I bought a 8 3/4 rear end, the 741 391 3rd member was redone but I dont think the bearings were replaced,anyway its got a humm at 2000 rpm and it quites a bit as the rpm goes up but if I let off the gas its gone,any ideas apprecate the help!

IMO,its used

runwhatyabrung

Long as it's humming "Bad to the bone" i'd leave it alone

I doubt it's new, as 3:91's are no longer available new for the 741 case. 3:55's and 3:73 ring gear sets are still being sold (new) for the 741 case.

Anyway, I had the same problem with 3.91's in the 741 case. I sold them cos' I got tired of hearing them howl. I chased the noise and tried everything and nothing went.

Your gonna get lots of advice here on how to fix what you already have, but I'll level with you by saying that your existing ring gear and pinion are gonna howl until you replace them, or buy a complete new re-manned drop-out.

Dr. Diff sells new re-manned SG sections for an unbeatable deal

My car is at the shop right now for the same thing.

I had a guy rebuild a 489 case with a 3.73 and the thing howled like a mother and was VERY tight. Took it to another tranny shop and they pulled it and boy what a mess...10 of the 12 ring gear bolts were stripped and nearly every measurement was way off.

Now this guy is having a heck of a time getting a good pattern. once he would get a good drive the coast sucked and vice versa. He settled for the best he could get and we took it for a spin and it still made some noise. Way less than before, but he was not satisfied...so after some to the Motive gear rep he's ordered another set to try again.

Anyways...This guy swears up and down that bottom line you should not be hearing the gears over the exhaust and he bassically was pleading with me not to take the car because he was not happy with what was done and it does not represent his shop. I was pretty impressed at that and he's still got it.

If it's howling either the gear is fubar or the thing just isn't set up right to begin with. After watching Bob set up mine with all of the things to check I gotta admit that it really is more art than science IMHO!

Thanks for all the help, Ive been driving it like this for two years and hasnt gotten any worse, I was wondering how to tell if the axle bearings are shot,or I heard theres an adjustment for the bearings. thanks again!

end play is set on pass side rear axle

you could pull the axle and repack the wheel bearings with some grease

the do not oil with the diff fluid in the chunk

most likly need it,

a good lube change might not hurt,I used some lucas oil stabilizer in mine and it quitend it down some

if ya been ridin it that way it most likly not hurt just showing its age

you could pull the drive shaft and check the play in the oinion and backlash on the ring and oinion

change the fluid and pack the bearings...then call it good and sleep at night knowing its lubed

Just one last question if it was the bearings humming would they hmmm constantly or only when im on the gas pedal . thanks again

constantly. if it's on the gas/off the gas noise, it's the R&P not properly set up. I've been told once they start making noise, it's virtually impossible to make them totally quiet. pattern and/or backlash isn't set up right.

Also my somewhat limited experience is that you cannot get some brand ring and pinion kits silent. Then again a little noice will not hurt the world...

give the doctor diff a call or PM him here on the board

good advice and service