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I'm looking for suggestions to help solve a vibration problem that has cropped up. The vibration is through the steering wheel and accelerator pedal at speeds of 45-60mph (2000-2700 RPM) with the worst resonance at 55-60mph.

The vibration was first felt after replacing the T-case, but does not seem to be related. Our first thought was wheels and tires because we rotated them when we were dealing with the T-case. We balanced them and returned them to the orig. positions thinking that would sort the problem. NO CHANGE.
Then we dove into the driveline. U-joints condition and phasing was fine, pressure plate was tight, flywheel was tight, T-case was tight. NO CHANGE.
Then we replaced the rear engine mounts (front was a year old). They were tired. NO CHANGE.
Then came the front shocks, I had a NOS set that came with the truck so we swapped 'em. Rides better, but, NO CHANGE.

After all this monkeying around I started to suspect that the vibration that's manifested in the steering and accelerator was being driven by the engine alone. After a few runs to and from work and trying neutral/idle/55mph, clutch in/idle/55mph, and running the engine through the RPM range from idle to 3000rpm this seems to be the case. There has been no performance change of late and we checked the tune and compression pressure and all's fine. We also adjusted the fan belt to see if it influenced the vibes and it did not.

So, for some reason the engine has developed a new vibration that transfers VERY well through the steering and accel. linkage at the speeds the truck cruises at. So does anyone have any suggestions or ideas?

Thanks,

Andy

Hi Andy,
Sorry for the difficulty; brainstorming:
Bent rim?
Bad tie rods?
Crankshaft pilot bushing to the tranny (missing)?
Plug fouling out at high rpm?
Bent drive shaft?
Loose wheel bearing?
Fat Lady hanging on to an NDT and singing?!

Let us know what you find
Gary

What engine do you have in there?

Gary,
Of your list the following are out, it vibrates while stationary .
Bent rim?
Bad tie rods?
Bent drive shaft?
Loose wheel bearing?
Fat Lady hanging on to an NDT and singing?!

Plug fouling out at high rpm? Maybe, but performance has not degraded. We're going to have a run on the dyno today and tomorrow and see if we can uncover anything. It would be nice to get a scope on the waterproof ign.
Crankshaft pilot bushing to the tranny (missing)? Doubtful, the clutch position does not have any effect on the vibe.

just me,
It has a stock 230, 4.89 gears, 36.3" tall tires.

The vibe is relatively high frequency, it's more of a "buzz" than a "shake".

Andy

Easy check. Remove the fan and run it again. At those speeds, it isn't helping anyway! Harder to check, loose flywheel bolts. Missing dowel pins allowing misaligned bellhousing or trans. Loose damper bolt.

Plug gap too wide and spark blowing out at speed? Dwell off and not allowing coil saturation.

darn sonic resonance..... sounds like she is too advanced, dial her back a bit. if the problem was not new I would ask did you turn an oil grove in the mains and rod bearings.

just me,
We're going to pull the belt today briefly and see if there's a change. We checked the F-wheels bolts & P-plate bolts the other day. The problem is new, so I don't thing it's in the bell housing. We'll check the crank pulley hdw. today. Plugs were checked when we did the comp. test, all looked OK and were gapped to .028. The truck has a pertronix so dwell is what it is.

RMS,
The timing is at 4 deg BTDC and has not been altered recently (set well prior to the vibe).

I may actually loosen some of the engine mount bolts and allow it to find where it's "happy" and see if that has an effect. Hopefully it's nothing internal.

Keep the suggestions coming and I'll post any progress. We're on the dyno in about 2 hours.

Andy

generator bolts ?

had that on mine but it sounded like a rod knock

and id love to know what kind or power your making

Looks like I misread your post-I apologize.
Gary

Several loose floor pan bolts resulted in a buzzing sound in one of my first M37s.

vibrates when stationary would make me want to do a compression check. a very small leak between cylinders might cause this. Whenthe leak is big its obvious but when small you don't lose much power and symptoms are strange

Andy,

I would guess it would be in the engine since it happens while stationary.

I would take the top off the oil fill tube, close the fording valve to see if you have excessive blow by. A slight pressure will be felt if you hold your palm over the filler tube, but if you if you feel it pulsing hard I would guess head gasket failure. If you have a radiator pressure tester with gauge I would hook that up at the same time to see if you have excessive pressure or needle flutter there while doing the test with the fording valve closed.

Does the vibration stay at a constant or vary in pitch while raising RPMs?

Bert

Thanks for the ideas Crew!

Carter,
Floor pan bolts are tight.

Kaegi,
We did a compression test and all looked fine. Admittedly we did it dead cold, but the #'s looked typical and the spread was <15psi from the worst to the best.

**********
Edit:
In the interest of science:
Last week's Cold #'s in order: 120,110,110,110,105,110 *15psi spread*
Today Hot #'s in order: 122,115,120,118,112,120 *10psi spread*
WOT, 5 Revolutions, Good Battery (s)

**********

Carter,
No massive blow by or pressure in the rad.

Unfortunately the dyno decided to crap out today, but we did some inertia runs, power looks like it usually does, right around 50hp. The vibe is worst at 2300-2700. If you touch the engine it feels normal, but if you touch the steering shaft it's singing. Seems it has a sweet spot the matches the engine's shaking.

Between this, the dyno issue, and other unfinished projects it's going to be a busy "vacation"!

Andy

does engine have a harmonic balancer on it?