Engine and Drivetrain angles

[Tonker1]

I've taken apart the shed in back of my garage, moved the car back and acquired a hoist for the weekend so I can replace the engine mounts. Working on the concept of do it once do it right, I have a couple of questions. If it matters, I have a 73 Chall with a 340 and 489 case 8 3/4" diff.
1. What is the ideal angle of downwards tilt for the engine/ upwards tilt for the diff?
2. Obviously the engine and diff need to have the same angle, if the correct angle can not be achieved on engine, how much deviation from the ideal angle of tilt is acceptable?

I've read around and websites seem to universally suggest three degrees down on the engine and three degrees up on the diff, but I confirm that applies to dodge small blocks as well.

Thanks in advance.

[72cudamaan]

You're gonna want the pinion angle down. It will want to twist upward when you put a load on the driveline.
So both ends should end up pointing down towards each other as in the first picture.

[Tonker1]

You're gonna want the pinion angle down. It will want to twist upward when you put a load on the driveline.
So both ends should end up pointing down towards each other as in the first picture.

Would that put a lot of stress on the rear universal joint?

Sorry for the late reply, someone my block is redeveloping and they put the head of digger through the internet and waterlines, so I've only been able to check in with the internet on my phone occasionally.

[Chryco Psycho]

the Universal will roll with the angle but it is designed to do that .

[ToxicWolf]

Don't mean to jump in here, but I just ordered a snubber for my pinion to deal with the roll. Just wanted to recommend that people check for it. There wasn't one on my Challenger and I think having one is important, though not absolutely required.   

[1970GranCoupeConvert]

Regarding the pinion angle it depends on your application (what you are planning to do with the car).

If you are drag racing then the top picture is what you want.

If you plan on cruising on the freeway/ around town mostly then you REALLY WANT to have the driveline operating angles to cancel out and in phase like in the second picture.

In other words the transmission yolk will be pointed down toward the pinion and pinion will be pointed up (toward the radiator cap) ...and... both of these angles should be as close as possible so that the universal joints cancel out the vibration at cruising speed (most important with low rear gears).

ALSO...the angular difference between the transmission and driveshaft angle and the angular difference between the driveshaft and the pinion angle MUST BE less than 3 degrees with a common load in the car (half tank of fuel and driver).


Watch this video and it proves why you want the angles aligned like the second picture:

Drive shaft velocity

Watch this video to see how to measure the drive line working angle:

Measuring Driveline Operating Angles

Go and buy a $40.00 digital angle meter from Harbor Freight:

[Tonker1]

Don't mean to jump in here, but I just ordered a snubber for my pinion to deal with the roll. Just wanted to recommend that people check for it. There wasn't one on my Challenger and I think having one is important, though not absolutely required.   

I never thought to check for that, I'll take a look next time I'm under the car.

Regarding the pinion angle it depends on your application (what you are planning to do with the car).

If you are drag racing then the top picture is what you want.

If you plan on cruising on the freeway/ around town mostly then you REALLY WANT to have the driveline operating angles to cancel out and in phase like in the second picture.

In other words the transmission yolk will be pointed down toward the pinion and pinion will be pointed up (toward the radiator cap) ...and... both of these angles should be as close as possible so that the universal joints cancel out the vibration at cruising speed (most important with low rear gears).

ALSO...the angular difference between the transmission and driveshaft angle and the angular difference between the driveshaft and the pinion angle MUST BE less than 3 degrees with a common load in the car (half tank of fuel and driver).


Watch this video and it proves why you want the angles aligned like the second picture:

Drive shaft velocity

Watch this video to see how to measure the drive line working angle:

Measuring Driveline Operating Angles


Go and buy a $40.00 digital angle meter from Harbor Freight:

Thanks for the video links. Now I just have to wait for my drive shaft to arrive and measure everything up.

[Tonker1]

I've had the drive line angles for about a month now and I've been taking sometime to think about options before I replied.

With the car sitting on flat ground and the transmission up as high as possible the drive line angles are as shown in image 1

With these drive line angles the first point of contact between the transmission and and car is the over transmission chassis rail as shown in image 2,3,4,5

If the transmission where contacting the floor pan, I would not be as concerned as I could cut up the floor and fix the drive line angle from there.
The problem is the engine is leaning so far back and the trans is hitting the chassis.


Below is my logic for why the trans is hitting the above trans chassis rail, when it does not on some many other e-body TKO 600 installations.  Any other suggestions would be much appreciated?
At some stage in the cars life the floor pan has been replaced, this was done before any subframe connectors were installed. I'm thinking that when the floor pan was replaced, the internal structure of the car was not braced, so the car drooped downwards in the centre. The new pan was then welded in and the centre of the car remained bent downwards.

Last year I had some subframe connectors installed, so if the car is drooped down in the centre, then there would be some un-intended forces (potentially problematic??) being applied to the subframes.


Any other suggestions or reasoning would be much appreciated.


To see if the car is bent down in the centre I plan to take some measurements of the chassis, if anyone has any schematics, or dimensioned diagrams of how a chassis should be on a 1973 Dodge Challenger, that would be excellent.


Thanks in Advance

[1970GranCoupeConvert]

How is your engine mounted?  Can you come down on the front of the engine without the oil pan hitting the center link?  That would reduce the tilt down of the engine and trans.

[Mopar_Mudder]

On my TKO that area is machined off to gain clearance. You can't get it up to exactly where the factory would have had it but it is really close.

Don't know if you can tell in this picture:

[johns cuda shop]

Yeah, I had seen someone do that before.. I think it was a leaf spring car.I believe he still had some issues with vibration because the rear needed deg or 2 nose. down.

[Tonker1]

On my TKO that area is machined off to gain clearance. You can't get it up to exactly where the factory would have had it but it is really close.

Don't know if you can tell in this picture:

Was that machined down straight out of the box or did you do it yourself?

Yeah, I had seen someone do that before.. I think it was a leaf spring car.I believe he still had some issues with vibration because the rear needed deg or 2 nose. down.

Raising the tunnel and above trans chassis rail is looking like a more promising option. I would hate to run into an unrelated issue with the tranny somewhere down the road and have the warranty void due to a modified case.

[Mopar_Mudder]

Was that machined down straight out of the box or did you do it yourself?

It came that way, from Hurst Driveline Conversions.

If I would have known ahead of time I would have done something to get that cross member out of the way to allow more movement.

Here is the thread on how I found out mine was way to low http://www.cuda-challenger.com/cc/index.php?topic=89279.0 & http://board.moparts.org/ubbthreads/showflat.php?Number=7488649

Probably something along this line:

[dodj]

Your intake manifold is designed for your engine to have about 3* down (from level not from the d-shaft) attitude to keep the carb level. Before you do anything with the rear end, you will need to do the tunnel mod to get your engine in the 3* area. Once you do that, the rear end angle will be different. Then re-measure and determine what shim (or remove and re-weld the spring perches)you need to get about 3-4 degrees down, not up (from the driveshaft, not from level). 

[Tonker1]

It came that way, from Hurst Driveline Conversions.

If I would have known ahead of time I would have done something to get that cross member out of the way to allow more movement.

Here is the thread on how I found out mine was way to low http://www.cuda-challenger.com/cc/index.php?topic=89279.0 & http://board.moparts.org/ubbthreads/showflat.php?Number=7488649

Probably something along this line:

Cheers for the links and picutres. Did you have to remove the torsion bars when you cut the over trans chassis rail?

Your intake manifold is designed for your engine to have about 3* down (from level not from the d-shaft) attitude to keep the carb level. Before you do anything with the rear end, you will need to do the tunnel mod to get your engine in the 3* area. Once you do that, the rear end angle will be different. Then re-measure and determine what shim (or remove and re-weld the spring perches)you need to get about 3-4 degrees down, not up (from the driveshaft, not from level). 

The tunnel mod is looking like the only option to resolve the engine angle. I did the maths on how far I would have to drop the nose of the car get the engine to 3 degrees down, it was a bit under 4"!
Unfortunately the level of welding required for this sought of modification is beyond my skill. I'll have to take the car in to a shop.

Thanks in advance.