So I’m switching over my 99 cobra to 4:10s after doing some research I figured I should get a new diff carrier to and have everything fresh but it’s hard to find 28 spline diffs for my car and see people switch over to 31 spline diffs and axles, I also can’t even fine 28 spline halfshafts anywhere, so what do I need to convert to 31 spline, just a diff, gears obviously and half shafts? Are the 31 spline halfshafts 28 spline at the hub or do I need new hubs?
99 cobra rear diff
- Thread starter Chrisl459
- Start date
You'll need the diff and half shafts. I would try to find a set of 03/04 shafts. But the 01 shafts are 31 spline as well. The hub is the same for all the years. Only the spline count in the diff changed.
Thank you appreciate it, don’t know if I should just find some used 03/04 halfshafts for now or just spend the $1700 right away for good ones, keep in mind I’m stock power
For a new differential I highly recommend a Torsen diff. they are best for street and road race but not drag racing. If your drag racing or doing alot of straight line street gear banging then Trutracks are best, but they make a little more noise than the Torsen.
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Depends on your goals. The 03/04 shafts are pretty stout. I'm a little over 700rwhp and running stockers. But I don't hit the drag strip a whole lot. If you're planning on drag racing then upgraded shafts and slicks would be the way I'd go.
Do you know if it has had the knuckles replaced? I'm sure there was a recall for that years ago.
Seems like a good idea to upgrade as the cost of some new 28 spline half shafts has gotten outrageous and I doubt anyone rebuilds them for cheap.
I have the Detroit Truetrac and like the ratio. It is virtually indestructible.
The 01-03 knuckles can be added or you can press in some SPC cross axis joints into the 99 unrevised rear knuckle/spindle.
SPC seems to have some without the clip ring that will work on the 99.
FTBR and MM has info on how to tell whether you have the revised 99 IRS rear spindles or your still have the OEM.
I have the Detroit Truetrac and like the ratio. It is virtually indestructible.
The 01-03 knuckles can be added or you can press in some SPC cross axis joints into the 99 unrevised rear knuckle/spindle.
SPC seems to have some without the clip ring that will work on the 99.
FTBR and MM has info on how to tell whether you have the revised 99 IRS rear spindles or your still have the OEM.
Sounds good thanks, as long as I can literally just put a new traclok 31 spline and 03/04 cobra axles and it work is good to know, I’ll be ordering everything today
Would I still be ok if I have one knuckles with new one cross axis shafts?
I'm unsure of that, unfortunately.
I think you could replace one rear irs knuckle/spindle/hub at a time or as needed..or as you can afford. The geometries are likely the same for the 99 and the newer revised knuckles.
You can sometimes run across the revised ones used on ebay, but you have to be hawking for them on a regular basis as they get snatched up pretty quickly...same as the terminator or 01 half shafts.
Contact FTBR directly for real answers on that.
The geometry the same across the years. I have 01 knuckles on my 04 right now. When I bought my 04 I had DSS level 5's in my 01 and wanted to keep them. It was easier to swap the half shaft and knuckle at the time.
Like to add that you need to careful that someone isn't trying to dump the 99 knuckles on you as the revised ones.
The same is being done to folks looking for the '01 lower intakes.
You have to know what you are looking at.
The maximum motorsports and FTBR sites are where to go to get educated before you shop.
The same is being done to folks looking for the '01 lower intakes.
You have to know what you are looking at.
The maximum motorsports and FTBR sites are where to go to get educated before you shop.
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