Mazda RX-7 GSL-SE Rear End Swap -- Spriso Motorsports

[sfdaugherty]

Goldhawg:

I live in Albuquerque too. If you're interested in spending a few hours on a weekend pulling these, PM me. We could each take one if they're worth it and having two people do the work would make it MUCH easier.

Shannon

[GoldHawg]

Oh...and the Colorado Springs location shows two 85 GSL-SEs...

http://coloradosprings.upullandpay.com/Search.aspx" onclick="window.open(this.href);return false;

Shannon: you have PM

[Daryl Smith]

I picked one from a u-pull-it yard a year or so ago. Took a cordless reciprocating saw and had it out in about 5 minutes.
Hardest part was carrying it out to the truck afterwards, then they told us they would have been happy to truck it out for us...............

[MBrannon]

awesome work! that is exactly what I want to do to mine.

[nomadtrash]

I used an 84 GSL rear in my race car. It has non-vented rotors and a 4x110 bolt pattern. With the machine work needed to respline the axles I'm sure you could have a new bolt pattern drilled in the hub. The RX7 uses screw-in lug bolts and I replaced them with a screw-in stud kit. The only questionable thing is the thickness of the hub. I don't think it is the same thickness where there are no studs.

There are two different types of axles. The GSL models have a heavier and stronger axle than the SE. The SE axles have a taper in the middle where the GSL is uniform diameter. Scott McQueen built the mondo bad a@@ three rotor 500 HP bugeye which wins the SOLO II nationals every year using this axle. He was able to grind the weld that holds the hub on the end of the axle and then cut the axle to length and reweld. No need for resplining. I found it much easier to send the axles to Moser and let them handle it.

I bought my entire 84 RX7 GSL for $100 and pulled a bunch of parts. I then sold the hulk for $100. It is well worth any additional machining to change the bolt pattern if the alternative is a $2000 SE model.

I built a tool to measure break-away on the limited slip. In stock form it was at 42 pounds and I could easily spin one tire. I could jack one side up and spin the tire by hand. I took the plates out of the LSD and stacked them in a different order which increased breakaway to around 80 pounds. There are 4 plates on each axle and the way they are stacked leaves the two end ones rotating with the housing and the end gears. You basically have only a couple of friction surfaces. I restacked them in a different order and got many more friction surfaces. I then used some pinion shims at the very end of the stack until I could just get the case back together. It would not hold even one more shim. At that point the breakaway increased to over 140. Now I can really tell a difference on the track. It does the cool shimmy in the parking lot at slow speed impressing bystanders.

I set mine up with a three link, coil overs, panhard bar, and 3.90 gears.

I hope this helps,

[nomadtrash]

I forgot to mention that many RX7 owners complained about chatter in the rear end from the limited slip. Mazda's fix was to replace one of the driven plates with a stationary plate. This leaves each axle with three stationary plates and one driven plate. You basically have two friction surfaces, one on each side of the one driven plate. The solution is to buy additional driven plates from the Mazda dealer. They still sell both the stationary plates and the driven plates in a range of thicknesses.

I think the Miata torsen is a good alternative to the clutch type stock unit. I like the clutch type because it drives both wheels. The torsion drives the wheel with the most traction. They allow for turning without pushing and in general are wonderful technology.

[GoldHawg]

Any specific years rear ends w/torsens to look for? There were 3 88 RX-7s in the pick a pull today; didn't know if these have the torsen differential...

Are these a bolt in replacement for the limited slip in the GSL-SE?

thx!

[sfdaugherty]

Goldhawg and I pulled one today. Unfortunately, one of the axles had already been snagged. We decided to go ahead and take it since it was only $127 with all the taxes and fees. We were able to get both calipers with the emergency brake cables intact.

Three questions for you Michael:

1) How big a problem will it be to get the axle replaced or should we keep looking for an axle?
2) Can other axles be used?
3) We didn't take the driveshaft. Should I go back and get it for the yoke?

Shannon

[spriso]

Shannon wrote:

Three questions for you Michael:

1) How big a problem will it be to get the axle replaced or should we keep looking for an axle?
2) Can other axles be used?
3) We didn't take the driveshaft. Should I go back and get it for the yoke?

1. You are going to want to find a GSL-SE rear axle-- and remember it must be from a GSL-SE to get the right bolt pattern.

2. As far as I know, you must use a GSL-SE version, there are no other ones that fit.

3. Yes, get the driveshaft, you will need it to fit onto the differential, and you will replace the front yoke with the Datsun unit.

Michael

[DnCrs13]

Have you decided upon a cost for this conversion if we supply you with a GLE-SE rear end? I have a line on one now. The guy wants $250.00 already pulled. The seller says it has 105K.

Dan

[spriso]

Dan wrote:

Have you decided upon a cost for this conversion if we supply you with a GLE-SE rear end? I have a line on one now.

Before we start taking customer orders, we want to be 100% sure that everything is working as designed (axle length, pinion angles, etc.) We have all been busy with our projects and the only installed under a car right now is Eric's (and that car is a few weeks out before it is drivable).

As soon as we have put a few hundred miles on that car to make sure that it is all good, I will figure out how we are going to bill these conversions. I will update this thread when we know more!

Michael

[ppeters914]

We have all been busy with our projects and the only installed under a car right now is Eric's (and that car is a few weeks out before it is drivable).

Canby is a few weeks....two to be exact. Any chance it'll be there?

[GoldHawg]

Michael--
Could you expand on your thinking on getting rid of the stock Mazda panhard rod/"crazy control arms". I'm sure you wanted a bolt-in, but wondered if this was your only consideration, i.e., is the stock mazda suspension a really good idea, just a lot more complicated to fabricate/install, or is it really not a great upgrade to do? Seems like the ride would be smoother with the coil springs and the panhard rods would keep the rear end very stable, but I'm sure it would be much more difficult to put in the roadster; obviously not a "bolt in". Your thoughts on trying to put the whole rx-7 suspension in the roadster?

thx!

[jake7140]

The original RX-7 suspension was a 4-link with a Watts link for location. One of its flaws was that the pivot point for the Watts link was off-center, and the links bound up especially when the susp was lowered, then compressed in a corner. You then had go-kart solidity, and prone to snap spins. Lower link front location points were lowered in 84-85, but the issue persisted.

Race RX-7s generally went to a Panhard bar setup for location (G-Force & Tri-Link), and really soft (foam) upper link bushings to keep it free. It worked very well, and within the rules.

I'm not real familiar with the SE's (raced 12Aa), but for 84-85 the axles were bigger on the 12A models than previous years, and the bolt pattern and ratio was different than on the 12A GS and GSL models. Don't know numbers, but not nearly as many as the 12A, and the owners tended to "collect" them a bit more, hence the higher prices and need to most often buy a whole car I suppose.

'86 and up were IRS.

[spriso]

Michael--
Could you expand on your thinking on getting rid of the stock Mazda panhard rod/"crazy control arms". I'm sure you wanted a bolt-in, but wondered if this was your only consideration, i.e., is the stock mazda suspension a really good idea, just a lot more complicated to fabricate/install, or is it really not a great upgrade to do? Seems like the ride would be smoother with the coil springs and the panhard rods would keep the rear end very stable, but I'm sure it would be much more difficult to put in the roadster; obviously not a "bolt in". Your thoughts on trying to put the whole rx-7 suspension in the roadster?

As Jake7140 noted, once the RX-7 rear suspension gets lowered, the rear suspension stops working as designed.. Mix that with the fact that we narrow each side of the rear end 4.5-5" PER SIDE, we would not easily be able to convert the existing suspension arms (plus, they would all be too long anyway!)

Our solution was to create something that could be bolted into ANY roadster with no fabrication to the existing chassis (as there are many people who prefer it that way!) Yes, a four-link like Alvin's would be great, but they are outside the scope of many roadster owner's abilities.

Eric's car is nearly on the road with his RX-7 setup. Dave's axle is setup and hopefully will be in before Shasta. We are going to put 1000 miles on the setup trying to make sure that everything is 100%, then we will start offering this conversion to our customers...

Michael