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Heavy Duty Solid Axle Swap for RX7

Posted by mhooper 
mhooper
Michael Hooper
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Heavy Duty Solid Axle Swap for RX7
June 16, 2016 11:36AM
Still bench building RX7....This would be 1st gen, bigger dif, FC front suspension, 13b rotary with <250 hp. Don't know squat bout rotaries yet. I searched the site a bit and some other forums and Ive seen people go several routes.. Ford 8.8", Ford 9", Toyota 8", etc. I also believe John has recommend a Dana variant from Volvos for AE86.

I am not thrilled about the weight of the Big Toyota axle, and from looking at Gravity Feds issues doesn't seem like fun. What do you guys think is a good compromise for $, minimum of custom machining, and durability?

I have the following thoughts (limited to Toyota stuff cuz that's my background... )

1st choice so far.. Previa 7.5" dif with a Altezza LSD seems like good option, but the LSD may be weak? still looking into this but I think it may be Torsen. Their were swanky TRD units but discontinued. Aftermarket LSDs seem to be limited for 7.5". I seem to recall these axles being wider than the 8" as well. Not sure if u can get the 4.30/disc combo, may have to get the SC model 3.90 to get disc, but gears are cheap and itll need to be opened for LSD anyways. COmes 5x114 to match FC front

2nd choice- 4runner 8"- Get from 4 runner and had 4.88 4 pinion, lots of traction devices available, but 6 lug and drum. Also heavy (250 plus pounds).

Possibly tied for 1st or 2nd is the FOrd 8.8, but don't know enough... can get 5x114 with LSD and disc, not sure on gearing but cheap. Explorer models with LSD/disc likely have offset pumpkin and will require work? Mustang model may be better option... but not sure.

Ford 9" not ruled out yet due to availability of parts (ie aluminum carrier that Pete just posted), but again seems like overkill unless the aluminum bits get weight down a LOT. Havnt weighed one, but assuming worse than Toyota 8".

Thoughts? Thank you!
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john vanlandingham
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Re: Heavy Duty Solid Axle Swap for RX7
June 16, 2016 12:06PM
Mike from Pirate 4x4:
Quote

Front axle weighs 260 lbs. according to the UPS scale. Their max is 200 lbs. for regular ground, so if you get the axle under that, it'll ship that way.

Pulling the third member and shipping it seperate will save you 50-ish lbs.

260 lbs. was:
tierod
draglink & steering arms
full set of brakes
u-bolts
steering stabilizer
gear oil! Imagine my surprise... <IMG SRC="smilies/rolleyes.gif" border="0">

I've lifted and heaved one around without drums and backing plate stuff and I hain't no he-man fool.

And bear in mind poor Alex has NO machines to work with except a 5" angle grinder...

8.8 is also big diff offset so that means hacking off a tube, shortening it and scaring up another short one...

That damn Toiletta 8" is really a nice thing--including the drop out 3rd member dealio.



John Vanlandingham
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Robert Culbertson
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Re: Heavy Duty Solid Axle Swap for RX7
June 16, 2016 01:30PM
The weight of the 8.8 and a similar width Toyota 8in is within 5-10 pounds from all of the searching I've done.
They both require machine work and/or welding work to install, so that's a draw.
I'd use whatever happens to fall into your lap.
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DanielSL
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Re: Heavy Duty Solid Axle Swap for RX7
June 16, 2016 01:34PM
Michael;

Don't know if this would be usable for you, but I got something in the storage unit, that may be of interest.

Back when I was doing a lot of Land Rover stuff, I bought a hybrid axle to build a truggy, from a guy on the Pirate 4x4 website. It ran on the winning King of the Hammers truck the year before I bought it. Years later, it is still in storage, as i sold the truggy project as there are no hills in Florida.

Dana 60 outers, mated to a Ford 9" carrier. Moser H.D. axles. Drum outers, but there are a ton of disc conversion kits out there. It was narrowed to fit under a Land Rover Defender 90, so it may work in a car application.

Don't know, but just throwing it out there.
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tdrrally
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Re: Heavy Duty Solid Axle Swap for RX7
June 16, 2016 01:36PM
Fox mustang has a centered carrier 57" wide 4x108 but 5x114 is an option as are discs
sn95 mustang centered carrier is 58 1/2" 5x114 discs
new edge mustang centered carrier is 59 7/8" 5x114 discs

all have ford four link hardware that can be removed
gearing options are very good; 2.26, 2.47, 2.73, 3.08, 3.27, 3.31, 3.45, 3.55, 3.73, 4.10 & 4.56, 5.14.



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Re: Heavy Duty Solid Axle Swap for RX7
June 16, 2016 01:52PM
the ford explorer 8.8 has discs and a 4.10 and close to the right axle wide. Aside from that, the 4runner axle i have is really the only other "easy" choice. Don;t mess with 4.88 8" toyota axles, as they have specific one of things in them.



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Robert Culbertson
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Re: Heavy Duty Solid Axle Swap for RX7
June 16, 2016 02:41PM
What power/torque are you looking to spit through the diff?
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Pete
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Re: Heavy Duty Solid Axle Swap for RX7
June 16, 2016 02:54PM
I wouldn't run an 8.8 on anything without cutting the axle ends off and putting 9" style ends on it, which requires new axles anyway.

The 8.8 is lighter than the 9", iron case to iron case. But C-clip axles scare the bejeezus out of me and really compromise what you can do diff-wise.

The rear I'm building (note present tense, not past tense) is a good example of what not really to do. For the effort I'm putting in, for a few bucks more I should have just called up Speedway Engineering (I think) in California, they will make a full floating 9" with aluminum 4x4.5" hubs for $1500, includes everything but the suspension bracketry and the dropout. That looks expensive until you try to save money doing things yourself...



Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.



Edited 1 time(s). Last edit at 06/16/2016 02:56PM by Pete.
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Robert Culbertson
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Re: Heavy Duty Solid Axle Swap for RX7
June 16, 2016 03:45PM
Quote
Pete
I wouldn't run an 8.8 on anything without cutting the axle ends off and putting 9" style ends on it, which requires new axles anyway.

The 8.8 is lighter than the 9", iron case to iron case. But C-clip axles scare the bejeezus out of me and really compromise what you can do diff-wise.

The rear I'm building (note present tense, not past tense) is a good example of what not really to do. For the effort I'm putting in, for a few bucks more I should have just called up Speedway Engineering (I think) in California, they will make a full floating 9" with aluminum 4x4.5" hubs for $1500, includes everything but the suspension bracketry and the dropout. That looks expensive until you try to save money doing things yourself...

Moser and Strange make bolt-on/press-on c-clip eliminators now, which is a really good idea.

https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=8.8%20c%20clip%20eleminator

The aluminum quick change diffs can be had for cheap from roundy-round racers. Upgrade to a clutch type lsd and profit...?
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mhooper
Michael Hooper
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Re: Heavy Duty Solid Axle Swap for RX7
June 16, 2016 03:46PM
Quote
Robert Culbertson
What power/torque are you looking to spit through the diff?

Prob 250 hp or less. If my tire budget went up maybe just maybe up to 300 ish but doubt it
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mhooper
Michael Hooper
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Re: Heavy Duty Solid Axle Swap for RX7
June 16, 2016 03:49PM
What about the Toyota 7.5"? The Toyota and ford dif just seem so big, then again the bees knees atlas in the mk2 is super heavy too.

How are the rx7 dif failures happening... Differential or bending stuff from impact
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Pete
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Re: Heavy Duty Solid Axle Swap for RX7
June 16, 2016 04:02PM
Quote
mhooper
What about the Toyota 7.5"? The Toyota and ford dif just seem so big, then again the bees knees atlas in the mk2 is super heavy too.

How are the rx7 dif failures happening... Differential or bending stuff from impact

When they were being rallied, they were having housing failures.

I personally was having housing failures and more housing failures, twisting them so the pinion angle would climb higher and higher, bending them so the backside would crack open like an egg, ugly stuff. Axles were a constant battle keeping bearings on them (exacerbated by the housing flexage) and then they started just snapping off in the splines. And note THIS WAS NOT stage rally...!

I wanted to go to 9" more for the stronger housings than anything else, and a strong housing makes the axles happy too. Never had a problem with the bearings or gears...

No matter what you put it, I'd truss the thing to make SURE it doesn't move around.



Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.



Edited 1 time(s). Last edit at 06/16/2016 04:03PM by Pete.
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mhooper
Michael Hooper
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Re: Heavy Duty Solid Axle Swap for RX7
June 16, 2016 04:30PM
Quote
Pete
Quote
mhooper
What about the Toyota 7.5"? The Toyota and ford dif just seem so big, then again the bees knees atlas in the mk2 is super heavy too.

How are the rx7 dif failures happening... Differential or bending stuff from impact

When they were being rallied, they were having housing failures.

I personally was having housing failures and more housing failures, twisting them so the pinion angle would climb higher and higher, bending them so the backside would crack open like an egg, ugly stuff. Axles were a constant battle keeping bearings on them (exacerbated by the housing flexage) and then they started just snapping off in the splines. And note THIS WAS NOT stage rally...!

I wanted to go to 9" more for the stronger housings than anything else, and a strong housing makes the axles happy too. Never had a problem with the bearings or gears...

No matter what you put it, I'd truss the thing to make SURE it doesn't move around.

Wow. What sort of power are u running?
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Pete
Pete Remner
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Re: Heavy Duty Solid Axle Swap for RX7
June 16, 2016 06:52PM
I started having problems when I got over about 170hp.

I started REALLY having problems when I stopped using ancient Michelin worn-out too-big rally tires and bought a set of right-sized Black Rockets. That is when the breakage went from stuff to keep an eye on, to look it over every event if the car managed to make it through.



Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.



Edited 1 time(s). Last edit at 06/16/2016 06:54PM by Pete.
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john vanlandingham
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Re: Heavy Duty Solid Axle Swap for RX7
June 16, 2016 07:47PM
Quote
Robert Culbertson
The weight of the 8.8 and a similar width Toyota 8in is within 5-10 pounds from all of the searching I've done.
They both require machine work and/or welding work to install, so that's a draw.
I'd use whatever happens to fall into your lap.

Yeah i forgot--Mr. 40 years experience---ANY and ALL machine work is always exactly the same..
That's why you're brilliant. Cause you think things thru so carefully.



John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

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CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.
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