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Refurbishing Brake Caliper Pistons on your Boat Trailer

by | Sep 9, 2020 | Repairs & Maintenance | 0 comments

Refurbishing and Recondition Brake Calipers

Refurbishing Brake Calipers on your caravan or boat trailer can be an expensive exercise when caliper pistons seize. This problem is particularly common on boat trailers due to excessive exposure to corrosive environments. Of course, there are solutions and suggestions for ongoing maintenance; however, first, we must understand the underlying problem.

Suppliers manufacture calipers in Dacromet or Stainless steel versions for Australian boat trailers. old caliper piston jammed

Electric over-hydraulic actuators pump hydraulic oil to the brake caliper. The hydraulic oil pressure varies from 1000 psi to 1600 psi, depending on the trailer’s weight and the brake actuator’s size.

During braking, the hydraulic oil activates the caliper piston as it enters the cylinder chamber, thereby pushing the piston onto the brake pads, which in turn causes friction on the disc rotor.

This friction causes braking. The more pressure applied by the brake controller, the stronger the braking.

Purchase replace galvanised disc rotors below

Phenolic Pistons

Phenolic plastic, aluminium, or steel are all material options for caliper pistons. The term “Phenolic” refers to a variety of hard plastic that is exceptionally strong and heat resistant. These types of Phenolic pistons reduce heat transfer into the brake fluid. These are resistant to corrosion that could cause caliper binding and are lightweight.Caliper Slides

Whilst phenolic pistons indeed resist corrosion, they are known to scratch over time and can also sit for long periods. As a result, the hard plastic material becomes hygroscopic.

Therefore, reconditioning phenolic pistons is not recommended.

When its surface is scratched, a hygroscopic substance readily attracts water from its surroundings through either absorption or adsorption.

Badly jammed pistons are challenging to remove. Before installing a new piston and seal kit the piston housing will require honing

We recommend inspecting the stainless steel slides before the honing process. If they jam, they need to be replaced, and repair costs begin to rise dramatically.

If you find yourself jamming slides, our best solution is to buy new calipers with stainless pistons. While it is possible to purchase a new replacement slide kit, remove the old slide and clean the bore before installing the new slide kit—the time and cost of doing so often justifies the purchase of a brand new caliper.

If you wish to recondition calipers, keep reading for tips.

Disassemblycaliper with piston removed

Caliper pistons are relatively simple to remove with the correct tools, but it is essential not to mark the bore during removal.

Couplemate uses a specially designed air hose that screws into the brass adaptor. With this, 70 psi of compressed air pressure ‘pops’ the piston out of its housing.

If a similar air hose solution does not work, the phenolic piston must be mechanically broken out of its housing. During the piston breakout, take care not to mark the piston housing with tools.

Piston Housing Explained

The piston housing has 2 two holes.

  • One hole is the inlet for the hydraulic brake line. This inlet is 3/16″ UNF, where you may insert a brass adaptor within the tube or hose.
  • The other hole is a bleed hole. It contains a bleed nipple, which must always be installed higher than the inlet hose.

Immediately after removing the piston, the bore must be honed to remove the remnants of corrosion and any sharp protrusions that may be left in the bore. The caliper hydraulic bore must be pristine before replacement pistons are installed.

Tip: Remove the bleed valve and the adaptor for cleaning. Small animals may try to nest inside bleed nipples.

When looking at a jammed Phenolic piston, the outer dust cover looks like a seal; however, an inner seal performs all the hard work.  The two rubber rings inserted into the piston body include:

  • A lower slot – for a rubber hydraulic ring that seals the piston into its housing.
  • Upper ring – for a boot ring. It holds the dust boot into position and is a secondary sealing ring.

Inserting new pistons and seals is certainly a challenge for most servicemen and almost impossible for the handyman.

Couplemate prefers to coat the bore and piston with a silicone-based lubricant before inserting new pistons, as grease is unsuitable for caliper bores or slides.

Caliper reconditioning featuring Australian Made Couplemate Stainless Steel Caliper Pistons.

Stainless Pistons

Couplemate pistons are made in Australia from 316 Stainless. Commercial fishermen prefer stainless pistons as they dramatically reduce their maintenance and downtime.

The caliper with phenolic pistons was swapped for Couplemate stainless pistons. This caliper shows the installation of new seals, bores honed, and stainless guides served with silicone grease.

We found half of the stainless guides ceased.

Couplemate provides the following services on Trojan or Al-ko pistons only:

  • Supply Stainless Pistons
  • Supply and fit stainless pistons to new dacroment or stainless calipers
  • As well as supplying and fitting stainless pistons to used Trojan or Al-ko calipers

Take a look at the assembled Stainless Steel Disc Brakes here:

Our experienced team can repair or fulfil refurbish caliper pistons for various trailers. To access this service, please send your existing Trojan or Al-ko hydraulic calipers to Couplemate Trailer Parts. 136 Glenora Street, Wynnum. 4178. Queensland.

Please include contact details and instructions for the intended work you require. Upon receipt of your package, we shall inspect the job and call you with pricing to complete the refurbishment. For an indication of pricing, the link below shows what you can expect to pay to make your caliper look new again.

Finally, thank you for reading this post. I trust the information has been helpful in deciding on the best course of action for your trailer brake calipers.


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