Plz help diagnose a bad vibration!!!

[Dicintio619]

OK so i finnally got my truck ready to drive to take emissions and on the way there I realized something was wrong. While driving i get a very violent vibration. It comes in 3rd 4th and 5th Gears about 90 percent of the time. 1st and 2nd gear dont do it. The cab starts shaking pretty good and there is a grinding sound coming from the drivetrain somewhere. The problem is not speed related because i can go 45mph in 2nd gear and no vibes but as soon as its in 3rd it starts. The vibration happens while in the lower rpms and sort of smooths out in the higher rpms. If i push the clutch in while driving and vibrating it goes away so i assume that eliminates the chance of it being a drive shaft vibration right? because the drive shaft is still spinning at the same speed and the vibration is gone. i put the truck on jack stands and ran it and it sounds like its coming from the tranny. I checked the clutch and pilot bearing and thro-out bearing and all seem to be fine with no slop. There is No play in the rear pinion flange or the t-case flange Please help me dianose this problem any input is apreciated thanks.

 

[Crawlerdad]

What size tires are you running? Do you have stock steering? What year model truck is it? Does the steering wheel shake?
Over size tires on stock steering can cause vibration. Loose steering componants can cause vibration. It's called the death wobble.
If I am off track start crawling around and shaking stuff. Look for something loose.

 

[KLF]

Ya it would help to get some info about your truck. Years? Miles? Modifications?

Things to check: shocks, tie rod ends, alignment, tire balance, basically anything that rotates.

 

[2ndGenToyotaFan]

Sounds like engine mounts to me, check the drivers side first.

 

[Dicintio619]

sorry guys its a 1986 toyota 4x4 22r g52 5 speed tranny on 33's high cross over steering and sas swap and 63" chevys in the rear. the steering wheel doesnt shake its definately coming from somewhere in the drivtrain behind the motor. 1st and 2nd gear dont do it even if i go 50mph in 2nd it doesnt vibrate at all so it not something speed related like a tire off balance or alignment. thanks for the replys

 

[Dicintio619]

ill check the engine mounts tonight

 

[Dicintio619]

it has 190k on the dash but it has a rebuilt motor and tranny that was in it when i bought it.

 

[Bastler]

Looking at the diagram in the Bentley manual, it looks like the 1st/2nd gear assembly rides on the rear half of the main shaft, and 3rd/4th and 5th/rev ride on the front half. (please forgive me if i'm misinterpreting - it's been a couple of decades since i tore down a manual tranny...)

It sounds to me like there might be a damaged 1st/2nd synchro, clutch gear, or shift fork, which causes (or allows) that side of the main shaft to vibrate when disengaged, and tightens back up when it's engaged.

Does it vibrate in reverse?

 

[Dicintio619]

Bastler, i havent tried it in reverse but i have the tranny out right now to inspect the gears so i cant try it but everything in there looks to be in good shape no chipped teeth or worn gears or loose bearings but there are also a lot of needle bearings that i can't see... I think you might be onto something though. i am going to put it all back together this weekend and i will try in reverse and let you know. I will also try a few more test to try and pinpoint the problem a little better.

Thanks for the input everyone!

 

[jynx]

Looking at the diagram in the Bentley manual, it looks like the 1st/2nd gear assembly rides on the rear half of the main shaft, and 3rd/4th and 5th/rev ride on the front half. (please forgive me if i'm misinterpreting - it's been a couple of decades since i tore down a manual tranny...)

It sounds to me like there might be a damaged 1st/2nd synchro, clutch gear, or shift fork, which causes (or allows) that side of the main shaft to vibrate when disengaged, and tightens back up when it's engaged.

Does it vibrate in reverse?

I was thinking this might be the case, but I hadn't checked my FSM to see what shafts the various gears were on. If the shaft bearings are going out then it would cause those gears to give problems but not the rest. I know on my W56 I had 5th gear go out like this several years ago and ended up having damage to the gear set and replaced them as well as rebuilding the trans.

 

[Bastler]

So - did you figure out what's wrong??

 

[Dicintio619]

yea im pretty sure its my drive shaft. the operating angle on my u joints is too extreme so i need a cv style driveshaft but im having a little trouble finding one. after i lifted it so high my driveshaft is at a really steep angle.