grind and thump

[CMiddlebrook]

I've got a 93 CC W-250 w/ 190,000 miles and a 91. 5 W-350 w/147,000. Both have the Getrag five speeds and 4. 10 limited slip rears. When backing there is a grinding sound in the rear of the truck and a loud thump that shakes the truck when turning left while backing. It will do it sometimes when unloaded but mainly when gooseneck is hooked up. I've tried to duplicate the noise when I'm listening, but no luck. Pulled diff covers and all is intact in the rearend. Must be a Dodge thing. I've had several Dodge's over the years and when they break they seem to self repair if you keep driving

 

["Mad Max"]

sounds like the lim slip clutches are a little old/tight. Had similar problem - fixed by draining all fluid from diff and refilling with fresh gear oil and one bottle of mobil 1 synthetic - worked great. The M1 works just like the hypoid gear additive, which is just a friction reducer, so the clutches will slip on turns. Mobil1 is available at most WalMarts while the hypoid additives are not as common, but NAPA has it in stock if there is one local for you.

I wouldn't recommend all M1 as it is so slippery that it doesn't stick to the gear teeth well enough to go 100% M1 (or any other synthetic for that matter), but one bottle of it is great for a diff.

- Max

 

[bgilbert]

Do you have limited slip additive/friction modifier in along with the gear oil? You need like 7-8oz of additive.

 

[CMiddlebrook]

Do you have limited slip additive/friction modifier in along with the gear oil? You need like 7-8oz of additive.

Yes, I've got modifier in both trucks. I've even tried different brands and Lucas seems to keep the noise toned down the best.