Rebuilding-Restoring Lotus elan Rear Brake Calipers.

Through neglect and exposure over time to the elements, the rear brake calipers on the elan can take a beating, and often look to be in a very sad state of repair, in reality they should be serviced at regular intervals, but like many things automotive, they seem to fall under the banner of… if it ain’t broke, … don’t fix it.

No one wants a pair of grungy brake calipers (Front or rear) on their elan… So lets see what can do done to DIY rebuild and refurbish the calipers in your own workshop.

But first things first, a word of warning. If your mechanical knowledge is not up to scratch, and you don’t have the workshop facilities, then it might be best to take the calipers to a professional service rebuild centre.
But on the other hand, if you know your way around the workshop with the right mechanical skills, and the proper tools, then this can be a very rewarding rebuild project.

Here’s another snippet of advice. You will read in the lotus workshop manual, and I quote “Under no circumstances should the calipers be split in two”. This is a complete Furphy (Lie). The caliper body is basically nothing more than a simple hydraulic press held together with four high tensile bolts, and between the machined faces of the caliper bodies a special flat faced O ring seal resides in a machined recess in each caliper half, if the special O ring is NOT replaced, your brakes will FAIL. Maybe that was the reason for the warning about not splitting the caliper bodies, just in case an absent minded DIY person did the unthinkable??

But please bear in mind, that the caliper bodies are matched pairs and should not be mixed with other split caliper pairs.

The other two seals are those that seal each piston inside of the caliper body. They will eventually wear out, but will give an excellent service life. The pistons and bores are protected with flexible outer rubber seals which help to keep moisture and dust out of the piston/caliper assembly.

Rebuild kits can be purchased through most brake service centres, the author lives out in the bush, and the local brake centre spares guy never seems to have any trouble supplying the parts.

The internal bores of the calipers can, and will rust, unfortunately, the cast iron caliper bodies are rust prone, and another good reason to renew the brake fluid on a regular basis (Brake fluid absorbs moisture). The bores of the calipers can have slight corrosion without any detrimental effect on their performance. But if the machined groove recess designed to retain the piston seal in each caliper body is corroded, then a very careful inspection will be required to ascertain its serviceability.

BUT, if there is sign of pitting and wear on the outer surface of the pistons, then they should be replaced with new stainless steel items, it is essential to have a perfectly smooth unblemished surface for the seal to do its job on the piston.

This particular type of twin-piston rear brake caliper (With handbrake mechanism) was employed on a certain model Fiat, and also the Dino Ferrari, so it probably made a lot of sense to Colin Chapman to adopt same for the Lotus elan. Obtaining spares should not be an issue when the time for a rebuild arrives.

The image above illustrates the rust and corrosion that can occur to the original steel/chrome plated pistons. Damage such as this is totally unacceptable, because the flaking and peeling Chrome plate with tear the internal square section seal to shreds, resulting in sudden brake failure.

After the calipers have been dismantled/cleaned/inspected, they should be carefully bead blasted, then all orifices cleaned out with air pressurem then painted with a high temperature brake caliper paint, several light coats will be required to build the colour.

When bead blasting and painting the caliper halves, turn up a neat fitting wooden plug to prevent paint from adhering to the inner seal groove and the piston bores, and don’t forget to mask off the caliper body mating faces also.

Note the “like new” look of the unpainted metal, created by bead blasting all of the parts. HIGHLY important of course to thoroughly clean and blow all cavities and galleries out with compressed air (Wear your eye protection).

Photo shows the small rectangular section O ring seal seated into the machined recess, the O ring protrudes a small amount above the mating face of the caliper, which creates a compression seal when the parts/fastening bolts are carefully tensioned or torqued up during the rebuild.

With all of the parts refurbished, renewed, repainted, the rebuild can begin. Insert the piston seals into the grooves first, smear a light coat of rubber grease onto the components, which will make the assembly much easier to achieve.
The outer rubber dust covers must also be inserted before the pistons, the operation can be a little fiddly, but with patience the parts will all go together quite easily.
Note the new stainless steel pistons in the above photo, the set of four pistons were DIY machined to factory specs in the authors workshop, using free machining stainless bar, there is no need for any higher grade of material. (303 Grade SS or similar)

The piston is carefully re-inserted into the body of the caliper half. Do not pinch/damage the dust cover, make sure the piston pushes freely back into the bore. Now, can you imagine just how frustrating and fiddly this job would be IF YOU COULD NOT SPLIT the caliper halves?

Build/fabricate a brake caliper bench assembly holding rig, one of the best things around to make the job so much easier for brake caliper re-assembly.

The brake caliper during assembly. The original caliper high tensile fastening bolts were inspected and passed for re-use, and then re-plated to prevent future corrosion. All bolts are assembled with nickel anti-seize compound applied to the threads.

 

Having arrived at the point of complete assembly, we should have commented on the pins that support the hand brake assembly, as is often experienced, the pins are nearly always corroded in, and can be difficult to remove, they may require a long period of soaking in a bath of WD40 or similar, they may also require a fine point of heat applied as can be done with an Oxy Acet small welding heating tip… and then quenching, to break the rust bond, there is not much else than can be done to loosen corroded parts.

The day finally arrives when the brake caliper assemblies can be installed back onto the rear strut hub housings. Make sure that the threads of every bolt is smeared with anti seize compound, you will thank your self when you go to remove them again at some future date.
The high tensile bolts that fasten the rear caliper bodies together, are both 5/16″ and 3/8″ UNF thread. The torque loadings are 22-27Lbs-ft for the 3/8″ and 12 to 15Lbs-ft for the 5/16″.

No, you wont find that figure in the brake caliper section of the workshop manual, because they suggest not to dismantle, the specs are under the general bolt torque loading figures… and some well practised mechanics can get within 5% of the quoted figures by hand fastening, sans torque wrench. 

If by chance a set of very old calipers have been purchased and the pistons are jammed in tight, they might need to be forced out with hydraulic pressure, or forced out with compressed air. BUT BE VERY CAREFUL, both methods can be dangerous, particularly air pressure, the author has witnessed pistons that release like missiles, wrap plenty of blanket or similar around caliper before applying any pressure.

Setting up to bleed brake lines is as per normal practice, also bedding in new pads, follow the recommendations of the supplier.

Good luck.