Rolling Chassis – Page 3 – Chris Vine

Refurbishing the braking calipers …. again!

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 pump The 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 ….

Front Suspension Ball Joints

Front Suspension, Rolling Chassis No Responses »

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 washer In 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 cup The 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

IRS strip down

Rear Suspension, Rolling Chassis No Responses »

Aug 312012

The section in the service manual for removing the independent rear suspension (IRS) unit gave the false impression that it was simply a matter of disconnecting the handbrake cable, the hydraulic pipe and prop shaft, undoing the roll bar mounts and knocking off the radius arms. The IRS cage could then be lowered after unbolting the four cage mounts.

It probably is that simple for well maintained cars but mine had seized solid, resulting in bloodied knuckles and much cursing. In fact I couldn’t even get the wire wheels off as they were rusted to the hub splines! The brake connections and prop shaft were fairly easy to undo but everything else was struggle after struggle! The radius arms connect to cup fittings secured to underneath of the floor pan by what look like rivets. However the radius arms had well and truly rusted to the cups. Wooden wedges were hammered in but they still refused to budge.

I later found out from the E-Type forum that they are not rivets but something called Huck bolts, which are designed to shear in the event of an accident. I also found out others’ tricks to release the radius arms from the cups once the retaining bolts have been removed. Too late for my removal but no doubt they’ll be very useful in future. The first is to drive the car slowly backwards and forwards, with the aim that the changing loads breaks the radius arm/cup bond. The second is to chock the rear wheels and then jack up the front creating a load in the radius arms.

I briefly tried applying heat but all this did was burn the rubber bushes, producing acrid smoke. They eventually came free after applying penetrating oil over a period of several weeks and then jumping up and down on the end of a very long lever, inserted between the floor pan and the radius arm. To the untrained eye, the jumping up and down in a frustrated, childish manner while shouting ‘aaaargh!’ might have come across as a method of last resort …. but it worked!

The next setback was the removal of the roll bar. The bolts securing the mounting brackets were also seized but as they angled slightly downwards it wasn’t possible to apply penetrating oil so that it could soak in. Again I tried using localised heat but, like the radius arms, the bushes started to burn. By this time patience was in short supply, so I gave up and ground off the bolt heads to release the roll bar brackets.

The bolts securing the four IRS cage mounts had also rusted but fortunately they could be still undone. The main problem was the confined space so initially they could only be undone a 1/4 of a turn at a time. As I’d been unable to get the wheels off, it was rather an unconventional removal. Wooden blocks were placed under the cage’s base plate and the car raised away from the supported IRS.

The final dismantling of the IRS was equally unconventional for the same reason. The wheels and hubs were removed with the drive shafts and lower wishbones still attached and taken to a local garage so the hubs could be pressed out of the wheels. There was quite a build up of oil on the differential which suggested some of the seals might have perished. Although they’re interchangeable, and I didn’t know at the time, the aluminium hub carriers are not correct for the E-Type, which should have straight rather than sculptured sides.

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