Read many drive line post and info on web,but still confused.

My engine/tko is minus 5.5 degrees and my differential is plus 5.5 degrees. The drive shaft looks like zero degrees maybe minus 1 degree.
Should I adjust the differential to make it plus 4.5 or so?

Read many drive line post and info on web,but still confused.

My engine/tko is minus 5.5 degrees and my differential is plus 5.5 degrees. The drive shaft looks like zero degrees maybe minus 1 degree.
Should I adjust the differential to make it plus 4.5 or so?


This is in a 66 Chevelle that is mainly used for street. 383 w/tko 600, 12 bolt posi with adjustable upper control arms.
Anyone care to give me some advise about this before I bolt it back together?

You want a minimum of 1/2* and a maximum of 2-4* (depending on who you talk to) working angle on all of the U-joints. You also want the differential and transmission to be at same angle, which it sounds like you already have.

If I read you right your drive shaft is pretty level? Sounds like the car has been lowered? If the car has been lowered you may need to raise the transmission tail to reduce the operating angles down.

Car has not been lowered. I have a 3/8" shim under the trans mount now. I think that is all I can go. Very close to tunnel.
By my measurements I have 5.5-1-1.5= about 4-4.5
Is this correct?

With a 3/8" spacer... if the dimensions work out similarly (see my measurements here: http://www.chevelles.com/forums/showthread.php?t=257194)... you raised things about 1.5" at the differential. That is around 1.5* of operating angle reduction as well. If the math is close to the same ;-)

Your front working angle is 5.5* transmission - 0-1* driveshaft (presuming driveshaft is slightly higher in front than back) for 4.5-5.5* working angle. This is a bit more than you want. If you cannot raise the transmission can you lower the engine?

Have you checked the rear ride height against factory spec to see if it has dropped over the years?

With a 3/8" spacer... if the dimensions work out similarly (see my measurements here: http://www.chevelles.com/forums/showthread.php?t=257194)... you raised things about 1.5" at the differential. That is around 1.5* of operating angle reduction as well. If the math is close to the same ;-)

Your front working angle is 5.5* transmission - 0-1* driveshaft (presuming driveshaft is slightly higher in front than back) for 4.5-5.5* working angle. This is a bit more than you want. If you cannot raise the transmission can you lower the engine?

Have you checked the rear ride height against factory spec to see if it has dropped over the years?

I do have big block springs in the front with a small block 383. I like the look.
Could that be making the difference? And should I be concerned with this set up as it is or not worry so much about it?

That will not affect the relationship between motor/transmission and frame that sets up the driveline angles.

ok, I wasn't sure abuot that. Do I need to worry about my current set up as it is then?

Well...

Your transmission and differential angles are right in there relative to each other but your operating angles are on the high side.

Conventional wisdom would also say that you want those operating angles optimized around normal ride height.

But my measurements have shown that there can be a +/- 4* swing of the driveshaft as the rear suspension moves through it's full range. So there may be an alternate wisdom that would say optimize those operating angles around the mid-point of suspension movement.

Since you have good alignment between transmission and differential you can probably run it that way and it will probably be fine. The U-joints may wear out in 50k miles instead of 100k miles but if you drive as much as most of us you will never notice ;-)

Well...

Your transmission and differential angles are right in there relative to each other but your operating angles are on the high side.

Conventional wisdom would also say that you want those operating angles optimized around normal ride height.

But my measurements have shown that there can be a +/- 4* swing of the driveshaft as the rear suspension moves through it's full range. So there may be an alternate wisdom that would say optimize those operating angles around the mid-point of suspension movement.

Since you have good alignment between transmission and differential you can probably run it that way and it will probably be fine. The U-joints may wear out in 50k miles instead of 100k miles but if you drive as much as most of us you will never notice ;-)

Thanks for all the info. I guess I will put it back together and run it for now. I will check for wheel hop. I have been reading about cures for wheel hop. If I remember correctly I read " get the rear lower control arms level with the ground and use relocating brakets to do this" like these

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=8053863760

My lowers are at about a 6* angle (up toward the front of car)
How would these help?
Am I missing something?

The relocation brackets of course change the angle of the lower control arms. This in turn reduces the length of the SVSA - Side Virtual Swing Arm. This is where the axle pivots around as it goes up and down as though that was where it was mounted. When the SVSA is shortened the rear end windup has more leverage against the chassis. This can lift the rear of the car and also push the rear axle down more strongly. Which increases rear traction.

Note that the relocation brackets make the rear lower control arms anything BUT parallel to the ground. I would not even try and get them parallel with relocation brackets in there.