Differential questions

[jeff denton]

Having researched the forums about diffs and axles, I have a couple questions somebody out there might be able to answer.
One, can a 70 style housing be set up to run the later axles with the sealed bearing and outer retainer?
Second, has anybody ACTUALLY changed the ring and pinion to the 3.9 Isuzu gears. The forums mention it can be done, is it really that simple?
Thanks, I appreciate any input.

[RallyBob]

Originally posted by jeff denton
Having researched the forums about diffs and axles, I have a couple questions somebody out there might be able to answer.
One, can a 70 style housing be set up to run the later axles with the sealed bearing and outer retainer?

No, totally different axle tubes and flanges. I suppose you could cut and reweld a later axle's tubes onto an early diff housing, but then again, if you have a later axle to steal the tubes from anyway....

Second, has anybody ACTUALLY changed the ring and pinion to the 3.9 Isuzu gears. The forums mention it can be done, is it really that simple?

Direct swap, but I suggest you use the Opel pinion nut with the Isuzu crush sleeve. The Isuzu pinion nut is a larger diameter and it's tough to get a socket on it. I've built 4 rear ends with Isuzu gears, using Isuzu bearings and crush sleeve, but with the Opel pinion nuts.

HTH

[GTJIM]

Here's an idea:

If you have the complete Impulse diff but find it is too wide then narrow it to GT width and use the later GT Axles and GT bearings (you may even be able to use the early axles if the Impulse wheel bearings can be fitted where the early Opel bearings ran directly on the axle). The Impulse bearings are the same diameter on the Outside Diameter.

Better still graft the Impulse axle tube ends onto the GT early diff and that way you would have the GT spring mounts etc. with the Impulse flanges that would accept the Impulse discs. Would need GT axles for GT width. See above for bearing options for early or late type. Transfer the gears and GO!

[Killer Texas GT]

The axle diameters between the GT and Impulse are different. I can check to see if the outter diameter of the bearings are the same size. The other option, cut the spring perches and panhard mount of a GT rear end and weld them to the Impulse Rear end, use the GT Torque tube and shaft.

[GTJIM]

The Outside diameters of the Late Opel and the Isuzu Impulse non-Turbo diffs wheel bearings are the same. The Inside diameters are quite different - the Opel being larger.

I just wondered if the early GT axle with the bearing that runs on the axle (without an inner race) was anywhere near the Isuzu size - or if it could be turned down to that size so the Gt axle could be used with the Isuzu tube ends to get a GT width diff with the mounts for the Impulse discs. It would make those early axles useful again - particularly if that is the type of diff Jeff already has.....

[jeff denton]

Thanks, guys, I greatly appreciate all the expert help and wisdom.
While I love the idea of going entirely to the Isuzu rear, I really need to keep the housing stock. Rules are rules.
We are, however, allowed to use any gear ratio imaginable (or would that be "obtainable"). I don't think any body could question where the ring and pinion came from.
As to the wheel bearing question, I just can't help but think that the later unit would be more durable for the kind of insane use we will be subjecting Speedway GT to. Then again, could I be wrong, would the 70 style retainer hold the axle in? It would be the left axle that is pulling on its retainer, left side shouldn't be hooked up to the track THAT good, huh?
Should I be worrying less and spend more time on something productive like grinding tons of bondo off our poor little wreck of a GT?
Thanks again, and remember, " keep the pointy end forward " as they say in boat racing...

[GTJIM]

The early Opel axle is held in with a "C" clip on the inner end - break an axle and the rest just winds out of the housing (just like Chevy 10 and 12 bolts.

The later axle is held in by the shrink fit steel ring just inboard of the bearing so is far less likely to come out if a spline twists off or the axle shaft breaks - yep more durable in the axle department.

Some of the Impulse non-turbo diffs have limited slip units too - mostly the automatic g/box cars for some strange reason
Wonder if you could use one of them and call it "stock"???
The Isuzu diff IS an Opel B-series diff!!

[RallyBob]

Originally posted by GTJIM
Some of the Impulse non-turbo diffs have limited slip units too - mostly the automatic g/box cars for some strange reason
Wonder if you could use one of them and call it "stock"???
The Isuzu diff IS an Opel B-series diff!!

Jim, here in the US the Isuzus never had a limited slip, even though they listed one as 'available' in their literature. I checked with numerous dealers, and they simply could not even locate a part number for one...meaning it was not a US option.

[oldopelguy]

But you can feel fee to send me one, Jim, if you have an extra sitting around.

[GTJIM]

Bob & Stephen, Three of the four Piazzas' I dismantled had twin cam engines and auto transmissions - they all had limited slip diffs.
One was worn out, leaving me a good one and a spare.

It would not be "free" to ship one to you over there - the postage would be horrendous!