Hello all,

I've been chasing a vibration in my truck for the longest time and finally noticed something that could possibly be a clue. All of my u joints are solid, driveshaft is balanced, transmission and the T-case have been replaced due to a bent transmission input shaft. The only thing untouched is the clutch and flywheel and I'm looking to be certain before pulling the transmission. Can anyone give me some insight on what this is in my video? I looked up diagrams but could not find it. My truck is a 99 F250 with a ZF6 manual transmission. Any help would be fantastic!

 

From your video it looks like your exhaust pipe is making contact with the T-case. That will give you a healthy vibration for sure. I'm guessing that little plug is a breather plug.

 

I did notice that also, but my vibration still exists when I turn the truck over by jumping the starter solenoid. Im not certain that is a vent plug because it's solid when the truck is off, also there is a big vent on the underside of the transmission that you can feel the air coming out of. I can't find anything picture related or diagram related to know what this is.

 

In answer to your question, that is your clutch fork pivot anchor. This part is made out of plastic on this particular transmission. If this part vibrates with the engine running, it stands to reason that the fork is vibrating as well, causing the shaking you see in the video you posted.

 

So... if my vibration happens when the truck is turned over (also while running) and still continues with the clutch pushed in. Would that only leave the flywheel as suspect?

 

Quite possibly. With the clutch pedal pressed in (clutch disengaged), only the flywheel, pressure plate and throwout bearing are the moving parts. That vibration could easily be transferred from the clutch fork to that plastic pivot. I don't quite remember if that truck was originally equipped with a dual mass flywheel off the top of my head, but what I do remember is that dual mass flywheels were notoriously prone to eventual failure. They were also astronomically expensive to replace, hence the part went obsolete very early on, superceded to the much more reliable single mass unit.

 

Thank you for the replies, from what I can tell, my truck has a single mass flywheel. When I replaced the transmission it was due to someone not putting loctight on the bellhousing bolts. The transmission eventually backed the bolts out, then I noticed a vibration at 35-40 mph. It was bad enough to bend the input shafts on the transmission and break the transfer case. I paid someone to put the new transmission and transfer case and now wish I could have inspected the clutch and flywheel while it was out. I believe the previous owner did put a clutch in the truck and didn't properly torque and loctight key components. So... that also makes me think they didn't resurface the flywheel/ replace it when a clutch was put in.

 

STUPID QUESTION. Are you sure the original failure was caused by bellhousing bolts backing out? Those are pretty big and beefy bolts if I remember correctly. Even if only moderately tight, I would be hard pressed to believe they could back off on their own. Do you, by any chance remember if the engine block-to-transmission dowels were present or MIA? If those dowels are missing, that would easily cause the original failure you've described. And if they're missing again, you may very well have an out-of-true flywheel causing your present issue. Hope this helps.

 

That does help a lot, thank you. The dowels are present in the new transmission, there was really no telling if they were when she gave last time. Here is a question, can single mass flywheels become out of balance over time or could it have done that when the transmission broke? I have a picture somewhere of the damage, I'll dig it up soon.

 

I've never heard of a flywheel "become" out of balance over per se. Chatter during clutch engagement? YES. But that would be just normal wear. The only way for it to "become" out of balance would be if there were balance weights welded onto it, that had fallen off. But I don't think I've ever heard of that happening. My suggestion would be to pull the unit and the flywheel to have it checked for trueness. If you do elect to have it surfaced, be sure to stay within minimum thickness specs. You could also have it sent out to be balance checked if it would give you that piece of mind. I'm wondering if a driveshaft shop would be able to provide such a service. I would also pay particular attention to the surface where it mounts onto the crankshaft flange for runout.

 

Thank you for all of the help, an intermittent vibration can make you go mad when you can't seem to pinpoint it. Life would be easier if I had a lift to make the job go smoother. I believe I would just replace the flywheel when I do finally put a clutch in, there are several clutch kits available with a matching flywheel.

 

When you do get around to replacing the clutch and flywheel assembly, please provide feedback on the results. If I remember correctly, these ZF6 transmissions have always felt a little difficult to shift, even from new from what I've remembered through the years, regardless of which engine it was behind.

 

I will do that, just a note though, my zf6 is brand new and it is still a difficult shift. Wish there was a way to change that.