Another 7.5 Rear end "what to do" thread.

[mrpostman]

I know this subject is beat to death here, and I have read countless threads on the subject. I wanted to get a personalized answer as I haven't come across a thread that really spoke to my situation.

I am not a wrencher, motorhead, gearhead whatever you want to call it. I recently picked up an 86 Cutlass with a 327/TH350. I am not afraid to mod or work on this Gbody, with that being said I have never restoed or modded a car in my life. I have taken in a sh*t ton of info since joining the site and I want to say thanks for that.

Now for the thousand dollar question "Which direction should I go with this rear end?"

The car will be strictly street and a cruiser with maybe a few Friday night test and tunes, it is our 3rd car and will need to be driven 1-2 days per week. The motor is cammed up nice and the TH350 was rebuilt, I was told the 327 was pushing 400HP but I am skeptical. I won't be adding any mods to the engine so a "beefed up" 7.5 may work fine. I want a posi rear however, I want to burn both tires, and I want it to hook nice on Friday nights. Maybe a LSD would work but honestly I don't know, I'm a friggin n00b. I do not want a spool, I had a gbody with a welded rear end and I assume a spool would be similar to that, I hated how that handled. I believe swapping an 8.5 presents the easiest project for my skill level assuming it doesnt need to be pulled apart and rebuilt in any way. I am also open to swapping out the carrier etc etc so I can get posi/LSD and a 3.42 into the 7.5. I believe the option of an aftermarket 9" (even the cheap one from Quick Perf) is a bit more investment than this car requires considering the output and the limited upgrades I have planned for it. I guess a third option is the 12 bolt mod/swap or even the 8.8 The problem with these 2 solutions is for 1, I have limited contacts, as far as a trusted shop in my area, and 2, doing the mods and swap myself are way beyond my skillset (I do not weld)

1. Is swapping out 7.5 for 8.5 "easier" than swapping the carrier/gear etc? Keep in mind my basic skills and basic garage (I honestly have no clue what a shim or crush sleeve looks like).

If the swap is the way to go, I would still be putting a 25+year old part(s) on this car, I assume there are preventative maintenance steps that need to be taken (bearings/seals/fluid?)

2. What parts/tools exactly would I need to turn this into a posi/LSD with 3.42? What car is a donor for the carrier? for the gear?

Is there anything I should be aware of or watch out for when contemplating and completing this project? Thanks for any help and answers you can give in this thread.

 

[Minion1186]

I would just grab the 7.5 and rebuild it with low gears and either a limited slip or trutrac. I built my 7.5 with new internals at around $1200. The prices may vary depending on how "souped" up you want the rear to be. I have c clip elminators, 28 spline moser axles and a girdle which is why my build costs a hair over a grand. 400 some horse or under will not kill a 7.5 that is rebuilt correctly either.
Get a rebuild kit from yukon, convert (if necessary from) 26 spline to 28 spline, grab a good set of low gears (anything from 3.23-3.73) would be good with a 3 speed and either a eaton limited slip or detriot trutrac. Spend the money and get it rebuilt correctly and you'll be happy.
On another note, 9 inches can be expensive if you're on a budget and 8.5's regardless of their strenght are still like any other rear, it will eventually have to be rebuilt at some point in time.
Here's a good build of a 7.5 rear
http://www.chevyhiperformance.com/techa ... index.html

 

[CHRIS.O]

For the price of new gears and a posi unit, assuming you buy new you may as well upgrade the rear end in my opinion. I do not think you would have a problem drag racing it occasionally though with a 7.5 other than peg legging it. With your power level you do not need a 9"

To answer your question about the swap, ya I think it would be easier just to bolt in a complete rear than change gears and carrier if you have never done it before. You need a few tools that you probably do not have laying around.

 

[mrpostman]

The problem is locating a cost effective 8.5 There is a 442 down the road from me with a crate 307 with 5k on it for 1500. Im going to grab that and swap rear ends I think. Those 8.5s are hard to come by.

 

[pencero]

Hey bro, I suggest buy the Moser 8.5 unit grab brake pad from box blazer/s10 or s15 platform and I'll sell you 3.73 detroit tru-trac for 8.5'' cheap if you do R now, Im dead broke and the 3.73 gears just sitting @ shop and the car in storeage. Why rape and pillage a more collectable 442 car than the one you're currently working on for this rear end?! It sound like a bad plan to me - who will buy the other car when it sitting behind your house on bricks and cant even roll away?! And nobody will want it if you downgrade it to the 7.5 rear end so then youll have other car which might eventually get scrapped because of this decision set you are considering!

Theres 9'' ford rear end $300 near me right now btw and it only need hubs/brakes ready to go 3.42 I believe - why overspend and get stuck w/ all this extra equipment in backyard? Consider the female problems that might arise if you go that route too!

 

[mrpostman]

Since I am not really restoring the 327 Cutlass I have, buying that 442 for cheap would give me a real resto project to work on, and I would always have the 8.5 to put back in it. I kinda want to rescue the 442 anyway it looks like the owners just want it gone and it has a good motor etc. 9" are everywhere used, the trick is finding one that is already narrowed and set up for a g-body.

 

[pencero]

wow, I was surprised you were online @ this time of night also. *_^

sorry I misunderstood that you were 'balling out of control' and would just ditch the 442 to mod out the cutlass your working on now. I hate when ppl do that and then the car sit outside for a couple years and get scrapped its such a waste when that happens! Anyway, at least you didnt make the mistake I made. When I ordered the tru-trac 3.73 I misunderstood that the brougham model had the 8.5 rear end - then I lost the reciept and couldnt trade back for 7.5 rear end gear! Your car looks alright wish you best of success

 

[85GPLef41]

wow, I was surprised you were online @ this time of night also. *_^

sorry I misunderstood that you were 'balling out of control' and would just ditch the 442 to mod out the cutlass your working on now. I hate when ppl do that and then the car sit outside for a couple years and get scrapped its such a waste when that happens! Anyway, at least you didnt make the mistake I made. When I ordered the tru-trac 3.73 I misunderstood that the brougham model had the 8.5 rear end - then I lost the reciept and couldnt trade back for 7.5 rear end gear! Your car looks alright wish you best of success

I may be interested in the 8.5 tru-trac... 🙂 PM with info if you are interested in selling.