Trailer S-Cam Kits: Camshafts, Bushings and Why Brakes Drag

What the camshaft actually does

The brake chamber pushes the slack adjuster, the slack adjuster rotates the camshaft, and the S-shaped head spreads the shoes into the drum. Everything about brake feel and balance passes through that shaft, so its condition and its support matter as much as the chamber and the linings people usually blame first.

The shaft rides in bushings at the spider and often at an outboard support bracket. Those bushings are the wear item. As they open up the shaft moves off centre, the cam head no longer spreads the shoes evenly, and the same air pressure produces different braking at each wheel end.

Length, spline and hand

S-cams are specified by three things: shaft length, spline count at the slack adjuster end, and hand, left or right, because the cam head has to rotate the correct direction to apply. Getting hand wrong is the classic mistake. It goes together and then releases instead of applying. Length and spline both have to match your axle and your slack adjuster, and axles from the same maker use several combinations, which is why measuring beats guessing from a model year.

Trailer shafts cluster into two spline families. Ten spline is the Meritor Q Plus pattern and covers most of the longer shafts. Twenty-eight spline is the older Meritor and Dana Spicer pattern, and in our stock every 28 spline shaft is listed for a 16.5 in brake. So the spline count on the end of your old shaft usually tells you which family you are in before you have measured anything.

Length is where you have to be exact. Our stocked range runs from 17.31 to 28.19 in, which is a spread of nearly 11 in across nine shafts. On the short end sit the Meritor E5506 left hand and E5507 right hand at 17.31 in, 28 spline, and the Dana Spicer E9731 left hand at 17.44 in, also 28 spline. In the middle are the Meritor Q Plus E1425A left hand at 20.44 in, 10 spline, and the Meritor E5511 right hand at 21.06 in, 28 spline. The long shafts are the 10 spline Meritor pairs: E1094 right hand with E1095 left hand at 23.44 in, and E11866 right hand with E11867 left hand at 28.19 in.

Those pairs matter. Four of the nine come as matched left and right for the same length, which is exactly what you want when you do an axle rather than a corner. And if your paperwork carries a Meritor R-number instead of an E-number, they cross directly: E1094 is R607001, E1425A is R607082, E9731 is R607227, E11867 is R607316 and E11866 is R607317. Aftermarket numbers cross too, so a Fortpro 41538, a Torque Parts 17-639 or CS41508, or a Newstar 2210-B-7620 all land on shafts we carry.

The symptoms worth acting on

Uneven lining wear across a single axle, a brake that drags after release, a slack adjuster that will not hold its adjustment, or visible movement of the camshaft when someone applies the brakes are all pointing at the same place. So is a wheel end that runs hot without a hard application to explain it.

Do the wheel ends on an axle together. A rebuilt end beside a worn one changes the balance across the axle, and balance is the whole point of the foundation brake. A trailer that pulls under braking is more dangerous than one that simply brakes a little late on both sides. Shafts in this range weigh between about 7.5 and 12 lb each, so the parts are cheap next to the labour, and doing one side twice is the expensive way to find that out.

S-Cam Kits we stock right now

Live prices and stock from our Tacoma, WA warehouse — every part a Premium Quality aftermarket Direct Replacement with a 6+ month warranty and published cross-reference numbers.

Frequently asked questions

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