85 s10 2.8l 2wd vibration

When I got this truck not too long ago, there was no vibration.  Now, at about 1000-1500rpm there's a very noticeable vibration.  I thought it could be the clutch due to the oldness of it and the rubbing sound the disk gives off when starting off in first, but it vibrates when I'm just sitting there and either have the clutch petal pressed or not and idling in neutral.  I've looked at the engine mounts and don't see any cracks but I'm not so sure that's not the issue.  To be honest I don't know what's causing it.  It could be something interior.  I need help.

Very well could be a radiator fan deformity. I know if the radiator fan gets loose and crooked it'll make the whole vehicle shake.  How is the engine running?

IT could also be dirty injectors, but the vibration might be more constant at any RPM (ore noticble on lower though/Idle)

I didn't figured it would be the injectors because the problem occurred in such a short amount of time. It is also possible that the timing may be slightly retarded.

quote:

ORIGINAL: EuroGoldLS

I didn't figured it would be the injectors because the problem occurred in such a short amount of time. It is also possible that the timing may be slightly retarded.

 
agreed which I sort of stated, but the fact that is such a consitant issue   figured I would through it out there.

Hey, thanks for the imput guys buy I'm not sure it's either the injectors or the fan.  I have ran the suggested fuel treatment through the gas and changed the plugs and wires and the truck runs great.  No hesitation or anything.  I'm not sure if it's the fan.  Does the fan increase in speed as the rpms go up?  If that's the case it'll be worth checking out.  Also, I've noticed as oil leak from somewhere on the backside of the engine. I've checked all over and I'm 95% sure it's not the head gasket or valve cover gaskets.  I'm thinking it's the rear bearing seal which if it is would be bad news and would mean if it is, the bearing could be the cause of the vibration.  Or thinking of the clutch again, it could be the flywheel...maybe it's a little loose?

And remember, the vibration is only noticeable when I slightly rev the rpms around 1500 or 2000, not above that or below it.   It doesn't have a tachometer so I'm making an educated guess. 

On the 2nd gen, The hfan speed will not increase after you get to about 2000rpm. It has a centrifugal clutch that keeps it from getting too fast. 1500-2000 RPMs is about when the clutch engages. Whether thats true on the 85, i'm not sure.

Well, I've checked the fan and it seems to be normal.  I suppose I could look at the engin mounts again and see if they're loose at all.  Does anyone know what 5-speed transmission I can get to replace this 4-speed?  One that will fit this truck with the 2.8l engine.