Adjustable Rear Control Arms, GM A Body

[pggto]

Hello, looking for some advise. I have a 70 GTO convertible that has some drive line vibration issues. I had the drive line angle checked and was told the angle is not what it should be. Just wondering if a set of upper adjustable rear control arms would help solve this problem by changing the pinion angle. The suspension on the car is stock. Would this be a good route to go to correct the angle? What would be a good control arm to use? Thanks.

[WildCherry66]

Are the engine, transmission, transmission crossmember, and rear end all stock? Have you checked the condition of the 8 rear control arm rubber bushings? If the rubber is badly worn out (as ours was), the suspension points are not held where they should be and could cause the vibration. Also check the condition of the driveshaft front slip yoke and mated transmission tail housing bushing and the driveshaft U-joints for wear.

[pggto]

The car is not stock engine wise. All the suspension components have been replaced. New engine and trans mounts as well. Over the years I have replaced or changed just about everything and that damn vibration remains.

[killer69]

check the drive shaft!!!
if it is stock replace it. we have eliminated a few vibration issues with Mark Williams Drive shafts.

[pggto]

check the drive shaft!!!
if it is stock replace it. we have eliminated a few vibration issues with Mark Williams Drive shafts.

Thanks for reply,
The driveshaft has already been replaced with new U joints.

[UMI Tech]

Check the trailing arms to make sure they are 22" lower and 10-1/4" upper respectively.

We use Tremec toolbox or Spicer tool kit on smart phones to determine if driveline angle is within range.

You can use UMI uppers to tweak the pinion angle a little bit. Oftentimes, one half degree is enough to knock the harmonic out of it.

ramey

[pggto]

Check the trailing arms to make sure they are 22" lower and 10-1/4" upper respectively.

We use Tremec toolbox or Spicer tool kit on smart phones to determine if driveline angle is within range.

You can use UMI uppers to tweak the pinion angle a little bit. Oftentimes, one half degree is enough to knock the harmonic out of it.

ramey

The trailing arms are still the original factory ones. I was looking at your control arms on the UMI website, whats the difference between the poly bushing and the roto joint functionally? Thanks

[BMR Sales]

What is your Driveline Angle?

[pggto]

What is your Driveline Angle?

I don't remember what the numbers are.

[andrewb70]

I don't remember what the numbers are.

That's kind of important...

Has the car been lowered in the rear?

Andrew

[pggto]

That's kind of important...

Has the car been lowered in the rear?

Andrew

The suspension is stock and has been gone through. I currently have the rear end out so I figured it might be a good time to replace the upper control arms if that would help my vibration. I don't remember what the numbers were, I'll message the guy that measured it and see if he remembers.

[WildCherry66]

Check out Ridetech rear adjustable uppers through Matt's Classic Bowties too. That's what I ended up going with along with rebuilt stock lower arms and rubber bushings.

[pggto]

What is your Driveline Angle?

The guy seems to remember it being 4 degrees, but that was 2 yrs ago. What should the angle be? Thanks

[UMI Tech]

The poly bushings are firmer than rubber and are used for mainly street applications. The Roto-Joint is a way to get rod end performance with quietness. There is still some firmness but they make for a high performance street car situation. We also use them when we want smooth articulation for auto-x and road race.

For driveline angle, the quick and dirty number is around 2 degrees between driveshaft and pinion. The more complicated number is to know the transmission angle and make the pinion equal but opposite. You can also use the idea that the driveline should be straight at ride height but never completely straight (i.e. minimize driveline angle to zero, almost). The reality is the system is dynamic and even if you go totally zero, it isn't there for long. We use total zero in oval track quite a bit to maximize power transfer...

ramey

[BMR Sales]

The guy seems to remember it being 4 degrees, but that was 2 yrs ago. What should the angle be? Thanks

Should be about 2, but since your measurement is memory of 2 years ago, you need to find out for certain where it's at now

[pggto]

I bought some adjustable control arms. What is the center to center distance supposed to be for the bolt holes on a 68-72 GM A body? 10 1/4? The arms came preset according to the instructions but since the jamb nuts were loose I need to check it before I install them so I know my starting point. Thanks

[raustinss]

See post #6

[E.rodz]

everyone makes an adjustable uppers to tweak it into place.no need to reinvent the wheel for this aplication. UMI. makes a great adjustable upper and a viable choice. first get some #'s so you not just guessing. and make sure you do it on a level surface too! and by the way if you would make an adjustable lowers you won't have the sway bar mounts on it anymore.