2nd Gen Non-Engine/Transmission rear- end hop

[cgage]

I have a 98' quadcab, 4x4. At about 45 mph the rear axle has a bounce/hop. It goes away +or- 5 mph. It has done this with three different sets of tires. Does anybody have any suggestions on where I should start looking to try to solve this problem? Any ideas would be greatly appreciated. If you have any ideas, but need more information let me know.

 

[TSRAM]

Have all of the tires been on the same set of rims? Has the bounce moved from corner to corner?

Just thinking maybe a bent or out of round rim.

 

[TFabian]

My 96 has been doing this for a few years. New tires, wheels, brake drums/brakes, U joints, center carrier bearing, driveshaft rebalanced, axle bearing preload adjusted, still there. It hasn't gotten any worse, I finally gave up. Checked all of the engine and trans mounts to make sure they are tight. Don't notice it accelerating moderate to hard. Seems to be worse with the AC on, especially coasting with no braking. My current guess is the pinion bearing preload or the bearing itself is shot as it started seeping gear lube over the last couple of weeks. That is my next project after finishing up the front end rebuild. I'll let you know if it makes a difference once I fix that. If anyone else has any ideas, I'm all ears.

 

[dkosheba]

TFabian,



I have two friends that owned 98 2500 gassers and they both had issues with bent factory steel rims. Even had them replaced under warranty to be out of balance again within 10K miles. Fix was at the salvage yard and switch to later model aluminum rims.



My first guess would be the rims, then I would run 60 PSI front - 50 PSI rear empty and replace the factory shocks.



I have also forgot to mention the drive shaft angle. The phasing of the drive shaft needs to be the same angle on trans yoke to drive shaft and the drive shaft to pinion within one degree. If that is off, the difference in angular velocity of u-joints with put a speed dependent vibration into your truck as well. I read a really good post on this the last week and am now unable to find it. Basically if you find the angles to be different by more than the 1 degree, you will need to put angle shims, or wedges between leaf spring and axle to adjust.



http://www.4xshaft.com/driveline101.html



I have not experienced any rear end out of balance so good luck!

 

[TFabian]

Currently running Alcoa rims, bounce still there. I went through the factory service manual procedure on the driveshaft angles and setup, still there. Shocks have been replaced twice with aftermarket shocks( different make), no change. The strange thing is that it is always at 45mph indicated. Plus or minus 2 or 3 miles an hour in either direction and it goes away. And for the kicker, it doesn't always do it???????

 

[Evil Otto]

i don't know if it is an auto or stick but if its a auto see if it does it in different gears. wind out second to 45mph see if it does it. then try it with the over drive off see if it does it. just a starting point. to see if it is in the trans. it would be great if you can do this test on a dyno.



ED

 

[TFabian]

Mine is a 5 speed. Does it both in gear and in neutral, mostly coasting or under a very light throttle. This one has had me stumped for quite a while. I think the pinion backlash is excessive in my truck. That is why I am leaning toward the pinion bearing/preload. I can't think of anything else that hasn't already been checked/replaced.

 

[DToy]

I have a '99 Quadcab 4x4 Auto that does the same thing, except that mine does it between 35-40mph, usually while coasting or under light throttle. Mine didn't show up until I put a leveling kit in the front, which leads me to believe that maybe the driveline angle is off slightly. I have tried different wheels and tires and it's still there. I'm thinking about trying some axle shims to put the rear pinion back to where it was stock.

 

[TFabian]

My truck has the stock suspension. Mine started this between 40K and 50K miles. Truck now has 120K on it. It hasn't gotten any worse or better. I've seen posts on this over the last couple of years, but no definitive fix for it.

 

[BV]

My 99 Q-Cab 5sp did this at about 40-45 however it would go away when I rotated the rear wheels to the front and would return on the next rotation.



It finally went away when I sold it last year

 

[Brand-X]

MY 99 QC does the same thing at 40 I swapped out the after market aluminum rims to steel rims I know are strait with different tires still does it...

 

[Evil Otto]

the next thing i would try would be to pull out the front drive shaft. it is quick and easy. and that will tell you if the front drive shaft angle is out. the only other thing i can think of is the the trans being off center a little bit. we use to loosen up the trans mount at cross member and at the trans give it a good shake and let it self center it self. re torque the bolts not hammer them on re torque them!!!!! this would some times work for slight drive line vibrations. good luck



ED

 

[TowPro]

my 98 2wd quad cab with 5 speed did this, I thought it was the wheels, but when I started running 30-35psi empty in the rear, it went away.



Sounds like low air pressure? weigh your truck empty, take the rear weight and devide by 2. Its like 750 lbs per tire or something if I recall. Then look in those papers that came with your owners manual, there is a graph that shows PSI per tire load, the graph don't even go as low as you need for an empty truck!



My original badyears were showing center wear running 45psi at 10K miles, thats when I started dropping the pressures.