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.

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