Rear end

[Supa.Slo.SS]

What motor/HP are putting out? If it's stock or near stock, I think it would be "cheaper" to replace the 7.5 with another 7.5 if you ever blow it. If your HP is near stock, I would expect your trans or something else to go before your rear end.

 

[Zippymac]

the engine is a 5.3 Tahoe 2005 - I initially put this motor in a 1980 and it twisted the frame and broke the spider gears.
Also later in the 86 MC the transmission blew out 3rd and 4th and had to be rebuilt with heavier sprags and z-pak clutch set like 7 clutches - same as in a corvette C5
I should have pulled the cam and top end down to at least figure out what is in it, but it showed signs of having been fresh rebuild and I wanted to keep the project on track.
after the 1980 MC got destroyed I located another G-Body a 1986 Monte Carlo LS rolling chassis.
The ECM has a performance tune on it and after running it on a dyno briefly it was at around 450Hp conservatively on first pull - the tester saw some electrical issues with ECM and stopped the test its been fis=xed since then and have not taken it to have it tested again.
.
after oil pan and hooker clam shell mounts - this is a Tahoe 2005 drop out I got from a salvage in Ohio.

Below is the intial install of the engine - everything fit under hood

this is after the first trial run - front end lifted and the rear end twisted and threw the car off the road
Frame twisted and broken and the spider gears were busted...
I kept all the body parts I could since my dad has an all original stock 1980 I restored for him a few years prior to this.

 

[565bbchevy]

My Solution - I called Currie and got a ford nine inch with stock mounts, and axles chevy bolt pattern 5x120mm and 70mm diameter wheel hub basically ALL the stock dimensions except I asked to have it 4 inches wider track overall.

For a 4" wider track width I am surprised you just didn't go with a 12 bolt out of an A body and use the conversion arms since some of those are already 4" wider than the Gbody rear end.

 

[64nailhead]

I like my Foxbody 8.8 with Trick Chassis arms, I got 5x4.75 axles and it's pretty darn bolt in aside from having to weld spring perches onto it. I'm in it for less than a 1000 bucks too.

I’d like to try these, but Foxbody 8.8’s are nearly impossible to find on the cheap.

 

[gnvair]

The drive shaft length difference is not for the 2004r transmission but for the 8.5 differential. The larger 8.5 rear requires a shorter drive shaft that is approx 1" shorter. The 2004r uses the same length driveshaft as th200,th250/350 and the Saginaw/Muncie manual transmissions.
Of course my statement applies to all 78-88 A/G bodies except El Caminos which have a longer wheel base.

 

[Zippymac]

For a 4" wider track width I am surprised you just didn't go with a 12 bolt out of an A body and use the conversion arms since some of those are already 4" wider than the Gbody rear end.

liked the idea f being able to switch gears - just remove a handful of bolts and swap gears is easier - 12 bolts are nice too

 

[Ugly1]

Will a 8.5 bolt in to replace a 7.5 rear end im trying to plan out my next move. Also if so what car can I pull a 8.5 rear end out off? I’m trying to be able to do some burnouts here and there and maybe a few donuts once a year haha anyways thanks in advance I’m going to be askin a bunch of beginner questions

You can also put a 1968-1971 A body rear end ( possibly 72’-73’ but they may be wider) if you use adjustable upper control arms. The rear ended needs to roll forward to work in a g body. The biggest thing is to do the finale adjustments with the car sitting on the ground or a lift that allows the suspension to sit naturally. In the late 80’s early 90’s we didn’t have the adjusters. You would roll it forward drill or torch the holes then cut off the excess as it would hit the top of the pumpkin. Mine sat 1” left when set on the ground, it tracked fine, but you could not get it to do donuts !! It go about 3/4 of the way around and just stop.
Anyway this will allow you to put in a 12 bolt with the OEM springs

 

[-dw-]

I believe it’s 72 olds 8.5 in my 84 now. Redrilled the mounting to tip the pinion down. Used the gta/iroc rear rims on the back. Worked just fine.

 

[JD1964]

What is the weak spot on the 7.5”? What breaks first? Can the 7.5” be strengthened?

 

[pagrunt]

You can also put a 1968-1971 A body rear end ( possibly 72’-73’ but they may be wider)

It'll be '68-'72 for 2nd gen A's. Now 1st gen A's ('64-'67) fit the same way as the 2nd gen but a shorter width at 60.5" vs. 61.25". '73-'77 should be about 61.5", our generation is 58". There are upper control arms out there to allow '64-'72 rears to be used in our cars.