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8 3/4 REAR END Question
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Author:  ArchLAB [ Tue Jul 29, 2008 10:27 am ]
Post subject:  8 3/4 REAR END Question
I've got way too much gear right now - a 4.56:1 in a 742 case. Since I want to drive this beast on the highway, I need a higher gear.
Can someone direct me to a link that might help me decide:
1) Which Rear End to Use. I have the following on-hand:
a) 8 3/4" 742 case
i. 2.76 Non-Posi Chunk ready to install
ii. 3.55 gear & Pinion that I can swap for the 4.56

-or-
b) An 8 1/4: unit out of a 1985 5th Avenue
i. It has a 2.76:1 that was nice in the 5th Ave when it was running

I also like the 8 1/4" because it had a good width for my A-Body (BCuda) & it had better rear brakes. Down side is that it doesn't swap like the 8 3/4 & the spring hangers need shifting.


2) Since I've never swapped out a Rear End, I'm not sure I've got the right facility & tools to pull everything apart & replace the bearings (which are noisy as all git-out). Or, is pulling the axles & replacing the bearings easier than I think?

Thanks.
Author:  Doc [ Tue Jul 29, 2008 10:40 am ]
Post subject: 
Just so I am clear...
You already have a 8 3/4 rear end in the car with 4.56 gears?

If so, swap the center section, install the 2.76 gear set that you have, just to get a "feel" for that ratio (sounds like you like that high of a ratio) and also, to get some practice with doing a gear swap in an 8 3/4.

If the axle bearings in the 8 3/4 are bad, replace the bearing while the axles are out.
DD
Author:  ArchLAB [ Tue Jul 29, 2008 11:04 am ]
Post subject: 
Thanks for your reply.
Yes, the current setup is a 4.56 in the 8 3/4. it's not that I want to give up that low-end, I would just like to stop paying for too much gas & go easier on my enigne (4000rpm for 60-65mph is no good on the hwy).

I forgot to mention that some joker (yeah, that's me) put on wheels spacers (1.5" each side) to get the wheels to fit & look better. the width was just way to skinny. Since I didn't have a larger axle housing & didn't have the money to buy a wider one w/ new axles for a 4.5" wheel spacing, the $20 spacer option looked OK at the time.

But, over time, I think those spacers cause the axle housing to leak @ the brakes. they may also be responsible for a noisy ('whup! whup! whup!) sounding bearing. The bearing may have already been bad, but it's been a long time.
Author:  ArchLAB [ Tue Jul 29, 2008 11:09 am ]
Post subject: 
BTW. The spacer issue was making me look at that 8 1/4 rear end.
Author:  Aggressive Ted [ Thu Jul 31, 2008 1:50 pm ]
Post subject: 
I am running a 8 3/4 2.76 Auburn Posi in a 489 case. I really like it over the 3.23 I was running. However, my engine is built for allot of torque....
When cruising at 50 mph I am a little over 2000 rpm. At 60 mph I am at 2500 rpm.

I am also running 7" wide rims and P235 60 14's on the rear which fill out the wheel nicely. In fact I was running P245's which were nice too but I kept wearing out the center of the tires no matter how little air pressure I ran. No need for wheel spacers........

I have a bad habit with the temptation to bust them loose now and then. :D

I went through (3) 7 1/4 rears in 5 years. The 8 1/4 C-Clip kind of scared me for racing and the driving I do on twisty roads. The 8 3/4 gives me a peace of mind. Randy's Ring and Pinion set it up for me and did a great job!
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