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Discussion Starter · #1 ·
I have read through as many posts on several different sites as I can without going cross-eyed and I have yet to come up with a definitive route on the axle swap issue. I am transplanting a 3SGE Beams from an Japanese Toyota Altezza (60% complete) into my 72 GT. I know the rear end will be an issue at some point and I want to nip it now that I am still in fabrication mode. HP will be in the 180 range to the wheels NA but I want to have a setup in place that if I go forced induction (max 300hp, realistically 250hp ish but I want a buffer) in the future I am ready. The plan for this car is occasional autocross / time attack & all around fun car. Width is not a huge issue as I will be adding wide body kit.

Options - I know there are quite a few options out there but here are the 4 I have narrowed down to:
1) LSD- There is an operation out of the UK that makes a drop in LSD for these but good god are they spendy ($800+). Will the other components hold up if I go this route? Then at a minimum I still have to worry about the brakes.
2) Chevette- I found a relatively cheap axle with no brakes but will this really hold up to lets say a maximum of 300hp if I turbo the car?
3) Isuzu impulse rear end. Lots of options for brake improvements with minimal fabricating but I have not been able to find any locally.
4) Myriad of Ford or Chevy rear ends that would have to be shortened. Stronger but heavier. I am capable of doing this but the extra work doesn't sound too appealing at the moment.

I have not read any posts with rear ends that actually failed. For you that have had failures where they limited to the diff? Is the whole darn thing an issue?
 

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Just Some Dude in Jersey
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Go with a Ford or Chevy truck rear end. Parts and options will always be available and it can handle anything you throw at it. Never a worry that you underbuilt your rear. The other options you mentioned might cheap and available now, but in 5 years tough to get. Go massive overkill.
 

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I have read through as many posts on several different sites as I can without going cross-eyed and I have yet to come up with a definitive route on the axle swap issue. I am transplanting a 3SGE Beams from an Japanese Toyota Altezza (60% complete) into my 72 GT. I know the rear end will be an issue at some point and I want to nip it now that I am still in fabrication mode. HP will be in the 180 range to the wheels NA but I want to have a setup in place that if I go forced induction (max 300hp, realistically 250hp ish but I want a buffer) in the future I am ready. The plan for this car is occasional autocross / time attack & all around fun car. Width is not a huge issue as I will be adding wide body kit.

Options - I know there are quite a few options out there but here are the 4 I have narrowed down to:
1) LSD- There is an operation out of the UK that makes a drop in LSD for these but good god are they spendy ($800+). Will the other components hold up if I go this route? Then at a minimum I still have to worry about the brakes.
2) Chevette- I found a relatively cheap axle with no brakes but will this really hold up to lets say a maximum of 300hp if I turbo the car?
3) Isuzu impulse rear end. Lots of options for brake improvements with minimal fabricating but I have not been able to find any locally.
4) Myriad of Ford or Chevy rear ends that would have to be shortened. Stronger but heavier. I am capable of doing this but the extra work doesn't sound too appealing at the moment.

I have not read any posts with rear ends that actually failed. For you that have had failures where they limited to the diff? Is the whole darn thing an issue?
If you use the stock differential the weakest point is the standard pinion gears and side gears. They are extremely hard and therefore long wearing, but this makes them brittle. A limited slip would eliminate that weak point.
The next weak point of the stock rear end is the torque tube shaft itself. But the torque tube shaft can be sleeved which will make it much stronger, it just takes time and a little bit of labor. Lastly if you’re making enough horsepower the pinion gear itself is the next weak point. This only gets worse if you happen to run a higher numerical ratio such as 3.89 or 4.22, since those ratios have smaller pinons compared to 3.18 or 3.44 ratios. In general Opel did not try to use more than 210 to 230 hp with the standard differential. For example, on the Ascona 400 and the Manta 400 rally cars they use the larger Opel Commodore rear axle. Those cars were making between 240 and 275 hp. That axle also deleted the torque tube design.

Chevette rear axles are smaller and therefore weaker than the Opel axles. It is not a step forward.

The Isuzu rear axle is the same size as the Opel axle, so there’s no advantage other than the fact that it might have rear disc brakes and the axle housing itself is wider. This is fine if you want to widen the track but otherwise it shows the same strength characteristics as the Opel.

I’m sort of fond of the 8 inch Toyota rear axle because of the weight, the strength, the front loader design and the accessibility and availability of different gear ratios and limited slip differentials.
 

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Discussion Starter · #7 ·
Go with a Ford or Chevy truck rear end. Parts and options will always be available and it can handle anything you throw at it. Never a worry that you underbuilt your rear. The other options you mentioned might cheap and available now, but in 5 years tough to get. Go massive overkill.
Every time I think about doing the swap twice I always come back to a one of these. Do you have one you would recommend? I keep circling back to the Ford 7.5. I feel like anything bigger may just be overkill and add excessive weight.
 

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Discussion Starter · #9 ·
If you use the stock differential the weakest point is the standard pinion gears and side gears. They are extremely hard and therefore long wearing, but this makes them brittle. A limited slip would eliminate that weak point.
The next weak point of the stock rear end is the torque tube shaft itself. But the torque tube shaft can be sleeved which will make it much stronger, it just takes time and a little bit of labor. Lastly if you’re making enough horsepower the pinion gear itself is the next weak point. This only gets worse if you happen to run a higher numerical ratio such as 3.89 or 4.22, since those ratios have smaller pinons compared to 3.18 or 3.44 ratios. In general Opel did not try to use more than 210 to 230 hp with the standard differential. For example, on the Ascona 400 and the Manta 400 rally cars they use the larger Opel Commodore rear axle. Those cars were making between 240 and 275 hp. That axle also deleted the torque tube design.

Chevette rear axles are smaller and therefore weaker than the Opel axles. It is not a step forward.

The Isuzu rear axle is the same size as the Opel axle, so there’s no advantage other than the fact that it might have rear disc brakes and the axle housing itself is wider. This is fine if you want to widen the track but otherwise it shows the same strength characteristics as the Opel.

I’m sort of fond of the 8 inch Toyota rear axle because of the weight, the strength, the front loader design and the accessibility and availability of different gear ratios and limited slip differentials.
That is interesting. A Toyota axle is not one I have thought about. Is there a particular one you recommend? A quick google search led me to a ton of results. Which is promising. I like options!
 

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LSDs came usually in ambulances and police cruisers, but could obviously also be ordered on any car. There are LSDs made by Gripper, Quaife, Wavetrac and others, but the prices seem to be quite steep.
Wavetrac, differential, diff, lsd,limited slip One could also buy a cheap used ZF 006 from an Opel Omega and adapt it to fit the Volvo housing and ring gear(both use the same carrier bearings).
 

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This is another one I have not thought about. I will need to do my homework but rear discs is a huge plus. Do you know of any models with a LSD?
I put a Volvo 240 rear into my 24v powered wagon. 3.73 gears for the automatics and 3.31 for standards. LSD is readily available from an early 90's model. I think my total cost for everything was less than $600. ($200 for the rear end, $150 LSD)
 

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That is interesting. A Toyota axle is not one I have thought about. Is there a particular one you recommend? A quick google search led me to a ton of results. Which is promising. I like options!
I use the 2wd axles. There were a few versions of that. Different widths depending on the generation of truck were in.

They made a 7.5” and 8” version. 2wd and 4wd versions. Also 4 cylinder and V6 versions (2 pinion versus 4 pinion).

2wd were narrower and had a 5 x 114.3 mm bolt pattern (5 x 4.5”). The 4wd were wider and 6 x 5.5” bolt pattern.

Here’s a thread on a Toyota 8” diff installation into a GT.

 
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Opeler
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LSDs came usually in ambulances and police cruisers, but could obviously also be ordered on any car. There are LSDs made by Gripper, Quaife, Wavetrac and others, but the prices seem to be quite steep.
Wavetrac, differential, diff, lsd,limited slip One could also buy a cheap used ZF 006 from an Opel Omega and adapt it to fit the Volvo housing and ring gear(both use the same carrier bearings).
Phantom Grip still makes their rub-block style LSD for Opels. I ran one in my autocross Manta for many years.
 

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Discussion Starter · #16 ·
Through a stroke of good luck I was gifted a Ford 7.5 off of a 96 Ranger. I pestered the guy on marketplace and he needed his shop space bad enough that I was in the right place at the right time. Unfortunately it has an open diff and drum brakes but both can be remedied for a decent cost. Based on nothing but forum threads written by people of varying brain power I have gathered the 7.5 can handle 300ish HP. That should give me enough cushion if I end up adding forced induction to the car in the future. Hopefully they are correct as I don't want to have to make these modifications more than once!
 

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Discussion Starter · #17 ·
Since I will need to chop this 7.5 up to fit the GT anyway are there any modifications I should to to make this rear end to get more performance out of it? Different linkage structure? I will be adding an LSD and disc brakes.
 

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Opeler
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I have heard mixed reviews about the Phantom Grip "LSD's". I have heard some call them Phantom "slip". Did you have good results?
I had good results but then was only putting 80 hp to the wheels. I an a welded rear for years but that gave the car terminal understeer. I tested the Phantom Grip with all 3 spring sets and ended up using the softest set, as it reduced understeer the most, but still allowed me to put some power down. Increasing the spring rate just started increasing the understeer. If I ran the car on-track I would have used a stronger set of springs.

Over all I was very satisfied, especially for the price. Keep in mind, if you put serious power to the wheels, the Opel rear end still has its inherent weakness outlined by Rally Bob.
 

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I put a Volvo 240 rear into my 24v powered wagon. 3.73 gears for the automatics and 3.31 for standards. LSD is readily available from an early 90's model. I think my total cost for everything was less than $600. ($200 for the rear end, $150 LSD)
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