More driveline angle help needed. This time with illustrations.

This isn't working so well. The front end is a Ford T5 with a slip yoke, u-jointed to a stock Foxbody driveshaft. The back end is u-jointed to a conversion plate sold by Jags That Run. The conversion plate has a standard u-joint mount face on one side, and the bolt plate/pattern for an E36 differential input shaft on the other. I had to use a Spicer conversion U-joint to hook up the driveshaft and the adapter plate.

I have the driveshaft mounted with a downward slope, because that's what I thought I was supposed to do. I also have some working angle on both u-joints, and the angles are in opposite directions, because that's what I thought I was supposed to do.

I'm thinking the problem is I have a slightly wider angle on the rear end than I do on the front end. Is that it?

Can I fix it by shimming the subframe mounts that attach the differential to the rear suspension a bit, so the input end of the differential points downward a little more? Then the face of the differential input would be parallel to the face of the transmission output.

Or are there other problems to boot?

Hang on, I'm trying to get the pic linked.

Link to illustration

JBasham wrote: Can I fix it by shimming the subframe mounts that attach the differential to the rear suspension a bit, so the input end of the differential points downward a little more? Then the face of the differential input would be parallel to the face of the transmission output.

I think so, based on your illustration anyway. In what way is it not working? Getting vibration?

That looks like a lot of downslope on the driveshaft. Your are correct in opposite angles for the rear and trans, but depending on the length of the driveshaft, you are working the u joints pretty hard. I believe the trans and rear should be pointing more to each other, again with offset angles.

¯\_(ツ)_/¯ wrote:

JBasham wrote: Can I fix it by shimming the subframe mounts that attach the differential to the rear suspension a bit, so the input end of the differential points downward a little more? Then the face of the differential input would be parallel to the face of the transmission output.

I think so, based on your illustration anyway. In what way is it not working? Getting vibration?

Couple things. One is, until I get the rear wheels rotating a fair bit, like enough to be moving about 15-20 mph, it lurches along. The other is, as I'm cruising along smoothly at speed, hitting a pavement joint or something will give me one quick lurch.

On vibration, I'm getting a 20db increase in the noise floor when I move up into highway speeds. BUT I'm not sure whether that's driveline or tires.

Don49 wrote: That looks like a lot of downslope on the driveshaft. Your are correct in opposite angles for the rear and trans, but depending on the length of the driveshaft, you are working the u joints pretty hard. I believe the trans and rear should be pointing more to each other, again with offset angles.

Thanks, I guess I need to gather more information about how much angle they can take. If it's just a matter of wear rate, I don't mind changing them really often, because they don't cost much and it's easy to do now that I have the tool. But this is a track car and shaft speeds are super-high on the straights, and swinging back and forth anywhere from 30 to 90 over and over the rest of the time. Not much I could do to move the plane of the transmission and the plane of the diff closer together. The stock chassis has a 2-piece shaft and I may have to go that way.

In the second picture, "A" is wrong

https://www.youtube.com/embed/Idk3BVDVHq4

You also want to make sure that the driveshaft was assembled properly so that the joints are "phased."

Would not hurt to take the shaft in to a driveline shop for a clean bill of health since it is for the racecar; cheap insurance.

Just did this job a week ago on the Molvo. The lines extended from the gearbox and the differential need to parallel but on a different plane. If you watch the video, you will see that they run the drivetrain way past 3 degrees of angle.

In reply to NOHOME:

Coincidentally, I watched that youtube video this morning. Not for any reason other than youtube recommended it.

Thanks everybody, now I just need to find the time to get up in there and fix it.

P.S. this calculator is cool. Gives actual data showing how bad or good particular combinations are. Note, it's a two-pager.

the Original Dana torsion calculator