drwet

When I installed the Tremec TKO 600 in my '79 the transmission mount lined up perfectly. I installed the shortened driveshaft tonight, and it looks to me like the rear of the Tremec sits a little lower than the 700R4 did. Hard to measure now that the trans is in, and its not something I thought of measuring before I pulled the automatic out, but it looks to me like I am going to have to shim the rear of the transmission up about 3/4". I'd love to hear from someone who has done this swap - how did you deal with the mounting height of the transmission?

Garys 68

You need to buy an angle finder, about $12 at HF. Check the trans, pinion, and driveshaft angles. There are a few dozen articles online on setting it up. The best are from trans and driveline parts manufacturers (ie spicer).

Barry's70LT1

I did the swap several years ago, not from an auto trans. (TKO600 replacing the M21). At the time I was quite concerned about drive shaft angles and finally decided to deal with it only if it was a problem.

I assembled everything without checking drive shaft angle. In the first road test there was absolutely no vibration at all, at any speed, and continues to be vibration free. So, the angle never did get checked.

OzzyTom

Get the angles on the driveline correct now. it will save you a lot of frustration later.

I fought driveline vibration for about a year after installation of my TKO 600.
Similar to you, the rear of the trans needed to be higher, but there was insufficient clearance to the trans tunnel. I fitted a tapered shim between the diff and cross member to change angle at rear uni to provide necessary opposite angle to front. It improved the vibration situation considerably... I still notice a slight hum at 45 mph, but it is not a problem.

If I need to drop the box out in future, I'll carve out the tunnel where necessary to provide the clearance to raise the trans to correct position.

Good luck with the project. The trans conversion from auto to manual transformed my car immensely.
Cheers

drwet

Thanks. I've done that a number of times on previous projects, and I do have an inclinometer. Preblem is there isn't enough room in the driveshaft tunnel for me to get it on the pinion yoke.

I've done some searching on the web and there are a number of guys who've reported having to shim the rear of the Tremec up. Numbers seem to be in the 3/4" range. I''ve compared the dimensions on the Tremec to an M-21 I had lying around, and there is a 3/4" difference in the mounting height. I just don't know if the crossmember bracket for the 4 spd and the 700R4 place the mount at the same height.

I was hoping to hear from some guys who have been through this.

Garys 68

It was tight but I got the angle finder on the pinion yoke but had to use a mirror to see it.
Mine was with a Richmond 6 speed but I've seen some early TKOs that shimmed the back of the trans up as high as possible. I think the U joint making contact with the tunnel was the limitation.
The vette angles on my car were almost flat, 0 degrees on the engine, diveshaft, and pinion. With my trans, best I could do was about 2 degrees down. I was able to raise the pinion as high as possible by trimming the rubber frond diff mount down to about 1/8" thick. It's not perfect geometry, but no vibrations.
Btw, when measuring the angle, the car needs to be on all 4 tires.

drwet

Thanks for the input. That's great information. I will try the inclinometer on the pinion yoke again. That will certainly be the best solution if I can get it in there. I know I will have issues with floor clearance at the slip yoke but its a '79 and has a metal floor so that problem can be solved with a hammer. I think my limiting factor may be topside. I had to build an adapter to get the shifter in the right spot and it may interfere with the console if I get it too high.

I'm curious why you say the car should be on the tires. That won't change anything. What is the logic there?

Garys 68

The frame, especially on my 68 convertible, flexes, A LOT!
Putting jackstands on the frame right behind the front tires caused the frame to bend, and engine/trans to angle down in front.
Absolutely critical full weight on the tires.

jnb5101

what about the half shaft angles? i've often wondered if driveline oscilations stem from the shorter half-shafts. in pictures of rear suspensions there is sometimes a large difference in the center lines of the diffy yoke and the ta axle. and with the half-shafts short length, the angles are magnified. guys should measure the height difference and report as to whether they have vibrations. i've lowered all three of my cars (longer spring bolts) and have no vibrations.

Garys 68

Vibration due to misalignment or extreme shaft to pinion/yoke angles are due to a combination of the angle and rpm. The higher rpm of the driveshaft vs the halfshafts results in it more prone to vibrations.
Check out the spicer site, it give specs like max driveshaft, yoke angle for a given maximum rpm.
A little light reading:
http://www2.dana.com/pdf/J3311-1-DSSP.pdf

jnb5101

a quick read of the spicer paper on driveline vibration pointed out two things. one, the propeller shaft is a single plane system. and two, the half shafts are a compound system(especially when the trailing arm is swinging in a vertical direction it also moves fore and aft). the rpm's of the half-shaft are only a third of the engine speed, but the shorter length makes the angles more critical.
i still think a survey of members would help determine if the major cause is propeller of half-shaft angles.