Brake caliper rebuild

 Brakes, Rolling Chassis  Comments Off on Brake caliper rebuild
Jun 242013

The components for the front calipers - including the small circular seals between the two halvesCaliper rebuild kits are readily available from many of the usual suppliers and contain the square sectioned seals which sit in recesses in the caliper piston bores and the outer dust shields.

The dust shields are similar to a expandable bellow with the ends sitting in a recesses in the piston bore and piston. This enables the rubber shield to stop ingress of foreign particles for the full travel of the pistons.

The kits however do not contain the small square sectioned ‘O’ rings that seal the two halves of the caliper.

I think the reason being that the manufacturer provides the following warning:

Girling “split” calipers should not be separated for any reason. They were not designed for separation and reassembly and proper torque specifications are not known, other than the inner and outer bolts are torqued differently.

It seems odd for the manufacturer to give the reason that the torque specifications are not known for their own product! I can understand their wish in avoiding customers trying to split the calipers in case they are not sealed correctly and the likely consequences. Again, being of a cynical nature, I suspect this has as much to do with fear of litigation.

However, when I contacted a caliper reconditioning firm, they suggested that as long as new seals are used and the bolts are sufficiently torqued there shouldn’t be a problem. Leaks were more likely to occur elsewhere. Although I will keep an eye on the calipers once in service … just in case.

Their recommendation was to torque the 7/16″ diameter bolts to 70 lb-ft and the 3/8″ diameter bolts to 40 lb-ft. Also to work from the outside in and alternating sides each time, ie torque the outer bolt on one side then the outer bolt on the other, followed by the inner bolt next to the first outer bolt and finally the remaining inner bolt.

The front calipers have internal passageways to enable fluid to pass between the two halvesThe photo to the left shows the passageways for the brake fluid from the face where the two caliper halves join (the tip of the screwdriver is just about visible at the top of the upper piston bore). A corresponding passageway exists from the face of the other caliper joint and a small channel links the two piston bores. Thus providing the free flow of fluid between all the pistons in both halves of the caliper.

The rebuild is very straight forward. The bores and seal recesses were given a coating of Castrol Red Rubber Brake grease before the bore seal and outer dust rubber shield were fitted.

Grease was also applied to the cylinders before pressing home. The main point is to ensure the pistons were pushed in squarely to avoid damaging the seals. The outer lip of the dust shield pops into place as the piston is inserted.

Piston bore greased and seal inserted Dusty shield inserted before fitting piston

The piston bore and seal recess were covered with Girling Red Rubber grease before the seal was inserted into the recess

The rubber dust shields are insered into their groove in the caliper before pressing in the piston

Two smaller pistons & combined dust shield Greased pistons before pressing home

The front is a 3-pot caliper so one half has two smaller pistons with a combined dust shield

The pistons are also given a generous covering of rubber grease to ease fitting

Finally the two small seals between the caliper halves were greased and inserted into their recesses and the caliper bolts tightened to the torque setting above.

A square section 'O' ring sits in a recess  and provides the necessary seal between the two halves of the front caliper

Completed front and rear main calipers

The main difference between the front and rear calipers is the rears employ an external pipe for the fluid to passed between the two halves and therefore there isn’t the need for the small seals.

Jun 182013

My initial plans were to upgrade the brakes to vented discs with calipers from either Zeus or Coopercraft. By all accounts deficiencies with the original S1 brakes were addressed for the S2 cars so I’ve had a change of heart and will be fitting the original braking system for now. I’ll see how it goes and decide on any changes once I’ve driven it for a while.

All the calipers were sporting many years worth of brake dust, dirt and grease and were to be stripped back, cleaned and rebuilt. The rears were worse but once liberated from the IRS unit they were fairly easy to dismantle.

The rear calipers have the additional handbrake mechanisms attached

Rear caliper with external hydraulic pipe connecting the two halves

The handbrake ratchet mechanism and retraction fork

The handbrake mechanism was simply removed from top of the rear calipers by knocking back the lock tabs and removing the two retaining bolts. The other differences between the front and rear calipers is that the fronts have three pistons compared with two at the rear and the rears have and external hydraulic pipe connecting the two halves.

At the start I was somewhat bemused how one half of the front caliper worked as it didn’t appear to have any hydraulic feed. Obviously there must be an internal passage to transfer the brake fluid but I couldn’t see how the clamping force alone would create the necessary seal between the two halves of the caliper.

All became clear once it was split in half. In the middle of both clamping faces was a channel to the rear of the piston chamber thus providing a path for the brake fluid to flow between the two halves. Machined recesses contained rubber washers which would be compressed to create the required seal.

Unfortunately I’d not documented the rebuild of the calipers as it was done a number of years ago and they had been stored ever since. To my dismay, when I dug them out again, the zinc plating had already started to corrode …. and that was after storing them indoors!

The zinc coating on the refurbished front calipers had already corroded before they were even installed!

The worst corrosion areas were at the joint - I suspect it was a combination of poor plating and a pitted surface

It was probably due to poor plating but they’d certainly look quite shabby very quickly if they were fitted to the car and exposed to the elements.

The calipers would have been cadmium plated which isn’t an option nowadays due to the toxic chemicals involved. I’m relaxed over deviating from originality, especially for practicality reasons, and decided to strip them down again and paint them rather than re-plating. So it was another case of one step forward and two back!

The problem with the plating was limited to the cast iron components so only the main calipers and handbrake caliper arms will be painted. The handbrake ratchet mechanism will be left as passivated zinc.

The pistons were forced out in stages using an air foot pumpThe easiest method of extracting the pistons was to insert a bleed nipple into the hydraulic feed and use a foot pump to force the pistons out.

It’s a good idea to place a piece of wood between the pistons to limit their travel. The pistons can be pushed out in stages be reducing the thickness of wood each time. This enables all of the pistons to be pushed out rather than one popping out and the rest staying put.

It was also necessary to separate the handbrake caliper arm from the ratchet mechanism by removing the split pin and pressing out retaining pivot pin. The internal spring could then be removed more easily.

Handbrake ratchet mechanism and brake pad arms

Removing the handbrake mechanism cover reveals the spring which needed to be detached to remove the handbrake caliper arm.

The calipers were first soaked in a hot degreaser and then the joint faces and piston bores masked ready for painting. The paint kit ordered from Brake Caliper Specialists was a 300ml two pack paint (200ml paint & 100ml hardener) specifically designed for calipers, which was sufficient for all four main calipers and the handbrake caliper arms. Hopefully the 2 pack paint should prove more durable than other VHT paints.

A clothes rack provided an ideal hanging frame for the parts to be painted

All that remains is the caliper rebuilding ….

Jun 052013

The fuel lines within the boot space are made of a hard, opaque, white nylon and exit via a union mounted on the far right of the rear bulkhead. Metal piping is then used between the union, around the rear axle mounting panel and along the underside of the chassis, to the fuel filter within the engine bay.

Fuel filter just needed to be cleaned up and the filter replaced Dismantling revealed only small amounts of deposited fuel residue

The filter and union just needed to be cleaned up. So the alloy body had the ultrasonic cleaning treatment to remove the fuel residue and the other parts zinc-nickel plated. Leaving the difficult part of bending the Cunifer fuel pipe ….

Ultrasonic cleaning brought the filter lid up nicely Cleaned and re-plated; the rear bulkhead union and filter assembly

A 5/16″ diameter pipe is used for the fuel line so it is less forgiving than the brake pipes if minor tweaks are needed. The difficulty is that the entire section around the rear suspension cage needs to be bent into shape before it can be offered up. This involves bends in a variety of different planes, a sharper bends to then pass along the underside and ensuring the pipe passes through two retaining clips.

Fortunately I still had a slightly deformed original pipe to use as a template otherwise it would have been an altogether harder task. Again, as with the brake piping, I deviated from the original routing around the bolts for the torsion bar reaction plate. The only bit I’m not entirely happy with was the small section of pipe from the inline union in the engine bay to the filter which ought to be more horizontal. Still, it’s hidden by the vacuum tanks so shouldn’t stand out.

The good thing is that, now this pipe is in, the completed rear suspension cage can be fitted. Half way to a rolling chassis!!

Below are a few photos of the pipe routing:

Bulkhead fuel union Around rear suspension Double curve to underside

5/16 Cunifer pipe is used for the external piping from the rear bulkhead union to the filter in the engine bay

From the union, the pipe follows the IRS mounting section

A double bend is needed to clear the welded floor/bulkhead flange

P-clips secure pipe to chassis Avoiding reaction plate bolts Double bend to inline union

The pipe then runs underneath the car, attached to the strengthening section with P-clips

The pipe was diverted around the reaction plate mounting bolts to provide access for spanners

Another double bend is needed to pass around the welded floor/toe box flange to an inline union

Inline union to filter

Finlly from the inline union, the pipe passes behind the reservac tank (not fitted yet) to the fuel filter

Jun 042013

An almost standard replacement for the front suspension lower ball joint is the later sealed for life units. Less so is fitting a modern upper ball joint as it requires the case hardened wishbone to be machined to fit. If wear occurs in the upper ball joint, it is often as a result of wear in the wishbone’s ball joint seat, which becomes more oval in shape.

After a lot of deliberation, I opted to change the upper ball joints as well, using a kit from CMC as the local machine shop agreed to do the necessary milling of the wishbones.

I was less convinced of their ability when the kit was taken round and thought it wise to seek someone else to do the work. The instructions suggest annealing by heating the wishbones to cherry red and allowing it to cool slowly. All the larger firms weren’t interested and the independent machinists were few and far between.

The components of the CMC ball joint kit, including the mystery small nylon washerIn my hour of need I turned to E-Type International Rescue – McLaren’s Skunk Work team. There was some bemusement as to why the kit contained a pack of 9 shims rather than machining the wishbones correctly.

Also the brevity of the instructions had not explained the need for a small nylon washer in the setup.

After a few discussions it was decided that a grease nipple inserted into the cover plate would protrude below the plate. So the kit included a nylon spacer and a similar depth of shims to allow for the depth of the nipple below the cover plate. Ideally the plate should have been designed accordingly rather than requiring shimming and therefore additional machining.

The wishbone was media blaster before profile milling to match the shape of the nylon ball joint cupThe ball joint bores were profile milled with a ball-ended tool around the circumference, progressively stepping down after each revolution until it had cut to the required parallel depth.

At which point the wishbones were machined to match the curvature of the green nylon ball joint cup by reducing the circumference with each step down.

I’m really pleased as I had precious little chance of fitting newer ball joints without their help. I now owe several loans of the car … once it’s finished!

The completed wishbone and new ball joint awaiting fitting of the circlip