Rear Brake Vibration

[Bdeal223]

So I got a problem that has completely stumped me. When I started working on my T4 in July I replaced the rear brakes (new rotors, shoes, wheel cylinders and springs) because they were shot, this was at about 368K. Well I have put 4K on the car since then and the rear brakes have had a very noticeable vibration to them when braking at higher speeds, say 50 mph or higher since I replaced them, mostly when braking hard getting off the freeway and such. Well in the 4K miles that I have driven it this vibration has gotten progresivley worse, so I broke down and bought new drums and shoes (different brand). I installed theses tonight, test drove it and it is still doing it. I was initially under the assumption that the drums I had put on before were not perfectly round from the factory. I have verified that the rear axle bearings are good and I have not differntial oil leaking and getting on the shoes. Again I am completely stumped on this one. Has anybody experienced this problem before? I never have and have do dozens of rear drum brake jobs in my day.

Thanks in advance for any input you guys can offer here.

[4wdEconoBox]

I've never experienced anything like that either. The only thing that comes to mind is maybe some type of bushing is bad possibly? Are you sure the vibration is in the rear? Just wondering.

[Bdeal223]

Absolutely in the rear, I can make it happen specifically when pulling the emergency brake. The most baffling thing I have experienced in 25 years of working on cars.

[Notmikeb]

Did you use new hardware? Aftermarket brake hardware kits can sometimes be a bit too "universal" so they can use the same part number for multiple vehicles. I had that happen with my old truck where the pins were too long and didn't let the brake hold down springs compress enough to hold the shoes tight. Vibrated like crazy at high speeds.

[4wdEconoBox]

I would have have to say it was some sort of worn out bushing then, maybe you didn't notice it with the old brakes because they didn't grab like they should and the new brakes grab and make the worn bushing noticeable? I know that doesn't give you much to go by, but maybe taking a look at any bushings connected to the rear axle might help? I wish some of the pros would chime in on this, because it seems very interesting! I've never heard of anything like this...

[lannvouivre]

You may also see if the rear tires are still balanced, and check everything on the rear suspension for wear.

Then check the rear bearings.

Then check the drum hardware (it's cheap, usually; maybe just throw some at it for laughs), then maybe check the wheel cylinders. You may also look inside the drum and make sure it didn't get contaminated with grease or oil. You may also consider making sure they are adjusted correctly. I have to do it on my 2006 Matrix pretty often because even though they're "self-adjusting," they either fall behind or don't actually self-adjust at all. Yours may be too tight or something.

I haven't really heard of this happening in drums before. I'm used to it being in the front from a bad rotor or out-of-balance wheel, so I'd say just look at everything and mess with it to see if you can find weird play.

[Bdeal223]

Thanks for the suggestions guys, I will dig into it further this weekend.

[Bdeal223]

The more I think about this, the more I think that worn rear suspension bushings causing slop in the rear end is the cause of this vibration. I do not think it is a brake system issue, all brake components are new and adjusted properly with no grease or oil present to cause problems.

[4wdEconoBox]

Thats the only think I could think of too, but I wouldn't even know which ones to start looking at haha.

[ARCHINSTL]

See for rear suspension info: viewtopic.php?f=3&t=5830&hilit=bushings
Tom M.

[Jarf]

The few times in my life I have run into this scenario, it has always been an issue with the park brake mechanism. The very fact that you can induce the same behaviour with the park brake lends further credence to it being a brake issue.
Did it do this before? does using 4WD alter the experience any?

Look at both cables to ensure they're fully returning, verify the lever pivot is free both sides as well as the adjusters and that all the springs are where they should be. (I know it's all new, but it's still worth going back over, especially if the behaviour wasn't present before the repairs)
Also make sure that the leading shoe has the smaller surface area of friction material and inspect the lining closely to ensure theres been no bonding failure, maybe even swap in the old shoes just to see if it makes a difference?

Generally bushings will be sloppy all the time not just when braking, but still worth putting a bar to them all, just to make sure they're tight.

[Bdeal223]

Well I ordered rear sway bar bushings last weekend because the ones on the car were shot, thinking that maybe (fingers crossed) that was the cause of the rear end vibration. Well I got the bushings today, installed them, which was not easy. The hangars on each side which connect the sway bar to the frame, the studs were rusted bad and sheared off when tring to take off the nuts. I ended up welding new studs on to the hangars.

Well when all said and done I got the bushings installed and took it for a drive and low and behold no more high speed brake vibration. I am very happy and glad that my initial thoughts ended up being correct.

FYI, for anyone who may have this problem.