Transmission Alignment

[jimwallace]

I have installed my engine and transmission in my Mk4 roadster (351W and Tremec TKO500 & IRS), and the transmission appears to be offset around 1/4inch toward the passenger side of the transmission tunnel. The driveshaft definitely has a slight angle to it when viewed from above. Is this normal? How much angle is acceptable with the driveshaft?
I also have a slight angle of the driveshaft due to the transmission being lower than the differential input shaft. I used all of the washers provided with the Energy Suspension transmission mount to raise the rear of the transmission, but it is still slightly below the differential input shaft. Again, is this normal and how much angle is too much?
Thanks for any advice that you can give.

[ZoaFan08]

The engine is offset on the passenger side by design.

[Bob Cowan]

Like most production cars, the engine is ofset to the passenger side a little bit. Not much, but a little. Make sure the engine/trans is aligned in the frame. The line drawn from the center of the crank through the center of the trans should be parallel with the frame rails when viewed from above.

The drive shaft alignment is called the pinion angle. Do a search here and you'll find lots of good info and some pictures.

I can't remember what the maximum u-joint angle is. I think it's something like 25-30*.

[Cone Basher]

Back when I built my Coupe I noticed that the drive shaft on the IRS was slightly to the right. Your driveshaft needs a little angle in it to keep the bearings rotating and not flat spotting under hard acceleration, but who ever does that with one of these cars. Anyway what you need to do is add shims under the rear of the trans so that the drive shaft is horizontal, I think I added about 1/2 inch to mine with the energy suspension poly bushings but you can check this with a level (JEGS has one you can use for this it you do not have one). You might also try the following for info. Go to google and enter site:ffcars.com IRS drive shaft angle or any thing else you wish info about. I found this on the forum and it is a great source of specific info on Ackerman, bumpsteer, SAI mod, sway bars ETC.
HTH
CB

[Bob Cowan]

Originally Posted by Cone Basher

Anyway what you need to do is add shims under the rear of the trans so that the drive shaft is horizontal,
CB

That is not correct. Do a search on this forum for "pinion angle", and see how it's done.

[gyow]

Forte sells spacers for the transmission. Give him a call.


Sent from my Autoguide iPad app

[ROADRACER83]

Jim:

The transmission and engine are slightly offset to the passenger side on purpose. The rear end pinion or input shaft and gear by another name are on the right (passenger) side of the ring gear in the differential housing but the housing is essentially centered in the rear axle. On the Mustang the engine is slightly offset to the passenger side so FFR followed that pattern. When the car is on the ground, the horizontal angle of the driveline will be set by the ride height of the car. You want the pinion angle down so it is parallel to the slight up angle of the transmission output shaft centerline. Lots of threads on this in the search function.

Ron

[Cone Basher]

Bob: I read the info about drive line angle on the IRS am now I'm starting to rethink what I've done with the shims. With the frame level I checked the flange on the IRS and it was vertical this suggested to me that the pinion in the IRS was also level. I then added shims to the rear of my TKO 600 so the the drive shaft was level and offset in the drive line was created by the engine mounted slightly to the right of the car. I thought this would give me the best power transfer to the trans. What changes would you suggest I make as I have not detected any vibration or had a bearing failure?
Thanks CB

[Bob Cowan]

There are a couple of angles that effect power transmission. The greater the angle is, the less efficient the the joint becomes.

OTOH, you do need a little bit of an angle at the u-joints so they'll work correctly. You only need a couple of degrees there, and for most installations that's really not an issue. The issue is usually decreasing the angle to as small as possible.

The important thing to remember is that the pinion angle is measured against the crankshaft/transmission - NOT the horizon. For example, if the transmission points down in the back 5* and the pinion points up 3*, your pinion angle is 2*. It's the difference between the two angles that counts.

The goal of setting the pinion angle is to get them as close to 0* as possible when under full acceleration. At that time, the differential will try to rotate the pinion upward. How much rotation you get depends on your set up. A stock factory leave spring rear with a few mile on it may change as much as 5-6*. An IRS changes 0* if you have solid bushings, more with poly or stock rubber bushings.

The easiest place to measure the crankshaft angle is on the front of the balancer - compared to the horizon. Then measure the pinion angle at the front flange - also compared to the horizon. So just put a level on each area, and write down the number.

The difference between the two measurements is the pinion angle. With an IRS, it doesn't really matter whether it's a positive or negative angle, because it won't change during acceleration and deceleration - solid axle cars have to be careful about that.

To get the angle you want you can raise/lower the rear of the transmission, or raise/lower the front of the differential. Be careful how you do it, though. Pay attention to the U-joint angles. Try and get that angle between 0 and 5*'ish (not 0*). The U-joint angle is less important. But as long as you're doing it.........

As you set the angle, don't forget that this is all operating in a 3 dimensional environment. Look from the bottom up as well as from the side. Try to get both the differential and engine/trans in the frame as straight as possible. Not aligned to each other, but aligned in the frame rails.

[Cone Basher]

Bob: So what I think you are telling me is I need a small angle in both the horizontal and vertical planes to ensure rotation of the U joint bearings. The IRS set up sets the horizontal plane but you can adjust the vertical plane buy adding or removing shims from the rear of the trans. So I need to change my spacers since my trans output and IRS input are both vertical and parallel?
Thanks again this has been fun and informative;
CB