Rear axle options for small RWD

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b00sted

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Pete
I've already built a 9". It's not what I would call "cheap" and the jury is still out on if it is light or not. I need a scale to weigh it, my goal is 140lb with brakes. I think a Ford 8.8 would still have been the lighter way to go, certainly it would have been lighter than if I had used an iron pumpkin.

There are lighter options I'm sure...But the Ford 8.8" is super durable and has almost limiltless options when it comes to axles, gears, diffs/spools/etc. But one out of a Ranger for cheap and weld your own brackets on.

Then narrow it and either keep the 8.8" ends or weld on 9" ends. Axles can be had relatively cheap from Moser or Strange, and they'll make them in any length you need.

A good set of 31-spline axles built to your specs with a rebuilt Explorer diff(31-spline, can be built with carbon fiber clutches) will be super reliable in an average rally car.

It's not for a rally car. If I was going to build a rally car, I'd put a cage in a Cobalt. Cobalts are super cheap and common. I wouldn't want to run something over ten years old, anything more than that is too expensive/difficult to get parts for in this neck of the woods.

I have close to $2000 in the 9" for the RX-7, starting with a $450 rear I bought off of RacingJunk due to its having a locker and 5.43 gears. And by the time I had axles made ($450 w/shipping), bought brakes to suit ($140: $20 for rotors, $40 for pads, $60 for a pair of VW Lucas aluminum calipers, $20? for "Wilwood" caliper flanges that are the same bolt pattern as the VW units), shortened it ($330: $140 for tools, $90 for axle ends, $100 to have it straightened, plus time off work to go to the rearend shop an hour away twice) replaced the bearings (???), bought an aluminum centersection ($450), bought a flange type yoke and had it machined to suit the Daytona pinion ($70, machine time free), and bought another locker for it ($200 w/shipping on eBay for a NASCAR takeoff), I said "self, I ain't doing this shit again". And there's also things I forgot how much they cost, like the backbrace, and the lightweight springs for the locker, and the links brackets, and misc. fasteners like the T-bolts.

I just added that up, it's $2090, plus maybe two hundred more in forgotten expenses. I *know* I have a couple hundred bucks in the lower links alone. And none of this counts the Panhard I have to make and the mount I have to fabricate and the exhaust I will have to engineer to clear the Panhard mount.

Gee, wonder why I bought another RX-7 and now an RX-3 in the time where I was avoiding trying to add up the numbers and figure out how to make it all fit...

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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 12/19/2017 07:58PM by Pete.

Now I'm really curious as to how heavy that 9" turned out to be. I presume you have gun-drilled axles too?

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Self-righteous douche canoe

Gun drilling was not an option, although it WAS an option if I'd bought the full floater setup from Speedway. (Not THAT Speedway, a smaller shop in California) Was quoted $1500 for one of their floater rears with aluminum 4x4.5" hubs, solid rotors, and 31 spline axles, built to whatever specs I needed. Just add caliper brackets, link brackets, and the centersection of my choice.

I probably should have done that route, but nooo. I do have close to $700 in my centersection parts, but all that isn't included in that price is ring and pinion, and if you can't find a cheap 9" gearset...

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Pete Remner
Cleveland, Ohio

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

Certain 1990ish+ Volvo 740s were a 4.10 1031 that will swap into any of the 1031s. Any Dana 30 diff will work with the 1030 or 1031.

That is my plan for the 240 I am picking up tonight...

Are you telling me, you've lost another submarine?

Err, bought another Volvo.

This brings you up to twelve or so, yeah?

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Pete Remner
Cleveland, Ohio

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

14 total cars, only 5 are Volvos. And they aren't all mine so it's ok.

I am thinking that i will ignore the axle situation until I get the arches siuation sorted. I found a set of MkII type arches in composite, not alloy, for about $400 shipped to the US. Then i'll worry about how wide the axle can or cannot be.

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Pete Remner
Cleveland, Ohio

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

RX-3 arches? Where from?

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Self-righteous douche canoe

Escort arches. Was why i want fiberglass, easier to force into fitting the wrong car than aluminum, or even aluminium. I saw an image of a four door RX-3 rally car with Gartrac type arches grafted on and it looked perfect.

Oddly enough it has proven impossible to find Escort arches on this side of the Atlantic. There is a fiberglass RX-3 shop in PR but i have a feeling the recent unpleasantness down there would make things difficult.

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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 12/25/2017 04:42PM by Pete.

Oh, I see. Yeah, I was wondering if the Grp4Fab stuff would fit. This thing's been running on 14's but I want to be able to run it on 15's and to do that it looks like it's going to need cutting in the back. In front, well, you can get whole fenders from Phil's in AU but the fitment is rough and requires massaging. The guy I bought my replacement shell from used them on his resto car and was showing them to me. Also there was some guy in Hamilton, Ont who was making fiberglass ones (http://www.showcars-bodyparts.com/) but I think he ran out and was waiting for enough orders to do another run or something.

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Self-righteous douche canoe

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hoche
Also there was some guy in Hamilton, Ont who was making fiberglass ones (http://www.showcars-bodyparts.com/) but I think he ran out and was waiting for enough orders to do another run or something.

My understanding with Showcars-bodyparts is to run away as fast as you can. I have numerous friends who've ordered things from them and never reveived anything. Buyer beware!

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

And their "RX-3" page goes to GLC parts, not RX-3.

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Pete Remner
Cleveland, Ohio

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

OK then. *scratches them off the list*

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Self-righteous douche canoe

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john vanlandingham
But this is merikuh, land of do it because there no sensible reason, but a gut feeling! What look at numbers like the RX ring gear is what? 6.29" ring gear and the half shafts are 20 or maybe tops 22mm, why bother, numbers are elitist!!!

Cue Stephen Colbert rousing speech on Truthiness!

He did already say by the way that he's doesn't intend to go the Toyota 8" route...
a Full 2.5 inch bigger seems about right in the over-the-top-school-of-overkill

Stock RX-3 rearends are 7" ring gear (they make Dana 30 stuff look like toys, from what I see at Summit) and the "small" axles are 25mm at the splines. The "big" axles used in '84-up everything are 27mm at the splines.

The neat thing is that the solid axle Kia Sportages have a "7.5" inch rearend that has a dropout that plugs into anywhere the 7" goes, and uses 28 spline x 29mm axles. Same as the Honda S2000, which uses the 7".

I never had a problem with breaking R&Ps, just rearend housings and axle bearings. Started breaking axles when I really started turning housings into bananas.



SOON

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Pete Remner
Cleveland, Ohio

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

Quote
hoche
Now I'm really curious as to how heavy that 9" turned out to be. I presume you have gun-drilled axles too?

RX-7 rear: 140lb with rotors and lower links, but no calipers.
9" rear: 181lb with rotors and lower links, but no calipers.

The 9" will be using little aluminum Lucas calipers from a New Beetle rather than the big iron Mazda calipers. So maybe the total difference is 30lb.

The driveshaft bolts right up and doesn't need to be shortened, at least.

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Pete Remner
Cleveland, Ohio

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