Tremec app & O/D Trans with Hotchkis Springs

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RogerRamRod

RogerRamRod

The Older I Get, The Faster I Was
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Let’s see if I can make this not too long
I put a 42RH transmission in while building my project. I have Hotchkis springs in the rear, and currently have them on the factory hangers. The driveshaft runs “uphill” from the transmission to the differential, A little over 1°.
Using the TREMEC app, I can’t get myself in the green on the first angle ((trans to Driveshaft). I have spacers under the transmission mount to push it up as far as I can, anymore and I’m hitting the floor. I am at 3.3° here. (guess I should have made more clearance when I was banging sheet-metal)
The driveshaft to differential angle is in the green at 2.8, and the overall operating angle is in the green at .5
The differential is currently not parallel, (or equal but opposite) the transmission, but if I point it up more, it will make the first angle even further out.
I think I’m fine with that part, because my understanding is that a lot of people point the differential down 2° from the transmission anyway to account for axle wrap, though this will primarily be a street car.
At a 3.3° angle, do y’all think it’s close enough to send it, or am I asking for problems?
 
I think 2.5 degrees down is MAX and should not be equal too or more than Zero (i.e. pointed up). This is probably why the Tremec App is failing you. So trans needs to go up, which you say you can't do any more, so can the motor go down? Like is there a shim under the mounts? I know some people shim the motor up to clear headers, PS, or compensate for sacked mounts. If not your back to getting the trans end up somehow.

But, what is the parallel relation between transmission center line and pinion center line?

Also, are you measuring on a known parallel to the output shaft location on the trans?
 
I have the 42rh in 72 dart and driveline goes down don't know what is different in yours what car are u working on?
 
I knew somebody was going to say lower the engine. I do indeed have quarter inch spacers for the headers to clear the steering box
68 Dart.
For the engine/trans I used a foot-long straight edge on the oil pan rail next to the bolts because I got the same reading on both sides. I couldn’t hold the phone well enough to consistently get the same numbers on the crank pulley or transmission shaft.
Here’s the readings I just got
Engine/Trans 2.2° down
Driveshaft 1.1° up = angle one, 3.3
Differential 1.8° down = angle two, 2.9

C5BF00B6-FE93-4207-B960-C17A82B5F32E.png
 
The diff is what I would call up, but it is considered down by the app, I guess because the phone/ measuring device is tilted the same way. Rather than 1° Difference, it is less than that at .4
 
Here’s what I’ve got,
BD3D9D30-770B-4E10-AE02-F01C522E24E5.jpeg


Im gonna try moving the diff from 1.8, to 1.2. As per cudafacthack, that will be 1 less than the engine/trans. That will make the driveshaft less uphill, but I’m not a mathematician, so by how much, who knows. That will also decrease angle one, then I’ll see where I’m at
 
I don't have an overdrive trans but when I installed my Hotchkis leaf springs, including the front hangers that raise the front mounting point of the springs up, my diff angle was too far up. I had to install wedges between the leaves and axle spring perches to get the driveshaft angles back to equal/opposite on each end (rotated the axle housing so the pinion was pointed more downward).

This stuff can sure be confusing so I may be off track but from looking at your drawing I think putting 4-degree wedges under the leaves would get you much closer to where you need to be. Having the driveshaft-pinion angle pointed up like that is bad news for a leaf spring car and the Hotchkis springs aren't very rigid in terms of twisting into an S on a hard launch so you need plenty of downward angle at rest to keep the axle from winding up too far.
 
My car will plenty low without the dropped front hangers. With the dropped hangers, the pinion was pointed why too much upward.

Even with the stock hangers I added wedge to get it set right.
 
autoxcuda said:
My car will plenty low without the dropped front hangers. With the dropped hangers, the pinion was pointed why too much upward.

Even with the stock hangers I added wedge to get it set right.
Click to expand...

Not to hijack the thread but... I've considered putting the stock hangers back in myself but supposedly the raised ones improve the rear roll center, or something to do with geometry? I have adjustable shackles I use to fine-tune the rear ride height which also of course affects pinion angle but to a much lower degree since the distance to the axle centerline is so much farther than from axle to front hanger.
 
MopaR&D said:
Not to hijack the thread but... I've considered putting the stock hangers back in myself but supposedly the raised ones improve the rear roll center, or something to do with geometry? I have adjustable shackles I use to fine-tune the rear ride height which also of course affects pinion angle but to a much lower degree since the distance to the axle centerline is so much farther than from axle to front hanger.
Click to expand...

Yea, that makes sense in theory. But I would have had to put multiple wedges in there to get the pinon angle right. And most of all it was just too low to drive. Even without it, mine's on the brink of too low.

RCVD2_zpsocdfwqeg.jpg
 
Thanks for keeping the info coming. I fiddled with it & dropped the front of the engine between 1/16 & 1/8th. That made the tail of the trans pivot up slightly making it too close to the floor for much spacer under its mount. Actually touching close.
Im going back out of town for family stuff, so I’m off the case for a week +.
I’ll try to remember to post back once I get back on it.
 
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