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Old Opeler
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5,564 Posts
Hi from New Zealand,
Lots of Isuzu Piazzas here (known as Impulses over there). The Isuzu diff is an Opel "B" serries diff which is very similar to the Opel GT "A" serries diff. Same gear and carrier sizes but about 1.5 inches wider. They also have neat disc brakes on them that numerous people have fitted to the GT diff. The disc fits on to the GT axle end, without modification but an adaptor plate is needed to replace the GT backing plate and mount the Isuzu caliper.
The whole Isuzu diff can be fitted to a GT using the GT torque tube and drive shaft ( it all bolts on to the Isuzu diff, replacing the Isuzu torque tube!). This gives a slightly wider track and rear disc brakes. The Isuzu rear sway bar also fits and another bonus is that some Isuzu diffs have Limited Slip units. Spring cups really need moving inwards about 1/2" per side.

At the front end Isuzu have very light 16mm thick ventilated discs which go onto the GT spindles but caliper mounting is a bit tricky. I am investigating using the Isuzu spindle in the GT front suspension ( look very similar but castor/camber need evaluation).
I have a 1972 GT under restoration (body work completed this week and now in primer) and presently drive a 1985 Piazza with several parts cars for useful bits and easy comparison.
 

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Detritus Maximus
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3,105 Posts
What is the center to center spacing on the Isuzu spring seats (cups)? There is a write up on installing the Isuzu brakes on to a Manta A rear end, but if swapping the entire axle is possible.....
 

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Member
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240 Posts
What is the center to center spacing on the Isuzu spring seats (cups)? There is a write up on installing the Isuzu brakes on to a Manta A rear end, but if swapping the entire axle is possible.....
I dont recall seeing a torque tube in the Impulse...I could be wrong.

Garry
 

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Member
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299 Posts
i advise not using the impluse rearend unless you narrow it if you autocross or something the rear track on a gt is already wider in the back than the front which is not good for handling


whats the difference on the impulse and gt caliper mounts
 

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Old Opeler
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5,564 Posts
Isuzu Impulse Diff

1440mm or 56 3/4" wide (wheel mounting face to face)

Centre distance of spring pockets 972mm or 38 1/4"
 

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Registered
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Isuzu LSD

The Thread about the disk breaks mentioned that an Isuzu LSD would fit an Opel diff. Has any one done this and is it a direct fit or is there fabrication involved. Also what year Isuzu would fit a '73 rear end?
Thanks!
 

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Member
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240 Posts
I dont recall seeing a torque tube in the Impulse...I could be wrong.
Just looked under a 84 Impulse. That one had a very "Opel" looking torque tube. There must be some variation year to year. I can recall seeing one that was a front loader (removable carrier).

Makes me wonder if there might be other parts of Impulse drive trains that might interchange with Opels?

Garry
 

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Old Opeler
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5,564 Posts
Piazza Rear End

The standard Impules has an Opel "B" diff - like the Manta "B"
1975 - 88
The Turbo Impulse has the five link front loading diff after 1988,
some of the earlier ones (1987) had the "B" type. I supose the five link is stronger but it is a different diff.

Lots of good bits on Impulses - 4-speed overdrive autos - all the electrics are (Japanese) Bosch - nice air conditioning compressors - the entire torqe-tube diff (has been fitted to GTs) - the front, coil spring suspension (also has been fitted to GTs) - the front and rear discs (much lighter than GTs & there are two sizes:F&R 239mm fits inside 13" wheels :254mm F & 266mm Rear from some US Impulses and Turbo are bigger and ventilated.

Only three GTs in New Zealand so I had to start loking around for things that fitted - some bits require adaption but Kiwi ingenuity and a bit of No. 8 wire can do wonders!
 

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impulse rear

i was wondering how much stronger is the impulse rear if any more stronger than the opel rear? i may swap the whole rear in my opel anyway for the LSD, disk brakes, and 3.90 gears, but if the impulse rear was strong enough for a mild v6 that would be a super plus. any input is greatly appreciated

Moderators Note: Thread merged
 

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Opeler
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77 Posts
I just got an 84' Impulse rear end from the local pick your part and i am preparing for the swap. I read somewhere that Roger's Opel Engineering (CA) did this swap. My main concerns are:
1) Is the sway bar a direct bolt on?
2) The impulse RE has a curved bar that runs along the top of the axle and bolts to the bottom of the rear floor pan, i am wondering if this needs to be modified or does it bolt up directly and where?
3) Do the spring cups really need to be moved inward? (cutting and welding those cups back on really make this a big job!)
4) Which shocks do you use? the Opels or Impulse?

I will try to figure out these issues and post my results, any remark or suggestions greatly appreciated.

Mauri
 

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Old Opeler
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5,564 Posts
Does it Fit!

What ever happens you have a set of rear discs and a 3.90:1 ratio gear set ! Check to see if it has a Limited Slip unit too. Strangely enough mainly the Auto gearbox Impulses have the LSD unit - the Auto was a $1,500 option and they added the LSD to the diff as well with that option.

My GT has been at the body shop for 14 months but is coming home on Thursday so I will be doing this swap too. I have been down at the shop doing all sorts of measuring and:

1) The Impulse sway bar looks a pretty good fit. On my 1972 GT there are four (two on each side) threaded holes in the floor pan each side of the torque tube in, as near as I can measure, the right place to bolt the Impulse sway bar to the GT. I haven't done it yet but it is close.

2)See above - Also you need to use the GT torque tube and inner driveshaft as the Impulse one is a bit longer with a slightly different mounting - some bits may be usable??

3)The Impulse diff is about 3/4 inch wider each side (20mm). It may be usable like it is BUT for liability reasons the spring cups should be lined up correctly. It might even be better to use the GT spring cups and certainly the GT springs as the Impulse is a heavier car - check the spring rates.

4) The GT and Impulse shocks are directly interchangable - I have Impulse shocks on my GT already. However the Panhard rod length may need changing to locate the diff correctly.

Hope this helps - updates as my effort goes ahead:)
 

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Reborn Opeler
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32 Posts
I've been reading the conversations on the impulse rear for a year now, and opel masters correct me if I'm wrong.

Take the impulse limited slip or open diff and disc brakes with backing plates and just install them on the opel housing so you don't have to cut and weld.
 

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Old Opeler
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5,564 Posts
Gears Too!

Yep, the discs can be adapted to the GT diff but when the 3.9:1 Impulse gears and limited slip unit are wanted too it involves a bit more expense and skilled work. The gears too will fit into the original GT case but we always look for short cuts. So fitting the whole Impulse diff has attractions in that discs, gears and LSD could be fitted to the GT with just a bit of welding.
Probably just creates more work!
 

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Opeler
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77 Posts
Isuzu rear end done

Hello everyone, i just had the rear end swapped and i think it has come out very well. Everything went well, the torque tube bolts right up as well as the sway bar. My only concer was the passenger side coil spring cup that was about 1 inch wider, i did not refit the cup but i think it should be refitted. The driver side cup lined up well. It runs and drives very well, the brakes are awesome and i did'nt even use a proportioning valve! The handling with the sway bar is excellent. I think its worth it, not a big job, the only issues are relocating the panhard rod bracket and the coil cups. Thanks for reading
Mauri
 

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Opeler
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89 Posts
LSD in non-turbo impulse w/ torque tube?

I thought the isuzu locking rear was going to work, until I actually picked it up from the junkyard and started checking it out. Come to find out - the TURBO impulse is apparently different from the NON-TURBO. The part I currently have does not have a torque tube to adapt to it.

I still want to use the impulse rear (I am fabing new a-arms for the front end to make it 6 inches wider track, I've molded in stienmetz flares to accept fatter wheels, and if I increase the track enough, I'm hoping to get wide enough that I can get away with using ricer-kid FWD offset rims for normal street driving.)

I really WANT the wider track, disc brakes, locking diff, and more torque handling capacity as I'm swapping to a V6. Can I get all this out of the Non-turbo Impulse rear? (I really am reluctant to go on another isuzu safari - the last one I found at a reasonable price was 70 miles away.)

Currently, I'm planning on just making the Turbo rear work. I've already fabricated a yoke on the rear end that works with the Opel U-joints - planning on using a shortened S-10 driveshaft from the tranny to where the torque tube is on the body, then fab'ing the drive shaft from there back with opel Ujoint on the rear and s10 ujoint on the front. I was planning on connecting a torque arm as nearly as possible to where the torque tube connected before to avoid blatent violations of SCCA SM2 rules.

There's a post on here somewhere about this - all I've done since then is fab the yoke for the isuzu rear to an Opel u joint.
 

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Old Opeler
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5,564 Posts
Turbo/Non-Turbo

Think I mentioned the diff-erence in an earlier post.

Look on the bright side - the Turbo diff you have is stronger than the non-turbo one. Turbo Isuzus were rated at 180 PS and destroyed the earlier "torque tube" Opel diffs. After 1987 the diff. you have was introduced to solve that problem. It will probably have a limited slip unit in it too. The gears and LSD don't fit in the GT diff. though - the earlier non-turbo and 1987 turbo "torque tube" type do fit.
 

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Opeler
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12 Posts
What about Kadett rear ends?

Arn't the GT and kadett similar except the gt has a little bit longer and wider stance. I'm wandering are there kadett lsd rears and if so would they fit or are they like the GT's and not available in the U.S.
 

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Fit into a '69 GT?

I'm rebuilding the rearend in my '69 GT with a 1.9L. The pinion bearings from OGTS are $180, thats a heck of a price and if the Impulse ones will press in there I'd like to do a price comparison. So what exactly can I use from the Impulse rear end in my GTs? I've not modified anything and it is the orginal rear axle through and through. Thanks guys.
 

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Old Opeler
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5,564 Posts
Diff Bearings

The reason that the pinion bearings are $180 is that they are obsolete and have not been available from any manufacturer recently.
The Isuzu ones are the same - and just as hard to find.
Though I did find an eBay supplier for Opel Manta "B" diff bearings on eBay.UK a while ago. Called himself "bearingsuk" - GBP87.50 for a complete set of pinion bearings AND the two side carrier bearings too! May be worth a try.

The Isuzu Impulse non-Turbo diff crownwheel and pinion fit the GT diff housing along with the carrier and the inside bearings are very similar - the outer wheel bearings are quite different and don't fit on GT axles though.

HTH
 
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