Rear end higher than trans output...okay?

[absintheisfun]

67 camaro with a heidts subframe and a ridetech rear setup.
I have all the recommended mounts from heidts.

The ls/t56 sits perfectly without cutting the body but...the trans output angle is 4 degrees down. Not ideal, but not horrible. After squaring the rear-end (which was a pain) and getting the pinion angle 4 degrees up so they match, I noticed how close the pinion is to the floor pan, and it kinda has me spooked. Its only about 1.5-2 inches from the floor pan at ride height. Is this okay? I was measuring for a driveshaft and realized that the driveshaft will actually be going uphill. I'll get some pictures up in a bit, but is this a common issue?

To raise the trans up, I will have to modify the tunnel. With the car this close to done, I don't wanna do that if I can avoid it.

[dhutton]

You’re going to have a problem. I would install a Speedtech trans tunnel and get the transmission up. Either that or you need to raise your ride height.

Don

[absintheisfun]

Here are the pictures

https://static1.pt-content.com/images/pt/2021/03/51040947827_614e05b9e9_k-1.jpg (https://flic.kr/p/2kLjcxR)



https://static1.pt-content.com/images/pt/2021/03/51040126163_2aafa13569_k-1.jpg (https://flic.kr/p/2kLeZie)


Even if I raise the tunnel, it still looks like it will be lower than the pinion. How close should the trans be to the tunnel?

...one step forward, seventeen back...

[dontlifttoshift]

You need more clearance from the driveshaft to the tunnel. You need to get those working angles lower, because right now they are probably about 5* You can:

A. Raise the tunnel, as Don stated. It's a solid plan and would solve your problem.

B. Roll the pinion down, a lot, until your working angles are the same.

Both of those options work. Both of those options can be a lot of work. If the 4 link was set up for the pinion to be way up like that, you may end up with problems rolling it down, such as bars being too long or short and the bearings in the shocks binding through travel.

[absintheisfun]

Im accepting that ill have to cut the tunnel, however if my research is right, the trans should point down 1-3 degrees and the rear should point up 1-3 degrees. They should be the same angle ( trans 3 degrees down, rear 3 degrees up for example).

Unfortunately, I got the rear ride height right where I want it so how high do you think i will have to raise it to get it below the trans? (effectively pushing the rear down)

I was looking through some old posts and found this
https://www.pro-touring.com/threads/128580-inverted-driveline-angles?highlight=Trans+tunnel
It looks like this is a more common issue than I thought ( diff being higher than trans)

[dhutton]

Maybe a driveshaft shop CV driveshaft is an option.

Don

[dontlifttoshift]

Don't get too hung up on what angle your engine should be at. You would have to work very hard to screw that up. There are two numbers that matter. Working angle of front u joint should be the same as the working angle of the u joint.........ideally both of those numbers should be below 3. For the sake of a driveline angle discussion, you can install the engine at 37 degrees if you want.......as long as you can get the working angles under three for both U joints, and more importantly get them the same, you would be fine in that ridiculous scenario.

Working angle is the difference in angle between two adjacent driveline components. If they are sloping the same direction, subtract. If they are sloping opposite, add.

In your case your engine pointed down towards the diff 4*. If your driveshaft was level your working angle is 4*.

If your driveshaft ran downhill towards the diff at 1* your working angle would be 3*

If your driveshaft ran uphill towards the diff t 1* your working angle is 5*.......that is probably pretty close to what you are looking at right now.

So now lets measure the working angle at the diff. Driveshaft is running uphill towards the diff at 1* and the pinion is running uphill towards the driveshaft at 4* so it looks like this /\ your working angle is 5* Cool! Equal but opposite, just like you're supposed to do, on paper it works fine. But your driveshaft will hit your tunnel and those working angles are too high. In the above scenario if the pinion was lower and the driveshaft ran downhill towards the pinion 1* it would be just about perfect. So now we can see equal but opposite (or parallel pinion/engine if you prefer) works as a general rule of thumb but it is not ideal when the pinion is higher than the tail shaft.

I very rarely set a car up equal but opposite any more. My car runs with the pinion down. I don't remember the numbers, but working angles match and are under 2.5* the car is vibration free at 140 mph.

[absintheisfun]

Thanks for the insight from everyone here, yall are always helpful. I'm going to raise the shock mounts up a notch and see what it does to the rear, and start clearing out the interior components in preparation for surgery. We'll see how it goes in a couple of days/weeks.

[Lonnies Performance]

There is no problem with the rear being higher than the trans as long as the angles are similar.

You have the angles pretty good now, you can lower the pinion close to an additional degree without much issue... most do this to account for torque reaction under load.
This will give you more floor to pinion clearance. I would guess you need about 3" of suspension travel under compression from ride height.

As you get your trans closer to level (most shoot for about 1 deg down, but with a low car, level would be preferred), then you can correct the rear so it is a similar angle.

I had a similar issue with my Firebird... remember you can possibly lower the engine slightly instead of raising the trans, so look there as well.

[absintheisfun]

The mounts on the heidts are pretty specific. The ls adapter plates and mounts tuck the engine in pretty tight, and lowering it will probably run the headers into clearance issues with the steering intermediate shaft. I'm going to pull the interior back a bit and carefully cut the tunnel and see if I can get some more clearance.

This morning I set the shock lower mount blocks up one notch on the axle, and it made a big difference in the pinion/tunnel clearance. I didn't measure, but it's at least 3 inches now. If I can get the trans up an inch, I think it will work out. There is a tab on the driver side of the trans that I think I will have to shave, but other than that, the speed tech tunnel cover should work out fine.

[67-LS1]

185953I feel your pain. Mine was all back together but I wanted it lower so had to pull the interior and raise the tunnel. I raised it from the trans output through the back seat. The trans portion had already been enlarged. Now I have plenty of clearance.
Do it now and be done with it.

185951

[absintheisfun]

The pain is real, for sure! My biggest concern is the center of my dash has been modified with a significant drop down over the tunnel. I have to be extremely careful in my cuts.

So far, I've raised the rear...I don't love it, but I'll hold my judgment until I get the final wheels/ tires in. As of now, the wheel arch is at 27.75 from the ground.

Before the raise:
https://static1.pt-content.com/images/pt/2021/03/51043155943_3468d70e4d_k-1.jpg (https://flic.kr/p/2kLvvWP)

After:
https://static1.pt-content.com/images/pt/2021/03/51043155948_865bea9794_k-1.jpg (https://flic.kr/p/2kLvvWU)


But it did give me an extra 1.5 inches between the tunnel and pinion. I now have 3 inches of clearance.
https://static1.pt-content.com/images/pt/2021/03/51043876276_bd10a3b340_k-1.jpg (https://flic.kr/p/2kLzd5m)


The trans is interesting. I made a small relief opening near the firewall for an ear that stuck out and it gave me about 3/4" of raise.

https://static1.pt-content.com/images/pt/2021/03/51043964492_88f49ce323_k-1.jpg (https://flic.kr/p/2kLzEij)

It now sits with the bump stop against the tunnel. I have ordered the speedtech tunnel, so next weekend I'll cut some more. What gets me though is the ear in the picture below...it seems to serve no real structural purpose so I'm thinking of cutting it off. Another concern is how close the header collectors are to the body. I have about half an inch, and that's going to disappear quickly as I raise the trans up more.
https://static1.pt-content.com/images/pt/2021/03/51043964442_4d7cc57a15_k-1.jpg (https://flic.kr/p/2kLzEhs)

[Lonnies Performance]

The ear where you cut the floor has a bolt that holds the belle housing to the trans... it is needed.
The one to the left in your picture is extra.

Also the trans will raise probably double the amount than the headers will as everything pivots off the engine mounts.

For example, raising my trans 2" put my collectors 1" closer to the floor, but only raised about 3/8" at the firewall on a vehicle I just built.

Also there is a possibility to space the subframe away from the body to gain more floor clearance if you need another 1/4-1/2", but it does effect the front suspension geometry.

[absintheisfun]

It's the mating flange for the collector and it will hit if I go any further up with the trans. Rather than raise the body off the subframe, I would instead cut the floor. With the trans bumps top hitting the floor, the trans and rear are pretty much level after dropping the rear. I'm looking at the cv driveshaft to see if that's going to work. Also, the trans is at 2.5 deg. down with the adjustment. I'm fairly certain I'm going to leave it there.

I'll still put the trans tunnel cover in for movement clearance, and its the passenger side so it at least won't move up under throttle. I'll know more this weekend when I have some time to play with it. All I can think is that thes cars have been built thousands of times with similar problems. If they found a work around, so will I. Just frustrating to hit these roadblocks this late in the game. All filed away as an education for the next build.

[joeko23]

I believe Andrewb70, has a GTO and his rear is higher than the trans. He has a CV driveshaft from the driveshaft shop and he doesn’t have any issues. I think he said it was very common on GTO when you lower the car the rear will be higher. In my build I have a Heidts IRS and it too is higher than the trans. I called Heidts and they recommended a CV driveshaft as well. Then again on an IRS there’s no movement of the pinion. Anyway send Andrewb70 a DM.

[absintheisfun]

I'm looking into the cv driveshaft, but my call to them was underwhelming. The guy I got didn't give me any insight into whether or not it would be beneficial, he just kept saying, fill out the sheet online and it will answer your questions. I'll try again this week and hopefully get someone a little more giving with information.

Until then, I got the speedtech tunnel, and it unfortunately won't work for me. It doesn't line up well with the firewall, and I would still need to fabricate a cover for the hole I made previously. I made a template out of cardboard that looks like it will work better, be easier to weld in (given how low the center dash is and the ac box is in) and give me the clearance I need.

Now I just need to get some new clean steel and go to work.

https://static1.pt-content.com/images/pt/2021/03/51060067908_e37693b79b_k-1.jpg (https://flic.kr/p/2kN1chq)
https://static1.pt-content.com/images/pt/2021/03/51060783736_e631c7a348_k-1.jpg (https://flic.kr/p/2kN4S5h)
https://static1.pt-content.com/images/pt/2021/03/51060866792_41cc1b5c78_k-1.jpg (https://flic.kr/p/2kN5hLh)

[67-LS1]

My rear end yoke is higher than my trans yoke. I think this is pretty normal. As long as you keep your joint angle correct it should no make a difference.
That said, I do have a CV driveshaft but not for angles. My trans does not have a slip yoke so with a live axle the CV is what makes up the length difference as the rear end moves.
186183