I have a 98 dakota sport with a 8.25 rear. So I changed my rear diff fluid with lucas full syn 75w-90 and it says that it already has the additive for limited slip. The next time I got on the highway the truck started to shake at 45+ mph. Since the shaking didn't start till after changing the fluid i'm assuming that has something to do with it. I wasn't able to get the diff cover off due to a couple of stripped bolts. I tried a few different methods but to no success and I don't have the money to take it somewhere and have them take it off. So I just suctioned all the fluid out.
After reading multiple forums, I noticed some have suggested different oil. Some have said that 75w-90 is fine others say 90w-140? Also I noticed that some suggested to add the limited slip additive even though lucas already has it?
Also to mention I bought the truck from a private owner about a year or so ago and it didn't come with owners manual. No idea when the fluid was last replaced and 18x,xxx miles on the truck. I would have liked to have done this a year ago but money has been tight.
any and all help/advise is welcome and appreciated
thankyou

 

Hi Medic,

The fluid change is not likely causing the shake. 75w-90 is fine and even without the additive it won't shake. You might notice a chatter noise on turns - IF you have an LSD.

Is this a 2wd or 4wd? Try shifting to neutral while driving to see if it gets "better." Maybe it is powertrain related. It could be a tire/wheel problem, u-joint/driveshaft, lots of things.

 

it is a 4wd. I realize that this symptom could be from something else and the only reason I feel like it has anything to do with the rear diff is the proximity in time with the fluid change. before the change no symptoms, after changing fluid, next time I drove it, noticed truck start vibrating or shaking when exceeding 45mph. So I'm assuming because of that that it had to be the rear diff. or i'm extremely unlucky and something else happened at the exact same time. the rear diff was the only thing I touched by that point.
Thanks for the input

 

another symptom I forgot to mention is that I only notice while under acceleration, as soon as i take my foot of the gas it subsides.

 

It still could be a driveshaft problem including bad u-joints. Can you tell is it stronger in the front/rear? Do you notice it under your feet - bad front propeller cv joints is common.

 

I feel as if it is coming from the rear of the truck. definitly notice it more in the seat than my feet. was going to get under and look at it some more and see if i couldnt notice anything obvious, but it started to downpour so I'll have to wait till tomorrow.
Again thanks for the assistance.

 

Sounds like a driveshaft issue to me, too. Did you disconnect the driveshaft for some reason when you changed the diff fluid?

 

may put a bind on something when you jacked it up ?

 

No I did not disconnect the drive shaft, didn't need to. There was a rubber plug that can be pulled out to change the fluid.
Didn't need to jack the truck up. Has plenty of ground clearance to be able to get under there and work.
thank you for the replies and thoughts.