I'm new to the Jeep world so I am looking for a bit of help here. I recently bought a 92 Cherokee with 85,000 on it. The thing runs and drives great, but I am getting a knocking noise from the rear when I apply the brakes. This is the only time I hear it and its seems to only happen when I apply medium pressure to the brakes. If I brake hard it doesn't happen. The knocks also seem to be speed related, the slower I go, the slower it knocks. Any ideas or help would be greatly appreciated. Thanks!
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Knocking from rear while braking?
- Thread starter robeport
- Start date
Matthew Currie
NAXJA Member #760
- Location
- Vermont, land of big clay
I assume you've made at least a cursory look under there for loose things such as a shock mount, broken spring leaf, etc.
A couple of possibilities come to mind. First, the self-adjusters on these rear brakes are pretty notorious for failing, and if one brake has gone way off, it could knock when engaging. You should open them up anyway, just to inspect everything. Although the mileage is pretty low, the age is sufficient for rust problems to develop. Look especially at the adjuster cables, which can rust right off, and the "nails" that hold the shoes to the backing plate, which can rust, as can the springs between shoe and plate. Those can make noise when they go. The good news is that the hardware for these brakes is pretty cheap and easy to find. When you put them back together it's a good idea to do a manual adjustment. Even if the adjusters look all right, I don't trust them actually to do the job consistently.
When you get the drum off, check it carefully for cracks and damage. Unlikely, but a cracked drum can make weird noises. Again, although it probably isn't badly worn, it might have rust buildup at the edges, including the groove that goes over the edge of the backing plate, and this can also make noise when the brakes cause a little flexing of the drum. If it isn't too bad you can knock off the rust and clean the groove out a bit.
A final thing to check is the rear universal joint. If it is either loose or binding, it can make noise. I recently had a noise from mine, and found that it had a binding cap, which only revealed itself when I actually took the shaft out. But if you jack up both rear wheels, and put it in neutral (BIG HAIRY JACK STANDS, please! - we don't want to lose potential members!) you might hear a crunching or creaking when you turn the shaft by hand.
A couple of possibilities come to mind. First, the self-adjusters on these rear brakes are pretty notorious for failing, and if one brake has gone way off, it could knock when engaging. You should open them up anyway, just to inspect everything. Although the mileage is pretty low, the age is sufficient for rust problems to develop. Look especially at the adjuster cables, which can rust right off, and the "nails" that hold the shoes to the backing plate, which can rust, as can the springs between shoe and plate. Those can make noise when they go. The good news is that the hardware for these brakes is pretty cheap and easy to find. When you put them back together it's a good idea to do a manual adjustment. Even if the adjusters look all right, I don't trust them actually to do the job consistently.
When you get the drum off, check it carefully for cracks and damage. Unlikely, but a cracked drum can make weird noises. Again, although it probably isn't badly worn, it might have rust buildup at the edges, including the groove that goes over the edge of the backing plate, and this can also make noise when the brakes cause a little flexing of the drum. If it isn't too bad you can knock off the rust and clean the groove out a bit.
A final thing to check is the rear universal joint. If it is either loose or binding, it can make noise. I recently had a noise from mine, and found that it had a binding cap, which only revealed itself when I actually took the shaft out. But if you jack up both rear wheels, and put it in neutral (BIG HAIRY JACK STANDS, please! - we don't want to lose potential members!) you might hear a crunching or creaking when you turn the shaft by hand.
Thanks for the ideas! After driving it around some more today, I think it may have something to do with those rear drums. The underside is pretty clean as far as rust goes. Geuss I'll try and make room in the garage and see what I can find. Thanks again for the help.
Cherokee91Red
NAXJA Forum User
- Location
- Charlotte, North Carolina
I have had the same problem with my jeep sometimes. Take off the drums and scrape, spray, clean them out. Dirt and dust get caught in there. I've cleaned mine out twice after the knocking begins and it goes away afterward.
Matthew Currie
NAXJA Member #760
- Location
- Vermont, land of big clay
Z22_Z33 said:
Funny behavior, especially grabbing, when wet is a common complaint that nobody seems to have come up with a definitive answer to (note: man, that's a clumsy sentence structure, isn't it?). Various recommendations include just about every possible thing that can be done to a brake. The lining material seems to be partly at fault. Mine started grabbing again shortly after an almost total rebuild, and the only thing I've found that controls it is frequent manual adjustment.
