8.8 IRS upgrade questions

[Ace23]

Finishing up our work on my Superformance. My car has the 8.8 ford differential. The diff is out and we are ready to drop it off for the gear swap. I contacted the driveshaft shop in NC and elected not to go with a 31 spline upgrade. I am instead having them build me a set of their level five 28 spline replacements. The stock half shafts may have lived but I did not want to have to worry about them. We are running a 427 Windsor with a 6-speed, upgraded rear gear and drag radials. Strictly just a street car with a little twist to it.

1. Is the stock differential cover okay or is it a good idea to upgrade while out of the car. If it needs to be replaced please explain the reasoning.

2. Craig's cobras offers solid diff mounts....we noticed poly diff mounts are also available. Has anyone had experience with either? I've read somewhere that the aluminum mounts can create noise.....with 3" sidepipes in an open roadster is this really noticeable? The main reasoning behind the use of the solid mounts are to avoid wheel hop.

[LMH]

My opinion is the differential should be solid mounted to keep it from moving. That said, I haven’t heard of any issues with poly mounts.
And yes, change the cover to a stronger one. The differential is out of the car, so there’s never a better time to change it. The production cover is very weak and not worth the worry. When you hold both covers in your hand, you’ll see exactly what I mean!
Larry

[1985 CCX]

I used Delron type bushings in my mount.
Has yet to fall out....

[eschaider]

Originally Posted by Ace23

Finishing up our work on my Superformance. My car has the 8.8 ford differential. The diff is out and we are ready to drop it off for the gear swap. I contacted the driveshaft shop in NC and elected not to go with a 31 spline upgrade. I am instead having them build me a set of their level five 28 spline replacements. The stock half shafts may have lived but I did not want to have to worry about them. We are running a 427 Windsor with a 6-speed, upgraded rear gear and drag radials. Strictly just a street car with a little twist to it.

1. Is the stock differential cover okay or is it a good idea to upgrade while out of the car. If it needs to be replaced please explain the reasoning.

The stock differential cover is not OK. It needs to be replaced. If you do not replace it this is what you are risking. Notice how thin the cover casting is. There is insufficient strength for performance applications. The one in the pic below is from an 03/04 SVT Cobra.



This is a pic of the diff cover I use. IMO it is the strongest diff cover you can get. It was manufactured by Fore Innovations. I may be wrong but I don't believe they offer them today. The covers are bullet proof, modestly expensive and can be difficult but not impossible to find used in the enthusiast community.



JBL offers a similar style cover for their cars but at the time I had contacted them, the part was only available to existing car owners.

This is what the inside of the Fore cover looks like;



The two ports at the bottom of the pic and again at the 8 o'clock point are the oil cooler feed and return ports and the lube fill and drain ports. With this style of cover you either need an overflow canister that the heated oil can expand into and later return to the diff after cooling or you need to run an oil cooler. I prefer a thermostatically controled oil cooler.

If you need the cover immediately and do not have the time to search for the billet version then your best bet is the Ford M-4033-G3 cover. The Ford cover looks like this;



This cover will still require you to run an expansion overflow and recapture system or an oil cooler.

Originally Posted by Ace23

2. Craig's cobras offers solid diff mounts....we noticed poly diff mounts are also available. Has anyone had experience with either? I've read somewhere that the aluminum mounts can create noise.....with 3" sidepipes in an open roadster is this really noticeable? The main reasoning behind the use of the solid mounts are to avoid wheel hop.

1985 CCX nailed it on the bushing material. Go get yourself a bar of delrin and make up some sandwich style biscuits for your front and rear mounts.

Although you have not asked I will suggest you might want to look into a Wavetrac differential. It is an all gear torque sensing design with a patented application mechanism that will significantly increase the positive driving experiences the car is capable of. This is a link to their site => Wavetrac They also come with an unlimited lifetime warranty for track or street use.

While I am still answering questions that were not asked, the 28 spline vs 31 spline decision is I believe worth a second look. This is a write up by Mark Williams on axles, splines and strength, click here => Axles. This is an excerpted comment on his assessment of 28 and 31 spline, "... For bracket and street use, avoid OE 28-spline axles; in fact, even 31-spline (OE) axles are borderline ..."

After you have attended to all the above you still have the cast aluminum main caps that hold the ring gear carrier into the diff housing. These are a known weak link if you hook up your tires and/or experience wheel hop. Mark Williams makes billet steel replacement caps to correct the fragile cast aluminum breakage problem. Click here => MW Steel Caps

Last item. As long as you have the diff out you might want to consider looking into an 8.8 diff housing from an Explorer. They were the strongest aluminum 8.8 housings Ford has ever offered. The housing on the left is the Explorer;



When everything is said and done, choices always come down to time, economics, availability and personal preference. It is always better to begin that selection process with more information rather than less. Hope this helps.

Best of luck with whatever you finally decide.


Ed

[vatdevil]

I run Craig's solid diff mounts and yes they do transmit a bit more noise, but not enough to notice over your side pipes. 31 spline is significantly stronger than 28. My setup uses 31 spline bars from DSS attached to inner/outers from factory new 03-04 Cobra half shafts. Drag, road course, auto cross with 600+ ft/lbs on sticky Nittos...no issues.

Also installed the Ford aftermarket cover. Winter plans are to replace the rubber mount it attaches to with delrin.

[Ace23]

Thank you guys for the insight....quite a bit more than I expected to receive. The ball is kinda in motion on the level five 28 spline shafts at this point but I can proceed with upgrading to the Ford Motorsport cover. We definetly have time on the bushings to look at some additional options. Never say never but I have no intent to ever track the car and even on the street I do not launch the car. After saying all that you may wonder why I'm even going through with some of the upgrades. I just thought with the nitto drag radials and added gear a few upgrades might take care of some potential failures. I cannot express how excited and grateful I am to be getting this close to having the car completed. The refurbishment started august 2016 and it has been quite the journey selecting components and upgrading as we went through the car.

[bobcowan]

In my FFR, I used a cast iron housing, factory rear cover, and aluminum front "bushings". I used a Ford R&P, and an Eaton Tru-Trak. I bought the strongest 28 spline axles I could find at the time. The 427W made over 500hp on the chassis dyno.

I beat the cr ap out of that car on the road course and the street for 12 years. I loved to pop the clutch and burn rubber. Donuts always make me laugh like 12 year old. Never had any problem with the differential. It easily held up to all that abuse.