gone away!

[oldtimer]

David,
Another job well done

[ptjs1]

David,

Great job and excellent photos as usual!

Just one comment that I'd make to any member working on their front brakes. Do not EVER push back the front pistons at all without first slackening the bleed nipple and attaching a tube for fluid to drain out.

This is because there is an increasingly frequent problem of tiny particles of debris being forced back to the ABS valve block and then causing huge problems resulting in complete failure of the brakes on one side when applying the pedal. You really don't want this to happen!

The problem wasn't known when the cars were current, but is happening more and more now. So always allow the fluid pressure to exit via the bleed nipple whenever changing pads etc.

Cheers

Paul

[davidr]

Thanks Paul - good point! The movement here was fractional - just enough to release the pads but I'll follow your tip in future!

[davidr]

One mistake I made was with the braided brake hoses I bought. I'd actually bought 2 sets some while ago for both cars. I'd fitted one set to my 1989 V12 when I got them and then the other pair were left in stock for an opportune moment.
When I went to fit them to my 1996 Celebration I realised that the fittings were updated in the later cars so the ones i had wouldn't fit.
Here they are

So these are for sale - make me an offer!

PS I think they will also fit XJ Series 2 & 3