I have a 1994 Toyota SR5 extCab 4wd V6 pickup. Yesterday when I left the house I noticed a vibration that started at 40 mph and increased as I increased in speed. Below 40 mph it seemed to go away. I tried to rotate the 4wd drive shaft and it wont move freely. Tires have been rotated and balanced. There was a small vac hose at the top of the engine that was cracked and has been replaced. Any idea as to what is making the vibration?

 

Can be a few things really, U joints, out of balance drive shaft, low rear diff fluid, low transfer case fluid, bad steering stabilizer, low front diff fluid , worn pinion seal making the pinion wobble a little. for a few.

 

Pull your rear drive shaft and check the joints for slop. Most U joints have grease fitting on them but many home maintenance people forget to lube them. Also go have your tires balanced. Could something as simple as an out of balance tire.

Is it only under power?
Does it change if you let off the gas?
Any clunking in the steering?
Pictures of the trucks front end steering components might help. But wear items like that can be had to just visually ID.
Start with the basics and work up from there.

 

when you have a vibration that starts at 40-45 mph 95% of the time it is tire and wheel related. just because the wheels have been balance does not mean they are round. I have seen many times where a tires tread spinning on a balance machine can be seen to wobble side to side or up and down slightly, this can cause your symptoms. Also these trucks are susceptible to "cold flat spots". They run a fairly low pressure for the size of the tire since they are so light and when parked sometimes the tires will get a flat spot in them that will go away when you drive and build up some heat in the tires. So, if you take your truck to a shop for a tire balance and they don't get to it right away (especially in cold weather) you get a flat spot, they balance the tires and when you drive the flat spot goes away and presto... they are out of balance again.
The best way to balance your tires would be for the shop to drive your vehicle for about 5-10 miles and pull it straight into the shop and get it off of ground then balance them.
When the tires are spinning on their machine they should be looking for signs of a bent wheel or out of round tires.

Start with some basics, does the steering wheel shimmy back and forth if you let go of the wheel while it's vibrating or do you feel the vibration more in the seat?
this can tell you if it is from the front or back.

 

Thanks for the info. I noticed that the axel from the transfer case moves when my wife pulled it forward for me so I could look at things underneath the truck. Should this spin or not?

 

You must mean the driveshaft, the rear one will move whenever you rotate the rear wheels. The front one should only move when you are in 4 wheel drive, or if you have the wheel hubs locked. Do you have manual or automatic hubs? If you have the truck in 2 wheel drive and the hubs unlocked the front driveshaft should not move unless you reach in and rotate it by hand (which it should do freely). If you have automatic hubs you may have to move the truck back and forth a few feet for them to unlock (in 2wd) or to lock (in 4wd) or if they stay locked something is wrong.

 

OH, wait a minute... 94 is a drive flange with the disconnect in the differential right? if so it's been too long since I dealt with one to help much, but same deal when you put it in 2wd the front driveshaft should be free and not spinning.

 

Thanks! I have the automatic locking hubs. Any suggestions on getting them to unlock?

 

Jack up the front end after putting it in 2wd and see if you can rotate the front tires without the cv shaft moving. Roll the tire forward then backward and see if the hub is unlocked or unlocks while you do this. If you rotate the cv shaft only, the hub should lock either direction. (anyone chime in if I am wrong on this!)

 

On the 1994, the ADD (Automatic Differential Disconnect) has nothing to do with moving backwards or forwards. There are vehicles where you have to back up to disengage 4wd, but this isn't one of them.

When the ADD is open and the transfer case is in 2Hi, the driveshaft is not DRIVEN. But there's always a bit of friction in the system, so I would not be surprised if the front wheels could drive the drive shaft through the (open) differential. Just lie under the truck and try to turn the front driveshaft; you should be able to turn it by hand. If not, either then front diff is not disengaging, or the transfer case is not disengaging. Only then do you need to jack up the front so that you can spin the wheels.

I've ridden in cars with "cold flat spots," but that was back in the 60s when tires had nylon cords in the casings. I've never felt a flat spot since all tires went to polyester (and steel). But I did have a tire with a "hop" as described by akwheeler when I bought it (2003). I thought it was out of balance, and the shop (Costco) said it was balanced fine but had a hop. I took it to the Goodyear dealer and they replaced the tire under warrantee. It's tread-depth pro--rated, but the tire was so new I paid nothing.

 

Thanks for some clarification on the ADD scope, it has been over 20 years since I worked at a Toy stealership and I never did dig into one. Don't all of the ADD trucks have drive flanges rather than auto hubs?

On the "cold flat spot" issue, I first came across this in Juneau Alaska in the early to mid 90s when I was at the Toy dealer there, we had issues with balance on several vehicles and after going round and round with technical assistance we tried the test drive then balance technique and it worked every time. we also had a fixture to mount the wheels on the balancer using the lug holes rather than the center hole and it helped in some cases. The basics still hold true though, whether it's a manufacturing defect, cold flat spot, bent wheel or whatever, the balancer will make the spinning mass balance, but if what is touching the ground isn't true you will have a vibration and it usually shows up around 40-45 mph unless it is a badly out of round tire or bent wheel which will be noticeable at a much lower speed.

 

If a tire gets a "flat spot" that's big enough, it could affect balance. But the usual flat spot (the ones I remember as a kid in the 60s, and probably the one's akwheeler noted in an even colder climate), change the SHAPE of the tire. It's still balanced, but you're hopping the flat spot. That's what happened to me; the tire was correctly balanced, but it wasn't round. No amount of balancing could fix that.

Akwheeler mentioned something else; tire centering. I'm no expert on this, but my alloy wheels have a precisely sized center hole that fits over a corresponding projection on the hub. So if I have a badly bent stud, the wheel will still be centered. I'm not sure when you would use a fixture to mount by lug holes rather than center hole. Maybe if the center hold had been damaged so that it was no longer in the "center." Do you get much ice and salt in Juneau?

 

Scope, I left Juneau in 1996, lots of salt air, but not much used on the roads. Still lots of rust due to wet conditions and the salt air though. I still live in Alaska, but now I'm on the Kenai peninsula almost directly south of Anchorage. No salt here either, it's a long way to ship salt and the roads are better when it's packed ice anyway. We just learn how to drive on ice or get studded tires.
Some wheels are "hub centric" and some are "lug centric" if I remember the terms correctly. If the center hole doesn't fit tightly on the center hub they are "lug centric" or "centered" and the raised portion of aluminum wheels gets beat up sometimes and it wont sit perfect on a balancer anymore.

 

Driftseeker, do you have any information on this for us?