Driveline Angle Issues on Lowered Car

[83hurstguy]

First off, thanks for opening this thread and reading, since there are million topics on this already. I've read a good portion of them and understand the basics, but have a few questions for my situation I haven't seen explicitly answered.

My Olds G-body is lowered close to 2" all around. With some new rear adjustable control arms, I decided it was time to check driveline angles. I had checked them years ago, but realized I made a mistake of using the trans pan rail for the engine/trans measurement... and that doesn't correspond to the flexplate/starter block/front crank pulley measurement.



Right now, my rear end yoke is at 0*. The driveshaft runs uphill from the pinion yoke to the transmission tail shaft at 1.5*. My engine/transmission angle is 3.5*, with the tailshaft as the low point. Therefore, I have 1.5* of angle in the rear, and I have 2.0* of angle in the front.

Seems like it's spot on... however, the issue I have is that the driveshaft is at a shallower angle than the engine/trans. The U-joint angles are not parallel, but are opposite in orientation. The current arrangement looks something like this (not to scale, just a crude Paint sketch):

Therefore, I have one of two solutions that can be pursued.

Option 1. Shim up the trans mount on the crossmember. I ran a few preliminary numbers with rough geometry, and it looks like I'll need a 1 - 1.25" spacer on the trans mount to correct this. That's a lot of spacer! With a 1.25" spacer, my engine angle will only be approximately 1.75*. How critical is engine angle to performance? I assume it helps with oil drainback, and obviously the carb/air cleaner angle could end up looking a bit funny. I also have a mechanical fan to contend with (for now) that I would prefer to keep out of the shroud. After I spaced it, I would make the pinion angle match the engine/trans angle.

Option 2. Make the pinion angle equal the engine/trans angle and don't touch the trans mount. However, at that point, the driveshaft will most likely be level or running "up" to the rear end. This is not desirable for pinion climb under acceleration, as the pinion will be nosed up to the driveshaft, rather than nosed down. Here's a picture from the Inland Empire Driveline showing the situation I am describing:

(Full document located here: www.iedls.com/asp/admin/getFile.asp?RID=10&TID=28&FN=PDF)
Inland Empire references this is good for "street rod" applications and smooth running, but I'm not sure it's desirable for a performance application.

Does anybody have experience with this situation, and what solutions worked for them? Did I miss any other options? For reference, this is an Olds V-8, 200-4R trans, and 8.5" rear end.

Thanks in advance for any help!

[SSLance]

Hey Luke, this is a topic I fought with for a while myself. It is why I worked so hard to raise the tailshaft of my T56 as high as I could get it during initial mock up. I ended up with the tail shaft in just about the exact same location as the 2004R tailshaft was.

The problem I was fighting was driveline vibration between 55-70 mph. It varied at different times in severity, depending on what parts I was running at the time. What I ended up doing was raising the pinion angle to match the trans tailshaft angle and the vibration went away completely.

Using a digital angle finder on the bottom of my harmonic balancer, I verified that my tailshaft is 3.5 degrees down much like yours. I had previously verified that the drain plug guard on my axle housing was perpendicular to my pinion yoke so I used it to measure as I raised my pinion angle to 3.5 degrees up.

Pinion climb wasn't as much of a concern of mine as was getting rid of the vibration at highway speeds. A very slight adjustment in ride height effects this angle so it has been adjusted a couple of times since. It is amazing to me how just a small pinion angle adjustment makes the vibration go away.

What exactly is the detriment of "pinion climb" and what other ailments are you working on in correctly the u-joint angles?

Are you still running a 2.5" drive shaft? If so, I'd have Inland Truck Parts build you a 3.5" driveshaft before I did anything else. That upgrade made a huge difference in my driveline stability.

Also, have you ran a string to check to make sure your crankshaft\tailshaft is directly in line with your driveshaft? Mine was off in that respect as well.

[83hurstguy]

Lance, thanks for the response and detailed info. I have had some minor driveline vibration... with the car out of commission this summer I don't remember details. I had a new steel driveshaft made years ago, but I can't remember if it's 2.5" or 3". I'll try to crawl under there and measure it tonight.

In regards to pinion climb, I know most drag racers want to set the optimum angle slightly down, so when under power, the rise is accounted for and can help plant the tires. If you have the angle set with the driveshaft running upwards to the rear pinion yoke, your angle theoretically gets worse under power. I'm having a hard time figuring out the load path back there to determine what the final effect will be. I am hoping some experts here could chime in to describe how having the rear end being "pinion up" relative to the driveshaft will effect the suspension's behavior both for handling and drag strip duty (or if it matters at all, and it's just a matter of u-joint proper implementation - even the drag racing forums don't agree). The new engine has 500 lb-ft, so I'm sure I'll see some pinion angle change back there under power.

I haven't done the string check yet. I definitely will though. I got the car on the ground last weekend to go for a quick ride, check the brakes and clean up the garage before our weather took a dump. I'm planning to get it back up on the race ramps soon and get this straightened out.

[SSLance]

I guess I'd have to decide what I was most concerned about and how I planned on using the car the most. Vibrations drive me crazy, one for a comfort reason and two for a wear issue. If it's vibrating, it's causing unneeded wear on something.

I came from the 4x4ing world we fought driveline vibrations from lifted suspensions constantly. I've seen and felt the worst of the worst in this regard. The one sure way to make the majority of them go away was to get the u joints operating at the same speed, which meant they had to be on a parallel plane.

I've read all of the different things drag racers do to try to help launch traction and I kind of understand the theories involved, but I don't think I'd sacrifice highway comfort for launch traction in my case, your results may vary. Hopefully someone with more experience setting up a 4 link for multipurpose use can help steer you the right direction here.

[83hurstguy]

I measured the driveshaft tonight... it's 3" diameter (steel).

I completely agree with your philosophy on vibration. I won't tolerate it for the car since it's 95% street, and don't want to eat up u-joints. I guess it's just a question of either raising the trans tailshaft to get that rear end pinion "nose down" to the driveshaft or whether I do exactly as you described above. Either way has its potential tradeoff. Thanks!

[TheJDMan]

I don't think a drag race setup is going to apply to you at all. For street use you need to raise your transmission to 3deg down angle and raise the pinion to 3deg up angle like Fig 5 on your post. Depending on how low your stance is the driveshaft should be close to level keeping in mind that the driveshaft angle is not static.

[72BBSwinger]

You want 2 things:
1. Opposing u joint angles
2. Pinion and tailshaft parallel under power

[83hurstguy]

Thanks guys. I was leaning towards a combination of my two options that you described. Using an approximate 3/8" shim to get the engine/trans angle back to 3*, then move the pinion upwards. Should be fairly straightforward I would think.

[carguykeith]

You're on the right track, if drag traction is really a concern than 72BBSwinger has it right, otherwise just worry about opposite angles. With a lowered G-body 4-link the best I found was lower control arm relocation brackets on the axle (for anti-squat) and adjustable upper control arms (to get the pinion angle right).

[andrewb70]

You want 2 things:
1. Opposing u joint angles
2. Pinion and tailshaft parallel under power

You actually want three thing…

3. You want the operating angles to be as low as possible, without being zero.

http://www.markwilliams.com/driveshafttech.aspx

Here is a link to a PDF of a MW tech bulletin:

http://www.markwilliams.com/servicebull/sb0049.pdf

There is a great chart that shows a graph for operating angles vs. driveshaft speed. With modern overdrive transmission, it is easy to have driveshaft speed of 4000RPM at 75 MPH. At that driveshaft speed, the operating angles should be less than 3 degrees.

I fixed my driveline angle problem by using a custom driveshaft with a CV joint at the transmission slip yoke.

Andrew

[83hurstguy]

Thanks guys. I got material to make shims for the trans tailshaft and will adjust the rear pinion angle accordingly. I had just installed relocation brackets as well with a 2" drop on the axle side. It will be a few weeks, as I won't get to the car after the holiday, but I'll update with the results. That Mark Williams information was an interesting read.

Andrew, where did you get your CV shaft made?

[andrewb70]

Thanks guys. I got material to make shims for the trans tailshaft and will adjust the rear pinion angle accordingly. I had just installed relocation brackets as well with a 2" drop on the axle side. It will be a few weeks, as I won't get to the car after the holiday, but I'll update with the results. That Mark Williams information was an interesting read.

Andrew, where did you get your CV shaft made?

Luke,

My CV driveshaft was made by The DriveShaft Shop.

Andrew