Cracked Diff....not cover

[dpancer]

Last night I put the car on the lift and noticed that there was tiny hairline fracture on the bottom of the diff housing. I'm not talking about the diff cover. It barely leaks oil, but i'm fearing its only going to get worse. Also, and what is very strange, I swear it looks like the oil is sweating through one part of the housing. This is just to left of the crack behind the exhaust pipe. It looks like condensation on a cold soda can. I wipe it clean and it just appears again. I cant find any sign of a crack that would cause such a thing.

Has anyone ever seen this? Anyone have a spare diff housing their not using?

 

[P49Y-CY]

if it is truly cracked, I would try to get it replaced asap because if it starts to come apart, even slowly, you will probably ruin a lot of the parts inside (and not to mention probably dangerous).

not sure if they still sell it but frpp was selling the entire shebang (housing, caps, and upgraded cover) for a reasonable price a few years ago

best of luck with it

 

[dpancer]

FRPP is not selling it anymore just checked with them this morning. Second hand market it is. I just wanted to see if anyone else had this problem. Most people seem to be busting the covers, not the diff itself.

 

[SlowSVT]

Disassemble the diff, take a dremel with a cutter blade or get a cutoff wheel and grind down thru the crack until you removed all the material around it. Then get it TIG welded. Grind smooth after welding.

 

[Jefe]

Wow pic? Hard launches?

What IRS mods have you already done?

 

[ac427cobra]

This honestly sounds like it could possibly be a cold flow (casting flaw) in the original casting process. There is no way you are going to crack the lower portion of that diff housing as it is about 3/4" of an inch thick (or more) at the bottom of the case.



I agree with gouging it out a bit and TIG welding it.

:beer:

 

[Tractionless1]

Disassemble the diff, take a dremel with a cutter blade or get a cutoff wheel and grind down thru the crack until you removed all the material around it. Then get it TIG welded. Grind smooth after welding.

Good advice. If OP decides to get a replacement housing you can try a MarkVIII as well, they are the same and will be much cheaper. I got mine for $50 and had it tested for cracks/tolerances before assembly. I removed my OE unit and sold and bolted up the build MarkVIII unit.

 

[dpancer]

Alright thanks guys. I'll pull the diff when I get a chance and and inspect it more thoroughly. the option of welding sounds promising, I just hope I wont find any other surprises. If that doesnt work ill look into the MarkVIII (thanks for the info tractionless1)

Only IRS mods I have is the diff cover brace and the 9/16" diff bolts. I have not done ANY hard launches or beat on it much. I'm starting to looking into replacement poly bushings. Might as well do it now.

 

[SlowSVT]

Put urethane bushings in an IRS and you'll be replacing the diff cover next :nonono:

 

[dpancer]

Really? I'm planning on getting the FTBR Full IRS kit (without the lowering mount). I'll have to replace the stock diff cover even though I have the billetflow IRS brace?

 

[dpancer]

This honestly sounds like it could possibly be a cold flow (casting flaw) in the original casting process. There is no way you are going to crack the lower portion of that diff housing as it is about 3/4" of an inch thick (or more) at the bottom of the case.

View attachment 15802

I agree with gouging it out a bit and TIG welding it.

:beer:

Have you seen this sort of thing on a cobra diff before? That pic you posted, prep for a diff cooler?

 

[ac427cobra]

Really? I'm planning on getting the FTBR Full IRS kit (without the lowering mount). I'll have to replace the stock diff cover even though I have the billetflow IRS brace?

What Russ meant was if you put poly bushings in you'll be asking for trouble. You'll be ok with our aluminum front diff mounts and the Delrin rear diff mount in the OEM bracket utilizing the OEM cover and aftermarket rear cover brace. But, if you have upgraded power and you like to drag race you'll be much better served with the upgraded Ford Racing diff cover and our Delrin isolated lowering rear diff mount which are both infinitely stronger that the OEM components.

Have you seen this sort of thing on a cobra diff before? That pic you posted, prep for a diff cooler?

Never saw a diff housing leak from a casting flaw. Not saying that it's not possible, I've just never seen it. But from your description it sounds like that could be the issue however. Pics would help.

Yes that pic is showing you the tapped hole for the suction line of my diff cooler. As you can see in the photo, the case is honestly about 3/4" of an inch thick at that point.

:thumbsup::coolman::beer:

 

[dpancer]

Oh i got you...i meant to say delrin/aluminum before, not Poly. Basically I was saying im going to replace the stock bushings with TFBR bushings.

So just in one day I managed to get a deal on a new diff housing with a new LPW cover. Will this cover be compatible with the FTBR's rear mounts? I think I read something about a fitment issue but im guessing that has to do with the isolated delrin lowering mounts.

 

[ac427cobra]

Oh i got you...i meant to say delrin/aluminum before, not Poly. Basically I was saying im going to replace the stock bushings with TFBR bushings.

So just in one day I managed to get a deal on a new diff housing with a new LPW cover. Will this cover be compatible with the FTBR's rear mounts? I think I read something about a fitment issue but im guessing that has to do with the isolated delrin lowering mounts.

The LPW will be ok with an OEM rear diff mount bracket with Delrin bushings in it. You'll just have to grind off the LPW letters because they will interfere. I honestly cannot tell you how aftermarket rear diff lowering mounts will fit the LPW cover because I do not know. Maybe someone can chime in on that.

 

[SlowSVT]

Bruce

Doesn't that location of the diff cooler outlet puts the fitting precariously close to the pavement?

I went thru a lot of trouble to minimize the chance of the fitting getting sheered off from a road hazard.

Any pics of the finished results? What did you do for a cooler? Just want to compare notes.

 

[ac427cobra]

Russ:

The subframe hangs MUCH lower than my suction fitting. I've been running the car for 10 years with no issues. Here's a pic:



Here's the pump and heat exchanger. Remember, this is a Cobra R with a fuel cell and not a Terminator:

 

[SlowSVT]

Bruce

I don't have the car fully assembled so its a little hard to judge where the fitting will be in relation to everything else so this is good news. I used a 90 degree mandrel bent fitting which extends a bit more beyond the right angle fitting your using which is much less prone to getting hurt. Either way it sill safer than a street car running a sumped fuel tank with the sump and fitting just inches from the ground. All it will take is to jump a curb and it will open that fuel tank like a can of sardines!


Do you have gauge to measure the diff temp and how hot does it get on the track? I've got a pretty sick idea for a diff cooler that might work better than a folded fin cooler in the very tight confines of the rear undercarriage in the stock car. I'll model it in CAD and post it at some point.

 

[ac427cobra]

Bruce

I don't have the car fully assembled so its a little hard to judge where the fitting will be in relation to everything else so this is good news. I used a 90 degree mandrel bent fitting which extends a bit more beyond the right angle fitting your using which is much less prone to getting hurt. Either way it sill safer than a street car running a sumped fuel tank with the sump and fitting just inches from the ground. All it will take is to jump a curb and it will open that fuel tank like a can of sardines!


Do you have gauge to measure the diff temp and how hot does it get on the track? I've got a pretty sick idea for a diff cooler that might work better than a folded fin cooler in the very tight confines of the rear undercarriage in the stock car. I'll model it in CAD and post it at some point.

Yes I do have a diff temp gauge and you can see it in the photo posted above. There are some kits on the market that turn on the diff cooler automatically at 180, 200 or 210 degrees. I did not like that. If I turn my diff cooler on at that temp, it's too late. It can overheat and run at 250 or more for the session without getting any cooler. I like monitoring the temp myself, turning the diff cooler on at 150 or 170 and it runs cool as a cucumber and stays under 230 degrees no problem.

I might have had different results if I would have installed a larger heat exchanger but that's a little late at this point. The diff cooler set-up we offer on our web site is significantly larger than the one I have currently on my car.