Factory Five Racing Forum banner
Status
Not open for further replies.
1 - 12 of 12 Posts

·
Registered
Joined
·
886 Posts
Discussion Starter · #1 ·
OK, I've been trying to not look stupid but I have a question. The FFR irs is setup for certain "vintage" irs's. I've noticed a few stating they have 99 or later Cobra aluminum IRs's. What's involved in using these later IRS setups?

Leonard
 

·
Banned
Joined
·
5,303 Posts
it is my belief that the 99 cobra IRS is inferior to the "vintage" 8.8 t-bird IRS. its only 10 years old, not really vintage in my book.

you can get an aluminum housing from a mark VII, but they dont have an LSD.

hmmm, come to think of it, since im replacing my lsd anyway.... i could get the trick aluminum housing... =)

-james
 

·
FFCobra Craftsman
Joined
·
1,333 Posts
The FFR IRS suspension, driveshaft, CV's, etc. are the same whether using the iron differentials (T-bird, Cougar) or the aluminum ones (Lincoln Mk VIII, '99 Cobra, new FRPP unit).

The Ford 8.8 IRS differential mounting points, axles, etc. are all interchangeable.

One thing to note - the Lincoln MkVIII unit does not have Trac-loc (limited slip) installed, while the Cobra unit does, so it is the preferred aluminum differential to find. The Ford Racing aluminum diff has the Trac-loc included (and a 3.73 ring and pinion as well).

Roger, the 3.27L on your unit m,eans it has a 3.27 rear ratio (ring and pinion gears) and has Traction-loc installed.

NMCobra - A Limited Slip Differential (LSD) is a mechanism that divides up torque between the rear wheels at a fixed ratio, to prevent uneven wheelspin...without LSD (i.e. an open differential), if one wheel begins to slip (spin), all the engine's torque is routed to the spinning wheel...in other words, you either accelerate slowly or (in mud) get stuck.

An LSD will allow a fixed amount of slip on one side before "locking up" - this is to allow the driven wheels to travel at slightly different rates, to allow going around tight corners, etc. without one wheel 'scrubbing'. Usually the ratio is about 30% (slip), i.e. a "70% LSD".

If you've ever seen a "one stripe burnout', you've seen an open diff in action. There are many LSD types with different characteristics and mechanisms, too many to go into here.

[ August 15, 2002, 01:57 PM: Message edited by: Barry Mattingly ]
 

·
Banned
Joined
·
5,303 Posts
a working LSD is extremely important to these light cars that live or die by how much traction they can get.

-james
 

·
Registered
Joined
·
886 Posts
Discussion Starter · #7 ·
Thanks for the info guys. My concern was whether the mounting points, etc. on the Cobra diff were different than the TBird. I was thinking of the MkVIII aluminum housing as well but wasn't sure whether it would take a standard 8.8 IRS LSD. I was hoping to save some weeight so I was looking for something in aluminum that would fit. Do the axles in the FFR IRS kit fit the Cobra diff as well? I know they mentioned some of the lighter duty IRS's would not take the axles that are included.

Leonard
 

·
Banned
Joined
·
5,303 Posts
im no expert, but i think you CAN put the trak-loc in the mark VIII aluminum pumpkin, and the 99+ cobra diff is 31 spline, opposed to the 28 of the others.

-james
 

·
FFCobra Fanatic
Joined
·
690 Posts
Leonard,
The lighter duty IRS units are 7.5". An 8.8 is an 8.8. The aluminium unit weighs about 7or 8 lbs less than the cast iron job.
 

·
FFCobra Fanatic
Joined
·
616 Posts
Originally posted by Ophitoxaemia:
im no expert, but i think you CAN put the trak-loc in the mark VIII aluminum pumpkin, and the 99+ cobra diff is 31 spline, opposed to the 28 of the others.

-james
Actually, the 1999 Cobra is a 28 spline. The 2001 is a 31 Spline. (I have a 2001 Cobra)
 

·
FFCobra Craftsman
Joined
·
1,333 Posts
Kadunkadunk is correct - as I mentioned in my earlier post, the FFR-supplied axles will fit fine in the MkVIII and '99 Cobra differentials. You can instal a Trac-loc in the MKVII diff but need to change a few parts (retaining clips, etc - see the FAQ).

Didn't know about the '01 cobra splines being different - good info to know!
 

·
Registered
Joined
·
886 Posts
Discussion Starter · #12 ·
Thanks all. As usual, it is always pleasant to deal with other FFR owners.

Leonard
 
1 - 12 of 12 Posts
Status
Not open for further replies.
Top