Drivetrain 33 spline SN axle with ABS and parking brake build


Apparently my ex-husband made that mistake.
15 Year Member
Jun 14, 2004
Acworth, GA
This should be my final edit on this post. The car is running now, and the axle is working as it should. This axle was fabricated by Attitude Street Cars in Marietta, GA. There are very few fabricators that build axles like this, and I had a very positive experience dealing with Attitude. Quick to respond to questions, very flexible on the parts I wanted to use with helpful suggestions, but no abject negativity for my opinion on parts or otherwise. The build time was approximately 2 months, and the fabrication labor was around $1500, which I considered to be reasonable for the effort and expertise required. Axle work is very detailed, and you do not want to go for the lowest bidder on this job.

This is a build thread for a 33 spline replacement axle for an SN that retains both the ABS, and the parking brake. This axle will replace my current 28 spline Moser axle with a 3.55:1 gear ratio. The goal was to have a functional axle with full size 9" bearing bolt on style axles that retains all the factory features of the car. Originally the plan was to go with a 9" axle end housing to get more brake options. I later found that there were no large brake options that fit a 9" housing end where you could retain both the parking brake and ABS, and fit inside a 15" wheel. Moser Engineering offers a housing end that accommodates a full size 9" bearing, but has a factory 8.8" flange bolt pattern, which is the route I ended up going with. Moser Engineering does not list this option on their website, and they do not have a part number for it; you have to call and ask for it. I also wanted to use an Eaton Truetrac differential to maintain full street manners and no compromise torque distribution for drag racing. It is not a cheap differential, but I believe it will save money in the long run, as it has no wear items, and is maintenance free. This is not DIY project. In order to convert to a bolt on style axle, the axle ends have to be cut off, the axle has to have a jig put through it, and then the new axle ends are welded on. The jig is about $650, which makes it economically non viable to do at home. If you want to save money and do this at home, consider a C-clip eliminator style end. The downsides to the C-clip eliminator is a smaller bearing that is not as durable, and a number of gaskets and seals that tend to leak. It is quite a bit more affordable though.

So I'll shoot out the parts list for the basic axle:

Axles, bearings, housing ends: Call Moser
Differential: Eaton 913A701
Ring and Pinion (3.55:1): Ford Performance M-4209-88355
Axle girdle: UPR 3024-01
Axle Braces: UPR 2024-01 (check your exhaust clearance)
Pinion Seal: National 3604
Differential Cover Gasket: FelPro RDS55341

The Eaton True Trac requires 80W-90 Mineral based gear oil with no friction modifier. That would be the cheap stuff at the parts store. This is the only item the differential saves you money on.

Brake Options. For now I am going to run Cobra brakes to get the car running. If you want to upgrade to Cobra brakes you will need:
Ford Performance M-2300-M
To clear a 15" wheel, you will need the low profile brake hose kit from Maximum Motorsports. The 3 hose kit is:
Maximum Motorsports MMBK2P
There is also a 2 hose kit available.
Maximum Motorsports MMBK12R

The Cobra brake upgrade is a huge improvement over the factory GT brakes. However, the clearances are down to the minimum 1/8" required clearance. You can either grind the calipers to clear the wheels, or run a very small spacer. You actually have to take the little rubber caps off the bleeder valves to get clearance; that's how tight it is.

If you want a 4 piston caliper brake that clears a 15" wheel with ABS and a Parking brake, Baer makes an SS4 12" rotor kit:
SKU 4262279
That is a drilled/slotted rotor with a quality 4 piston caliper available in multiple colors, and a sling style parking brake. The sling style is the desired style parking brake. I did not find any other manufacturer that offers this type of brake setup.


I ran into some issues, and I expected that. The forward brace kit does not clear the tail pipes on the car. I had to remove the bolt on front braces for the time being to get the car back on the road. I'll reroute the exhaust as neccesary in the future. If you are running a full exhaust so that you don't "get high on your own supply" then you might want to omit the forward braces.

There are 3 major aftermarket brands that build axles for Mustangs, Moser Engineering, Strange Engineering, and Mark Williams Enterprises. I talked to all 3 manufacturers multiple times before selecting this build. They were all excellent in communication and customer service. Each manufacturer machines their axles a little differently, and they are not interchangeable with different brand parts. That is to say, you can't put a Moser reluctor ring on a Strange axle, or visa versa. Mark Williams was not an option for this build, because they do not offer any ABS support. Strange Engineering has a few options. However, they do not offer a 33 spline axle, which is the largest axle that Eaton offers a True Trac for. If you are content with 31 spline axles, or 35 spline axles with a spool, and a 1 piston brake caliper, ask Strange Engineering about a B1706MC, or B1706MCC (cobra brake) kit. This is actually a little cheaper than the Moser option I chose. However, if you want a 4 piston caliper with ABS and a parking brake, there is no option from Strange Engineering that I found viable. Aerospace Components has a sling style parking brake with a 4 piston caliper available for a 9" end. It does not have a provision for an ABS sensor, and I don't know that one could be drilled, and even at that, I don't know if the reluctor ring will fit inside the sling assembly.

Moser Enginnering delivers a product that is very durable, but not so precise. This is very visable when trying to line up the brakes. As I understand it, this flaw is universal to all the aftermarket brands. I had to shim the brake caliper mounts to fit. This is not a fabrication flaw; it is actually an axle flaw. The brake offset is measured from the bearing retainment to the axle face. On my axle, it was off by 34/1000s one one side, and 30/1000s on the other side. I had to shim the brakes a little bit to fit. You can get M12 washers from Home Depot to get it in the neighborhood, and thinner shims are available from McMaster-Carr in 1/2" which is close enough.

This is a very expensive upgrade for your Mustang; it was in the neighborhood of $4,000 for me. It has completely changed the car for me, and was like a rebirth for a car I have owned and driven for just over 20 years. The 33 spline bolt on axle is quite a bit heavier than the factory axle, which corrects the inherit poor weight distribution of a Fox chassis Mustang. I am not quite certain what changed (the weight, the Truetrac, the perfect axle alignment) , but for the first time since the factory engine, the car hooks up in 1st gear. It could be the weight of the axle, the dynamics of the Eaton Truetrac; I am not sure. It just squats and goes on 275 Nitto DR tires. I was absolutely roasting the tires in 1st, and halfway through 2nd on the factory axles with the 347cid engine. This mod repays in dividends.



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I'm excited to see how this progresses. Thank you for posting. It sounds like you've put a lot of time and effort into engineering everything out for a full-featured indestructible combo - nice work!

P.S. At least you'll make your money back on the gear oil over time! ;)
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I'm excited to see how this progresses. Thank you for posting. It sounds like you've put a lot of time and effort into engineering everything out for a full-featured indestructible combo - nice work!

P.S. At least you'll make your money back on the gear oil over time! ;)

Yeah, this was surprisingly a huge PITA. You would think that building an axle for a Mustang would be a no brainer. I have a whole other soap box thread on it that I have to re title. It took about 6 months of phone calls, ordered and returned parts, etc. I was unable to find this build detailed on the internet anywhere. There is also an issue when you talk to local axle builders. These guys have had a career of building one of drag racing axles for cars that get trailer-ed to the track. So when you call them, they understandably are not familiar with the parts they need to order to build your street car axle. I really appreciate the time Ernie and Steve at Moser Engineering, and Jake at Strange Engineering put into helping me with this. I forgot the name of the sales rep that I was interacting with at Mark Williams, but he was also awesome. I would also like to thank GMS/Groff Motorsports in Snellville, GA for giving me insight into what makes an axle strong, maintainable, an safe. Unfortunately Strange Engineering ate the bullet on this one, and only got a $20 restocking fee out of it after they went out of their way to help me. They were actually emailing me detailed technical drawings to try and get this to work. That's phenomenal customer support.

I will be bring the axle to Attitude Street Cars in Marietta, GA to build. So far they have also been great to deal with. I with hold a recommendation until I have a completed axle that works well.

I do my best to title my build threads so they pop up first when googled. I think it is important to share the details of simple things like this so that others don't waste time trying to find the right parts combo.

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