Weird vibration from rear

[Caithness]

I just bought a stock 91 240SX 5-speed with 135k miles on it. During the test drive the only problems I noticed were a mild grind into 3rd gear at higher RPM, a bit of a squeal from the rear left brake hanging up for the first two or three minutes of driving, a slight bumping noise from the front end when turning sharply (which didn't seem major), and the usual timing chain clack. My friend drove the car back 100 miles without any problems.

The next day when I started driving it around I immediately noticed a rumbling vibration from the rear of the car at about 30 mph and on up that wasn't there on the test drive or the drive back. Also, when I go WOT in second gear, there is a bit of a screaming noise at higher rpm. In addition, it seems like there is a lot of "drag" on the drivetrain- when you let off the gas in gear the car slows down very quickly. And possibly related, when I let a friend drive it we found that loud popping noises come from both sides in the rear when you swerve back and forth sharply, loading the suspension on either side. I checked to see if the brakes were locked up or something, but the car rolls freely from a stop on the slightest down grade.

As far as I could tell the car has never been in an accident, and was a stock daily driver. What could be causing these issues? I'm going to jack it up and look under the car but I'm not sure what to look for.

[Caithness]

I did a lot of searching and then got under the car to check it out.

The clanking noises when turning sharply were IMO unrelated to the vibration and seem to be a simple case of worn out rear subframe bushings. You can see the marks where the subframe is banging against the underside of the body. I'm ordering some subframe spacer collars off ebay, although I consider that a bandaid fix until I get replacement bushings. If my bushings are really badly ripped or rotted out I may just resell the collars and get bushings from the get go.

The vibration seems to be related to the carrier bearing. One of the previous owners stripped out a carrier bearing bolt hole. They proceeded to cut the carpet to shreds under the seats to access the tunnel, which they then cut small access holes in with a hole saw. This compromised the strength of the carrier bearing mount and has also started to split a seam on the metal next to their cut. They drilled the bolt holes out and simply slid new bolts in and tightened them down with a nut and lockwasher up top on each side. They made no effort to make sure that the pinion angle was correct after this exercise. The vibration is 95% probably the incorrect angle on the driveshaft causing an imbalance. I'm going to have to do a bit of welding work to patch the holes/split and permanently attach the nuts so you don't have to have the carpet out and 2 people to tighten the carrier bearing. Then I'm going to have to try to shim the carrier bearing until it's back at the correct angle, which according to the mechanic I talked to at Driven Concepts is a trial-and-error thing of shimming then test driving until the vibration is gone. If all of this fails I'm simply going to get a one piece driveshaft, but I'd much rather fix it with some cheap shims than with a 350 dollar driveshaft. :)

[DJ_Sunrise]

Contact [email protected] . I bought my 1 piece aluminum shaft for 330 shipped from him. Same quality as DSS.. Lifetime warranty on welds and balance. Just save yourself the hassle now and in the future, and buy the shaft :) Sux the hear the previous owner butchered the center bearing mount.
-Bart