jimlab

If you have a 1993, your rear subframe is missing the rear mounting points (shown below) for the revised braces that 1994s and 95s came with. In order to install the lower part of the Cobra crade, you'll have to have mounting points welded to your subframe. We're planning on providing a pair of brackets bent to the proper shape for the subframe, but they'll have to be trimmed and welded in place. Unfortunately, I don't have access to a rear subframe without them, and wasn't willing to have mine cut off just so we could duplicate them.

jimlab

Here's a picture of a 1993 subframe showing the missing rear mounting points. The differential has been dropped to install a pair of my differential mount bushings, so it is not in its usual location.

jimlab

In addition, a small section of the lower cross piece (just behind the differential in the picture above) has to be cut out for clearance of the rear of the Cobra differential. For 94s and 95s, that's the only modification required, so other than that, it's a complete bolt-in.



The length of the axles has already been taken care of, and I have a schematic that can be faxed to the vendor to order a pair. The differential itself and inner CV joints are up to you to find so that you can shop for the best bargain to meet your budget.

jimlab

Not really. If you replaced the center shafts of your axles with Rotary Performance's 300M versions and installed a Kaaz differential, you'd have to do nearly as much work, and possibly more. Bolting the cradle and new differential in place is nothing if you've already got the rear mounting points. With the exception of the driveline change, there's not much difference between the two and one is much stronger with a far wider range of available gear ratios.



Keep in mind that this swap was intended for V8 FDs, not rotary powered FDs, but would obviously work for them as well. The elimination of the PPF will require the fabrication of a transmission brace, which doesn't take anywhere near the load you think it does. All of the FDs with V8 conversions are running transmission braces and obviously making more torque than a rotary, especially on the low end. They already have to have the driveline modified, so that's not an extra step for them either.



The entire point of the exercise was to make available a much wider range of gear ratios than just 3.90, 4.10, 4.33 and 4.77. Ford 8.8" ring and pinion sets are readily available from 3.xx:1 to 6.xx:1, and only cost a couple hundred dollars. I looked into having a custom 3.42:1 ring and pinion made for the FD differential and was quoted $4,400 for one set. Buying 10 sets brought the price down to a much more reasonable ~$2,100 ea.



Since I was going to have to upgrade the axles anyway, I decided to just change differentials, get more strength (the lighter weight was a fringe benefit), and get the gear ratio that I wanted. Even with all new parts and a lot of R&D, I'm still not much over the price of the quote for a 3.42:1 ring and pinion, and no one else has to absorb any of those costs now that I've developed an alternative solution. When you compare it to a Kaaz differential (~$900) and RP 300M axles (~$900 without boots or clamps), it starts looking pretty attractive because of all the other benefits I've listed.

jspecracer7

So you did the Cobra rear end conversion not to strenghten up the rear end(not initially anyways), but rather to get the final gear you desired?

jimlab

I would have strengthened whatever I could anyway, with RP's 300M axles and a KAAZ or other clutch-type differential, but I needed something in the 3.42:1 range for gearing. I ended up with 3.55:1, although I'll probably end up dropping to 3.27:1 eventually.



This solution offered even more strength than anything I could have done with the FD differential and axles, and was easiest to adapt to the existing setup because the '03+ Cobra axles are the same type as the FD. All I needed was a hybrid center shaft with FD splines on the outside end and Cobra splines on the inside to complete the package.

papasmurf

i figure i can find the diff housing for the cobra fairly easy, and im sure i can find the other stock ford parts. i mainly want to do this because of the new electric lockin diff's and on top of it all i need my rear to be strengthened.



my car is undergoing to v8 swap, but power is much higher than what most do right now (should be upwards of 750hp to the wheels) i dont think any fd drive parts will really work well with that power.



if you do make some sort of near bolt on solution for this count me in, as long as its a fair price n all.



is the u joint any different for mounting the driveshaft or do i need to do the swap before i get my drive shaft built?

TheCamel

I applaud the efforts you have made. You have shown there are alternitives.



Mazda did not do well in the gear dept, and I am acctually surprised with the amount of road racing they did on the factory cars. Its nice to see someone doing a little R&D to put something other than a 9" in

jimlab

I thought I'd just posted that I do have a near bolt-in solution.



I believe the stock U-joint for the Cobra 8.8" is a smaller 1310 or 1330-series, but I'm using a Mark Williams billet pinion flange made for the larger 1350-series U-joint, and a matching 1350-series billet yoke (sold by Denny's Driveshafts, who will be making my driveline also) for my T56.



If you're using an FD driveshaft that you had lengthened, you'll probably want to replace it. The good news is that Denny's has drivelines in various strength levels for any application. Their "nitrous ready" steel driveshaft is probably what you'd be interested in, although they told me that their HD aluminum driveshaft would be just fine for my application. The nitrous ready shafts are really intended for high horsepower in much heavier cars. They're also fairly reasonable priced.



http://www.dennysdriveshaft.com

jimlab

The weight and size of a 9" was unacceptable, not to mention that the only IRS applications I found that could be adapted use U-jointed axles (U-joint at both ends) like the C4 and Jag IRS setups. A CV-jointed axle was necessary because keeping the stock suspension requires the axle to be able to compress and expand as it cycles. Obviously, one with U-joints at each end would not.