Rear end upgrades for turbo car

David Neibert

SCCoA Admin
I'm going to need some 3.73 gears for the turbo car to help get it off the line a little quicker. While it's apart I think it might be a good idea to upgrade the diff from the standard trac loc to something a little better.

Please excuse my ignorance in this area, but what brand/type diff is it that doesn't use clutches but still has limited slip when going around corners ? Also is there some place I can send the stock centersection and have it built with the gears and diff I want ? Even better....I buy the entire center section ready to bolt in and just make the swap whenever I'm ready.

The shop that installed the gears in my 91 is no longer in business or I would have them do it.

David
 
David Neibert said:
I'm going to need some 3.73 gears for the turbo car to help get it off the line a little quicker. While it's apart I think it might be a good idea to upgrade the diff from the standard trac loc to something a little better.

Please excuse my ignorance in this area, but what brand/type diff is it that doesn't use clutches but still has limited slip when going around corners ? Also is there some place I can send the stock centersection and have it built with the gears and diff I want ? Even better....I buy the entire center section ready to bolt in and just make the swap whenever I'm ready.

The shop that installed the gears in my 91 is no longer in business or I would have them do it.

David
Dave,

Call me at home tonight and I'll give you the name and number to a very good shop here in town....they rebuilt the 5 spd in my XR7. For my next diff rebuild, I'm thinking about going with a Torsen Diff, but I'm not sure if that will handle 800 hp.
 
I have an Auburn center section in mine, don't remember exactly what type it is, but it works well. Bill M has/had one too.
 
David:

I have an Auburn Pro locking differential in mine. It uses a cone shaped friction surface in lieu of clutches. Seems to hold just fine.
 
Nettlesd said:
David,

You may be thinking about the Detroit True Trac or the Torsen as Kurt mentioned.

Duane, I don't think the Detroit True Trac has the necessary receiver grooves for the cur-clips, but I know the Torsen does. If you want something with a lifetime warranty, check out Quaife. The offer a forged torsen equivalent, but it's $$$
 
I think it might. "Detroit Truetrac’s are engineered for front and rear axles, semi-floating (C-clip axles) and transfer cases."
 
Our axles aren't "c" clip. They are spring clip retained. Thus a grove in the side gear that the spring clip pops into. It's not as firm as a C-clip, thus the ability to pop them out. C-clip retained axles can't come out unless you pull the c-clip out of the diff.

Regardless, the side gear has to be machined to accept the spring clip. I believe Vernon had to have his side gears machined to accept the clip in that post.

here's an old thread where options were discussed
http://www.sccoa.com/forums/showthread.php?t=32143&highlight=side+gear+groove
another old thread with helpfull info.
http://www.sccoa.com/forums/showthread.php?t=32135&highlight=side+gear+groove
 
David, FRPP sells an aluminum 8.8 center section with 3.73 gear and trac lok all assembled and read to be bolted right in. For the money that would be the way to go. Only down side would be that you will still have a trac loc.

Shane
 
Shane,

I don't like using the aluminum housing and I don't think the trac loc diff will hold up very long.

I did a little reading on the SVT boards and the latest version of the Detroit True Trac seems like the best option and it is compatible with the IRS circlips.

I'll just score a used pumpkin for someone and have the thing built locally.

David
 
DN, I have Wise's old pumpkin in the old mans garage. Drive the turbo up to get it, and give me a ride. That will kill 2 birds with one stone. :)
 
David Neibert said:
Shane,

I don't like using the aluminum housing and I don't think the trac loc diff will hold up very long.

David

Just curious David as to why you dont like them. Could you please explain?

Shane
 
Have you done the RPM/Speed calculations on using 3.73's? I didn't see what your 1/4 MPH was, but I'm thinking that 3.73's should be way short for the MPH and you'll be out of gear by the end and have to use OD.
 
Parker Dean said:
Have you done the RPM/Speed calculations on using 3.73's? I didn't see what your 1/4 MPH was, but I'm thinking that 3.73's should be way short for the MPH and you'll be out of gear by the end and have to use OD.
His redline is somewhere around 7000 rpms, so he's got a little more room to play with than most of us. Besides, he won't see a lot of track time. As soon as he blasts off a pass at the local track, he'll get kicked out until he installs a cage.
 
David Neibert said:
Shane,

I don't like using the aluminum housing and I don't think the trac loc diff will hold up very long.

I did a little reading on the SVT boards and the latest version of the Detroit True Trac seems like the best option and it is compatible with the IRS circlips.

I'll just score a used pumpkin for someone and have the thing built locally.

David

Just a couple of thoughts while you are on this as I have looked at a few things for this myself.

The aluminum housing isn't that big of a deal since it's not failing more or less than the cast iron one.

The cover is aluminum in both cases and that is what is failing. Rich over at MN12Performance as well as a few other places are selling braces that will strengthen the cover and secure the rear diff a little better.

There are at least a few guys over at TCCoA that are using the Torsen. 392bird is using a Detroit piece of some sort. You might want to put this question up over there too. I do doubt that there is anyone putting out the equivalent power that is being put out here though.

Good luck. Can't wait to see it run.
 
Shane,

I don't like the aluminum housing because it is weaker than cast iron. Would I break the aluminum one ?? I don't know but why risk it just to save a few pounds.


Parker,

I was reluctant to do the gear swap for the same reason you mention, but it looks like I will still be able to run 140 mph with a 26" tire and if I somehow manage to reach that speed, I can always switch to a 28" tire for the track.

The other benifit of the gears, is that it will increase my rpms at cruising speed which will help the transmission run cooler. With a non locking converter, driving at rpms below the stall speed generates a lot of heat. Right now I have a 2700 stall converter (non locking) and cruise at around 2200 rpms. It's not overheating but it is running warmer than I like and may overheat in the summer. If the gears aren't enough I can still restall the converter about 500 rpms higher and be no worse off than I am now. If I restalled the converter without a gear change I would be forced to drive the car in 3rd gear to keep rpms up, and that would be very annoying.

Martigan,

392 bird is using a Detriot Locker in his car and that is a little too extreme for me (too noisy going around corners). Since my car will primarily be street driven I want something quiet, but stronger than the trac loc.

I have posted something in the drivetrain forum on TCCoA, but so far there have been no responses.

David
 
David Neibert said:
Shane,
Martigan,

392 bird is using a Detriot Locker in his car and that is a little too extreme for me (too noisy going around corners). Since my car will primarily be street driven I want something quiet, but stronger than the trac loc.

I have posted something in the drivetrain forum on TCCoA, but so far there have been no responses.

David

Oh, ok. I wasn't sure what he was running. Too bad there aren't any answers. I have found that big power buildups don't seem to be "supported" that much over at TCCoA and I am not really sure why.

Good luck with your setup.
 
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