|Freightliner XC Chassis S-Cam Lubrication /
Meritor Brake Replacement
The Freightliner manual entitled "Recreational Vehicle Chassis" dated February 2003 contains several important
omissions, both involving brake S-cam lubrication. The first one is that in the write-up of chassis greasing in Section
00 of the Maintenance Manual portion, there is no reference to treating the brake camshaft bracket zerks, located
mid-shaft, differently from the other grease fittings. Lubricating those zerks (Item 7, one at each wheel), at the 12k
mile interval, even with only a couple pumps each time, will inevitably lead to contaminating the brake shoes with
grease, reducing or eliminating their stopping power. Make sure the person greasing these zerks realizes this and
greases them sparingly (if at all).
Secondly, Freightliner realized after this manual was printed that the S-cam and its roller pins will rust and stick after
about 5 years, leading to erratic brake shoe pressure. The symptom is a sharp "crack" sound from the affected
corner while braking briskly. Later manuals now cover these items in Chapter 42-12. Immediately below is a write-up
on how to lubricate the rollers yourself (yes, it is possible), and after that on how to replace brake shoes in the
Meritor rear end should you discover lining contamination.
It should be noted that these procedures require a great deal of physical strength, because the wheels and drums
are close to one hundred pounds each. And as usual, here's the disclaimer that you're on your own if something
Tools and Materials Required
The wheel nuts require 450 to 500 lb-ft of torque, so forget about 1/2" sockets and drives. This will require 3/4" drive
tools at the minimum. Here's what worked for me:
- 3/4" Sliding Tee breaker bar. Napa was convenient, but pricey ($60). Not necessary if you get the air tools
below, but might be useful on the road. A four-foot galvanized fence post or pipe section that fits over the
breaker bar gives you the leverage you'll need.
- 13" long 3/4" socket extension. Used to access the recessed rear wheel nuts with either the breaker bar or an
impact wrench. eBay was the best source ($25). If used with the breaker bar, will require support at the end
with a properly adjusted jack stand to keep the forces directed squarely onto the nut.
- 33mm socket, 3/4" drive. Again eBay was the best source ($20) because NAPA couldn't even find one in their
- 3/4" impact wrench with maximum torque spec of around 1000 lb-ft. Might be able to rent one with enough
torque for $20/day, but I bought a pneumatic one at Harbor Freight for about $100. Forget the 500 lb-ft model
they sell, because you can't actually get that much practical force out of it. Ideally you'll have access to a
powerful compressor with a 1/2" air hose and high-flow pressure regulator. I was able to use a standard 3/8"
hose, but only at an unrestricted 120 PSI. Electric impact wrenches don't have nearly the force required.
- Official brake grease (NAPA sells purple high-temp grease). I wouldn't trust any other type of grease not to
liquify and contaminate the brake linings.
- Two or three-foot lever for jockeying the wheels on and off.
- 3/4" box-end wrench for caging (releasing) the rear parking brake mechanism.
- 15" flat-bladed screwdriver or lever bar
Front Wheel S-Cam Lubrication
I did the front wheels using the breaker bar and extension handle (before I got
the air tool), without any socket extension. The motorhome jacks easily lifted the
front end to the point where the tires just touched the ground so I could loosen
the nuts without the wheel turning. Make sure the motorhome is completely level
when doing this, and I placed 4"x12" sections of wood under the jacks to get
extra lift. At four feet of lever action on the bar you'll need about 120 lbs of force
to break the hold. I used a 2-ton floor jack in addition positioned under the
I-beam to lift the tires off the ground for removal, and then to let them down just
enough to get traction while tightening the nuts.
The brake drum should come off freely, but you'll find a groove in the brake
backing plate near the top to allow a big screwdriver to get a good hold and help
lever off the drum. This is one heavy object, about 80 lbs.
Rear Wheel S-Cam Lubrication
After servicing the two front wheels in under two hours using a breaker bar, I realized how tiring it was to do it
manually. Twenty nuts on-and-off took most of the two hours and represented most of the effort involved, so I
decided to buy the air tool listed above. This make the job much, much easier, and avoids the side-forces involved
trying to use a long socket extension for the rear wheels. Using basically the same method as for calibrating torque
using the breaker bar, I noted the number of impacts it took to remove the nuts, and then practised tightening and
loosening until I felt confident with the torque setting. With the higher PSI but somewhat limited flow of a 3/8" hose,
even the 950 lb-ft impact wrench was working pretty hard, but watching the markings on the socket rotate and then
pretty much come to a stop made it easy to get the right torque repeatedly.
Before the wheels can come off you have to remove the decorative polished steel hub and Freightliner-badged
retainer cap. I'd recommend removing these before loosening the lug nuts, to avoid inadvertent damage to these
fragile parts. Because there are detents between the cap and the hub body, with every half-turn the cap will nestle
into a retained position, so the amount of loosening and tightening forces are minimal. But whatever you use to turn
the large hex cap should have a protective layer (several layers of cloth rag at least) or you will damage the thin
chrome plating. I had a large wood vise with two worm screws that was big enough to grip the cap but small enough
to fit inside the wheel. Be aware that the driver's side cap is reverse-threaded.
To remove the rear brake drum you have to cage (retract) the parking brake mechanism. Although you could air up
the brake system and release the parking brake as you normally would for driving, the official way to do it is as
follows (and is good to know how to do anyway). On the aluminum body of the brake actuator, generally toward the
back, you'll find what looks like a bolt holding two halves of the body together, but is only a service tool. The T-bolt
and its 3/4" nut are easily removed, and the "T" end of the bolt is inserted into a rubber-capped hole at the very top
of the actuator. With a 90-degree twist the bolt is held in place, and the nut (with the washer under it) is tightened
all the way - almost 3 inches, until normal force is not enough to tighten it further. This rotates the S-cam to release
the pressure on the linings so the drum can be removed. If the drum doesn't want to come off easily, you probably
haven't tightened the nut down enough.
Now you can perform the same procedure to lube the S-cam and its roller pins as for the front wheels. As
mentioned at the beginning of this write-up, if the "Brake Camshaft Bracket" grease fitting has received more than
just a few pumps over the years, you may find that your brake shoes and drum have been contaminated with
grease. If so, you'll need to replace the linings (don't just try to clean them), as shown below. Don't forget to release
the parking brake retractor and replace the T-bolt tool.
Brake Shoe Replacement
- The two springs holding the shoes together to the rear can be pried off with a large screwdriver.
- The shoes can now be separated at the rear and slid forward until the front spring and the shoes are free.
The relaxed front single spring can now be removed easily. Remove the old rear roller pins.
- The re-manufactured brake kit comes with two steel cross-pieces that hold the ends of the front spring to the
shoes, but they first need to be pressed into place in the new shoes. A sharp whack from a large hammer
with the shoes sitting on concrete will force them into position.
- To replace the shoes, hook the front spring on its cross-pieces and load the shoes back into position without
any of the roller pins in place. I attached the inner rear spring and levered the shoes away to insert the
newly-lubricated rear roller pins. The outer rear spring was then levered back into position with a
screwdriver. You might try replacing both springs after inserting the rear rollers, but I'm not sure how hard it
would be to maneuver the rear spring with a screwdriver around the back.
- The S-cam will need to be reset (rotated) to allow the drum to fit over the new shoes. At the inside end of the
camshaft you'll find a shallow 3/4" galvanized nut with a spring-loaded center collar. This collar needs to be
temporarily held away from the nut about 1/8" by a flat-bladed screwdriver so the adjuster can back off
freely. At the top of the whole assembly you'll find a square adjuster peg that you can turn with an open-
ended 5/16" wrench, until the roller pins would be sitting deep in the cups of the S-cam (retracted
completely). The fronts of the shoes can now be levered up or down to allow insertion of the lubricated new
cam roller pins.
- After the drum is replaced and the wheels put back on, with nuts at least partially tightened so the drum is
sitting squarely on the axle, turn the square adjuster peg until the shoes touch the drum, and then back off a
quarter turn (with the pawl retracted as before, of course).
- For rear brakes, don't forget to release the parking brake retractor and replace the T-bolt tool.
Tools and Materials Required
You'll need the same tools as listed above for S-cam
lubrication, but will also need:
- 5/16" open-end wrench to reset the S-cam.
- Large hammer to force pins into brake shoes
Although you could get away with merely applying grease to the ends and center section of the cam rollers, you
can lift the linings away from the roller pins with a 15" bar (or massive screwdriver) and remove the rollers
completely for cleaning and full 360 degree lubrication on the three wear surfaces. At that time you can clean off
the S-cam and lube its wear surfaces also.
I didn't want to spring for a proper torque gauge for 450-500 lbs ($700 from Snap-On), so I took care to remember
how much force it took to remove the nuts initially. After re-tightening them, I loosened a few again to see if I
needed the same effort to remove as originally found. It's admittedly crude, but I'm personally satisfied that the nuts
are on there pretty close to the original torque. And few service centers are equipped to measure this precisely
Brake replacement kits, one for each corner, are fairly
inexpensive ($60 + core charge), and come with new
roller pins and springs. The box is surprisingly heavy!
The upper and lower shoes are identical, so there's no
way to position them wrong inadvertently.
Follow the above procedure for removing the wheel
and brake drum. Then: