Driveshaft hitting cross member

[Bret B]

Guys, need some recommendations. Issue is, when lifting the truck at the frame, as the suspension extends, the driveshaft makes contact with the trailing arm crossmember. This was quite a surprise and not something foreseen. Once contact was imminent, we didn't lift any further, so I don't know if we were at or just about full extension.

Truck is a 1965 C10 short box, step side. Engine is an LQ4,4L80E. 12bolt rear end. Using a 1 piece driveshaft, believe it is a 4in diameter maybe 3.5 inch. All the suspension and crossmembers are CPP tubular. Drop is 5 inches I believe. Engine mounts are CPP "plate" perches with dirty dingo sliders. Engine is in full AFT position on the sliders. Trans mount is CPP with a Summit rubber mount. Truck can be driven, but no exhaust causes frowny faces by neighbors. Mechanic in town making the exhaust found this driveshaft hitting cross member problem. Said the trans and trailing arm members were install upside down and driveline angles were completely wrong. That started me down the rabbit hole. For clarification, no, the mount and crossmember aren't upside down. Both are installed per the instructions from CPP and I've doubled down with checking the web, and articles in magazines. Driveline angle, could play in, or does it?

Pics attached in this order: 1. Rear end angle 2. up close of pinion angle (6 degree) 3. Trans angle, don't know why it is upside down when uploaded. 4 up close of trans angle (-6.5 degree), same upside down graphic. 5. Cross member

Rear end angle is 6 degrees (pinion pointing up). Trans is -6.5 (pointing down). I didn't think the driveshaft angle was important, but guessing it is after reading the interwebs. I'll get that when it isn't so damn cold outside. However, the distance from driveshaft to crossmember where contact is made, at ride height, is about 1 inch. Now, the mechanic said I needed to raise the transmission mount up to make a better angle. So, I raised the trans off the mount 3/4 of an inch. The transmission angle then is -6 degrees. This I'm assuming is goodness. Yet that did nothing for resolving the driveshaft contacting crossmember, or very little improvement anyway.

I contacted CPP and tech support said he hasn't heard of this issue before. Their kits are designed for 1pc or 2pc driveshaft, but it is the first time he's heard of it. He didn't say it isn't possible, but clarified people who may experience this, haven't reported it and probably solved it without calling. He said options were limited. 1. I could cut mounts of rear end and re-position to make 4 degrees. Remove the engine perches and install OEM perches to lower the engine and raise trans rubber mount to obtain -4 degrees. 2. I could make limiting straps so the suspension doesn't extend. I see how this could work but ask myself why would I have to, the problem is still there. 3. Install a 2pc driveshaft, but I'd need to get the 4 degree angles.

This leads to the questions. What am I doing wrong, no one else seems to have problems with? What if I went to a 2 piece driveshaft? How would the pinion and transmission angles play in with a 2pc unit? Or, do I really have to worry about the angles if using a 2pc? Now, I don't want to throw away $600 for the driveshaft I had made. Money is money and it isn't free flowing. The angles currently are what they are from the geometry of the kit I bought from them. I didn't add or subtract a component to alter the results.

Input and ideas would be appreciated.

[Getter-Done]

To the top and flip for ya.

[Richard]

Angles are fine if you ask me. Ideally pinion and diff angles should be equal but opposite. Maybe allow 1 degree down on pinion with leafs. If they are within 1 Degree of each other you should be fine. As far as the crossmember. I would lop out the section under the drive shaft and jack up the truck to see clearance needed. Cut a short section of 4" pipe in half and weld back on with the added clearance.
Looks like the crossmember is designed for low trucks. If it is not dropped to low maybe you can turn it over to help.

[mongocanfly]

+6 & -6 are more than I do, I always shoot for the 3s, but it probably won't help you much changing that..if you don't have vibration issues I'd leave it alone and add a driveshaft hoop...problem solved
Figure out how much it needs to hang down, cut to fit, weld it in, or as Richard suggested, 1/2 a pipe

[Jason Banks]

I had the opposite problem(1 piece driveshaft hitting top of crossmember). But, I'm using different mounts. Basically this Holley set up - VK090202. I c-notched frame and have 4/6 drop.

Have you tried installing your exhaust manifolds/headers yet? Is there room? Sounds like engine/trans are low and if there was some good way to raise it up that would help you.

Looking at that replacement crossmember you have. It looks like it would have solved my problem, but is causing you a problem. The factory crossmember comes down lower than the frame rails and yours looks like it is straight across.

[Jason Banks]

Re reading your post I was thinking. I wouldn't be happy with the 6° . I'd aim for closer to 3°. Spacer between the transmission crossmember and trans(but you said you tried 3/4") and they make shims that go between trailing arms and rear end to change it...

It might end up, you need to cut the crossmember and put a lower loop.... ��

[Richard]

I would bet the working angle of u-joints are pretty close to 3 degrees as it is now. Figuring working angle was a bit of a mystery for some time. Made a drawing of how I understand in this post https://67-72chevytrucks.com/vboard/...6&postcount=14

[LS short box]

Hard to tell from the pics but it looks like you could raise the trans more than 3/4". I would shoot for around 3 degrees.
Too bad the CPP cross member angle cut the trailing arm brackets other wise you could drill additional holes to adjust the pinion angle.
I see that you measuring angles off the tail housing of the trans. I have found that measuring off the engine balancer gives a more accurate reading since its a machined surface.
Just another thought before you start cutting. Could the rear shocks have too much down travel? meaning could they be too long allowing too much drop?
My 68 C10 SWB had a 4/6 drop and I had to trim the top of the cross member.