Brake camshaft bush wear: checks and repair kits

A brake camshaft bush is the bearing sleeve that holds the S-cam shaft in place on a drum-braked trailer axle. When the slack adjuster turns the camshaft, the bush keeps it centred so the cam spreads both brake shoes evenly. A worn bush lets the shaft move up, down and sideways, and that costs you brake force, lining life and adjuster life. This guide explains how to tell when a brake camshaft bush is worn, which limits to check, and which BPW repair kits we supply for the job.

What a worn brake camshaft bush does to the brake

The camshaft runs through two bearings: one in the brake anchor plate near the cam head, and a support bearing near the slack adjuster. If the bush wears, the cam head no longer turns on a fixed centre.

Bendix explains the effect in its guide to S-cam foundation brake maintenance. Too much radial play leads to uneven brake shoe wear and a loss of stopping power. It also calls cam bushings a low-cost part that makes a large difference over the life of the brake.

Typical signs you see in the workshop:

• One shoe wears faster than the other on the same wheel end.
• The pushrod stroke keeps growing even after a correct slack adjuster setup.
• Grease does not come out at the seal when you grease the camshaft.

A worn bush is also one of the reasons a brake goes out of adjustment. Our article on slack adjuster checks explains why you should find that cause instead of turning the adjusting nut again.

How to check camshaft bush play

Check the bush every time the drums are off and the shoes are removed. It takes a few minutes and a dial indicator.

1. Remove the clevis pin so the slack adjuster no longer holds the camshaft.
2. Set a dial indicator against the cam head and zero it.
3. Move the cam head up and down by hand and note the largest reading.
4. Check the end play by pushing and pulling the shaft along its length.
5. Turn the shaft by hand. It should rotate freely without rough spots.

Use the limit from the axle maker, because it differs by brand and design. Some examples from public manuals:

• BPW's workshop manual for its axle stubs says to change the bush in the brake anchor plate when bearing play exceeds 0.8 mm. After assembly, the camshaft must rotate freely with no more than 3 mm of axial play.
• Bendix says a radial play of 0.030 inch (about 0.76 mm) or more means the bush or camshaft is worn and needs replacing. It recommends keeping play below 0.010 inch by changing bushes as needed.

Bendix adds a practical point: the next brake job may be a long way off, so a bush that is close to the limit today will be well past it before you open the brake again.

Greasing keeps the bush alive

Most camshaft bush wear starts with poor greasing, water and road dirt. BPW's advice on trailer lubrication is to grease camshaft bearings and automatic slack adjusters every six to eight weeks, and not more than 12 weeks apart for UK operations. Trailers that work on mine roads, in mud or through floodwater get more of the water and dirt BPW warns about, so do not stretch that interval.

BPW's guidance for greasing the camshaft:

• Use BPW ECO-Li Plus grease, the grease named in its manuals.
• Pump fresh grease until it appears at the seal. That shows it has reached the bearing surfaces.
• If grease does not appear after several tries, inspect the bush and seals for a blockage or wear.

BPW warns that missed intervals lead to excessive bearing play, faster wear and a shorter part life.

BPW camshaft repair kits we supply

For BPW drum-brake axles we supply two genuine repair kits for the low-maintenance brake camshaft bearing:

• The BPW 09.801.06.09.2 brake camshaft kit with iron bush.
• The BPW 09.801.06.09.1 low-maintenance brake camshaft bearing repair kit. Our part page lists it for BPW SN 300, SN 360 and SN 420 drum brakes built from January 1993.

BPW's HKN spare parts catalogue lists 09.801.06.09.1 as a kit for one axle, so one kit covers both sides, with bushes, bearing boxes, spherical bearings, grease nipples and seals. Ask us to confirm the contents of 09.801.06.09.2 against your axle when you order.

Fitment depends on the last digit of the brake camshaft code number. The same catalogue explains that BPW improved the brass bush and added an extra O-ring from February 2002, and changed the last digit of the camshaft number when it did. Older camshafts are replaced by versions ending in 4. BPW recommends replacing the bush and camshaft together when you move to the newer design.

If the shaft itself is worn, we also list the BPW 05.097.05.23.3 left-hand camshaft and the BPW 05.097.05.24.3 right-hand camshaft. BPW's manual notes that brake camshafts are not interchangeable left to right, and a removed camshaft must go back in the same wheel position. For York axles, camshaft parts such as bushes are on the York parts page. More BPW parts are on the BPW parts page and the brakes parts page.

Fitting tips from the BPW manual

A new bush only works if it goes in the right way. BPW's manual gives these points:

1. Mark each camshaft's wheel position before you take it out.
2. Drive the new bush in with light strokes, with its ring groove facing the grease nipple.
3. Fit the shaft seal with its open side facing the slack adjuster.
4. Grease the bearing before you slide the camshaft back in, then check that it turns freely.
5. Grease all bearing points through the nipples once it is assembled, then refit and set the slack adjuster.

BPW's catalogue also says to use ECO-Master automatic slack adjusters when you convert to low-maintenance camshaft bearings. Check the lining and drums while the brake is open; our guide to trailer brake lining wear lists what to look for.

What to send us for a quotation

To match the right kit, send as much of this as you can:

• The axle nameplate photo or the BPW axle number.
• The brake size, such as SN 420 or SN 360.
• The code number stamped on the brake camshaft, especially its last digit.
• Whether you need the bearing kit only, or the camshafts as well, left and right.
• The quantity, by axle.

If the numbers are hard to read, see how to find the part number on an old trailer part, or search the number on our spare parts search. The BPW axle and suspension page and the trailer and truck spare parts guide show the wider range. When you are ready, request a quotation and we reply by email with availability and lead time.