99 Rear end / axle / IRS Issue

[Shepp1691]

Ok, i have searched on here with no luck. my rear was popping a little when i pulled in and out of my garage. now it is popping pretty much anytime, when i pull away from stop lights, back out of the garage, or randomly when i shift, there is a loud pop from the rear and really pops through the entire car. now when i go through a long sweeper like an on ramp or off ramp, the rear of the car tries to stear the car. it will start pushing out and when i turn it in harder and it shoots down to the fog line, almost like a rear wheel is losing camber and then falling back into it. i also changed the rear end fluid and after only 8000 miles, it was a metallic sludge coming out. i have already replaced all four irs bushing with FTBR ones. any suggestions appreciated, i know there is a service bulletin for re torquing the bolts but think it is more than that. car also is completely stock besides the bushings with 117k miles on it. thanks for reading!

 

[BreBar21]

I have to imagine it's either half shafts or diff. Did you make sure to full seat the half shafts when you put them back in? You should hear a click. It almost sounds like those may be drifting in and out. I fear those are your metal shavings, which mean it might be time to do gears and rebuild the diff.

 

[Shepp1691]

the half shafts were seated properly, but are the original ones, dont appear to have an excessive play in the them, dont mind changing the gears, would like to get those 327s or whatever out of there anyway. will have to pick up some 373s and a rebuild kit i imagine.

 

[BreBar21]

Hmmmm...I'd have to think it's likely the diff then. Did you just do the control arm bushings or did you do the diff bushings as well?

Go steeper - 4.10s minimum. You won't regret it.

 

[IUP99snake]

Is it a "pop", "clunk", or a "clang"?

It might have to do with the carrier bushings. Get some poly bushings to tighten that up!

 

[Shepp1691]

its a pop, did not do the diff bushings, i had 410s in a camaro 6 spd and seemed like a lot of gear, esp for the highway driving i do

 

[blacksheep-1]

Did you remember to add the Ford additive to the diff fluid?
I've seen limited slips raise all kinds of hell without the additive. You would swear it had to be mechanical and all it was was the diff fluid. Still though, you need to jack the car up and reinspect the work and make sure nothing is loose.

 

[olgreydog7]

A DOHC is not the same as an ls1 or lt1. Not much torque and an eagerness to rev.

 

[Shepp1691]

When I flushed it 8000 miles ago I added the additive, this time I just flushed it with junk cheap stuff. Car will now be parked until I can pull rear, don't need it locking up on me.

 

[Shepp1691]

Olgrey, what kind of revs u running on the highway with 430s, trying not to kill my 22 mpg too much.

 

[olgreydog7]

I have a T-56. Plus, my big bore stroker with cams is killing my gas mileage more than the gears. IIRC, I still pulled over 20 when I just had FR500 cams.

 

[Darkc0bra]

I have 4.10s and a lot of "work" done to my car (look at sig for mods) and I still get 22-23mpg on the Highway. I travel at 80mph @ 2950rpm and still see that 22-23mpg

 

[99Cobra_vert]

I have 4.10s in mine, too. Love them.

 

[Black*Death]

Ok, i have searched on here with no luck. my rear was popping a little when i pulled in and out of my garage. now it is popping pretty much anytime, when i pull away from stop lights, back out of the garage, or randomly when i shift, there is a loud pop from the rear and really pops through the entire car. now when i go through a long sweeper like an on ramp or off ramp, the rear of the car tries to stear the car. it will start pushing out and when i turn it in harder and it shoots down to the fog line, almost like a rear wheel is losing camber and then falling back into it. i also changed the rear end fluid and after only 8000 miles, it was a metallic sludge coming out. i have already replaced all four irs bushing with FTBR ones. any suggestions appreciated, i know there is a service bulletin for re torquing the bolts but think it is more than that. car also is completely stock besides the bushings with 117k miles on it. thanks for reading!

The master of the IRS is Bruce at FTBR..AC427(?). He would be able to give you the best answer..

Sounds like something is binding up then releasing? I think something in the gears is wrong. Simply backing up?

Is something bent in the IRS carriage?

 

[4a7191a]

I had a bracket break on my cobras IRS that was the cause of part of my clunk problem.

 

[Shepp1691]

Had it up on the lift a few times and its def inside the rear end, either the posi has broke and bent a tooth on the ring and pinion or something, looks like ill be dropping it out as my next step, rebuild kit, true Trac, new ring and pinion, probably about $500 in parts, money I don't really need to be spending right now.

 

[71catruck]

a few months ago i shattered my diff carrier and cracked a cap and it was doing the poping but really bad i couldnt even role the car. i put in 3.73 and a true trac. its my rpm's are right at 2300 at 70 mph. your going to love the true trac its amazing.

 

[ac427cobra]

Had it up on the lift a few times and its def inside the rear end, either the posi has broke and bent a tooth on the ring and pinion or something, looks like ill be dropping it out as my next step, rebuild kit, true Trac, new ring and pinion, probably about $500 in parts, money I don't really need to be spending right now.

Most likely the side gears and spider gears if you had metalic in your gear lube. Pretty sure you're going to find broken pieces in there.

 

[shurur]

a few months ago i shattered my diff carrier and cracked a cap and it was doing the poping but really bad i couldnt even role the car. i put in 3.73 and a true trac. its my rpm's are right at 2300 at 70 mph. your going to love the true trac its amazing.

+1
My bearings were going and causing the traction control to engage at times on straightaways while accelerating..and thumping on left turns...
It eventually sounded like marbles..originally, it had lots of friction in reverse......

The great thing about the mustang and the aftermarket support is....something breaks and you can upgrade.

The truetrac raises the delrin IRS up yet another notch..It's a wonderful thing..

 

[Shepp1691]

Thanks for all the responses, Tom's Differentials seems to have real good prices on parts, ill be pulling it out, as soon as i have a free couple hours, and upgrading whats needed, I do a lot of highway driving so I will probably stick to the 3:73s in it.