a new rear end 8 3/4 "rummbling" noise...

[culp71]

well, I did a little shopping around, and while I really prefer to do everything myself as I have done everything to this car during the full restoration (aside from physically boring the block) I may order a complete setup unit from doctordiff.com as they complete , all bearings and gears are already set with proper preload and backlash/mesh etc.
I could pull my current one apart,and hope to find what's wrong and try to correct it, but I really don't know what I could do any different this time around compared to last time.

so looks like a few more bucks will be put into her.

anyone used such units from doc diff?
also my other thought is currently its a 741 they only have the 489 case.
did the 71 cuda 340 ever come with the 489 rear?

[Chryco Psycho]

In theory all 71s should have the 489  Carrier
Dr Diff is a Good person to do business with 

[303 Mopar]

Cass at Dr Diff is THE guy to go to for anything related to differentials. He will ask you great questions so you get exactly what you need.

[Brads70]

Any carrier will fit into the housing , tru trac is my favorite , best design by far , it unlocks with wheel input & locks with power , no clutches to overcome at all just gear pitch

Ove in CC.com days, I seem to remember tru trac having issues when in 8 3/4 rear ends?  Might ask Cass about that if your considering it?

[culp71]

perfect, appreciate it all guys!
going to order her up, from doc diff then.

[RUNCHARGER]

Yes: You can't go wrong with the Doc.

[culp71]

since I couldn't determine what was causing my noise in my completely newly rebuilt differential, and currently having a 741 without and Limited slip version, I decided to order a complete 489 case third member with proper gear ratio and their version of the LSD setup.

I received it yesterday looks very,very nice. I am planning on putting it in this weekend. my question is the yoke has the U bolt 7290 version yoke, they supply U bolts, but I believe originally the 7290 had the strap/cap style to attached joint from drive shaft?

I know the "U bolt version stronger" but I would like something closer to original.
can the strap caps off my 741 be used?
I believe I hade changed the pinion yoke to a 7290 version when I restored it.
or are they different?

also would a 489 be longer then a 741, would it require drive shaft to be altered?

what would be the correct strap/cap style?

[GoodysGotaCuda]

The yokes between a 489 and 741 are not interchangeable, by spine count at a minimum.

The length of the diff will not change, driveshaft is fine.


If you have a crush sleeve in that new diff, I'd highly recommend not taking the yoke off, as to not disturb the pinion bearing preload.


Sent from my iPhone using Tapatalk

[culp71]

no crush sleeve, doc diff says it has the "crush sleeve eliminator" but I will not be removing the yoke,
and thank you for the length info on drive shaft.


so originally did the 7290 have the strap/cap style?

I know the "U bolt version stronger" but I would like something closer to original.

what would be the correct strap/cap style?

cap? strap? and if so strap style, should they be round edges or square?

[Chryco Psycho]

The original would be the flat strap sty;e with bolts on each end , the Only way to change this is to replace the yolk

[RUNCHARGER]

Yes straps.

[culp71]

the noise is finally gone!!!
I was able to tweak/correct a few things during this winter, got to take her out for the first time this season last Saturday. one of things I replaced was a new 489 loaded third member, with 3.23 gear helical gear "Sure-Trac" differential from doc diff...and the sound is gone!
I did not really find anything "wrong" with the third member I removed, but no matter, the sounds gone, and more power to the tires now.
thanks to all for the help.
Doc diff supplied a very nice professionally setup unit for sure, I would suggest them to all.

[kawahonda]

I feel like my Dr. Diff could undergo some additional tweaking.

I get a slight noise at 38-50 MPH, primarily can hear it on deceleration. Still have 100 miles left in my break in, and need to replace the oil.

It's nothing to be alarmed about, it's just a slight wirr noise when before there was no noise. I'm thinking about taking it down locally for adjustment.

[dodj]

the noise is finally gone!!!
a new 489 loaded third member, with 3.23 gear helical gear "Sure-Trac" differential from doc diff...and the sound is gone!

I have an Eaton tru-trac in my 8 3/4 and it is noise free...what is a sure trac? is it the same thing?

[7212Mopar]

Sure Trac is Dr. Diff's own version of the Torsen style LSD. Eaton unit use 4 heli gears and Dr. Diff has 6. It supposed to correct the short coming of the Eaton unit that lots of people reported. I think is noise but not sure. I also read somewhere that Dr. Diff and Eaton had extensive discussion over the matters. I had about 300 miles on mine and so far so good. laid down two long tire stripes a few weeks ago.