Brake drums have a wear limit which is the maximum inside diameter the brake drum is allowed to be. This number is often cast on the outside of the drum it's allowed to be 422.1 millimeters or sixteen point six two inches. This is for your standard American trailer brake drum or drive axle drum. A brand new drum comes at 419 millimeters or sixteen point five inches.
My general rule is you can use two or three sets of brake shoes for every one drum. A good indication is feeling for a lip on the drum. A brake drum micrometer is by far the best way to measure a drum but if you don't have one of those this quick cheap and easy technique works well. Get a piece of wood or here I've used a piece of PVC pipe. Cut one piece at the maximum diameter 422 millimeters and cut another piece at the halfway worn point which would be 420.5 millimeters. Now by placing these inside the drum- straight not at an angle you can quickly tell approximately how worn your drum is. Be sure to check for out-of-round and bell-shaped drum. The maximum variation that I work off is one millimeter.
Anchor pin bushes and alignment are a major cause of brake shoes coming out of the drum and wearing unevenly.
The rollers are no longer sitting on the s-cam properly. They are rubbing up against the s-cam bush housing and these brakes wouldn't be working very well at all. Even with a new brake shoe you can see the alignment is not in the correct position.
This is due to the anchor pin housing being bent.
The second part of the problem is wear in the anchor pin bush. This also contributes to the shoe being able to misalign. You can make your own tool for replacing bushes by using the old anchor pin with the washes and the nut and bolt. Spend a bit of time on the bench grinder making your pin so it's a loose fit inside the new bush. Note that quick-release brake shoes have different anchor pins, the pins that you want are the general purpose brake shoes use these ones to make your tool.
To replace the bush put it on your tool get a pair of vise grips to lightly hold the bush together and prevent it from spreading. By hitting the new Bush in you hit the old Bush out. Anchor pin bushes are easier to replace if you have the hub removed. This is because you can have a clean swing at the bush. For stubborn bushes that will not come out I use a reciprocating saw or a hacksaw to cut a slit in the old bush.
Just be careful not to go too far and cut into the housing.
I've also had anchor pin bushes even with a new blade that are very difficult to cut a slit in the bush. So another method that I have had success with is using a porter power or a small jack to press the bush in and out. Make sure what you're jacking against is solid enough to withstand the pressure. It is worth putting a jack on the other side of the housing to what you are pressing it in. This will stop it bending and getting out of alignment.
To fix the alignment issues use a jack or a porter power against the housing and bend it back into shape. I recommend you have a few spare bushes in case you damage them on the stubborn ones.
Volvo truck reline. Fixed anchor pin type. First jack up the wheel you're going to replace the brakes on and use a jack stand. Remove the wheels. Remove the brake drum. The easiest way to remove this type of brake shoes is to get a lever bar and lever it down so the weight is off the rollers. Remove or unclip the retaining clip and slide the rollers out. The pressure is now off the spring and you can remove it. This allows the brake shoe to swing down and take the pressure off the springs on the other side allowing you to unhook them easily.
If you're reusing the brake shoes mark which one is top which one is bottom so they can go back in the same place. Make sure your wheel speed sensor is very close to touching the tone ring. This one needed pushing in a little. You can also see that this wheel seal is slightly leaking. I'm going to put the brake shoes back on for the sake of this video but that wheel seal needs replacing. Use brake clean to clean the brake drum. Make sure there's no oily residue. A general rule for reusing a brake drum is that you should get two sets of brake shoes for every time you have to replace a drum.
To fit the brake shoes sit your top brake shoe in place, get your orange springs and connect them to the bottom shoe and let it hang off the springs. I like to place the springs one up one down.
Have the green spring hooked into the top shoe swing the bottom shoe into place. Remember that the springs on the other end are already connected. This is the tricky bit getting the bottom part of the green spring to hook into the bottom shoe. I've tried not to edit it too far so that you can see that it is quite fiddly and can take a little bit to get the spring to connect in. Use a bar to lever down your brake shoes and fit your rollers. Make sure you fit the locking tabs. Repeat the process for the top shoe. Check to make sure the springs are still in properly. Then fit your drums and fit your wheels. There's plenty more where that came from go to truck mechanic basics dot com here you'll find notes to all my videos and much much more
Trailer (air) Brakes Reline- Inboard Drum- Part 1
Trailer (air) Brakes Reline- Inboard Drum- Part 2
There is two types of brake drums today we are talking about the inboard style
Inboard style drum- the type you need to take the hub off to access the brakes
Outboard style drum- the newer type that you can remove the wheels then remove the drums and access the brake shoes without disturbing the hub
There is times when you might want to follow this procedure even for outboard style drums- when the wheel seal is leaking or when you would like to check and repack the wheel bearings
The example I'm using is a trailer with BPW axles
Jack your wheel up, make sure you jack in an appropriate place where its not going to damage anything.
Make sure your brakes are released. Build up your air, chock the wheels, release the brakes.
Then Back off your brakes so the drum will slide off easily and not get caught on the lip
Remove your hub cap
Remove split pin- get the back section as straight as possible
Undo the nut, this one only has one nut because we have the split pin locking it. Others have two nuts with a locking washer that is bent over to lock it in place
A trick that I use when I'm not on concrete and I don't have a wheel dolly. Get a flat piece of tin put some oil on it so the wheel will slide. Then let the jack down a little bit so the weight of the wheel is on the tin but not too much that you start getting the weight of the axle
Slide the wheel off. Sometimes you need to get in behind it and give it a push to get it started
Wheel is off
Take brake shoes off- take springs off, use a screwdriver to get in behind them and flick 'em off
There is springs on the inside and outside
Mark the brake shoes before removing them especially if you are going to re use them. With new brake shoes sometimes you will see written on the box- radial ground and the shoes have a sticker saying this way facing out.
Brake shoes off, check the s-cam play. A general max movement spec is .75mm or 3 thou
Slide the inner bearing off the stub axle
This particular set up has a different seal than most. It uses two plastic/ nylon discs. One part of the disc pushes hard up against the inside of the hub, the other side pushes against the stub axle
When inspecting the drums you are looking for grooves and excessive cracks. There is a special tool to measure the diameter of the drum. You take this measurement against the manufacturers specifications or sometimes it is written on the drum itself. Generally if you can feel a lip- replace the drum
To remove the drum, undo the row of nuts then jar with a hammer and lift it off
Technically your are not supposed to hit the drum. I'm replacing these anyway so it doesn't matter
Clean out the hub, I like to use disposable gloves for this part of the job. Once you have the majority of the grease out of the hub get some newspaper or old rag and give it a wipe out
Ideally if you had a pressure washer/ steam cleaner you could use that
Clean the bearings by spinning them in kerosene, this gradually gets the grease out of them. Use an air blower to lightly blow the grease and kero out
Repeat the process with clean kero until the bearings are clean
Take your bearing into the light and look down into the inner cone. If you can see pitting or damage to the hard facing on the inner race or the rollers the bearings need to be replaced
Check the bearing cone in the hub for pitting or damage. Also grab hold of the cone and make sure you can't spin it in the hub
Fill the hub with grease, fill the valley level with the cones
Pack bearings with grease.
Take the new brake shoes and fit the hardware kit- Fit the rollers and fit the springs
Set your s-cam so it is horizontal- flat, this makes it easier to fit the brake shoes
Fit the brake shoes, fit the springs
Fit the brake drum- sit the wheel/ hub on a 45 degree angle. This makes it easier when sitting the brake drum on, it will now sit on the lip without falling off
Clean the brake drum with brake cleaner- the brake drums come with an oily residue on them to stop rusting
Brakes work on friction- oil and grease on the drum or linings will make your brakes not work properly. Be careful with brake linings as they absorb oil and grease and you cant get it back out. That includes dirty greasy fingerprints
Wipe where the seal is going to go
Fit new seals
Put bearing on stub axle
Put the flat piece of tin down with a small amount of oil on it.
Adjust the height of the stub axle. Make sure the brake shoes are contracted (s-cam flat)
Push the wheel on, fit outside bearing, fit nut
Try to get the hub on as far as you can before jacking up the wheel. Having the outside bearing and nut firm lets the bearings take the weight of the hub and doesnt put pressure on your seals. This is especially important for the other type of seal
Jack your wheel up off the ground
Tighten your bearing up almost as tight as you can get it turning the wheel as you do it. Then get a sledge hammer and hit the top and bottom of the tyre to jar it to make sure it is all the way home
Once you have it tight and all the "way home" Back the nut off 1/2 to a 1/4 of a turn. Then by holding just the socket do it up as tight as you can by hand. Put the bar back on and tighten it a little bit more.
Check your wheel bearing play. What your aiming for is to just take the play out of it. Hopefully the split pin hole lines up if not you will have to back it off to the nearest hole.
Check the wheel bearing play with a dial guage
Fit split pin, bend the split pin over
Fit the hub cap
Packing Bearings By Hand
Bearing Packer Tool
Note- You will need a bigger bearing packer for truck bearings
If you want a long, indepth, by the book, how to this is the perfect playlist for you. From Fanshaw Motive College.
If you want a video on brake reline- outboard drums