I installed a rear axle in my 1969 Malibu and checked pinion angle with only a digital cube on the pinion and driveshaft.
the pinion was -3* (pinion yoke pointing down)
the driveshaft was 4*
seeing a 7* "V" I did some investigation
I needed to measure the output shaft of the transmission, along with the driveshaft and pinion.
Tremec has a driveline angle tool for smartphone witch is helpful The engine and pinion needs to be near parallel
I found that because I had Moroso solid mounts on the big block, my output shaft was 5*
So I installed a 1/4" shim above the trans mount which brought my output shaft to 2.5*
I also installed Spohn adjustable uppers on the rear and lengthened the 10.5" (factory arm length) to 11.125"
the result is 2.6* pinion angle, 3* shaft and 2.5* output
My question is, is the machined surface for the trans pan parallel to the output shaft on a TH400? Is that surface suitable for output measurement?
What is the height of the car? Stock, lowered? The stock upper control arm length is 10.250, not 10.5. Yours are adjusted almost 1" longer than stock which more that likely has the spring in a pretty good arc. I will say stock Chevelles do not come with equal and opposite output and pinion angles and I gave up on thinking it had to be that way. Mine isn't close to equal and opposite and it doesn't vibrate at all.
I would measure off the engine oil pan rail or starter pad, not the trans pan.
the height of the car is stock. So you are thinking the rear springs have too much arc? I guess I can check that with a straight edge from the center of the spring...
or should I just back off of that 1" upper arm adjustment?
I have been checking from the oil pan rail only because that rail compared to the trans pan rail is 1.5* different
Hence my question.
Are you fighting a vibration? Why are you adjusting the pinion angle? If your car is stock height, I would set your uppers to the stock length which is 10 1/4" center to center of the mounting bolts.
Honestly I've never driven the car since I bought it three years ago!
The car is stock Height.
I just switched from 10 bolt to 12 bolt rear and the pinion angle came up in conversation so I checked it only to find the yoke was pointing to the ground by 3*.
BTW thanks for your help!!
I'm gonna check my measurements on the uppers and readjust to 1/2" over factory (10 3/4") and see where that puts me.
Honestly I've never driven the car since I bought it three years ago!
The car is stock Height. I just switched from 10 bolt to 12 bolt rear and the pinion angle came up in conversation so I checked it only to find the yoke was pointing to the ground by 3*.
BTW thanks for your help!!
I'm gonna check my measurements on the uppers and readjust to 1/2" over factory (10 3/4") and see where that puts me.
I see no need for you to go over the OEM bar's 10.25" length as you haven't raised the rear.
Start with the stock dims and see what's needed, not what you think is needed.
Too many focus on the vertical angle and forget the horizontal angle.
A small error in top bar length can set the rear skewed and cause more issues.
GM actually knew what they were doing back then.
I have a Kent-Moore Driveshaft Inclinometer and I use the u-joint cup face on the yoke for this measurement. I am not familiar with the Tremec Smart Phone one (see suggestion below) so I am not sure if you can attach / adapt easily to the u-joint cups but that spot is truly parallel to the output shaft if you can. I am sorry I don't know if the THM400 pan rail is parallel to the output shaft. If I had a THM400 in the garage I could use my inclinometer to check that against the yoke cups but I don't unfortunately. My cruiser buddies are all sticks so no luck there either.
If it is just uses the Smart Phone itself you could set a deep socket with the appropriate diameter against the u-joint cup to gain the clearance required and set the phone against the other end of the socket perhaps? If you have outside clips in your yoke you will need to temporarily remove them of course.
I agree equal and opposite is not the fix for every car. All it did on my Chevelle is make the springs curved instead of straight, pulled the driveshaft yoke further out of the tail shaft, and introduce more vibration.
habakkuk18 ,you said you have adjustable uppers.
Are the lowers the stock arms? Were the 50 year old bushings replaced in them?
Did you replace the upper housing bushings ?
There's more to this than just a fixed/one size fits all pinion angle setting.
In the pics of the pinion and trans ,how level was the base surface (floor) where you did the checking?
The car is setting at ride height on four level ramps. New energy suspension bushings. From what I see in this group 2.6* pinion down is the norm. I think my problem lies with the engine mounts being too tall causing the 4* ds angle
If you have a smart phone check out the "TREMEC" app....
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