jlcustomz

Have ls1/t-56/ 1983 steel driveshaft & g- body 7.5 rear with 3.73s & eaton posi. Rear was rebuilt 11 years & 13,000 miles ago. Had a slight osculating vibration at highway speeds for years only slightly noticeable over the exhaust drone. Swapped worn u-joints last year, not much change . Having to drive daily last few months, noise is becoming more a steady rumble, more so at higher speeds.

Put rear on jackstands today & ran in place at 40mph a few times. Making magic marker lines on driveshaft showed it to at least run true, so suspecting rear as main issue. Tires looked average amount of out of round. Ran it up as high as 160mph, nothing sounded horrible other than constant rumbling vibration even shutting engine off ,no gear whine, can't feel slack in outer axle or pinion bearings.

Haven't ran on jackstands before to know how much sound is normal. Also felt diff for heat recently after a 16 mile drive. Outer tubes were cool, center section slightly uncomfortably warm.
Sound like bad center axle bearings and/ or gears?

smitty2418

It's your DS. I have 4.11's in mine and the gears just overspin the steel ones. Got a 3" from Driveshaft Specialties and boom, no more vibration.

jlcustomz

Driveshaft was my first thought to begin with, have been considering an aluminum one for some time now. But noise is progressively worse now, sounds kinda like a test signal for bass, even at lower speeds.
Pinion area of differential is too warm to hold your hand on for more than several seconds, not sure how warm is normal since gears do produce heat.
Smitty, was your noise a steady rumble?
I do need 4.11 gears now anyways, check out my gauges, 160 mph was just past 3500 rpm.

smitty2418

I would definitely try the DS first. My 10 bolt just let loose right before this deployment so it's parked in are page broken right now I put some new 4.10's in it and was doing the same exact thing as what it was when it went the first time. From what I have heard the pinion is way to small for a 10 bolt to be putting up with but I'm not sure. It winds and grinds at any speed now. More high pitch the faster I go but cruising is horrible. When my DS went out it was just a vibration at highway speeds or if I was screaming down the highway racing someone. I didn't think the vibration was the DS at first because the sound and feeling wasn't consistent but I was wrong. Changed the driveshaft and now at any speed it makes no noise or vibration. Still makes a slight vibration and I mean SLIGHT but I'm pointing towards the bad rearend on that one. I only got to drive it with the new DS in it for about a week before the rearend went out again.

jlcustomz

I'm thinkin now the driveshaft may be most of the noise. Local drivetrain shop said pinion area being uncomfortably warm IS normal & a bearing starting to get that bad from my first heat check over a month ago would have went out by now .
Something interesting I just found on pro-touring forum. Person had continuing vibration problems with 2 different rears, shafts & t-56 trannys was told by Strange that t-56 shafts are a hint smaller than the th350,etc input yokes, which is what I have. Noticed it seemed a hint loose.

Soooo, if I don't have to get diff bearings, I will look further into an 8.8 ford or older 8.5 a body swap into my g-body to get 4.ll or even 4.30 gears.

jlcustomz

Well, had a new spicer u-joint going bad. It was tight fit into diff yoke & end caps were seizing up on the joint itself, causing all the rumbling vibration, even sometimes squealing like a bearing race coming apart, transferring bad sounds to the trans area, etc. Got a cheap china replacement last minute tonite & it felt like a different vehicle driving around the block, even shifted better. Was a new experience for me. So now maybe I can take my time looking into a budget rear upgrade & get a new shaft when I know if I'll need a shorter one for a different rear.