Drive with no driveshaft?

[dave833]

Trying to diagnose a driveline noise in the '98 OBW 5-speed I just bought and wondered if I could drop the driveshaft entirely and drive it that way briefly to see if the noise goes away, or would the tranny fluid just run out? Can I drop just the back half?

 

I found a previous diagnosis about the noise from the dealer that said 'driveline is separating and needs replacement' but that doesn't make much sense to me.

 

(If it was an auto I'd start by putting the 'FWD' fuse in!)

[NorthWet]

If you pull the front section of the driveshaft out of the tranny tail housing, you will dump gear oil. Doesn't matter much, since the center differential on the manual tranny will probably not allow the front diff to get enough torque to propel the car... you will just race the engine.

[idosubaru]

yeah, that's not a good idea on a manual transmission for various reasons, it's certainly not good for your viscous center diff.

 

but it's not necessary. if you remove the driveshaft you will definitely be able to diagnose a bad ujoint (the part of a driveshaft that fails) immediately. it'll be very obvious. it'll either be noticeably loose/broken/warn or feel very lumpy when you move the joint in your hand.

 

driveshaft ujoints fail, so what makes you disagree with their diagnosis?

[nipper]

It's a valid diagnoses. Just get a used one from a junkyard. He is prbbly balking at it due to the cost of replacement at the dealer.

 

 

nipper

[idosubaru]

if it is the driveshaft, you should replace this immediately. if the ujoint lets loose it can wreck stuff underneath, including destroying your transmission. the shaft will cut loose and smack/crack the transmission case.

 

like nip said, junk yard that thing or have a drive shop rebuild the failed ujoint. having a driveline shop rebuild it is a great option if you can do the pull and install yourself. probably only cost $100-$150 to replace it with a new regreaseable ujoint (Rockford - look them up online for more info and Subaru part numbers).

 

either of those options is much cheaper than the dealer. they don't fail enough to avoid using a used one. and you can check the joints before you buy. rotate each ujoint over a few times and make sure it's smooth. any lumpy-ness and get a different one. find a nice smooth one and it's likely to last the rest of the time you own the car.

 

the FWD fuse won't really help even if it was an auto. even in FWD the rear wheels are turning. the driveshaft still rotates because it's driven by the rear wheels. might change it a tiny bit because the load is still there, but having done it before it won't really be very efficient at confirming anything.

[dave833]

Well the puzzling thing is there's noise but no vibration-- I figured a bad U-joint would vibrate to some degree at least. I didn't disagree with the diagnosis, I just wasn't sure what it meant.

[idosubaru]

Okay, well that makes more sense. I've never seen a driveshaft make noise but not vibrate either.

 

I would wonder if your center carrier bearing is failing. The driveshaft is a two piece unit. There is a support structure that holds the shaft and has a bearing through which the shaft turns. If this fails I would imagine you'd get noise (like any other kind of bearing) without vibration. Of the two piece driveshaft this carrier bearing is part of the first half that slides into the transmission.

 

I've never heard or seen of those bearings being replaced though, so used would be your option.

 

the one thing you can do - is remove the rear half of the shaft. It has two ujoints (one on each end). you can remove it and see if the noise goes away. that would leave the front half inside the trans, holding the gear oil in place.

 

as a side note - the rear half driveshafts are identical between all auto's and manuals. it's only the front half that is different. so for the rear any driveshaft will work, for the front it has to be from auto/manual.

 

if the noise is still there, then it could still be the front half, which you can't remove without loosing gear oil. it has one ujoint and the carrier bearing assocaited with it i mentioned earlier.

 

either way - i would imagine you would be able to feel some place or vibrations by turning the bearing by hand. mechanics stethoscope on that bearing might be worth a shot.