Problem 96 Silverado when it down shift

[etbill52]

I have a 1996 Chevy Silverado, 350, 4x4 auto transmission. when it down shift from over drive it makes a sound like running over reflective bumps on the side of interstate just as it starts to shift, it does it more towing anything, or going up a mountain. I thought it was the U joints, replaced them but no help. To day after driving it for about 8 to 10 mile the front of the rear end was warmed up pretty warm. and the sound sounds like it is in the rear. Could this be in the rear end? or the transmission? also it makes a high pitch sound most all the time, I guess like medal rubbing medal. Anyone with a ideal? I would be grateful. Thanks

[Bob B]

Did you check the rear end to see if it has oil in it?

[etbill52]

Originally Posted by Bob B

Did you check the rear end to see if it has oil in it?

Yes it was a little low, I filled it up.

[ukrkoz]

Originally Posted by etbill52

Yes it was a little low, I filled it up.

well, you not supposed to just fill it up. better idea is to CHANGE fluid.

normally, whining noise from the rear is coming from rear differential. oil change is required ASAP.

having 4x4, you have many things to worry about:
transmission
front differential
transfer case
rear differential.

check your owner manual, but for my 2000, all fluids MUST be changed at 60K miles, and i have no doubt you have much more than that on your truck.

fortunately, it's 96, so you have OBD2. go to any major parts store and ask them to scan for error codes, it's no charge. THEN we can start building picture.

unless it was already done, i'd start with proper maintenance right away. keep in mind, GM is very sensitive on fluids for all those components.

[etbill52]

Thanks for your reply, you are right on mileage it has about 145000. I had a small pin hole in the rear cover of the rear end that leaked some of the oil out, I don't know how long the hole had been there. I have the drive line out now and was thinking about taking the rear cap off and checking the gears. I hope it is the rear end and not the transmission, I had it rebuilt in 1999 at a cost of 2495.00 dollars, a week later it had a electric short in it the company wouldn't fix it.

[ukrkoz]

Originally Posted by etbill52

Thanks for your reply, you are right on mileage it has about 145000. I had a small pin hole in the rear cover of the rear end that leaked some of the oil out, I don't know how long the hole had been there. I have the drive line out now and was thinking about taking the rear cap off and checking the gears. I hope it is the rear end and not the transmission, I had it rebuilt in 1999 at a cost of 2495.00 dollars, a week later it had a electric short in it the company wouldn't fix it.

definitely change ALL fluids. see, it's not the level of the fluid, it's the quality of what you have inside. your diff is running on half tar half metal shavings by now.
if you are referring to the diff metal plate in the rear of it, i'd fix the hole. or find one on junkyard and replace it. new seal won't hurt. and it's easy DIY job.

[etbill52]

Going now to pull rear cover, check gears and replace oil. Thanks

[ukrkoz]

Originally Posted by etbill52

Going now to pull rear cover, check gears and replace oil. Thanks

jackstand the rear axle SECURILY so that you can turn the wheels and do so. never know what's hiding on the opposite side of the gear. pretty much, you'll have to chock front end wheels so that it does not roll forward, as you'll have to put it all into neutral. unless you doing all this on a lift, of course.
all the best, good luck.

[maxwedge]

Your symptoms sound like bad pinion bearings.

[j cAT]

Originally Posted by etbill52

I have a 1996 Chevy Silverado, 350, 4x4 auto transmission. when it down shift from over drive it makes a sound like running over reflective bumps on the side of interstate just as it starts to shift, it does it more towing anything, or going up a mountain. I thought it was the U joints, replaced them but no help. To day after driving it for about 8 to 10 mile the front of the rear end was warmed up pretty warm. and the sound sounds like it is in the rear. Could this be in the rear end? or the transmission? also it makes a high pitch sound most all the time, I guess like medal rubbing medal. Anyone with a ideal? I would be grateful. Thanks

you never ever tow with the transmission in overdrive!!!!!!


open up the rear diff and inspect for damage....could also be transmission failure....the transmission was overheated every time you towed in overdrive....

[etbill52]

Originally Posted by j cAT

you never ever tow with the transmission in overdrive!!!!!!


open up the rear diff and inspect for damage....could also be transmission failure....the transmission was overheated every time you towed in overdrive....

This I did not know, I tow a boat sometimes. To night my son-in-laws and myself blocked the back up and pulled the ring gear the bearing was bad they were rough and lose in the race, going to replace them tomorrow. I can't here most high pitch sound. lost some hearing in Vietnam. So I don't know something is going bad until it's gone. I will post back on the bearing when we get them in. Thank all for your help, GREAT FORUM

[MT-2500]

Originally Posted by etbill52

This I did not know, I tow a boat sometimes. To night my son-in-laws and myself blocked the back up and pulled the ring gear the bearing was bad they were rough and lose in the race, going to replace them tomorrow. I can't here most high pitch sound. lost some hearing in Vietnam. So I don't know something is going bad until it's gone. I will post back on the bearing when we get them in. Thank all for your help, GREAT FORUM

Here is a link with some rear end noise and tech specs info.

http://www.differentials.com/install.html

Let us know how it goes.
Good luck
MT

[etbill52]

Thanks MT for the link, we replaced all the rear differential bearings yesterday and last night, put new brakes on while every thing was out.
But for for got to pick up new transmission rear seal. going to put it in today.

will post back as soon as I get to drive it, sure hope this fixed the problem.

[MT-2500]

You are welcome and good luck.
Thanks for posting back how it is going.
Let us know how it goes.

[etbill52]

Originally Posted by MT-2500

You are welcome and good luck.
Thanks for posting back how it is going.
Let us know how it goes.

Didn't help, after replacing all the bearing in the rear, the rubbing sound went away but when it down shift (on a pull) it still sounds like it is running over the warning bumps on the side of an interstate just as it starts to shift, after it shifts it runs smooth no noise. The transmission shifts good. Do you think it is the transmission? The tires on it are old and never was balanced when they were put on, when they were put on the truck is about the same time this problem started.