distributor

[Mart]

You're a mechanic and have probably tried this.. Get the old truck up to the speed where the vibration is at it's worst. Dip the clutch and hold it down, let the engine idle. Does it vstill vibrate? Get back up to the vibe speed and this time Dip the clutch, knock it into neutral and turn the engine off. Does it still vibrate?

If it is still vibrating in either scenario it's driveline. In the first scnario the clutch plate is still spinning in the second scenario it is stopped. A difference in vibration between each scenario could help pinpoint the problem.

If the vibration stops, what happens if you hit the same rev band in 2nd? Does it vibrate at higher revs in 2nd?

If it vibrates at the same revs in 2nd and top then it is indeed something forward of the gearbox. (Engine, clutch, etc.)

If the vibration is coming from the engine it should do it when revving in neutral at the critical rev band.

As my learned friend Martin says above, 50mph isn't high revs.

Do some testing, tell us what you find. If you can hook a rev counter up, that would be helpful.

Forgot to say, nice looking truck, by the way.

Mart.

 

[trucker 46]

Thanks everybody, at 50mph sounds very busy and feels like that is all it would do. Didn't want to push it any higher. Unless it has low gears in diff. Can't find any numbers on diff. I guess will take the engine out this winter and take it apart, see what I can find. Originally I had this engine built, 5 years ago by so called flathead experts? This year is the first time I ran the engine after frame off restoration. By the way I tried running engine without both belts and didn't make any difference. And I tried all what good man Mart mentioned. Those were the first things I did.
Sid

 

[Seth Swoboda]

It may well be that the crank/rods/pistons are way out of balance. A flathead engine should be a smooth running engine. What you describe sure sounds like there is an internal balance issue and I agree that a harmonic balancer is not going to correct that. It is normal used to smooth out harmonics in an already balanced engine.

My thoughts exactly! In all of the three flathead V8 rebuilds I have done I had the entire rotating assembly balanced. I have no engine vibrations at any speed. My engines run like a sewing machine.

Please don't install an overhead valve V8. You have invested the time and money into an apparent rebuild. What is the situation on balancing the rotating assembly?

 

[rotorwrench]

Flathead crankshafts generally don't need to be balanced at overhaul but now days you never no what kind of pistons you are going to get unless you have recent experience with a particular brand. If you weigh a set, you can find all sorts of differences on some manufacturers stuff. They have to be weighed with a gram scale too. The crank might be OK but the piston weights may be way off. Con rods can be off too but usually not as much as some pistons.

If a guy is out to do a good balance job you have to do the whole she-bang as mentioned previously. If that thing has a stump puller rear axle, I'd change it to 3.78:1 or so. At least that way you could go a decent speed without the high revs. Get it down to 2500 rpm at road speed and your eye teeth will be better off. By the way, that's a damn fine old Merc truck.

 

[scooder]

Sid,
Stock rear gear for these year pickups was 3.78:1 option was 4.11:1 this would still have you below 2500 rpm, just. Even with 4.55:1 area gears your only at 2700 ish rpm. To get 3500 @50 mph you'd be looking at 5.9:1!! So you see, if it feels " very busy, and feels like all it would do" at 50 mph (about 2200 rpm with stock rear gear) something is wrong somewhere, at this rpm it should feel like silk.
You say you've tried all the stuff my bud Mart mentioned, we've pretty much ruled out everything but the engine.
Is it worth talking to the "so called experts" ? I know it's been five years, but some folk stand behind there work, gotta at least be worth a call.
Do please keep us posted on what you find, and don't put a monkey motion in there. A stock Ford V8 car or pickup from the 40's is a very capable daily driver and keeps up with modern traffic just fine. Sure it ain't as relaxed as a modern 76 speed transmission with all its power this and rubber cushioned that, that sits at idle in 76th gear on the freeway, but he'll sit at 70 if you want to without hurting it. All depends on what your used to, with the 3.78:1 at 70 your pulling just shy of 3200 rpm. If your not comfy with that for whatever reason, stay off the interstate and have an adventure. Or fit some sort of overdrive.
Martin.
Like the pickup same colour as my pickup, different lipstick though.

 

[trucker 46]

Martin don't take me wrong, I do not seek hi speeds. Yah I'll be happy with 60 mph. Just have to hook up tachometer and and find what the rpm is. I don't really know, just sounds like a lot and ofcourse vibration is there regardless! But I think I would have to do the inevitable. Just get everything ballanced just like " Seth" mentioned. Good winter project
Sid

 

[scooder]

Cool beans,
Like you say, a good winter project. Be good to know what you find, keep us posted.
You'll be happy with 60 mph, that truck would go to the moo and back at 60. So you'll both be happy bunnies. All being stock the rpm would be in the 2700 rpm range.
Good luck,
Martin.