2500+ RPM vibration felt mostly through clutch

I got all the fluids and basic maintenance stuff done on my truck, so I have been daily driving it around to make sure everything is good. So far it run great and shifts really nice, but I have an engine vibration starting around 2500 RPM, then continuing up with engine RPM all the way till redline.

It isn't a knock or misfire vibration, but a physical vibration, which is most prominently felt through the clutch pedal (manual NV3500 trans). I have already swapped out the harmonic balancer, which helped a little, but did not solve the issue. Vibration occurs while driving or parked, so it is not a drive train balance issue.

I was going to investigate under the truck today, starting at the transmission inspection cover to check for missing bolts or a damaged clutch/flywheel. I have also read that a bad intake gasket can cause weird issues on these trucks, and are a common issue.

It is the 5.0L 305 engine w/241k miles on it. Not sure if engine is original.

Any other tips or places to check to solve this issue? Thanks!

I would check/replace the motor mounts and transmission/t-case mounts

Inspected the flywheel, does not seem to be damaged. No idea if all the bolts are there, as those are covered by the transmission. I did however take off the timing cover to check the chain, and it was REALLY lose. Had almost an inch of play in the chain between the cam and crank sprockets. I have replaced the chain, but have not started the truck yet because I am doing some other maintenance items while everything is apart.

Could the lose timing chain have caused my vibration issue? I plan to have the truck done by this evening, so I will have a definitive answer to report back.

I have replaced the timing chain and water pump and have driven the truck around a bit. Engine is really happy now, but vibration is still there. I am going to replace out the engine and trans mounts as previously mentioned. I waited on swapping those, as I was going to do the timing chain and water pump anyways, so no harm in narrowing down the problem. Thanks for the help so far!

I have replaced the motor and transmission mounts, and while it seems to help a lot in absorbing the vibration it is not gone. I think I am going to drop the transmission find out what the issue is after all, as every other possible issue has been resolved. I also need to replace my engine rear main seal and transmission rear seal, as those leaks are starting to get out of hand, so no better time to do that then when I have the trans out. Other than that I love this truck and have been driving it all over, and it has given me no issues. I am continually updating, fixing, or cleaning issues as I come across them. It is just a solid, honest, and reliable pickup truck. I am very happy with my purchase so far!

A little more info might help, is this something that just all of a sudden started happening, gradually started to happen? Sounds like it possibly could be an out of balance flywheel, maybe it had a weight fall off, or possibly a weak cylinder or two, could try and remove spark plug wires 1 by 1 to see if there is one or two that barely make a difference. I know you said it seemed to run great, but with 241k, it might just be getting tired. Would be even better if you could get ahold of a compression gauge to check. Just throwing ideas out there

Justin S said:

A little more info might help, is this something that just all of a sudden started happening, gradually started to happen? Sounds like it possibly could be an out of balance flywheel, maybe it had a weight fall off, or possibly a weak cylinder or two, could try and remove spark plug wires 1 by 1 to see if there is one or two that barely make a difference. I know you said it seemed to run great, but with 241k, it might just be getting tired. Would be even better if you could get ahold of a compression gauge to check. Just throwing ideas out there

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The vibration was there when I bought the truck (didn't sound like a knock or bad bearing, so no concern to me). I have no idea how long it was doing this since I have purchased the truck, but it does not appear till after 2500+ so under normal driving conditions it is not felt. When standing at the front of the truck and reving the engine, it revs up quick and sounds very healthy, so I am fairly positive it is not any thing wrong with the engine internals, such as a misfire or a "low" cylinder.

A compression test would still be a good idea to absolutely verify that, I'll see if I can borrow one from a friend/rent an auto parts store kit/, or even buy a cheapy at Harbor Freight. Out of all my tools I amazingly still don't own a compression tester...

I am still going to drop the tranny and swap those seals out, and check out the condition of the flywheel/clutch/bolts/weights/etc. I read these trucks are prone to loosing bolts on the flywheel/torque converter (in the autos), so it might be as simple as that.

Once again thanks for all the advice so far! I will keep you all updated!

I have a big update with the truck and vibration issue!

Over the last month I have been working on the truck when I had the time. I dropped the transmission, transfer case, drive shafts, front axles, and pretty much every thing else that was easy to get too without the transmission in place. I changed out every oil seal and gasket I could get my hands on and a bunch on "while I was in there" projects.

What I believe was the vibration issue was the flywheel/clutch/pressure plate assembly. Flywheel had tons of heat cracks and uneven heat wear, clutch was in terrible shape with uneven wear and the surface looking really rough, and the pressure plate looked just as nasty as the flywheel. I replaced all of these with new parts (Luk) and reassembled everything.

I finally got the truck out of my garage today, and it drove like a dream. Shifts really nice, clutch feels really good, and most importantly no vibration! It also leaks no more oil anywhere, as all the 20 year old seals were replaced with new.

The only small issue that I plan on (re)fixing this weekend is a terrible exhaust leak/ticking sound from the donut seals off the exhaust manifolds into the Y pipe. When I reinstalled those it didn't "feel" secure to me, but I was too excited to drive the truck again so I figured it would be fine. My own fault, but it doesn't affect anything important and will be an easy fix. I just glad all the important stuff works fantastic!

Once again thanks for all of the help!