Bad vibration, are my gears the issue?

[bird_dog0347]

My mustang has a bad vibration above 50mph that gets worse with speed. The biggest issue is the transition from on/off throttle at highway speeds and it's worse the faster you go. Is this the cause of that? Should there be this much play?

The car is a 92 fox that I put a 04 IRS in that should have stock 3.55 gears. When I swapped it in I had to change the pinion flange for the fox unit and when I did I messed up the seal so I replaced it and put it all back together and now this. I have a feeling I screwed up the pinion depth when I replaced the seal and/or the preload... I'd like to know if this seems normal before I pull the rear out as it's a pretty big job to do so.

[jw33]

Looks like your driveshaft is loose...

[svauto-erotic855]

Vibration is almost always an issue with the drive shaft and/or trans & motor mounts.

[Mysticcobrakilla]

It's the driveshaft.

[dsrtuckteezy]

i had a bad virbation on my vr4. was a seized u-joint

[Mach1]

Ouch looks like the pinion nut isn't torqued, don't drive it anymore, you will probably need to tear into the diff.

[Mysticcobrakilla]

Ouch looks like the pinion nut isn't torqued, don't drive it anymore, you will probably need to tear into the diff.

Yeah, give that pinion nut a good once over.

[Mach1]

Looks like your gear lash is massive because the pinion is flopping around all over the place due to no bearing preload, that crush sleeve take some serious torque to crush, I had a 4ft breaker bar and was probably having to put 700ftlb to crush the sleeve on my cmc car. With all the floppy floppy it may have damaged the pinion or ring gear.

[bird_dog0347]

The driveshaft was loose in the video as I was halfway through tearing it down. When I swapped the flange on the IRS to match my driveshaft I didn't record the preload as I didn't know at the time it was necessary. The diff is coming out and it's going to likely need new gears I'm sure.

[Mach1]

Bummer man, if you are doing it yourself post up if you have any questions, I have some 3.55s for sale for cheap if you need them.

[jw33]

Well that sucks. Grab a few crush sleeves while you're at the store in case you mess one up and need a do-over or four. It takes a ton of torque to get it crushed and then it is easy to get them too tight. You did and IRS swap so you're more than capable to setup the gears as long as you have the tools. I've always used the same pinion shim with Ford gears and never had an issue. I've got a fairly decent stack of shims for setting the backlash you're welcome to pilfer through if you need them.

[svauto-erotic855]

Y'all are going to rip me a new one for saying this but you do not need a crush sleeve if you know how to properly set bearing preload. Many of my work trucks and Mustangs with both 7.5s and 8.8s have combined 100s of thousands of miles on rear ends without a pinion crush sleeve in them. I have also used the solid sleeves that you add shims to.

[bird_dog0347]

Bummer man, if you are doing it yourself post up if you have any questions, I have some 3.55s for sale for cheap if you need them.

Thanks, I might just need those from you if they are in good shape as that's the ratio I want anyways.

Well that sucks. Grab a few crush sleeves while you're at the store in case you mess one up and need a do-over or four. It takes a ton of torque to get it crushed and then it is easy to get them too tight. You did and IRS swap so you're more than capable to setup the gears as long as you have the tools. I've always used the same pinion shim with Ford gears and never had an issue. I've got a fairly decent stack of shims for setting the backlash you're welcome to pilfer through if you need them.

I'm not gonna do the swap/fix, I don't have all the tools and only plan on this being a one time thing. I can do the IRS swap, weld shit, I can paint, but just pulling the rear and re-installing is such a PITA compared to a SRA that I need to make damn sure it's right the first time.

Y'all are going to rip me a new one for saying this but you do not need a crush sleeve if you know how to properly set bearing preload. Many of my work trucks and Mustangs with both 7.5s and 8.8s have combined 100s of thousands of miles on rear ends without a pinion crush sleeve in them. I have also used the solid sleeves that you add shims to.

solid brag (not barg)