Engine buzz/vibration 2800 to 3200 rpm

[Chris_67SS]

I've been chasing this vibration problem for a while, I need some input. The vibration is bad enough to make the interior buzz between 2800 and 3200 rpm in 3rd and 4th gear only, slightly worse with the torque converter locked, over that rpm in either gear is smooth. About the car.....67 impala SS, 350 one piece seal 4 bolt block with Edelbrock top end kit, hooker super comp long tube and Pypes 2.5" x pipe exhaust, 700R4, aluminum 1350 u-joint driveshaft, 12 bolt posi with c-clip eliminators. Global West suspension, C5 brakes and other stuff.....any ideas?

[andrewb70]

I've been chasing this vibration problem for a while, I need some input. The vibration is bad enough to make the interior buzz between 2800 and 3200 rpm in 3rd and 4th gear only, slightly worse with the torque converter locked, over that rpm in either gear is smooth. About the car.....67 impala SS, 350 one piece seal 4 bolt block with Edelbrock top end kit, hooker super comp long tube and Pypes 2.5" x pipe exhaust, 700R4, aluminum 1350 u-joint driveshaft, 12 bolt posi with c-clip eliminators. Global West suspension, C5 brakes and other stuff.....any ideas?

I would start by measuring your front and rear u-joint operating angles.

Andrew

[Chris_67SS]

I forgot to mention that if I drop the trans into neutral at the vibration rpm and coast the vibration goes away, like its an engine balance or exhaust resonance problem. But stopped and in neutral I can bring the rpm up to usual vibration rpm and all is smooth. I can drive the car 150+ and all is smooth....weird, huh? I'll check the ds angles again tonite anyway.

[WallaceMFG]

I had a similar issue with my Chevelle, it turns out the pinion yoke was junk and letting the drive shaft flop around and shake. At different speeds it would go away, and it would sometimes go away in neutral. It's most likely a driveline issue like Andrew suggested based on the symptoms.

[Chris_67SS]

Yup, ds angles are off slightly. I guess its not set and forget, last adjustment was several years ago. Engine is down 3.1 degrees and diff yoke is up 3.0 degrees, ds is rear down 0.2 degrees. Front ds runout is 0.004" rear is 0.002". The yoke was replaced about a year ago while chasing the vibration. I'll make some adjustments and road test.
Thanks for the input, I'll post results later

[carbuff]

I've read a bunch of different pieces of information on this, as I'm chasing a small vibe myself. Those numbers sound like they are pretty close if I understand them correctly. Effectively you have the transmission output and pinion yoke parallel to each other, and your working angles of the u-joints should be pretty close also.

The fact that you say it's present in 3rd or 4th at the same RPM implies that is it not speed dependent? In other words, it might be at 50mph in 3rd gear, shift to 4th at 50mph and it's not still there?

[Chris_67SS]

DS angle is now set, engine 3.1 dn, diff yoke 3.1 up, haven't road tested yet. The vibration seems to be rpm dependent, I can drive the car at 55 in third, vibe is there, then go to 4th, vibe gone, starts again about 80 then gone over 90. Smooth 80+ in third gear.
If is was an engine balance problem, I would expect the vibration to get worse as rpm increased

[andrewb70]

DS angle is now set, engine 3.1 dn, diff yoke 3.1 up, haven't road tested yet. The vibration seems to be rpm dependent, I can drive the car at 55 in third, vibe is there, then go to 4th, vibe gone, starts again about 80 then gone over 90. Smooth 80+ in third gear.
If is was an engine balance problem, I would expect the vibration to get worse as rpm increased

What's the angle of the driveshaft? All three must be measured at the same time.

Andrew

[Chris_67SS]

oops, I never checked that! u-joint working angle 2.4 degrees

[Chris_67SS]

Ok, I shimmed the trans up 0.20" to reduce the u-joint working angle. Now engine is 2.5 degrees down and diff yoke is 2.5 degrees up. U-joint work angle is now 2.2 degrees. Haven't road tested yet

[Chris_67SS]

Just finished road test...no change, vibe still there. In an earlier post I stated that the vibe was between 80 and 90 mph, that is incorrect. The vibe is 80 to 100 mph, smooth to 150

[Zanie]

Chris did you ever find this vibration? I have an 89 GMC dually that I chased a vibration for over 10 years. 454 T400 4.10 rear.
I bought the truck from my buddy who was the second owner and he chased the vibe the entire time he had it.
We both messed with the driveshaft on several occasions, changed the position of the torque converter, changed the harmonic balancer......nothing worked.
After 65 MPH the damn thing would rattle the change in the map pocket, it really sucked. but I learned to live with it.

10 years and 20,000 miles into owning it and fighting the vibration the T400 trans took a crap.
I had my trans guy fix it. He off handedly says: "somebody was in that trans before, and installed the light duty center support. I put the truck one in there for ya."
I thought nothing of it.
Next day I'm on the highway, I look down and I'm doing 75 MPH, and the thing was as smooth as silk!!!!
I never would have guessed the transmission causing the vibration. (the trans always shifted correctly and towed my 9,000 lb boat without issue)

I know this is an old post, but if somebody searches vibrations in the future...