Topic: Vibration starting from 3rd gear

[84Flatbed]

I'm not sure if this is the right section to post but here's what's going on. 84 pickup, G series trans, dual cases, Cv driveline with pinion pointing at tc. When I shift into 3rd gear, regardless of speed, Im getting a pretty bad vibration that continues but lightens up into fourth and fifth gears. Its not noticeable in 1st or 2nd gear. 3rd is by far the worst and is less severe while coasting.

I can't feel any play in the output flange or pinion flange, and not really any noticeable or excess play in the joints on the driveline. The driveshaft is a little dinged in one area though. Could what I'm describing be transmission or transfer case related or could the driveline cause this kind of symptom?

[blackdiamond]

If your driveshaft is out of balance I would expect the vibration to get worse the faster it turns and not get better, but maybe someone has a had a different experience.  Does the vibration still happen if you shift into 3rd and really low RPM?

[84Flatbed [OP]]

If your driveshaft is out of balance I would expect the vibration to get worse the faster it turns and not get better, but maybe someone has a had a different experience.  Does the vibration still happen if you shift into 3rd and really low RPM?

Pretty low, 2000rpm, can't say that I shift into 3rd any lower than that in this slug. As the speed increases it gets a little  better, still a constant vibe that shakes the rear view mirror to where I can't see out of it.

Seems strange that no matter what RPM or speed I go in 1st or 2nd I don't feel it, shift to 3rd foot on the gas instantly  there.

[David]

Don't know if this will help but I had a similar problem with my 83 5sp, became worse over a short period of time then I lost 1st & 3rd.
I replaced trans with a 2nd gen 5 speed but never opened the old case but assume it lost the bearings.
 

[84Flatbed [OP]]

Don't know if this will help but I had a similar problem with my 83 5sp, became worse over a short period of time then I lost 1st & 3rd.
I replaced trans with a 2nd gen 5 speed but never opened the old case but assume it lost the bearings.

Your 83 probably had the same trany too. This trans is not great, I cant shift fast or it will grind a little, but I was hoping it would still last for awhile. I wonder what I could do to narrow it down to the trans or not.

So could you feel anything in first and second gear? How about any abnormal noise? I don't hear any abnormal sounds coming from the trany.

[David]

Yes on the noise, 1st gear was hard to engage, lots of clanking and rattles then would not engage at all, used 2nd as 1st then 3rd went on the way home making same noise and vibs.

[84Flatbed [OP]]

I decided to start with the basics and have the tires checked for balance, the rears for now. Its much easier for me to have the tires checked than it is to find a driveline shop nearby that can check the driveline. I went to americas tire because of the slight chance they would do it at no charge, they balanced a set of tires on my tacoma for free once even though I didn't buy the tires from them, I guess because I was a previous customer. No luck this time.

After 15 min or so the tech who was balancing them said that the tires were showing they needed about 10 more oz. and in his opinion adding that much weight wouldn't help. Didn't really have a good reason as to why they were not balancing out other than them being a very large tire (36x13.5 irok). He offered to put them back to how they were when I brought the tires in and refund my $. I opted to have him do the best he could and pay the $. When the tech brought the tires back out to me he mentioned that his boss said one of the reasons they won't balance is cause they are bias ply, I pointed out that his boss must not have looked at them, says radial on the sidewall ha ha.

Anyway enough babbling, I haven't had a chance to see how it rides yet but there is a load of weight on the rim, I think 13 oz. on one and 11 on the other.

[blackdiamond]

Coming back from Moab my front tires were 5oz out before stopping at Discount Tire in Salt Lake. They rode pretty harsh but got worse with speed. They really shouldn't get better when you go faster.

[Tjcarter]

I've ran into this same thing... racked my brain until i finally lifted the rear end off the ground and had my wife put the truck in gear. I watched my driveshaft spin with a pretty good wobble towards the pinion- unnoticed at slower speeds and too fast to really notice at higher speeds. 3rd gear was where i felt it. Had the shaft re-tubed from Tom Woods and vuala- it was fixed.