Hello all

 

My soob has a loud rumbling/vibrating noise when my 4wd is engaged at freeway speed; the noise has a wave effect, get loud then gets quiet. Is this normal or indicative of a problem with my transmission?

 

Last, I was at Napa getting filters for my car; I bought a crankcase ventilation filter. Problem is, I have no idea where this filter would be on my car. I've looked everywhere. On my old non-turboed soob it was inside the air filter housing.

 

I have an 85 4wd Turbo Wagon Automatic 49k on it...

 

Thanks!!!

Edited February 24, 201115 yr by TPain

the rumble in your trans would indicate a problem, its not normal thats for sure

Check the U-joints in the rear driveline. I have had this kind of thing happen twice, both due to bad U-joints.

It's sounds like it's coming from the rear and not the transmission itself; only happens when 4x4 is engaged at freeway speeds.

 

Are U joints difficult to replace?

OK lets get something out of the way first:

 

You are not driving freeway speeds in 4wd on dry pavement are you? Cause that could be your problem right there. There is no differential between front and rear axles so 4x4 is only meant to be used when wheel slippage is likely.

it will definitely do it if your tires are different sizes and even different tread lifes. it needs to be exact to run 4wd on dry pavement. you will know its binding if it it difficult to get back into 2wd. The crank case vent filter goes inside the air cleaner housing.

 

don't use 4wd on dry pavement...not necessary and can break stuff. and kills your MPG

So it's normal? I'm not using 4x4 on dry pavement. We have tons of snow right now and I've been using during these conditions. Also, everything is stock, no mods whatsoever.

 

Weird, I've looked, my air cleaner housing has nothing inside it for a crankcase filter.

 

Thanks!

Does anyone know if there are straight cut gears in the transfer case? If so they could cause a rumble couldn't they?

mine never rumble. ever. i would think to check the u-joints at the carrier bearing first

Does anyone know if there are straight cut gears in the transfer case? If so they could cause a rumble couldn't they?

OP's car is an automatic. The transfer function is performed by a clutchpack similar to ones used in other parts of the automatic. IIRC, manuals use helical-cut gears for its transfer function.

 

Mismatch in tires or mismatched final drive ratios (your tranny is a 3.70 ratio, so your rear diff should match, but someone may have replaced it in the past with a 3.90). As mentioned, it might also be rear driveshaft u-joints issues.

 

RE: Crankcase ventilation filter - I am not 100% positive, but your engine would not have or need one. On your carb'd ones, the vent was inside the air housing but not in filtered air. On the FI-models (including turbos), filtering the air is done at the fender and well before the vent.

Edited February 25, 201115 yr by NorthWet

Thanks for the crankcase info. I guess I shouldn't put to much stock into what Napa says about filters.

 

What's the technical name for a U-joint, couldn't find it in my Chilton. If things were mismatched wouldn't the vibration occur all the time? My car is 100% stock and was babied by the previous owners.

 

Thanks!

check to see if your tires are the same size. also it can be affected if the fronts are bald and the backs are still good then the tire sizes are effectively different, even though they all say the same size on the side

Thanks for the crankcase info. I guess I shouldn't put to much stock into what Napa says about filters.

 

What's the technical name for a U-joint, couldn't find it in my Chilton. If things were mismatched wouldn't the vibration occur all the time? My car is 100% stock and was babied by the previous owners.

 

Thanks!

 

tech term would be universal jount, hence the U. I bet this is your problem. The part and design is similar to toyota, pressed and staked in. find a shop that does toyota. I believe even a toyota u-joint cross references as the same part.

 

if you are into a slavage part, all the u-joints are contained in the rear half of the driveshaft. you can replace that from an AT or an MT car of the same platform.

 

to remove the drivehaft, undo the nut side of the bolts, ans the head side is held stationary by the casting of the yokes.

 

take the driveshaft out, and if the noise is gone, that would be your culprit. have it rebuilt or exchange it at a salvage yard

 

good luck