Hi all,

First want to say thank you for the add to the forum, the information i will gather will go a long in the future for me on my current project i am working on (first chevy drivetrain). I am not very in tune withe the ins and outs of corvettes in general at this time but i am open to all recommendations, information, and positive feedback. I am looking at buying a 1985 corvette rear assembly to put into a project car i am working on which will be running a 4.3L V6 out of a 2001 Blazer. My main question is what transmission/transmissions would be acceptable (ratio wise) for matting to the 85 vette rear end. I would ideally want to go with a manual transmission but am not hell bent on it. Any guidance would be much appreciated.

 

Moving over to C4 Tech.

 

Thanks

 

C4s used 2 different rear diffs.
D36 7.5 gear that came in automatics. 2.59, 2.73, or 3.07
D44 8.5 gear that came in manuals 3.07, 3.31, 3.45, or 3.54
Need more details on your build.

 

It seems you're intent on using an '85 that you've located already 'somewhere'?
If that's a yes then you can ID what you've located by counting the bolts rear cover/bat-wing to differential. If it's an '85 that was behind a manual ratio will be 3.07 unless modified by an earlier owner. It would have 2 bolts across the top. If it was behind an automatic ratios could be 2.73 or 3.07.. All of these would have 3 bolts across the top. All '85 would have shoe-in-rotor for e-brake. If you were actually shopping, an '88 + would have caliper actuated rear e-brake. Some might prefer that!

For a project you can use nearly any combination engine/trans you like because you'll need to get creative with mounting the rear!

You might mention 'the project'!!!

There's likely a few thousand builds out there that have used a C4 rear suspension for drive!!

 

There is one exception to what Kevova said. All 1984 manuals cam with D36. 1985 was the first year for D44.

88+ rears are wider and use more offset on rims to compensate.
Personally I prefer "shoe-in-rotor" for e-brake.

 

Ok this is all good info to start with, much appreciated. I haven't gone and looked at the 85 that is being parted out yet and the seller hasn't sent me pictures of under the car just yet so i just wanted to gather any information i can before making the drive. The project i am working on is a 1976 Porsche 924 turbo. The car was stripped down to a roller by the previous owner so no sense in going back to stock, and i have been wanting to build something with a V6 for quite some time now. The current plan is to stick a 4.3L V6 that i acquired yesterday into it and use a corvette rear assembly which with a little fab work will mate up pretty nicely. I am only shooting for 350hp & 400+/- Tq. so i figured a stock C4 differential would be enough to get me rolling. As far as the transmission goes from the research i have done i have a good bit of options that will mate up with the 4.3. I am planning on having a driveshaft made. I just want to make sure the gearing is proper so i don't blow up the differential on its first rip. The car all said and done is just being built for fun. Doing burnouts, cruising around, and promoting my business. Not looking to beat any times at the local track or make it quick in a straight line or in corners for that matter. Just have a vision in my head that i think will turn out pretty cool. I am hoping to receive more information on the 85 that is available for part out today.

 

Wheelbase is close 924 is about 2 inches shorter. 4l60e transmission a manual driveshaft and c beam and a D36. Might all fit without alot of work. C beam supports front of diff and rear of transmission. C beam and driveshaft are different length between manual and automatic. Manual is shorter because D44 housing is larger than D36. If you fab support nose of diff, either model you will have more transmission options.

 

You don't need pictures of underneath.. Ask if it's an auto or manual. For an '85 there should be a label in the rear compartment drivers side that would likely display all RPO (Regular Production Options) the car was built with. A snapshot of that label would/should answer all of your questions. Do you have any snapshots of the car? A snapshot of interior showing clutch pedal, auto shifter, manual shifter??

Here's an '85 SPID

 

The guy has one picture on his his ad of the car from the back corner which doesnt give any information and is very on and off when it comes to responding which is why i have very little information been waiting over 24 hrs for a response on if it is a manual or automatic. Once i know more i will update thread to gather any additional information that would relate to the car.

 

Little update. I bought the car yesterday, it was dark when i got it back to my shop so i didn't have the chance to look at to much of it. I believe the panel that sticker is on is removed from the car already seeing that all of the interior down to the sound deadening has already been removed. It is a automatic. the previous owner said the motor is good but the started was grinding on the flywheel which is why he gave up on it (probably not the full story but its what i got) I am planning on selling the motor and trans for whatever i can get for it. Not sure if it is a LT1 or L98 just yet. Like i said before i am new to the corvette world. I did read a few threads talking about the visual differences between the two motors. can anyone give any insight based off of these few pictures. I know they aren't the best but its what i have until i get to my shop later today. Thanks for the input



on selling the motor and trans once i get them pulled today.

 

L98 and likely a 2.73 rear axle. If there's an AUX FAN in front of the 'radiator/condenser' package then you might look further. With an AUX FAN you might expect maybe a rear axle ratio of 3.07. It could still be a 3.07 but it would require further checks. There's potential 'build sheets' on the fuel tank or stuffed in the front cross-member. Condition after 35+ years?

 

It did have a small aux fan in front of the ac condenser if thats the one you are referring to. I am going to be getting the car on my lift tomorrow so will finally get a chance to get a good look at the rear end. I am thinking a turbo350 trans is the way i am going to go.

 

You might look for an oil cooler between the oil filter/block when you get it on the lift and you can use 'wheel rotation to pinion rotation' to confirm the rear axle ratio.That likely confirms most that might interest you .Very dependent on your finds, the front and rear springs might be of some 'resale' interest. Most anything else would be hit and miss maybe for value.

 

So all your guys help has gone a long way in deciding what to keep and sell off of the 85 i bought. I had a guy at my shop recently to buy the hood who shared a wealth of information with me which i was very appreciative of, he noticed the rear bumper on the car was a fiberglass Ecklers bumper. He was pretty excited about it and went on to say that they are worth a bit of money. It does need some very subtle body work mainly just a coat of sealer. can anyone confirm this and or give a value for something like this? the bumper is pictured above in a previous reply. Thanks for the help as always.

 

I had paid 'no attention' to anything other than your conversation regarding 'drive-train'! The rear cover is unusual and likely deserves more research. It's molded with provisions for the '90 ZR-1 tail lamps. It actually should/might have considerable resale likely. Much depends on condition. So easy to overlook the 'obvious' sometimes from here in the 'Wild and Wonderful'

Are there back-up lamps left and right of the tag?

The rear bumper might explain what actually did look odd to me when I first looked days ago. The 'VOID' top of the halo where the glass lifts. I had noticed that since a '85 wouldn't have had a CHMSL why it wasn't painted!

Ecklers looks to have a $640 ask or the bumper/cover (less lamps). Part # 25-100735-1 Ecklers links don't stick so just search the part #.

**** If the rear cover fits and all of the hardware is there and attached to the body - the more difficult aspect of a future install has been accomplished. if it attaches to your rear body panel with good gaps (fit & finish wise) , the next guy shouldn't have issues. What's used for the rear impact bar and absorber?

 

How much of the actual hardware is used on the bumper install?

 

18-19-20 stay on the car unless you are removing the fuel tank. Most of the other parts are attached to the bumper skin.

 

The OP needs to 'inventory' what's used from the original. We've all seen just a cover/fascia (call it what you like) hung on a car!!! No impact bar or absorber. If all of the retainers to the rear panel were installed correctly, then 'resale' could be much easier and bring likely more $$$$. Just hung there with little or no retainer retention I'd think certainly devalues the resale!!! Neither you or I installed this!! My cousin didn't either!!

 

Everything behind the bumper appears to bet stock. the fitment was really good and the gaps were consistent all the way around.