Heavy Duty Solid Axle Swap for RX7

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Robert Culbertson
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

If you read the fine print, they are not meant for anything that gets side loading, they're drag racing only. C-clip axle retention isn't legal below something like 11.49 ET, which is stupidly easy to get down to, so there is a large market for quick and dirty rules compliance.

And they generally leak a lot, too.

---

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 08:03PM by Pete.

Quote
john vanlandingham

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.

What machine work is required to get an 8.8 installed?
What machine work is needed to install a Toyota 8in diff?

Quote
Robert Culbertson

Quote
john vanlandingham

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.

What machine work is required to get an 8.8 installed?
What machine work is needed to install a Toyota 8in diff?

You tell us..You've been involved in so many. Both require machine work so they're exactly the same.. you said it..

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Since you lot brought up the topic of weights I actually did weigh my toyota 8 inch by weighing myself then picking the axle up (I aint a big guy) and getting on a bathroom scale... math was involved and the number I recall is 186lb and that was likely with all the crap on it (drums).

The volvo diff would be a touch simpler due to the fact that it already has brake tabs on it. But there are work arounds for that on the toyota. This would be the ONLY thing that makes it easier to swap in over a toyota 8 inch. You are still redrilling axles, welding new tabs for suspension to the axle, etc for both options.

Now consider the advantages of toyota...

-shimmed supra diff... affordable and good. Vs big bucks for a proper diff in a volvo 1030.
-Easier to find over a volvo 1030... atleast where I am. You dont want the 1031 unless you want $1000+ ring and pinions for anything shorter than 4.11 ratio.
-multiple width options
-stronger though on a rx7 pointless as the volvo should be stout enough

***REMOVEABLE Center section. Makes working on it way easier. Also when, like me you blow up a gearset right before a rally because you screwed up (I don't want to talk about this) you can run down to pick n pull and grab a complete center section and stuff it in rather quickly. No it wont have a nice LSD and it may not even be the ratio you want but at least it gets ya going quick. This brings me to my next point...

The removable center section also makes it easier to carry a spare if you so desire, or just a different ratio on hand. Maybe you fancy going and playing on a road course for a day but want a longer ratio for more speed? Easy: just unbolt and put a different center section in with the different ratio. Try that with the volvo diff.

Quote
Eric Ewert
Since you lot brought up the topic of weights I actually did weigh my toyota 8 inch by weighing myself then picking the axle up (I aint a big guy) and getting on a bathroom scale... math was involved and the number I recall is 186lb and that was likely with all the crap on it (drums).

The volvo diff would be a touch simpler due to the fact that it already has brake tabs on it. But there are work arounds for that on the toyota. This would be the ONLY thing that makes it easier to swap in over a toyota 8 inch. You are still redrilling axles, welding new tabs for suspension to the axle, etc for both options.

Now consider the advantages of toyota...

-shimmed supra diff... affordable and good. Vs big bucks for a proper diff in a volvo 1030.
-Easier to find over a volvo 1030... atleast where I am. You dont want the 1031 unless you want $1000+ ring and pinions for anything shorter than 4.11 ratio.
-multiple width options
-stronger though on a rx7 pointless as the volvo should be stout enough

***REMOVEABLE Center section. Makes working on it way easier. Also when, like me you blow up a gearset right before a rally because you screwed up (I don't want to talk about this) you can run down to pick n pull and grab a complete center section and stuff it in rather quickly. No it wont have a nice LSD and it may not even be the ratio you want but at least it gets ya going quick. This brings me to my next point...

The removable center section also makes it easier to carry a spare if you so desire, or just a different ratio on hand. Maybe you fancy going and playing on a road course for a day but want a longer ratio for more speed? Easy: just unbolt and put a different center section in with the different ratio. Try that with the volvo diff.

Very good write up..Thanks. I get tired of preaching. One thing you did leave out is where you got the wonderfully pre-fabricated tabs for the links and the shocks for the Toyota axle? Isn't that something in its favor?

Love dat drop out...

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Right!? The dropout is sweet. Oh i would of mentioned the tabs you make but I know you do them for both toyota and volvo so equal point for both axles.

If weight is a concern then skip to the 2.00 mark of this vid... black escort goes upside down. You need a keen eye but I'm fairly certain its got a toyota axle in the back of it. Ive also seen a number of uk built cars with toyota axles in them. Whats my point... if they were too heavy they wouldn't end up in sub 2200lb rally spec cars.








Edited 1 time(s). Last edit at 06/17/2016 02:28AM by Eric Ewert.

Good point on the center dif... A Toyota 8" with drims n axles of 4 pinion variant is closer to 250 pounds...

So.... Nobody has commented on the previa 7.5" that is my number one pick so far... Also has removable chunk, disc brake tabs, comes on 5x 114, cheap gear sets.

Only concern.. Strong enough?

John, I would be curious to hear the machining required for 8". Tabs and welding well within my skill/too set, but machining is gonna take going to others.

Looking at pictures looks like caliper mnt can bolt to flange where the 4 14mm head bolts hold the axles in? What about converting axles for 5/4 lug and disc...? What's it take?

Eric, in previous post I think u said oem 4.88 carrier is specific to 4.88? Is that correct, post was a little garbled. Think I remember that from Toyota days...

Quote
mhooper
Good point on the center dif... A Toyota 8" with drims n axles of 4 pinion variant is closer to 250 pounds...

So.... Nobody has commented on the previa 7.5" that is my number one pick so far... Also has removable chunk, disc brake tabs, comes on 5x 114, cheap gear sets.

Only concern.. Strong enough?

John, I would be curious to hear the machining required for 8". Tabs and welding well within my skill/too set, but machining is gonna take going to others.

Looking at pictures looks like caliper mnt can bolt to flange where the 4 14mm head bolts hold the axles in? What about converting axles for 5/4 lug and disc...? What's it take?

Eric, in previous post I think u said oem 4.88 carrier is specific to 4.88? Is that correct, post was a little garbled. Think I remember that from Toyota days...

I take it you have actually put the axle on a scale? maybe I weighed it without the drums on it. I can't remember for sure.

John can modify axles for reasonable money. Im sure he could do any bolt pattern you fancy too.
Fyi I have heard of the toyota 8 inch being put in 2wd pick up trucks with a 5x114 bolt pattern.

Yes your correct on the 4.88 housing being unique to oem 4.88. Aftermarket 4.88 gearsets are made for the standard housing.

You already stated why the 7.5 inch could be an issue...

Quote
mhooper
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.

So lsd options from what you said... potentially weak altezza diff, discontinued trd unit, torsen, and limited aftermarket lsd's. None of that sounded appealing. Decent chance the trd would be good if its a clutch type diff but if its discontinued that's a problem.

I cannot comment on the strength of the 7.5 inch toyota axle. If I had to guess I would say its probably more than fine in an rx7. But the lack of a good lsd is a rather big annoyance in terms of fun. You want rwd to do big skids don't ya!?

Edit... I did find this. http://www.weirperformance.com/maxgriplsdkits.html

Didn't realize this guy does a diff kit for the 7.5 inch diff out of a earlier supra. Its more cost than the 8 inch kit but not terrible. But be certain that the 7.5 inch diff will be stout enough.



Edited 3 time(s). Last edit at 06/17/2016 09:05AM by Eric Ewert.

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John can modify axles for reasonable money. Im sure he could do any bolt pattern you fancy too.
Fyi I have heard of the toyota 8 inch being put in 2wd pick up trucks with a 5x114 bolt pattern

All I've ever used are the 2wd 8" rear axles. Got mine from '84-'88 trucks, but I know there are narrower ones (older) and wider ones (newer). They are indeed 5 x 114 mm, and I've weighed one (with drums attached) at 160 lbs. It was lighter than the much smaller Opel axle I was replacing.

The trick, at least with those production years, was to get an axle from a 4-speed truck. Those trucks have 8" diffs, while all the 5-speeds I ever saw had the 7.5" diffs.

Here's the 5 x 114 2wd axle welded up and redrilled for 4 x 100. Center hub is machined to fit inside the new rotor.
https://flic.kr/p/4D78Ey

I used an E30 325i rear brake rotor, with MK4 VW aluminum rear calipers.
https://flic.kr/p/4D2SZD

---

Opel is a 4-letter word...
http://www.flickr.com/photos/10498579@N07/sets/



Edited 2 time(s). Last edit at 06/17/2016 11:11AM by Ascona73.

Quote
Eric Ewert

Yes your correct on the 4.88 housing being unique to oem 4.88. Aftermarket 4.88 gearsets are made for the standard housing.

You already stated why the 7.5 inch could be an issue...

Eric, goes like-a dis ...The 4.88 ring and pinion used OEM is unique thickness or whatever the fuck.. Haven't heard the axle housings are...

But hey if it was a hunnerd bucks say, then wot da fuq, eh?

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Hmm, I have weighed a lot of 8" difs but I think the reason my weights r so much higher is I'm dealing with 90 up models...

Sounds like you guys are using different variants...

Eric, nice link on the weir perf.... The mk 2 supra stuff should work for LSD in 7.5.

Didnt know 8" was even an option in 2wd pre v6 (88?)...

Think id have a tough time finding dif from 4 speed truck but good to know they r out there

As far as the strength of the 7.5" rear axle....I ran a supercharger on my 2wd '87 Toyota pickup and hammered the heck out of it. Autocrossed it, drove it hard like any 21 year old would. Never had a problem.

My cousin had a prepped 175 hp 22r in his own Toyota pickup with 7.5" axle and was merciless with it. 8" wide Hoosiers with a welded diff and 7500 rpm clutch drops. This was with 170,000 miles on it. The rear end never was an issue.

Probably fine on gravel....

---

Opel is a 4-letter word...
http://www.flickr.com/photos/10498579@N07/sets/

eh, the 8" has the best availability for parts. I'd go that route honestly.

---

First Rally: 2010 First RallyX: 2004 (a bunch)
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Last Updated, Apr 9, 2023

Quote
john vanlandingham

Quote
Eric Ewert

Yes your correct on the 4.88 housing being unique to oem 4.88. Aftermarket 4.88 gearsets are made for the standard housing.

You already stated why the 7.5 inch could be an issue...

Eric, goes like-a dis ...The 4.88 ring and pinion used OEM is unique thickness or whatever the fuck.. Haven't heard the axle housings are...

But hey if it was a hunnerd bucks say, then wot da fuq, eh?

opps i meant to say center section, nothing to do with the housing!

Quote
Gravity Fed
eh, the 8" has the best availability for parts. I'd go that route honestly.

The whole point originally---since I'm the guy who thunk of it---was Volvo guys could get a nice upgrade, be able to get a "pretty good" LSD (Not my absolute fave but for $75 versus 1200 bucks I can live with it), alternate ratios cheaply (as low as $15), common as dog poo nationwide and in The Great White North, and have enough of an upgrade that it should be dead relaible if one keeps oil in it.
And not be stupid overkill...

It really grew out of the Supra Diff Kit for Xratties--which has a 7.5" diff as opoosed to Volvos 7.2" ring gear...My dear friend Kevvi Hawkinson was drooling over the size of the half shaft at the splines compared to Dana 30 and Ford 7.5...

Its a good full step up....

The Volvo axles find their way downstream to guys with Japanese cars with little 6.2" ring gears...and impossible to find alternate ratios short enough...

Toyota into Volvo, Volvo into Toyota..
Some cosmic balance there.

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.