So I took the monster to its first autocross today. Apparently I'm "entertaining" to watch. At anything other that perfectly straight and any throttle more than 1/4-1/3 I'm just vaporizing the inside rear tire. Like big billowing ridiculous clouds of tire smoke.
Obviously this needs to change. I have installed a 7.5" Ford rear-end from an early 90's Thunderbird (IRS). Can someone please educate me on what I need to do to make this thing hook? Challenge budget friendly is better since I'd like to bring it this year. Thanks in advance!
Rodan
HalfDork
4/8/18 6:21 p.m.
You can always Lincoln locker it.... or upgrade to the 8.8/gm thing...
Keep the tire more planted by reducing body roll.
Don't accelerate until front wheels are straight.
Roll on the throttle instead of hammering it.
Install limited slip
The auburn style in the ebay link is not rebuildable, and when Ford discontinued the 7.5 Trac-lok the price of clutches doubled.
L/S for a 7.5 will cost more than swapping the full 8.8 pumpkin from another mn12 donor.
Google tells me this is the diff from a 93 thunderbird. Almost certainly 3.27 gears and open diff. With both tires in the air spinning one side sends the opposite side spinning the opposite direction.
Shame you're not closer, I'd give you a heel of a deal on an 8.8 with tracloc and 3.73s or 3.55s, can't remember.
In reply to RevRico :
Thanks, I may take you up on it if I can't find something closer. Although I'd actually prefer taller gears. 2nd is near useless if you're deep into the throttle. Apparently V8 Miata guys recommend the 2.95 gears.
Yeah when I was looking for lsd options for a 7.5 it was cheaper and easier to find an 8.8 with a Trac loc. Rebuild the Trac loc with the modern clutch packs.
Is the output splineing the same between the 7.5" and the 8.8"? Custom axles and all that.....
KyAllroad (Jeremy) said:
Is the output splineing the same between the 7.5" and the 8.8"? Custom axles and all that.....
If you mean the splines being the same, yes except explorers. Those are different.
Will a limited slip center section from a 7.5" Mustang solid axle fit in the center section you have? If so, I have one in a box in the garage. Came out of an 80s Mustang. Its sole purpose in life seems to be to sit on the base of my 2 wheel dolly and make sure it doesn't tip over and hit one of the cars. I have narrowed several 8.8s since this thing found its way into my garage, so I doubt I will ever have a use for it. FWIW 7.5" 28 spline axles and 8.8" 28 spline axles are the same.
Will
UltraDork
4/9/18 8:14 p.m.
You want an 8.8 out of a manual Supercoupe. Trac-Lok diff and 2.73 gears.
In reply to tr8todd :
I believe it does and will. If you care to shoot me an email at the yahoo place I'm armstrong390
Will said:
You want an 8.8 out of a manual Supercoupe. Trac-Lok diff and 2.73 gears.
Thanks for the heads up. A quick check of FB marketplace found one about 90 miles away. I went up and retrieved it this afternoon after work and paid a whole $75 for it.
The dude was interesting. Retired gentleman with a garage under his house full of large mills and lathes, a large garage beside his house with a lift inside and a lift outside. In there was a rust free spitfire, an old Rolls, and something that slips my mind. And in the big barn the cars got truly ridiculous. Model A, '68 Dart, '61 Pontiac, and more and more varied. Maybe 15 cars in there and I'm REALLY not doing the collection justice. I told him about the Challenge and he might be showing up on here. BTW, a bunch of his cars are for sale and I have his number if there are interested parties in some VERY well kept old iron. I'll try to get a list.
Oh people. It would have been good to know that while the 7.5" and 8.8" diffs "look" the same, they are in fact "not" the same. The Monster Miata cradle is REALLY designed for the 7.5" diff and the upgrade has me redrilling holes, grinding away metal for clearance and generally spending a lot more time on this than I anticipated.
Fun side fact. Hybrid Ford/Mazda axles are apparently longer than regular Miata axles and require more disassembly of the rear suspension to remove. This whole thing has become a job!
A mini-spool for an 8.8 can be made to work with (I’m told) a Dremel tool and some time.
I used this in the farmtruck superquick to install, not setup and it works great. There ARE time when turning into tight spaces that you have to throw it into neutral occasionally to get itto disengage, but for the amount of 11's I can now make, I'm ok with that.
Alright. After WAY more effort than I expected the new diff is in place and everything is bolted back together. It’s a factory LSD Ford 8.8” supercoupe rear end. Apparently they don’t take straight gear oil but rather a “friction modifier” mixed with 90 weight. Do we have a preference here? Don’t want to burn this thing up, it took enough effort to get it in place once!!
Royal purple gear oil already has the friction modifier in it, you can also buy additive at advance/etc
I use the blue and black K&w in current and old cars.
I would love to see video of this thing on the autocross course with the open diff.
In reply to Floating Doc :
Apparently the guy at the starting line behind me had to wait for the cloud of tire smoke to disperse before he started. I don’t think video exists.
I only run half the recommended friction modifier in my 8.8, it grips more and slips less that way. If you run with out any modifier you can get some chatter in tight parking maneuvers.
