[johnta1]

Take the driveshaft out and have someone tow you with a chain at 60 MPH and see if it vibrates?



If it ran good when you 1st put the other trans in, what changed now that it is vibrating again?

[pontiacmark]

Johnta1, it must have been wishful thinking after I spent the money.

I just measured the wheelbase, 112" on the dot driver's side. It was 111 1/4" passenger side! Triple checked the numbers. Maybe a trip to the frame shop is in order.

[leeklm]

Check your front end alignment settings first. If your caster setting is off, it will impact wheel base length if measured from the front hub. Caster setting is usually offset in circle track racing, which will impact wheelbase a fair amount.

Sent from my XT1585 using Tapatalk

[TedRamAirII]

I would check the lower arms and bushings first. Maybe measure from a spot on the frame to the lower ball joint grease fitting. Those lower arms take a lot of abuse.

[lust4speed]

A good check is to find the centerline on your front cross member and mark it. Then take a triangular measurement to a point on each end of the rear axle. It could be something like the shock mount bolt tip. These old frames and suspension pieces aren't all that accurate, but this measurement should be within a 1/4" for the vehicle to track straight. If this measurement is OK, then you can pretty well figure that the variation is in the front.

A car can track straight if the front wheels are each separately in alignment. An old drag racing trick was to offset the front wheels fore and aft from each other so that they would have a longer footprint in the staging beams. An extra 2" on leaving was a pretty good advantage on a close race. This was done on cars hitting over 170 in quarter so it definitely didn't hurt straight line stability. I would suspect all the negative results from the offset would show up on cornering.

[pontiacmark]

Originally Posted by TedRamAirII

I would check the lower arms and bushings first. Maybe measure from a spot on the frame to the lower ball joint grease fitting. Those lower arms take a lot of abuse.

The front end only has about 3-4k miles on all components although I do suspect a poor alignment from shop.

All the rear bushings have about 1000 miles on them. Center to center on the arms is correct.

[pontiacmark]

Originally Posted by lust4speed

A good check is to find the centerline on your front cross member and mark it. Then take a triangular measurement to a point on each end of the rear axle. It could be something like the shock mount bolt tip. These old frames and suspension pieces aren't all that accurate, but this measurement should be within a 1/4" for the vehicle to track straight. If this measurement is OK, then you can pretty well figure that the variation is in the front.
.
A car can track straight if the front wheels are each separately in alignment. An old drag racing trick was to offset the front wheels fore and aft from each other so that they would have a longer footprint in the staging beams. An extra 2" on leaving was a pretty good advantage on a close race. This was done on cars hitting over 170 in quarter so it definitely didn't hurt straight line stability. I would suspect all the negative results from the offset would show up on cornering.

Thanks, that is straightforward enough

[HWYSTR455]

Subscribing for personal learning experience...

When you measured the wheelbase, you went center to center on the axle/hubs? Can you determine if the difference is in the rear or front? Maybe by measuring in the rear?

.

[pontiacmark]

At the Pontiac US Nationals today. I have an offer to use a friend's lift so I can take a lot of measurements. It was also suggested to check if the axle tube is twisted in the housing or bent. I don't think it is bent because I had no trouble putting the axles in.

[wheneaglesfly]

Originally Posted by pontiacmark

At the Pontiac US Nationals today. I have an offer to use a friend's lift so I can take a lot of measurements. It was also suggested to check if the axle tube is twisted in the housing or bent. I don't think it is bent because I had no trouble putting the axles in.

I have ran into bent axle housings.
Pretty common & most are not aware.
Musclecars were driven hard.
Ran over parking curbs,
Hit a curb going sideways around a corner burning Rubber WOT back in the 1970's & 1980's.
True stories long gone or disclosed from all.

I was able to save a 1964 Pontiac GTO Axle housing that had the tubes moved 1/4" forward on one side & opposite side pulled back 3/16".
I used a 20 ton hydraulic jack, chains, & a 1" inch thick steel base plate fixture STICK WELDED With 1/2 " inch wide weld bead Fillets from a Boiler maker I knew back in 2003.
A convertible 64 GTO. Numbers matching.
Got it done. No easy feat.
A friend made me 1.00 " ID Puck discs for the housing ends from A-11 Tool steel at his work machine shop.
And he snagged the 1.000" Hydraulic rod, 6-feet of it.
Dial indicated all.
Rechecked.
Rechecked.
Pressed back to OEM Perfection & likely better.
I was not on forums then.
Nor owned a digital camera.
Sorry no photos, but its all in my head - memory How & got it done with a Machinists friend's help.

["QUICK-SILVER"]

Just got to share this here. At least it's a GM story.
40 year old vibration cured.
My 77 chevy van had bad vibrations since new. After changing everything on it, except the body (and they did blame it some), GM tech determined it was drive train angles. These old vans have the engine set to the passengers side so there's room for the drivers feet/pedals. So it has a left/right misalignment, of the drive shaft, instead of up and down. So no cure for it.
Vibration only happened in high gear at cruising speeds. Depending on engine load the vibration would fade in and out. There had to be at least some load on the engine for the vibration to happen. Nothing coasting, nothing in neutral, couldn't push it in neutral at speed and rev the engine trying to replicate the vibration.
After all these years I finally had to replace the spray pump in the quadrajet. Thought might as well go ahead and clean it out.
Underneath one of the primary jets was a piece of casting slag. Not enough to stop it up but just enough to cause a fuel restriction.

So, under the right conditions, cruising, it had four strong cylinders and four not so strong. Just enough to set some strange harmonics in motion. Which all added up to; being in high gear with engine rpm same as the odd angle drive shaft. That combination could flat get the walls of a van amplifying everything.

It's finally cured. Can't even feel the drive shaft.

That's my story
Clay

[TedRamAirII]

Originally Posted by "QUICK-SILVER"

Just got to share this here. At least it's a GM story.
40 year old vibration cured.
My 77 chevy van had bad vibrations since new. After changing everything on it, except the body (and they did blame it some), GM tech determined it was drive train angles. These old vans have the engine set to the passengers side so there's room for the drivers feet/pedals. So it has a left/right misalignment, of the drive shaft, instead of up and down. So no cure for it.
Vibration only happened in high gear at cruising speeds. Depending on engine load the vibration would fade in and out. There had to be at least some load on the engine for the vibration to happen. Nothing coasting, nothing in neutral, couldn't push it in neutral at speed and rev the engine trying to replicate the vibration.
After all these years I finally had to replace the spray pump in the quadrajet. Thought might as well go ahead and clean it out.
Underneath one of the primary jets was a piece of casting slag. Not enough to stop it up but just enough to cause a fuel restriction.

So, under the right conditions, cruising, it had four strong cylinders and four not so strong. Just enough to set some strange harmonics in motion. Which all added up to; being in high gear with engine rpm same as the odd angle drive shaft. That combination could flat get the walls of a van amplifying everything.

It's finally cured. Can't even feel the drive shaft.

That's my story
Clay

Wow, good catch. Who would have thought? Good for you to find that. So GM says no cure? they just didnt know what the sickness was.

[blueghoast]

X2 on the pressure plate.

GT.