FuelforWar

You stated you recently had a valve adjustment? If so your valves could have been potentially slightly over tightened if the mechanic or who ever did them didn't have a perfect idea of what he was doing. This happened to my buddies motor and he had a bit of vibration due to it. If this is the case the noise you hear could be a result of the motors vibration, instead of the noise your hearing being the cause of the vibration.

Gov't Mule

Had the same symptoms in my '82 on a cross country trip. Was in the middle of BF nowhere in southern Wyoming and I thought my clutch or transmission was going out because of the resonating vibration. Made it to a friends house in Colorado and started investigating...found that the waterpump had almost 3/16" of play in the shaft! (wasn't leaking a drop of coolant either)

Replaced the WP...problem solved.

JustDSM

Thanks for getting back to me on that.. As a quick test I just removed the accessory belt from the water pump and alternator and took it up the street and back. I can't say it's completely gone, but I'm inclined to say it has improved. So I'll replace the water pump and fan clutch tomorrow most likely. It's really quite frustrating I must add. The truck just seems WAY louder than what I remember my '88 sounding like. I'm determined to figure this out.. I really hope it's just something simple..

I'm not ready ($ wise) to do a 3RZ swap

Gov't Mule

Do you know how many miles are on the waterpump?? With the belt off or loose grab the fan blades and see if there is slop in the waterpump shaft by wiggling in up and down. The WP is gonna be cheaper to replace than the fan clutch I do believe.

JustDSM

Well, I have to swallow my pride a little here.. I went out to do as you said and noticed that I completely overlooked tightening the 17mm nut on the drivers side motor mount. It wasn't even finger tight. I'm so embarassed!

The water pump has a slight bit of play.. Maybe 1/16th of an inch or so probably slightly less.. So I reconnected the belt and went up street again. Noticed a SIGNIFIGANT improvement. Although under 2250RPM or so it's still a bit much. Not nearly as bad, but it still vibrates quite a bit more than I believe it should. Above 2500 RPM though ITS QUIET!!!!!!! Not quite like my '09 Silverado but for a 20+ year old vehicle I'm rather impressed..

I think part of the vibration at low RPM is due to the carb needing adjustment from the altitude change. The truck has lived at sea-level its whole life, and now resides at 4000ft ASL, so it's going to need some adjustment. I can already tell the idle quality has degraded from when I first picked it up.. I'll fix that and probably replace the water pump just because.. It's only $20 at AutoZone. I suspect it's probably got a few miles on it. I think the newest it could be is probably ~20,000 miles or so (about when the motor was replaced). Could be older...

Champ

I have the same idle vibration. At anything over 2000 RPMs she runs really smooth, and at idle it is really smooth. I do have alot of vibration right arount 1600 to 2000-2300 RPMs. From what yall are stating the Engine mounts will make it vibrate all the time? correct? The water pump shaft has that helped anyone yet?

80banana

Took a look at the exhaust manifold today. With the engine running and my (gloved) hand briefly holding the outer heat shield, I can feel a small vibration coming from the lower part that opens near the manifold's outlet, though I my eyes couldn't see anything vibrating. So I shut the engine down, pulled the outer heat shield off (broke most of the bolts) and started her up. This resulted in a significant decrease in that annoying resonating noise that would happen everytime I'd decelerate or rev the engine above 2000 rpms. Furthermore, upon flipping the outer heat shield over, it appears that the lower portion (near the exhaust manifold's outlet) was in contact with the manifold, as there was a portion of highly polished metal-metal contact. SO...it looks like I may just need a new heatshield and gasket set. Or maybe I'll spring for a header? I haven't pulled the exhaust manifold yet, but that's next on the "to-do" list.

Speaking of headers, how loud are the ones for the 20R trucks? Raspy? This is my daily driver/trip vehicle/gas miser so I'm not looking for performance; I have an RX-7 for that. Just looking to get rid of that annoying resonating noise.

truckman1966

headers don't necessarily make a car or truck "louder" and if you are searching for a good one, (i know they are expensive) LC Engineering, because of their very thick flange and wall thickness of the tube they use.

traveljoe

I finally got around to testing the water pump/fan clutch yesterday. It looks like that's the cause. I took the belt off and took it for a short drive. I still have the low exhaust rumble from a bad muffler, but the cab and body vibration is gone! I didn't think it was anything in that area because I replaced the water pump a couple years ago and then didn't drive it for a year. However, when I ran over that bear it broke my engine mounts, which could have caused my radiator fan to hit the shroud pretty hard and may have loosened things up or broken something.

I'll begin the process of inspecting that area and perhaps replacing parts. I'm convinced that this is the root of the problem and I'm very thankful for the suggestion.

I would highly recommend to everyone else having this problem that they do the same test.

Gov't Mule

glad you're making progress on repairs.

80banana

Glad you found the problem traveljoe! I pulled my belt off too, but the noise didn't change much I just got a set of motor mounts yesterday, so switching those is next. For $6 each, I figured even if they weren't bad, it's really no loss.

Oh, I forgot to mention that I took the truck on a long drive the other day and that resonating noise is pretty much gone. I'm pretty confident that it was coming from that outer heatshield.

traveljoe

Good to know, Banana. Did you remove the outer heat shield completely or just bend it away from the manifold? I'll look into that as well. I'm going to go work on it in a few minutes and hopefully all will be solved then. I'll let you all know.

80banana

Actually, I just removed the outer part of the heat shield and left the inner part (sandwiched between the manifold and the cylinder head) on. I may pull the inner part off as well once the weather warms up, but for now, there has been a significant improvement in lessening noise by just taking that outer half off.b

JustDSM

Well, I suppose I should throw an update up on my truck.

I've been DD'ing it for about a month now and the truck is running flawlessly, considering I have to climb about 2000 in elevation each way (have to cross a mountain pass) on my 25mi trek to work.

Some observations:

- Vibration/resonate sound is still ever so present. The largest contributor to the cabin noise is part of what is left of my OEM Radio bezel vibrating.

- The cab/truck still vibrates what I feel is excessively right around 2,000-2,250RPM. Which causes other odds and ends in the dash to rattle.

- I've been told by one of the locals who has had the LC Engineering motor mounts that this vibration/resonate sound I'm hearing is due to the motor mounts.

- I've tried removing the accessory belt to stop the alternator, water pump, and fan from turning. Noticed a VERY slight decrease in the NVH department, so I feel comfortable ruling those out as part of the problem.

Well.. Where do we stand? I'm going to try swapping in the OEM motormounts which are still in decent shape, and see what happens.

I should also note that I've also picked up on a vibration which feels like its coming from the drivetrain right around 50mph, totally seperate from the issues we're duscussing here. I've checked the U-Joints when I first got the truck home and they are solid. so I'm wondering if my shaft is bent or out of balance somehow.. I'll have to get it back up on jackstands and take a peek at that too..

Thanks to all of you who are helping keep this thread alive!

80banana

No problem. Back when I started this thread about my truck, I didn't realize that there were others out there with similar issues, so all contributions are welcome!

I take it you have LC Engineering mounts on there now? I can't really comment on those, but once I get around to installing the OEM motor mounts I bought, I'll post the results. Currently, my mounts are the originals (31 years old), so I'm hoping replacing them will help with the noise.

JustDSM

That's correct. I probably could have worded that a little better, but I've currently got the LC Engineering mounts installed in the truck. They sure do a good job of keeping the motor in place. It doesn't MOVE which is really nice when I'm wheeling and creeping around in 4Lo. Although the price I pay for that "luxury" is sure taxing in the NHV department..

I'll be sure to report back back with my findings on going back to a decent set of OEM mounts. Although I fully expect to notice a difference I think I'll end up with the LC Engineering mounts back in the truck though

traveljoe

So I took the radiator fan off and the pulley to check for anything loose. I started the engine just to be sure that that was indeed the problem area and I discovered that I had been wrong the other day. Having the fan and water pump not running didn't take away the cab vibration. Next I took the exhaust manifold heat shield off and ran the engine. Also no improvement. At this point I am wondering how much of the noise will be taken away when I replace the exhaust. However, I'm thinking that the vibration may be an issue of the engine being off balance from lack of spark in one of the cylinders, either from something as simple as bad plugs (they do need replacing) or perhaps a damaged part in the distributor. We shall see. Tomorrow I replace the plugs. If anyone comes up with anything let me know. I'm not giving up!

ducatipaso

i have a noisy rattly sound underhood too
any noticeable long-term issues with that shield removed?

oh, and I wanted to point out that I replaced my trans mount the other night, and have a pair of motor mounts waiting to go in.
just the trans mount alone quieted the ruckus down in my cab considerably. for the cost and ease of install... I'd say that swapping motor mounts out would be a great service to do to any truck with 200k+ on it!

traveljoe

Replaced the plugs. They needed it and the engine seems to run a little better, but there's not a huge difference in the noise level. On my list is the transmission mount, distributor, and the entire exhaust system. If that doesn't help I'll be checking valve train clearances and maybe even making sure my connecting rods aren't loose on the crank or some nonsense. If All else fails I'm going to insulate the heck out of everything!! I'll keep you all updated, but it may be a little while before I have the money to do anything else.

80banana

I pulled both motor mounts today. Both were bad. The driver's side was split all the way around and the passenger side was split about half way. Both had been stretched down by the weight of the engine. I put the new ones in, tightened everything down and took it for a spin. The vibration is gone! In fact, the ride is so quiet that I can now hear the tires on the road. The cab and the steering wheel don't vibrate at all now. I'm really glad I got this done because I'll be taking a road trip next week and I'm really looking forward to a quite ride. For the $12 I paid for two mounts, this was WELL worth the effort!