1999 Oldsmobile Bravada ... Grinding noise from the front of the vehicle

Hello,

My sister and brother in law own a 1999 Oldsmobile Bravada that is making a gringing noise from the front of the truck. I have checked the front wheel bearings and the appear to be fine. They had the transfer case fluid changed out about a year ago with the blue fluid that they bought at the dealership. The vehicle had the binding issue when turning and replacing the fluid fixed the problem for the most part.

Yesterday when I drove the truck there is a low pitched grinding noise from the front of the truck. I have a feeling that the front differential could be low on fluid. It was bad weather were I live and I didn't have my tools with me to check the fluid level. If the front differential fluid is at the full mark what else could be causing the grinding noise? If I dissconnect the front drive shaft would that take the front differential out of the loop? Could the truck be driven with the front driveshaft dissconnected?

Thank You for any help.
joet/camry

Sounds like possible front diff pinion bearings and/or carrier bearings. Driving without the front drive shaft on the AWD will smoke the transfercase. Pull the draing plug on the front diff and look for the metallic shavings that will probably come out. I'm assuming it's well over 100k miles and may also require and new gear set...

This all assumes the ft hubs are ok...

gmtech1,
What if the AWD fuse was pulled before removing the front drive shaft?
TIA

gmtech1,
What if the AWD fuse was pulled before removing the front drive shaft?
TIA

Thats a good question. Since the TCCM looks for a difference in the front and rear output shaft speed to engage the 4wd, if its not powered up it may not cause a problem. I've never done it, or seen it done, so I can't say for sure...

There's a coupla posts where after the transfer case/encoder motor was straightened out with a coupla blue fluid changes, removing the fuse or installing a switch to power up the transfer case electronics was employed.
I'll check.


Here's a post,

http://www.automotiveforums.com/vbulletin/showthread.php?t=905972&highlight=awd+fuse

Thank You for the help guys. The reason I was thinking of dissconnecting the front drive shaft was if the front differential had plenty of gear oil; but was still causing the grinding noise I thought I could dissengage it and they could just drive in 2wd mode.:smile:
I'm hoping all that needs to be done is add more gear oil to the front differential. I don't know if it will be that simple a fix.

Is the front differential engaged all the time regardless if the truck is in 2wd or 4wd? I am not farmiliar with this make of vehicle or 4wd for that matter.:uhoh:

Thanks again for any help,

joet/camry

The front diff will rotate all the time, but the engagement is done through the transfer case by applying clutches. Check the link that Chris posted above and see if that helps you out.

What are the chances that the grinding noise is coming from transfer case? I will actually get a chance to look at the truck and check the fluid levels of the front differential and the transfer case within the next few days. Just trying to prepare myself on what to do if the fluid levels are fine.

Rebuilding differentials and transfer cases is definitely beyond my mecanical ability. :shakehead Thanks again.

joet/camry

Do you have a way of getting the truck off the ground? If so, you can start it up, put it in gear and use a mechanics stethascope to identify where the noise is coming from. To answer your question, yes, the transfer case could also cause a grinding noise.

gmtech1 brought up an interesting point, the front differential, pinion, ring and spider gears, is active anytime the front wheels are turning.
Same goes for the transfer case, sprockets & chain are active whether AWD is engaged or not.
You might also check tire pressure as under inflated tires are noisy.

What are the chances that the grinding noise is coming from transfer case? I will actually get a chance to look at the truck and check the fluid levels of the front differential and the transfer case within the next few days. Just trying to prepare myself on what to do if the fluid levels are fine.

Rebuilding differentials and transfer cases is definitely beyond my mecanical ability. :shakehead Thanks again.

joet/camry

Well a few days ago I was able to check the fluid levels in the transfer case and the front differential. The transfer case fluid was still blue and was full. The front differential fluid was low and real dirty. I drained out the old gear oil and replaced it with brand new gear oil. I took the truck for a drive and bad news. It was still making that low pitched grinding noise. Not sure what to look for next. It might be time to take it to a professional mechanic that knows what he/she is doing.:mad: Just wanted to do an update. What is the most likely culprit that could be causing the noise?

Im sure brakes and the dust shield has been checked?

Is the noise related to vehicle speed? Does it get louder the faster you go? Front wheel bearings can be tight, and still make the noise....take the vehicle out on the road......get to about 30-40 mph.....now SAFELY, on a straightaway, turn the steering wheel slightly left and then slightly right, if the noise increases or stays the same in one direction, but reduces or goes away in the other direction, it sounds like a front wheel bearing....