High RPM - shaking the fj40.

brooklyn · 06-27-08, 08:55 PM

Need some help. I installed an SM420 into an fj40/V8. The truck had an SM420, but I am upgrading to a NOS SM420. I put the transmission in the truck and had some issues with the drive line hitting the case, so I am going with an Extreme Bends adapter, which should solve that problem.

However, with the new SM420 installed (no front drive shaft) I get a terrible shake throughout the truck when the transmission is in 1st, 2nd, and 3rd. This happens at high rpm. I am sure it would happen in 4th if I got it on the highway at high rpm.

I depressed the clutch and reveved the engine and the same shake, which led me to believe it was not the new SM420, but maybe the new clutch or flywheel I installed. My thinking is that the clutch is depressed transmission is not engaged.

But, when I took the SM420 out of the truck and just rev to a high rpm I don't get the shake. So now I am confused.

Am I missing something? What could cause a the truck to shake at high rmp - really feels like something is not balanced. It is not a wobble, but a real shake that increases as the rmp is increased. And only happen when the SM420 is in the truck.

I need to figure this out before I put the transmission back in -- again!

TheBossHog · 06-27-08, 09:02 PM

Check your motor mounts

Josie'sLandCruiser · 06-27-08, 09:48 PM

Hi All:

I dunno . . . . something up with the clutch assembly?

Good luck!

Alan

flaminbandit · 06-27-08, 10:03 PM

tailshaft outta balance or bent ?

e rock · 06-27-08, 10:16 PM

Behind a SBC the 420's input shaft is long enough to go all the way into the pilot bushing right?

I occasionally get a weird vibration, and I imagine that I didn't leave enough of the pilot bushing sticking out, but this is on an F motor, so it's probably not the same issue for you. Mine has gone away now, so I'm delaying pulling it all out again just to check that.

brooklyn · 06-28-08, 11:06 AM

Okay, going out to take a look at this in the daylight and see what I can determine.

One question, if the clutch is depressed does this remove the transmission from the possible list of issues? Or is the input shaft still spinning something in the SM420?

I am trying to isolate what I could have done, resurfaced the flywheel, new clutch (full kit/pilot bearing). I think it was all aligned correctly.

I am getting a new clutch kit - sending the first one back, just in case.

e rock · 06-28-08, 01:19 PM

If the tranny is in gear, and you aren't moving, nothing in the tranny is spinning.

Did the pilot bushing fit snugly over the end of the tranny's input shaft?

I'm starting to think that BossHog might be onto something with the motor mount idea. With the 420 on the back, it drastically changes the balance of the whole assembly. In fact, I still need to build a rear crossmember to support the 420 because on bumpy roads the motor can tilt up enough (due to the extra weight behind the mounts) to make the fan blade hit the shroud.

FJ40Jim · 06-28-08, 06:59 PM

Any idea what crank is in the engine?
Or what flywheel is installed?

brooklyn · 08-10-08, 05:50 PM

Thanks for all the suggestions on this one.

It turns out that the guy who worked on the flywheel had a new "tech" do the job and it was not done correctly. He apologized for his error, but said it shouldn't have caused the issues I was having. I think he was worried I would want some sort of refund or something.

Bottom line the flywheel is back in the truck and there is no more shuddering in the truck. The kick in the ass is that I decided to have the flywheel done b/c I read it is a good idea when replacing a clutch and then the "good idea" drove me crazy for weeks.

kyot4x4 · 08-10-08, 07:48 PM

well at least you found the problem. That sucks when you get something done and its not correct.

TOBASH · 08-10-08, 08:01 PM

Awesome that you posted a follow-up. Thanks.

They should have done a rudimentary balance after resurfacing the flywheel. I am a bit put off that they didn't check.

I would not go back there. It is bull when someone says it was a new tech at the helm. When someone says that, all I hear is "I screwed up and I don't want to get yelled at so let me try to get out of it with a sympathy story."

If you get an engine failure, it is because he screwed up your engine bearings and seals etc...

This went on for WEEKS. You may have done damage. I would send a letter to him detailing the problem and I would also demand a full refund.

Not trying to stir up $hit here. Just trying to make sure you wind up OK after an unbalanced drive train was attacking your motor and tranny for a long time.

Best,

T

P.S. I live in Brooklyn. Please let me know where this place is so I can avoid it.