It's an aluminum ring about 1/2" thick that fits in the axle seal to take up the gap that is there from the Tbird axle being a little different size. You can see it about half way down my blog post here: Jim and Jenna build diary, Miata LS1 Conversion: The 3rd half of the back half, 8.8 Ford axles in a Miata.

So is the splined part of the shaft longer? That doesn't look like that seal is doing anything useful?

Exactly the splines are longer and that spacer makes up the difference. The seal still does it's job of keeping crud out of the bearing. Normally the Miata CV joint housing is right against the seal and the spacer fills the gap so the seal gets the surface it's suppose to. The inside of the spacer is tight to the tbird axle. I never really thought about it but I suppose eventually that seal surface would wear a bit on it.

Hmm, def an interesting setup. Didn't I see something somewhere, where they used miata shafts and outer knuckles and inner knuckles from the tbird?

I'm sure it's been done with a little creative welding and the thought certainly crossed my mind!

The shafts are pretty close to the same length. But since thery're not, the spacer acts to make sure the bearing is clamped when the axle nut is torqued, and to ensure that the CV housing doesn't contact the spindle body next to the seal, and to provide the same sealing surface as the Miata CV. It is a little more than a dust seal, it gets pretty cruddy back there. There's been some discussion over the years as to the importance of having that spacer made from steel versus aluminum. IMO since it does take the clamp forces, it should be steel.

The dimensions I use are: 2.205" OD, 1.25" ID, .220" thick. Chamfer the inner ID where it contacts the face of the CV. The OD is taken from the Miata CV seal surface, the thickness is the minimum to simulate the Miata CV; it could be longer, but any extra length takes away from the spline contact. The ID is just clearance to slip over the stub.

Mike

Maybe I can clear up a few items.
The remanufactured CV axles from A1Cardone are plentyfull and inexpensive.
Part # 60-2023 $ 65. Ea. with a core charge of $45 ea. I return the Miata CV axles in the A1 Cardone box. Never a problem.
I have had two Audi CV boots tear at the axle.I think the axle is too big. One had a clamp. The other did not. I continue to use the old style as they work great as long as you keep them clamped away from the shock! No ballooning Tom :-0
I burp the air out. Going on 100+K miles on the shop car.
The aluminum spacer is on its 22nd year with no problems.
Any axle that is welded or uses a Ford inner CV and a Miata outer is going to fail. Probably when you are a long way from home. I know of at least 30 axle failures and as many Miata CV failures. They just explode and that's it. lots of greasy pieces.
Hope this helps,
Martin

For the Monster application, the 60-2023 CV axle is the one you want for 7.5 and 8.8.
The outer 7.5 CV diameter is 3.5". The 8.8 is 4"
Both differentials have the exact same width and mount locations. One wonders why the need for two very similar Diffs. But don't get me started.

Well there you have it from the man himself!

For what it's worth I'm running Martins set up with the axles he lists above with an 8.8 and probably around 390hp at the wheels. Over the last 11,000 miles it has seen countless full throttle launches and romps past 100mph with no issues or signs at all of wear in his stuff. But I am running Audi boots so I'm going take a closer look at them tonight!

Side note to the core charge Summit's core it only $23 but I sold my Miata shafts with the rear end and came out as good if not better if you factor in return shipping of the cores. http://www.summitracing.com/parts/AAZ-60-2023/

Thanks for that Martin!

on a side note for anyone looking at this thread, i get an odd squeak coming from the outer CVs/wheel hub area... it happends on both sides, and ONLY once i drive it and get things warmed up back there... I lifted the rear of the car after warmed up and slow turn the wheels and you can hear it squeak... sound like a rubber squeegie sliding on a glass surface... didn't do this before the new hubs and axles...

this may be fine and normal, but i just want to make sure... i made sure when installing the aluminum spacers to apply a thin film of grease and that it was sitting properly inside the seal, as i noticied it would have been easy to overlook it and bend part the seal walls inside/under the spacer...

anyone esle experience this?

Hey guys, I'm building my axles right now and my clips shattered when taking apart tbird axles. What did y'all use to replace those retaining clips?

Axle clips
 

You can get those clips at Ford.
The CV needs to be cleaned out as the broken pieces will damage the CV
Cheers
Martin

Awesome thanks. I just finished taking them apart and cleaning. Local dealer says the part is discontinued and autozone and orileys didn't have a clue. I guess it's another puzzle to solve

I can send you some.Two?
PM me your address.
You owe me a stamp.
Martin

That's some awesome customer service :)

I'm in the process of installing a blower in my 92 which has a sbf. My car has the ford 7.5 irs rear. You think I will need to upgrade the 7.5 to an 8.8?

Power will be 400-420 rwhp

Recommendations?

You will never get enough traction to break the 7.5.

Thanks for the reply. Do you use the 7.5 or the 8.8?

Wow I just saw this! Thanks for the offer. I found some that did the job (hopefully!)

Wrong focus the weak link is not the 7.5 vs 8.8 it's the CV joints and shafts. Case in point...
https://www.v8miata.net/attachment.p...ine=1449684169

And power didn't do that time and stupid did. To answer your question no you don't need to upgrade but if you do PM me I'll buy your 7.5.

There is no question the 8.8 will take more power and punishment than a 7.5 but the bottom line is no one has ever broken either a 7.5 or 8.8 without the driver or the mechanic or both doing something stupid.

Thanks guys. So in light of the supercharger addition, what do yo recommend upgrading in the rear to try to stay a step ahead of breakage? What do you use and where can I get it..

Thanks!

Ahh... the driver. You could put 600hp to what you have easy if you never shock the driveline on sticky tires.

I would like to be able to use all the power it makes, and drive it to my full capability....Any axle upgrades available or recommended if I plan to drive it hard on sticky tires occasionally?

Well you have asked 3 times and gotten the same answer all 3 times and clearly that is not what you want to hear. If you are worried about it change it. 8.8s are not that expensive and I'll buy your 7.5.

if you're still having this issue jack up the back of the car and spin the wheel, spray some dry silicone on the cv boot. It won't last long but if it goes away you'll know that's what it is. I see it at work on front CV's often.

I think I've asked the question 3 times and gotten different answers but none that answer the question I'm asking. I guess I'm not asking the question correctly or I need to clarify....

I've been told it's the driver....drive it easy and it will hold 600hp

I also was told the 7.5 is plenty strong and the 8.8 is not needed, and I'm focusing on the wrong end....I need to focus on the axles, not the carrier.

I've been told the car won't get enough traction to worry about breaking

Respectfully, I'm asking the same question and getting different replies that don't answer my question. Let me expand on my intended use and driving style for the car. The car will be making over 400whp, and eventually 500-550. it Will be able to use the power and put it to the ground relatively well, and I do not plan to drive it easy. I want to be able to drive it to my fullest capability, which means right foot on the floor, never lift, kick the clutch and snatch a gear.

Can the 7.5 with upgrades in these light cars withstand 400whp for now and this driving style? If there are upgrades that can beef up the 7.5 to handle it, I'm interested to know what they are and where to get them. If I need a different rear, I'm interested in feedback on what other units may hold the power and driving style.

I'm very familiar with the 5 liter drive lines and the 8.8 solid axles having raced them for over 20 years....but have never owned a 7.5 IRS and know very little about the IRS so your personal experiences and recommendations are appreciated..

Joe