Wobbling truck

Joel · January 20, 2002

My truck has a wobble problem that is inconsistant. I can drive along at freeway speeds no problem but then sometimes at 50, the rear of the truck starts to wobble. In the rear view I can see the bed moving, the cab shakes.

The tires have been balanced and the problem is sometimes invoked buy going over a bump. I'm stumped on what the problem could be. Any ideas? I thought maybe the driveshaft or axle could be out of round but if it were, the wobble would be consistantly reproducable.

Joel

AirForceAngler · January 21, 2002

You may have a U-joint gone bad. Sometimes those are only noticeable at certain speeds.

Torque Junkie · January 21, 2002

I have a similar problem (though not as bad). I just had my rear ujoints replaced but it did'nt fix the problem. My problem is an annoying vibration in 4wd under power, and in 2wd w/ the hubs locked inwhile coasting. My dad's pretty convinced it's the front U-joints or the Driveshaft is unbalanced.

good luck!

-Mike

Joel · January 22, 2002

I notice a brake pulse when after she's warmed up but not when cold. This may sound crazy but could it be the drum causing the rear to wobble after it heats up? I'm going to try replacing the drum.

Joel

76BBSub · January 24, 2002

Joel,

There are plenty of things that could be causing this, it's tough to diagnose without a ride and visual inspection.

I'd say your brake hunch is a good place to start. Maybe a sticking brake pad(s) is causing uneven ride. Also, check your shocks that one isn't sticking or hanging up somewhere. Did the tire shop check the tires to ensure they aren't out of round? I've had that problem in the past.

You should repost this in the Classic Truck Forum, that's where we "old truck" guys hangout.

Later

Jeff

95Yukon · January 24, 2002

Although there are lots of possible causes, yes it could be a drum. I have had this happen to me. If a drum is warped, it can go out of balance. Also the out of round condition rotates around and rubs up against the brake shoes which can cause a vibration as well. (and also a pulsation in the brake pedal) ..especially when warmed up, because the heat can increase the severity of the out of round or warped condition. If it is hitting the shoes it will heat up more and compound the problem. Next time you park the truck, try and see if you can feel a difference in the amount of heat the drums are generating. Most likely, if one is hotter than the other, thats the problem one. I usually replace drums or rotors in pairs, either way. Keeps it from pulling and the brakes will wear more evenly. If that turns out to be the problem, check and lubricate your backing plates where the shoes make contact. If a warped drum has been rubbing up on the shoes, there may be a groove worn in the backing plate which can eventually hang the shoes up on it. Theres 3 contact areas which should get a dab of high temp silicone based brake grease, as well as the adjusters (sliding areas and threads) and should all rotate freely.

If the backing plates have wear, the shoes may not adjust up automatically like they were designed to.

Also, if you put new drums on, clean the axle flanges real good with a putty knife and/or wire brush to be sure its not going to have and little rust chunks that can make the new drum wobble. Its not a bad idea to put some of that same grease on the mating surfaces. It keeps the rust away and makes removing the drums easier next time around.

Good luck.

Joel · January 26, 2002

Thanks for the response. I'm now 99% sure its a drum after pulling one off. The rivit groved into the drum on one side. Also, I left the e-brake on one time and felt the warped drum bigtime. I need a porportion valve (front left gets so much pressure it pulls hard left), 2 drums, 2 front calipers (one is frozen) shoes and brake kit. Not sure if I want to put that much more money into a $500 truck.

Joel

95Yukon · January 27, 2002

You probably don't need the proportioning valve. It only controls front to rear pressure, not left to right and wouldn't cause a pull. The pull is caused by the sticking caliper you mentioned. The stronger side is working properly, but the sticking side isn't grabbing like it's supposed to, causing a pull towards the one side that is working.

Assuming the rotors are okay and the rest of the hydraulic system, if you get a caliper (probably should get 2) and set of pads, rear shoes, spring kit and 2 drums that should be all you need to get it stopping well. If you are planning on doing it yourself, the parts are common and should be fairly inexpensive. Just bleed it out real good, lube all the sliders and adjusters, adjust the rears correctly, and break it in gently.

Good luck with it whatever you decide to do.

Frank S · January 27, 2002

I'm going to drop this over in the Classic Forum as it may get a little more attention and not lost in the General shuffle due to high traffic.

Welcome to the board Joel.

BmannZR2 · January 28, 2002

I also have this wobble in my '99 ZR2, but it has rear disk brakes. It started after I put on some 32x11.5 MTR's that I bought from Frank. I have had them balanced twice so far and still at about 60 MPH I get a wobble.

Think the brakes could still be sticking?

Joel · January 29, 2002

Are you sure the porportion valve is only front to back? When I was bleeding the brakes, the right front was getting SO much more fluid then the front left. Of coarse its closest to the master but I figured that is why it was pulling.

ALso, the front right caliper was frozen & I couldnt depress the piston so I replaced it and the pull is still there.

Within the next week or so I'll have the money and time to replace the rear brakes and front left caliper. Hopefully the porportion valve does not need to be replace because its $180 list

Bmann, if the tires were balanced to zero (some shops don't do that), it could be the driveshaft that is out of balance. Next time it does the wobble, put it in nuetral and see if the wobble is reduced. If it is, the problem could be the shaft.

Joel

SierraBlue · January 30, 2002

I'm new here, but to test the driveshaft theory out. You will need a TAC to do it, the problem will come in at the same RPM. So take note at what RPM the problem comes in, then start out in first and bring your truck to the same rpm as noted, then second and third. Normally if the driveshaft is out of balance you will notice it at the same rpm every time.

I've had that problem on my 87 GMC Seirra.

95Yukon · February 1, 2002

I'm sure the valve is only front to back, but if you are getting more flow to the left or right when bleeding, (or braking) you may have an internally collapsed brake hose. They can swell shut and cause a restriction. I have done a zillion brake jobs and have seen this before.

Did you put a set of new pads on with the caliper? If there are any imbalances in pads/rotors it can easily cause a pull. If you replace pads, make sure the rotors aren't grooved at all, and same with rotors (make sure the pads aren't grooved) if either condition exists, they will not break in properly and cause a pull. Unless the pads and rotors are like new, I usually replace them in pairs, and do both the rotors and pads all at once. If the rotors can be machined, just new pads is okay, but don't mix and match used pads or rotors with new pads or rotors or it will be hard to get it not to pull. Usually a pull comes from the front, but can also sometimes come from the rear. I also try to do calipers in pairs to rule out any possibility of any inbalances in braking. If one caliper was sticking, usually if the other is the same age, its close behind, and may not be sticking just yet, but sticking intermittantly or just old enough to cause a problem.

Joel · February 2, 2002

Thanks for the tips. I have enough money now to finish the job. Today I will be buying new drums, shoes, spring kits and the other caliper to do the rears and I hope the wobble will dissapear. I also hope the wheel cyclenders are OK

It makes total sence to replace things in pairs, the only reason why I didn't do that in the first place was because of $. Hopefully the parts store will have the rubber brake lines. I'd like to replace them and the caliper in hopes the pull will go away. Its pretty dangerouse.

The front rotors are new & pads are new. The surfaces were clean clean before assembly.

I'm glad the porportion valve is OK, that would have been 180 bucks

thanks,

Joel

76BBSub · February 2, 2002

I have to agree that the brake hoses are suspect, this is a classic symptom of a bad hose. If thery're not replaced you will most likely have the brake lock up on you before too long. The hoses are usually $12 or less at Auto Zone. Cheap insurance.

Jeff