Im new here and new to forums in general. Hopefully this is the correct place to post this question/problem.
just got a 1989 Pickup 2wd 4 spd manual has 252,xxxmi. Decent little truck and was maintained well. Only drove it a couple times so far.
Noticed a strange humming or whirling noise from the rear when im Not on the throttle mostly over 40 mph.
wondering if this could be a bad pinion bearing or low fluid in the rear diff. Im not sure how to diagnose this problem. any help would be great.

 

Correct forum, but usually better if you start your own thread. (If you can - not sure about the posting rules for new members.)

Anyway, congrats on your purchase and welcome to Yotatech! You'll find it a great resource for keeping your new (old) truck running tip-top.

Your rear-end noise is the classic symptom of a bad u-joint. Check those first, and if they're good investigate the pinion bearing in the differential. To check the u-joints, chock the front wheels, jack up one rear wheel, and support the axle safely on a jack stand. Leave the transmission in gear and the e-brake off. Have a helper vigorously rotate the lifted rear wheel back and forth while you carefully watch the u-joints on each end of the drive shaft. Look for motion in the joints, and listen for clicking or other strange sounds.

To check the pinion, try moving the drive flange on the differential in the radial direction, and then in the longitudinal direction. If you can feel movement, the bearing is suspect.

If these checks are inconclusive, visit a trusted mechanic who has more experience in this sort of thing.

It's always a good idea to check the fluid levels in all gear boxes in any new purchase of a used vehicle, so go ahead and do that. Change the fluids if you don't have any history on them.

 

Awesome thank you for the advise. I will check out both tests and report back.
the truck is old and a friend is welding rockers on this week.
again thank you. Testing myself will surely help me get to know the truck better

 

1989 pickup 2 wd 4cyl 4 spd manual
mixed results in searches.. I believe I have a 7.5 rear..
what size rear differential do I have?

 

You should have a 8in rear. I have a 89 2wd 4spped truck and it has a 8in rear. The door tag will tell you for sure though. Post a picture of it. It should say something like G292. This translated to the rear size and gearing.

 

What would the code say?
the sites I’ve seen says it’s a 7.5.
any other way to tell without taking it apart?

 

The code tells you your final drive gear ratio and if you have a 7.5 inch or 8 inch ring gear, among other things.

As Superex87 said, post a picture of your VIN sticker and we can decode it.

While most 2 Wheel Drive trucks had 7.5 inch ring gears, it is fairly common to see 8 inch ring gears in 4-speed manual and 1-ton models.

 

Jt4rn
81rok
00043
77

 

We need a picture of the vin plate in the drivers door jam.

 

Ok. So not the actual vin number. Right?

ill have to take pic when I get it back.

 

The axel code, you'll find it as "A/TM". Which tells axel/transmission.

 

Here’s the pic. Please help me identify the rear size

 

G662 is an 8" axle and 3.07 gears.
You can use any 4x4 rear 3rd member in that housing if you want different gears.

 

Sounds like a whirling noise when I’m off the throttle going over 40mph.
im not wanting to change gear and such. Just need bearings and seals.
Now that I know the size I can try to find the parts.
thank you very much for the help.

 

Remember way back near the top when you said you were going to check the fluid levels? We are still waiting