GM 7.5 LSD swap

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rab
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GM 7.5 LSD swap

Post by rab » Wed Jul 13, 2016 6:37 pm

ok has the merkur community ever got a clear answer on what GM 7.5 diff works and whats all needed to make it work?

From my research it sounds like it needs to be a 7.5 GM 26 spline diff pre 1989?
It also sounds like GM offed this 7.5 26 spline diff in a few different lsd version, ie auburn,Eaton Gov-loc style,and maybe a nother? also it sounds like some of them diffs can not be rebuilt? so which one would be the best to look for and is rebuildable?

Also does anyone offer a different speedo gear to match the new rear diff ratio if one goes this route to have the stock merkur speedo read correctly?

Could the mc2 diff install kit work with a oem GM diff ?
heres a link http://www.mc2racing.com/products/xr4ti ... index.html

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Grayson
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Re: GM 7.5 LSD swap

Post by Grayson » Thu Jul 14, 2016 4:32 pm

rab wrote:ok has the merkur community ever got a clear answer on what GM 7.5 diff works and whats all needed to make it work?
There are hundreds of GM diff installs in Merkurs and lots of installs in Sierras and Escort Cosworths worldwide. National Championships have been won with the GM diff installed. The install has been figured out using both open diff stubshafts and LSD stubshafts. So, the answer to your question is yes.

I think 99% of Merkur owners will never have to worry about diff rebuilds unless they're working with a used diff from Europe. Most owners don't put enough miles on their cars to wear them out.
Also does anyone offer a different speedo gear to match the new rear diff ratio if one goes this route to have the stock merkur speedo read correctly?
Installing a GM diff does not cause your ring and pinion to be replaced. Your ring and pinion ratio remains the same.
Could the mc2 diff install kit work with a oem GM diff ?
The install kits are geared toward the Eaton and Detroit aftermarket GM diffs. Since there is so much variance in the OEM GM diffs, I wouldn't depend on the mc2racing install kit working with a particular used diff. A lot of the parts are the same (seals, O-rings, cover bolts, etc), but certain OEM diffs would probably require different spacer thicknesses, and may not be able to take advantage of the usual no-spacer (offset outer bearing race) solution.

rab
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Re: GM 7.5 LSD swap

Post by rab » Sat Jul 16, 2016 12:00 am

Got this info from a G body chevy forum.
The 7.5 will hold up fine for street use. FYI... 2 series carriers go up to 3.08, 3 series are 3.23 - 4.11. you can tell the difference by the ring gear flange.
here is a link to the post, post number 4 has the info.
https://gbodyforum.com/threads/7-5-posi ... -go.56338/

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Re: GM 7.5 LSD swap

Post by my8950 » Sun Jul 17, 2016 9:10 pm

I'm listening...
Please keep talking.

rab
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Re: GM 7.5 LSD swap

Post by rab » Mon Jul 18, 2016 5:07 pm

here are some other post about the GM 7.5 diff swap.

1. viewtopic.php?f=30&t=10846&sid=4b3e93c0 ... 1537c06e9d
2. http://www.shoforum.com/index.php?threa ... put.93018/
3. http://www.locostusa.com/forums/viewtop ... 87&start=0

I'm going to contact deathbypsi today on turboford.org or a ranger forum, I have talked to him before about turbo 1st gen ranger stuff as i just build my ranger last year. I'm assuming its the same guy,same screen name and 2.3 ford turbo related forums..
Maybe will also search turboford.org in general for the GM 7.5 diff swap as it sounds some info was posted there.

Maybe GRAYSON can give us a part number on the eaton diff MC2 offers and we can differentiate what GM thats for, then we could narrow it down to figure out what used GM diff you could grab at the yard and work with the mc2 kit.

Also from the sounds of it guys have swapped all 2 or 3 kinds of GM 7.5 and maybe even the GM 7.625 26 spline diffs into a merkurs one way or another.

rab
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Re: GM 7.5 LSD swap

Post by rab » Tue Jul 19, 2016 11:23 pm

Got ahold of deathbypsi, he said he doesn't have any other info of the swap other than what is already posted.

my8950
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Re: GM 7.5 LSD swap

Post by my8950 » Wed Jul 20, 2016 7:42 am

MC2 has posi diff's listed on their site.

My thinking is this...
Sure you could go with a GM 7.5 for cheap, and then have to scavenge and find stuff to make it work. Once you figure it out it would probably be awesome and work really well.
And, since these are junk in the GM world, they're probably had for very cheap.

You might have to pay a little more, but MC2 has the parts and knowledge to get you a setup that will bolt in with minimal trial and error.
Then back on the road and burning both tires a lot quicker.

I agree its cool to figure stuff out and make it work. That is what hot rodding is all about.
However, in the end you may spend a lot more making something work, with your time and frustration involved, it may even be more....

Just saying...If there was a cut & dry answer to making the GM diff work, I'd be on it in a heartbeat. And I'd find one for my friends too.
This is on my list of things to do if I get my "ideal" car running and driving.

rab
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Re: GM 7.5 LSD swap

Post by rab » Wed Jul 20, 2016 5:19 pm

Well for the xr4ti project im working on, budget is the name of the game.
So for this project im going to try to find something that will work for cheap, plus all the machine work i can have done for free.
My goal with this is cheap and to get documented info out there for others too.

my8950
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Re: GM 7.5 LSD swap

Post by my8950 » Thu Jul 21, 2016 8:08 am

rab wrote:Well for the xr4ti project im working on, budget is the name of the game.
So for this project im going to try to find something that will work for cheap, plus all the machine work i can have done for free.
My goal with this is cheap and to get documented info out there for others too.
Good deal!
Maybe you get it done before I get there, and I can double check your documentation by installing in my car... :)

rab
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Re: GM 7.5 LSD swap

Post by rab » Sun Jul 24, 2016 1:49 pm

the progress will be slow with this project, my goal it to have it ready for install early next year.

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Re: GM 7.5 LSD swap

Post by DPDISXR4Ti » Sun Jul 24, 2016 3:15 pm

This thread might help you...
http://forum.merkurclub.com/forum/viewt ... fferential

If you're going to try to roll your own with a junkyard GM 7.5, it seems there are a lot of different variations. I once planned to go that route, but it just got too confusing. I have a 8.8 installed today, with no regrets.
Brad

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Re: GM 7.5 LSD swap

Post by Matt01 » Sun Jul 24, 2016 4:12 pm

I believe for some reason that the Eaton version we use is out of a 7.5 S10 pickup.

Since you can have the machine work for free, find one in a scrap, find out how to read door stickers and identify differentials, to know if it has posy before ripping it all apart to find out it does not.

Try and find out the mileage of the truck, if it has 200k miles, Ill bet a 6 pack that the LSD is scrap in it.

Rip out your diff and take a stab at it. If it fails, just weld the spider gears up and go drifting.

One thing that always bothered me about the Mc2 diff kit is that metallic shim tape. id love to get a stub shaft one day, machine it down, have a sleeve machined to the proper size (which i have no idea what it is anymore, but its written somewhere in mc2 documents) just for peace of mind.

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Re: GM 7.5 LSD swap

Post by DPDISXR4Ti » Tue Jan 24, 2017 11:50 am

Matt01 wrote:I believe for some reason that the Eaton version we use is out of a 7.5 S10 pickup.
Keep in mind, the donor would need to be roughly from the '78 to '87 era to get the correct 26-spline unit. GM moved to 28-spline somewhere around 1988. "G80" is the LSD code you'd be looking for on the specification sticker, assuming it's still there on a 30-year old truck.

It would be neat to stumble across the right part at the junkyard, but I think that ship has sailed for the most part. MC2 has the correct part for a fair price and has figured out how to make it work. I love to cobble up junkyard parts into something that works probably more than most, and I'd opt out in this case.
Brad

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