Rear end strength

cochran · 11-25-2003

We've all heard the discussions about the limitations of the GT rear end, especially in terms of engine swaps. I haven't heard any information on making the stock part stronger, or anything on how to help stock pieces handle more torque and horsepower without instant failure. I think I read that some of the people who race GTs have welded their differentials somehow. What is the net effect of welding, and does anyone have details? What else can you do to strengthen the rear end of the car?

madhatterpdc · 11-25-2003

I am interested to hear more as well. I would like to have my drivetrain be >200-hp-proof, as I am expecting my final output to be in the 165-175 hp range and would like a little headroom.

Anyone have any comments on this? Maybe also comments on incorporating the 3.90 gears from the Isuzu Non-Turbo rearend?

Paul · 11-25-2003

Welding the gears in the rear end makes the axle a Locker, meaning both tires rotate at the same RPMs all the time. Fine for racing and great for dirt tracks but bad on the street. It would be very dangerous in slippery conditions.

As mentioned by others here, the spider gears are brittle and are the weak point. You can do as a couple others have done and purchase/install the Phantom grip LSD. Since the load would shared more evenly between the spider gears, it will be able to carry a little more load.

GL
Paul

icemangt71 · 11-25-2003

where can the phantom kit be purchased?
opelgtsource?

Paul · 11-25-2003

But of course.........

www.phantomgrip.com

If you'll search this site and classicopels you'll find a write up from someone that installed one, even had pictures.

Paul

GTJIM · 11-25-2003

Some of the early (1985) Impulse Turbos used the "Opel" type diff with the torque tube and also had limited slip units in them - as did some of the non-turbo diffs. The Turbos were soon changed to a stronger diff with a four link + panhard rod setup so 180 PS (about 140-150 SAE horsepower) must have been a bit much for the "Opel" diff and torque tube system.

The Impulse 3.90 gears and LSD is a simple way to get a considerable upgrade to the GT diff - even the whole Isuzu diff can be used with the GT torque tube and drive shaft bolted on - but this still retains the "doughnut" and GT type three link suspension. The LSD does replace the weakest parts - the differential side gears but is still the same size as the GT diff. May be good for 140 to 160 Horsepower if driven sensibly and as much as 160 to 180 with an auto gearbox - but NOT for "stop-light" Grand Prix or "street" drag racing

The big advantage is that Impulse bits "bolt in" internally as they are the same type of diff. The whole Isuzu diff is a bit wider and needs the spring mounts moved inwards about 20mm but the extra width helps if you are using Front Wheel Drive type Mag wheels with a ET42 or ET45 offset as it gives inner guard clearence and puts the wheel centre right back where it should be with the same tread width as original.

Paul · 11-26-2003

A bid of info just came to light...

With the LSD installed, inside wheel spin is minimized. Also, less wheel spin during a hard 1-2 gear shift will probably make the spiders more prone to breakage, not less.

Just passing some good info along!

Paul

11-25-2003	#1 (permalink)
cochran Opeler Join Date: May 2003 Location: South Carolina Posts: 15	Rear end strength We've all heard the discussions about the limitations of the GT rear end, especially in terms of engine swaps. I haven't heard any information on making the stock part stronger, or anything on how to help stock pieces handle more torque and horsepower without instant failure. I think I read that some of the people who race GTs have welded their differentials somehow. What is the net effect of welding, and does anyone have details? What else can you do to strengthen the rear end of the car?

11-25-2003	#2 (permalink)
madhatterpdc 1450 Seeker... Join Date: Jun 2003 Location: Cape Cod, Mass Posts: 631	I am interested to hear more as well. I would like to have my drivetrain be >200-hp-proof, as I am expecting my final output to be in the 165-175 hp range and would like a little headroom. Anyone have any comments on this? Maybe also comments on incorporating the 3.90 gears from the Isuzu Non-Turbo rearend? __________________ Keep it Blitzed

11-25-2003	#4 (permalink)
icemangt71 Opeler Join Date: Apr 2002 Location: Palmdale California Posts: 88	where can the phantom kit be purchased? opelgtsource? __________________

11-25-2003	#6 (permalink)
GTJIM Old Opeler Join Date: Jun 2003 Location: New Zealand Posts: 5,686	Impulse Diffs Some of the early (1985) Impulse Turbos used the "Opel" type diff with the torque tube and also had limited slip units in them - as did some of the non-turbo diffs. The Turbos were soon changed to a stronger diff with a four link + panhard rod setup so 180 PS (about 140-150 SAE horsepower) must have been a bit much for the "Opel" diff and torque tube system. The Impulse 3.90 gears and LSD is a simple way to get a considerable upgrade to the GT diff - even the whole Isuzu diff can be used with the GT torque tube and drive shaft bolted on - but this still retains the "doughnut" and GT type three link suspension. The LSD does replace the weakest parts - the differential side gears but is still the same size as the GT diff. May be good for 140 to 160 Horsepower if driven sensibly and as much as 160 to 180 with an auto gearbox - but NOT for "stop-light" Grand Prix or "street" drag racing The big advantage is that Impulse bits "bolt in" internally as they are the same type of diff. The whole Isuzu diff is a bit wider and needs the spring mounts moved inwards about 20mm but the extra width helps if you are using Front Wheel Drive type Mag wheels with a ET42 or ET45 offset as it gives inner guard clearence and puts the wheel centre right back where it should be with the same tread width as original. __________________ GTJim Opel Owner since last Century! Copyright © 2000-2009 J D Henry All Rights Reserved Last edited by GTJIM; 11-25-2003 at 08:09 PM.

11-26-2003	#7 (permalink)
Paul Member 1000 Post Club Join Date: Mar 2002 Location: Ft Smith, Arkansas Posts: 1,481	Stock Spider Gears and LSD A bid of info just came to light... With the LSD installed, inside wheel spin is minimized. Also, less wheel spin during a hard 1-2 gear shift will probably make the spiders more prone to breakage, not less. Just passing some good info along! Paul

11-25-2003	#3 (permalink)
Paul Member 1000 Post Club Join Date: Mar 2002 Location: Ft Smith, Arkansas Posts: 1,481	Welding the gears in the rear end makes the axle a Locker, meaning both tires rotate at the same RPMs all the time. Fine for racing and great for dirt tracks but bad on the street. It would be very dangerous in slippery conditions. As mentioned by others here, the spider gears are brittle and are the weak point. You can do as a couple others have done and purchase/install the Phantom grip LSD. Since the load would shared more evenly between the spider gears, it will be able to carry a little more load. GL Paul

11-25-2003	#5 (permalink)
Paul Member 1000 Post Club Join Date: Mar 2002 Location: Ft Smith, Arkansas Posts: 1,481	But of course......... www.phantomgrip.com If you'll search this site and classicopels you'll find a write up from someone that installed one, even had pictures. Paul

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