Front Brake Calipers - Strip Down and Overhaul

The front brake calipers are now ready to go back on the engine.

You need to go back to manual 518 to find the instructins for rebuilding the calipers. It's operation DX.451-3. Considering the car hadn't been driven for about 15 years, removing the pistons was very straight forward. Just used a blast of compressed air and out they popped. The rubber anti-vibration 'diablos' were also easy to get off. Remember to take the metal liner tubes out of the middle first. It helps.

I seperated the caliper halves.

 

Each caliper half has a rubber seal - to provide the main seal against hydraulic fluid leakage - and a felt dust seal.

The old felt seals were winkled out.......

......as were the rubber seals.

Initially I gave the parts a clean in my ultrasonic cleaner.

I managed to get a lot of dirt off.......

..........but ultimately wasn't happy with the results on the alloy calipers and decided to have them vapour-blasted. After I got them back, I gave them a good rinse to make sure any stray glass beads were flushed out. All of that was more than four years ago!

Picking up the task again in 2023, I soaked new felt seals in LHM for a couple of hours before fitting and gave the rubber seals a brush with LHM before fitting those. 

Parts organised. Felt seals soaking

They went in very easily.

New seals fitted

With new seals fitted, some people have reported struggling to get the pistons to go back in the calipers but I didn't have any problems. I brushed the piston with LHM an carefully inserted it in the body - being careful to make sure that it didnt snag on the felt seal. The piston stops when it reaches the rubber seal. 

 

There is a very slight bevel on the lip of the piston which I think is to help it get past the rubber seal.

I just pushed down evenly on the rim of the piston with the palm of my hands and the piston suddenly went past the seal with a 'pop'. 

A piston refitted

I reunited the caliper halves and torqued them up (49 Nms).

The rubber anti-vibration 'diablos' that are part of the front engine mount set-up had been easy to remove, but were a pain to fit. The manual says to use a little water to help ease them in but they were stubborn buggers. All four of them.

 

My car is a bvh so the arrangement of the hydraulic pipes is different. There are no bleed nipples on the calipers. 

Working out the pipe connections

Instead the right hand brake unit is bled from the centrifugal regulator sitting over the hydraulic pump, and the left hand unit is bled from the accelerated idling device connected to the carburetor!

 

I found one of the bolts and the clamps for the brake pipes.........but then spent AGES looking for the one shouldered bolt that serves to hold a brake pipe clamp and also some other clamp that I simply can't remember. I'd definitely had it, as it was there in one of my disassembly photos.

I'd even put it aside for zinc-plating at some point.

But couldn't find it in 'box 14'.........I looked through all my other boxes before I found it. In Box 14 the whle time. Grrrrr!  With the bolt found, I refitted the hydraulic pipes that join the caliper halves. 

Refitting the hydraulic pipes

 That's that for the moment. I'm not fitting the brake units to the car just yet.