8-3/4 Differential complete center section change

[TeeScott]

Gents, After about 2 years of cruising with the original 4:10 (calculated by repeated driving test), rear diff. gearing in my "mostly original" '73 ralleye 340 auto challenger, I am planning a change to make it more "cruising friendly". Due to limited availability of local shops willing to change the ring and pinion & do the associated diff. set-up, i will likely simply change out the entire center section. I am leaning towards either a 3:55 or a 3:23. My car has a 489 casting sure-grip differential.
Have found a few sources for ("Quick Performance" , "Dr. Diff.", & "Classic Industries", so far...) but am looking for some referrals based on the group's experience. I am willing to pay several hundred dollars extra to get a quality unit since this is an area where I don't want to have to deal with future complications. I am not in any particular hurry, but want to get it done while I am still young-ish.

THX.
Tee Scott

 

[540HemiCuda]

Dr Diff.

 

[Avalanche]

I just bought a complete center section from Dr. Diff.
Haven't installed it yet, but I did a lot of research and he always comes up.

 

[MOPARMITCH]

+1 on Dr. Diff

 

[TeeScott]

All, THX for the feedback. During my review of related posts in the archives, I have noticed that Dr. Diff. seemed like the clear winner, but I wanted to get an updated perspective.

-TeeScott

 

[mrmopar340]

Dr Diff.

 

[MILOJ]

You can get a ring and pinion also bearings and with a few needed tools watch a video and do it yourself That is what I did. Also a few parts stores will rent what you need

 

[Ricks72Chlgr440]

All, THX for the feedback. During my review of related posts in the archives, I have noticed that Dr. Diff. seemed like the clear winner, but I wanted to get an updated perspective.

-TeeScott

Cass will take care of you. He's a fountain of knowledge if you call and ask him.

 

[TeeScott]

All,
SO, I ended up getting referred to a local shop that has a history of doing solid ring & pinion, differential and transmission work. I discussed my plans to swap to a 3:23 gear set with the lead tech and he seemed very familiar with the work and with mopar rear diffs. (My car car drivetrain from transmission to diff. has operated quietly for the several years I've owned it with the original 4:10 gear set.)
I ordered my ring & pinion gear set from Quick Performance and a Ratech 3010K Deluxe Ring and Pinion Install kit from Summit. Work in the shop went along without problems and it was taken for a quick test drive before I was contacted to pick it up. When I arrived, we discussed the various set-up parameters (pre-loads, backlash and gear contact pattern, etc..) and everything was reported to be IAW the specs. provided by Quick Performance. (The contact pattern was NOT in the center of the ring gear teeth on top and bottom but was one of the other approved patterns).
So, I was happy and left the shop. Along my 9-mile drive home, I started to notice the gears whining under load (basically whenever you were mildly accelerating or even just maintaining speed rolling along at 35-50 mph). The whine stops when you let off the gas and coast or decel. (I became less happy.) I confronted the shop tech the next day and we again reviewed the specs he followed during the set-up & they again seemed correct. He has agreed to fully stand-by his work and we are currently working on a schedule to return the car to him for pulling of the gear set and re-checking all the specs./troubleshooting.
Is there any else that we should be checking? U-joints seemed O.K. so we didn't change them.
Starting to think, I should have just bit the bullet and ordered the fully assembled unit as some of you suggested...... I was in a rush to get this done before winter & attend some local Fall cruises and Dr. Diff. site has listed the 8-3/4" 489 gear set as "out of stock" for several months. (probably should have called them...)

THX for any advice/wisdom
--TeeScott

 

[540HemiCuda]

Did you have the original gears in your third member changed? ANY time you have quiet gears nowadays, I would not mess with them. Gear sets are all over the place in quality and fewer and fewer guys/shops can get them right.

If you have whine under power and at steady throttle, that is almost guaranteed to be gear whine. Now, whether that is the gears themselves or their set up is another question.

One other thing; the 489 originally used a 'crush sleeve' to set the pinion preload. It is best to replace that with a solid spacer and shims. The crush sleeve will work as long as you don't hit the rear too hard. But the solid spacer is very little more money and is far, far superior.

I would certainly have the shop take a picture of the pattern on both faces of the teeth on the ring gear when they are done.

Good luck.

.

 

[Spyder]

I put a Dr. Diff 3.55 in mine last summer. Excellent product.

I now wish I'd have gone 3.23, after putting the 512 in it this spring.

 

[Ricks72Chlgr440]

I put a Dr. Diff 3.55 in mine last summer. Excellent product.

I now wish I'd have gone 3.23, after putting the 512 in it this spring.

Yeah the 3.23 is my go to ratio for street driving. Our big blocks don't need much to spin the rear tires! I've run small block 408 strokers in my Dusters with 3.55 gearing.

 

[Chryco Psycho]

Whine is because the set up is wrong once worn in the whine may not be possible to ever eliminate

 

[TeeScott]

All, THX...for the feedback.

Chryco, I have heard that from the local "expert" on this subject. He has agreed to give me a "second look" at the set-up once the first tech/shop pulls it back out of my car. He warned that even if we pull it, find the problem(s), and make the correct adjustments, I might still have a whine.. I have only driven the car about 12-13 miles so far, & he thinks it unlikely any permanent damage has been done that would cause a "forever" whiny set of gears (but no way to be sure...). I might just buy a new gear set for ~$200 from Dr. Diff and be sure this is the last time, I pull the diff. apart.??

540 Hemi Cuda,
Appreciate the advice about using a solid spacer & shims vice the crush block. I ordered this set-up from Dr Diff today. Will use it if we find that the pinion position needs to be adjusted OR if I just start over with a new ring & pinion.

 

[STROKERCHALL]

I put a Dr. Diff 3.55 in mine last summer. Excellent product.

I now wish I'd have gone 3.23, after putting the 512 in it this spring.

Same, my 512 is still running 3200 rpm on the highway with 3:55, 3200 stall

 

[Chryco Psycho]

I have done these set ups in the past but not enough to be expert at it , if it is set up properly there will be no whine under power or coast so something is not right & once it is set up wrong the whine may be permanent Ultimately it may have been cheaper to just get a center section from Dr Diff