vibration when i get on the gas... wtf is it now?

[Mephisto]

i just yanked the propshaft, and threw on some old tires, to go have some fun...

when i get on the gas, the truck doesnt really move and i feel all kinds of vibration in the shifter... definite signs of the tranny slipping? or possibly something eff'd up in the t-case? the reason i wonder if its something with the t-case is, that it never did this with the front prop in...

sound familiar to anyone?

 

[InvisiBill]

Have someone watch the front output on the transfer case. If that spins and the truck doesn't go anywhere, the viscous coupling is probably shot. All the power is going to the output-with-least-resistance, which is doing nothing to help you move.

If neither the front or rear output of the transfer case turns, then either the transmission or the transfer case is busted, and not outputting anything...

I was talking to my tranny guy about the Sy's AWD, and he mentioned that someone screwed up the AWD in their Bravada, and that they did in fact drive around without the front propshaft for a while. I think he said it was like $600 just for the viscous coupling from GM...

 

[steve-o]

bill,
how long can one go without the front propshaft connected to the x-fer case before damage starts to set in?

can the viscous coupling handle it if i were to disconnect the drive shaft, leave the prop shaft alone and sport around in fwd for a while? not that i'd do such a thing...... :drinking:

is this how most dyno their trucks on a two wheel drive dyno.....in rwd?

sorry to barge in on your post Neil.

 

[sy1907]

possibly the torque converter? Just an idea........

 

[Mephisto]

Have someone watch the front output on the transfer case. If that spins and the truck doesn't go anywhere, the viscous coupling is probably shot. All the power is going to the output-with-least-resistance, which is doing nothing to help you move.

sorry for the bad explanation on my part...

my truck moves, what i meant was... from a roll, if i get on the gas, it doesnt really accelerate normally, i feel a lot of vibration before it finally kicks in and the truck speeds up.

perhaps sy1907 is right? and im just gettin some bad TC shudder? but if that were the case wouldnt it do that with the front prop in also?

hopefully its nothing major, i kinda liked having 68k on my original motor, trans, t-case, and turbo. i felt elite hahaha

usually dont at least one of those go in the first 50k?

 

[InvisiBill]

I bought my Sy with 77k, all stock as far as I can (down to the paper air filter). I drove up to 124k when the forward sprag in the tranny went. I'm at 147k now, and the rest of that stuff is still stock...

Hmmmm, not really sure if I can provide any more info to help you out. I suppose it could still be a problem with the viscous coupling, if it goes away when you put your shaft back in. *shrug* Good luck with finding and fixing the problem.

Steve, no idea. I've just seen posts that removing the propshaft puts a lot of stress on the transfer case. When you don't have the front wheels turning the transfer case via the propshaft, it thinks both sets of wheels aren't spinning at the same speed, and tries to correct for it. People recommend changing the fluid before (to make sure it's as good as possible before being stressed) and after (to get out any heat-affected fluid) you remove the shaft, just to be safe. I mentioned this whole trying-to-correct thing to the tranny guy, and he thought it did make sense, and then remembered that they did drive the Bravada around for a while without the front propshaft. That wasn't necessarily the cause of the failure, but it could have possibly been all or part of it.

 

[GM TURBO]

If you pull the rear driveshaft you will damage the X-Fer case. And you will also find a large puddle of X-case fluid on your driveway.

 

[sy1907]

I'm having the same thing, with the propshaft in. My old one was shot, but this temp one does it sometimes when i get on it from a roll. Check to see if your tc bolts are tight. Might be the prob and it's an easy fix. Keep us posted.

 

[Mephisto]

well after more driving and more screwing around with this today... ive concluded that something is loose.

when driving around normally i dont really feel anything. when i get on the gas from a stop and some torque is put on the drive train thats when i feel vibration and like a slight banging through the floor where the tranny/t-case is. it almost feels like something is flexing? i went over some rough pavement and felt the bangin through the floor also...

so im guessing either a tranny mount is broken, or one of the t-case bolts are gone or loose. im gonna get under the truck tomorrow and see what i find. not that anyone gives a shit, but ill post results anyway hehe.

on a side note i went by a shop today to get a quote on rebalancing my propshaft... $90???

 

[Maverick87]

could be a swaybar mount

 

[sy1907]

I've felt that too. When I removed and opened the trans-case, the planetary was fried. Same exact thing you're describing. Then the tc went out. I'm guessing my diffs are next. Good luck

 

[myclone]

I dont have time to get into a huge explanation right now but you might get away with a cheap fix.

When I took the front drive shaft out for some fun I noticed that I would get slight wheel hop when I went 3/4 throttle at a 15mph roll. Not bad wheel hop but enough to shake the truck a little and cause some noise under the floor board. I know what wheel hop does/sounds like and the thumping under the floor board isnt part of it. I jacked the truc up and found a bad/worn trans mount. I replaced it and the thump was gone.

So, check the trans mount as even slight wheel hop like I had can bang the trans up and down on the mount if its busted/worn out. Its easy to check and cheap to fix so HTH.

 

[odium]

Re: vibration when i get on the gas... wtf is it now?

I have the same problem and if the problem has been fixed, please post what it was and how you fixed it.

 

['JustDreamin']

Re: vibration when i get on the gas... wtf is it now?

Hey Guys....

Just a word of financial caution:

I'd be real careful driving around without the front propshaft. At least if it was my truck & my wallet.

The transfer case in these trucks (and bravadas thru '97 & Astro's through '98) is a unique piece of hardware. Its basically a limited slip differential. And the viscous coupling is what determines how the split of the limited slip works. Without resistance from the front propshaft, the viscous coupling is working REALLY hard to make the rear output shaft spin and the truck go. All of these trucks are 12 or 13 years old, and I bet none of the parts (that haven't been replaced) are quite as stong as they were 12 years ago. Do you really want to tear up the t-case (or have to tear it apart)? I'll give you its not a guaranteed thing, like driving around with no oil in the oilpan (I'm pretty sure that'd be a fairly quick BOOM). But it is certainly a bunch of stress that it doesn't need to see, and sooner or later it'll leave you (somewhere).

I've looked at pricing on transfer case parts, and a new viscous coupling goes for at least $600, and that doesn't include anything else. For example: labor, other parts, towing charges, damages to your truck and other peoples property caused by the truck rolling away while in park with no front propshaft, etc.

Personally, I can do without causing perfectly good parts to fail. Especially ones that there isn't an upgrade path for. After all, having to fix / repair / replace the transfer case won't make the truck any faster (with the exception of making your wallet a couple of pounds lighter).

(getting down off soapbox now)

'Dreamin'