Wait what? Do you need to rebalance after a u-joint change?
Nothing I've ever done, was that luck?
Me neither.
Drums, when out-of-round, cause pulsation when braking. Drums, when out-of-balance, cause vibration. Consider removing the drums, having them installed on a "wheel balancer", and see if they're out-of-balance. If they are, they're defective and you should get "free" replacements under warranty. But you'll be out the cost of the labor to check the balance.
Yes! Brake drums
are balanced.
You can see the weights on these drums. Spot welded? But, when I'm buying new I'll avoid ones like the first pic.
Too much added for my liking. Those weights have been known to be flung off on occasion, too.
To me, all that added weight says something about the quality of the drum itself.
Bad pour at the foundry resulting in it being more porous (lighter) in one area?
Compromised somehow during the cooling process?
Either way, doesn't matter, cause I'd pass on those & pick ones more like the drums in the second pic with the lesser amount of added balancing weights.
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"Balancing" a driveshaft can be beneficial. They're balanced when manufactured, and the weights spot-welded on. The weights can be knocked-off. But don't forget about BENT driveshafts.
Local shop did both my trucks.
Re-n-re'd the D/S, new U-joints & balanced for $150.00. Done in less than an hour.
Cleared up the prob in the '98...somewhat.
Big diff on the '97.
(2) Is there any chance someone's removed / replaced the driveshaft in the course of work? If so...
At the rear pinion, disconnect the driveshaft and rotate it 180deg. Reinstall. Test drive for vibration change.
Problem solved.
I swear I read about this trick in the GM manual. Well, I'm sure in the manual they say to mark the rear pinion joint before disassembly and be certain to reinstall it the same way.
Yes! ALWAYS mark the driveshaft in accordance to the pinion.
One of the things drilled into my noggin by the ole man back when I first started messing with vehicles, 50 (ouch, ouch, ouch!) F'n years(!) ago. (Damn that hurt.)
The guys at the D/S shop were impressed when they asked if it was me that had done that with a yellow grease pencil.
Also...the ole man talking again...
Install the grease zerks on the compression side of the D/S's rotation.
That way, the weak spot in the universal created by the drilling of the hole for the zerk is being squeezed against as opposed to being pulled apart.
The zerk prevents the hole from collapsing under torque.
Mechanic found a wheel weight on the front and then another weight on the back of the rims opposite of each other ....as in 180*....the very thing the guy at Discount Tire told me should never be done!!!! WTF?? Talk about a rabbit hole. Does no one know how to balance a tire?
Always balance wheels with the least amount of weight possible. Excessive amounts shows something's outa sync. Large weights have a greater chance of being knocked or flung off.
Weight added willy-nilly is a crutch for a poor install.
Wasted lead.
When I balance tires & weird stuff like that happens, I'll break the tire from the bead & rotate it 180° on the wheel then rebalance. 9x outa 10, end up using 1/4 of those 2 weight's total, in only one spot.
Fewer weights make for a more balanced wheel, which then means a quieter, more comfortable ride, and a longer-lasting tire requiring fewer balancing sessions over it's lifetime.
Then there's the 'dot' thing.
On the sidewall of most new tires are yellow & red dots.
They indicate particular points on the tire which need to be aligned with certain points on the wheel.
Properly utilizing the dots reduces the amount of balancing weight.
The yellow dot indicates the tires lightest point.
That should be aligned with the heaviest point on the wheel, which is at the valve stem.
In the same way that tires are never perfectly balanced from the manufacturer, tires are never perfectly round either, even when new. They have high and low points which occur where the belts are joined, and these points can cause vibrations when a tire is rolling.
The red dot indicates the tire’s high point.
Most of the time a wheel will also have a dot—either a drilled dot or a sticker to indicate its low point.
If your wheels have these marks, the red dot should be aligned with the mark on the wheel and ignore the yellow dot. By doing this you minimize the vibration caused by the high point of the tire.
Red over Yellow. If both red and yellow dots are visible on your tire and you
do not have any dots or marks on your wheel, red takes precedence over yellow and you should align the red dot with the valve stem. Cancelling out the high point takes precedence over the lightest point of the tire, which can be addressed with wheel weights.
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Have I mentioned that I've gone vibration hunting with a parts cannon?
On my '98,
Tires, wheels, drums, driveshafts (plural!) axles, all new diff bearings, ditched the gov-lock for an Eaton w/a new 3.73 gear set (Vibration related? Probably not, but hey, I was already in there, so...) engine/trans mounts, torque converter, trans rebuild. (4L80e. It was gonna need that sooner than later, anyhow.)
A complete front-end rebuild.
A complete poly-urethane body & bushing kit including new upper & lower control arms with the bushings.
It's better. Mostly.
Mostly it was a chance to modify with an excuse! Lol!
But...
One thing I've learned about these trucks is that they have a quirk.
GMT400's suffer from a malady known as 'beam walk'.
A resonant vibration between the frame rails at certain speeds. Usually somewhere between 30-45mph & again between 60 & 75mph. Seems to vary depending on the individual vehicle, but those speeds have been the general consensus around here over the years.
The longer the model version, the worse it seems to be.
Crew Cab Centurions can be really bad.
GM is aware of the problem.
They have a cure!
300-400 lbs of 'ballast'.
Yea. They want you to throw some weight in the back in order to 'fix' their design flaw.
Another sure cure to the vibration prob?
Box the frame.
From the last cab mount to the shackle mount.
That's a big job! Both in fab time & $$$.
Now I realize that the O/P's vibration problem became suddenly apparent as opposed to being a constant, but the inherent vibration problems of these trucks should be taken into consideration when vibration hunting.
After my front end was rebuilt earlier this year, I had to buy a new wheel as one needed a sh*t load of weights. Everything was fine, I was rotating every 3k. Then after one rotation, I noticed a vibration on highway. I took truck to a tire shop and had them road force balanced on a Hunter machine. Still there, but when I saw the kid who jumped in my truck and did the work I wasn’t happy. He was pretty young and he looked and acted really miserable, like he just didn’t want to be there working. I mentioned it to salesperson inside and he acknowledged that they were desperate for help. Machines only as good as the operator. Maybe I’ll go back and insist an adult balance them.
