4" Lift Causing Decelleration Noise

pjp · February 11, 2010

My Son installed a 4” lift and 33” tires onto his 1987 full size Blazer. The kit included rear end shims to reduce that angle of the drive line. Unfortunately, it’s developed a noise upon deceleration from 55-65 mph. He’s changed out the transfer case, drive shaft, went to Drive Shaft shop who recommended to lengthen the drive line and added additional shims. After $600 the noise is still there, but somewhat reduced. To me, it kind of sounds like a pinion bearing, but everybody else says the rear driveline needs a carrier bearing and 2 drive lines to reduce the driveline angle. This seems extreme for just a 4” lift. Does anybody have any other ideas?

herkdriver007 · February 11, 2010

Way back in the day when I was in college I had a 1983 K5 with a 2.5" spring lift on it, running 33x12.5 BFG ATs. Same issues...when decelerating you could "feel" and hear the driveline spool down. It was really strange. Never did it stock either.

I tried different shims under the springs, and even had the driveshaft balanced a few times. It was weird in the fact that it didnt vibrate, or whine, until only decelerating, and only above 45mph (or at least that was when it was noticable).

If the shop you're using recommends a carrier bearing, take it to a different shop! I'm pretty sure you dont have the room for 2 driveshafts, and if you did the angles would be even worse!

You might think about trying, as much as I hate to say, an independent Jeep place where they specialize in the shorter drivelines. It might simply need a CV joint installed.

Silverado4x4 · February 12, 2010

Did he go with taller blocks in the rear? They are already angled for the rear driveline. The little wedge shims are for the front axle. I had a 87 Chevy shortbed with 7" of suspension lift and 3" body lift and did nothing with the lenghting of the driveshafts. The rear driveline does NOT need a carrier bearing and he is trying to rip you off. I have lifted alot of older trucks back in those years and what he is telling you is BS.

pjp · February 12, 2010

Thank you guys for the replies and help! If I still had hair I'd be pulling it out! I agree a two piece drive shaft is way overkill and something suggested by a parts replacer, not a true mechanic (and someone trying to take advantage of my son). I used to work on heavy equipment years ago including big trucks and repaired quite a few bearings on the transmissions and rear ends and you'd be amazed how many would wear strangely. The difference between acceleration and deceleration actually puts pressure from from opposing directions and could cause a strange wear pattern contributing to the noise. I may try using a stethoscope with a long hose and see what things sound like at different points on the rear end and transmission. If I ever figure this one out I'll let you all know.

J-man67 · February 13, 2010

U-joints? They could of been going before the lift, but the diff angles could of made it more noticeable. Just thinking aloud...

pjp · February 13, 2010

We tried a different drive shaft that a friend of his has (even slightly longer) and it made the same noise. Also when the shop lengthened my Son's driveline we had them put in new U joints and still the noise was there, so the hunt continues...