Drive shaft vibration

I recently swapped my peanut rear end for a 9" rear end with new bearings and seals. I took my original driveshaft (used with my 3 speed manual trans and my 200 ci motor) and the drive shaft from the 9" rear end donor van to my local drive line shop. The fabricator guy there built me a whole new drive shaft with the bigger u-joints at both ends with a 3" tube from all new parts. Cost $200, balanced. He told me to download the Tremec toolbox app to my phone and use it to verify that the angles in the driveline are all within acceptable ranges. He said I'd likely feel vibration if any of the angles were out of range. He also said the that drive shaft attachment point of 9" rear ends is lower than on my old peanut, which would make for a less in-line driveline.

I installed the drive shaft and used the app. The first angle measurement (between the transmission and the driveshaft) was 4.6 degrees, which is out of range. The second angle between the driveshaft and the rear end was 2.7 degrees which is in range. Despite the first angle being out of range, I test drove it. Near and at highway speeds there was a new vibration that is probably the driveshaft based on the speed of the transmission vs. the frequency of the vibration. The fabricator guy said if the back angle is out you can use shims to rotate the rear end up or down as needed. That part's OK with my driveline. Unless his balancing is faulty, it seems I need to angle the back of my transmission down. It's funny, I just replaced the transmission hanger bushing, see this thread:

https://vintage-vans.forumotion.com/t55412-transmission-hanger-bushing?highlight=bushing

The old bushing was worn, and the bolt routed through it was near its top. Replacing the bushing lifted the back end of the transmissing, probably by about 1/2". Now I'm wondering what's involved in lowering the back end of the transmission, and how much I should lower it by to get the angle within the acceptable range. I suppose I could do the math. See pictures below of both ends of the shaft. I suppose I could drop the transmission and weld new metal plates on the existing transmission hanger bracket, or just cut it out and make all new hanger plates. It's not stock, and I'm guessing someone installed it when they swapped in the 200 ci motor.

Any thoughts on why the vibration is happening, whether changing the angle of the transmission is the right fix, what the best way to lower the back end of the transmission is, and how much to lower it by? I'd drive it to the fabricator guy, but he's about 35 miles from me. I plan to call him tomorrow.


The out of range 4.6 degree angle.


The in range 2. 7 degree angle.

I don't have an easy answer, but raising the motor a bit could change the trans angle. How new are your engine mounts? Perhaps if they are old and worn the engine has settled and new ones would make it sit higher. Or you could maybe shim the mounts to gain degree or two.

Haven't done it. Just a thought, but you could unbolt the engine from the mounts and gently lift it with a floor jack to see if an extra inch up front would change the angle at the back.

OK, I removed the transmission hanger bolt, lowered the rear end of the transmission by about an inch, retried the Tremec toolbox app, and all the angles showed within acceptable ranges. I called my fabricator and he said lowering the transmission this way would definitely get rid of the vibration.

So, I guess it's time to modify the transmission hanger bracket. Pictures below show the lowered transmission and the bracket that someone must have welded in when they swapped engines. The welding's not pretty. Wondering what the best way to approach this is. Cut the old out completely and fab a whole new one? Weld longer plates on the existing side plates? I have an oxy-acetylene set up, but mainly use it for brazing bicycle frames. Could just fab the metal parts and hire a mobile welder.

Update: I just talked to a friend of mine. He had a sensible idea. Just bolt new plates along side the old. No welding. Think I'll do that.

I have a new gas tank I'll be installing. Maybe this would be a good time to drain the old tank and remove it to reduce the chance of fire.


The lowered transmission and mounting holes.


The bracket.

When I installed a 9" rear end in mine I had to install tapered shims, I needed 2° shims, on the spring perches bolted to the spring pack to correct the pinion angle. The angles of the transmission and and pinion should be equal but opposite. If you remove the driveshaft and have the truck park on a flat level concrete surface you can make a make shift angle finder out of strips of plywood or whatever and a clamp. With one on the floor and the other against the face of the output of the trans, tighten the clamp to lock them in position, then move it to the rear end pinion and see how far it is off. You can also use a magnetic angle finder. The # of degrees difference is the shim you need at the spring perches to correct the pinion angle iirc. The 2 1/4" shims are difficult to find, but I found the ones I needed from a jeep outfit online. I have a 15 3/4" driveshaft and zero vibration at any speed.

Btw, I looked into lowering the trans output and the amount required to get it to match the pinion angle was impractical. They should match as close as possible. Iow, within less than a degree. I'm using a non oem trans, but as far as I can tell the pinion angle should have been the same as stock with the carb level.

The angle of the drive shaft to the differential was within the acceptable range from the start with the new rear end. It was just the angle between the transmission output shaft and the drive shaft that wasn't. I'm fabricating bolt-on brackets this morning to lower the back end of the transmission. It only needed to come down an inch to make it well within the acceptable range. We'll see how that works.

I think what you are not comprehending is that there's more to it than the angle of the driveshaft and that is not the most important factor. The most important part are the angles of the transmission and the pinion and that they are the same. Irregardless of the angle of the driveshaft drop between them.

You don't want an extremely angled driveshaft b/c that also causes u-joint issues and vibration. You will never have that problem in your truck unless you put a massive lift kit on it. The most important factor is that the u-joints are operating in phase with one another. This is done by having the transmission and rear pinion pitched at the same angle. Iow, they are in parallel lines. That is the correct way to solve your problem, iow by tipping the rear pinion fwd/down until it projects at the same but opposite angle as the transmission. Simply, if the transmission is pointing 3 deg down, the pinion must point 3 degrees up, regardless the amount of drop between them. You can drop the transmission down to get the driveline drop angle(again you shouldn't need to) into range but you still have to correct the pinion angle if it doesn't equal the tran angle.

When calculating the driveline angle are you subtracting the pinion or trans angle? B/c that is how it's done and you'll more than likely find yourself well within spec which is like 6-7 degrees. And I've read that that is a pretty conservative # for the average street car. So if your trans is pointing down 3 deg and the pinion up 3 deg and there is 9 degrees of drop on the driveshaft tube you are still  in spec @ 6 deg of operating angle.

You're trans is likely sitting around 3 deg angle, but your rear pinion is pointing up 5 deg or whatever. So if after dropping the trans an inch or whatever you find that the trans angle matches the pinion angle then problem solved and I'll shut up and go away But I still think this is less than ideal b/c you are altering the angle of the carburetor mount from oem.

This page from Drivelines NW explains it all better than I can:

https://www.drivelinesnw.com/part-trouble-shooting/vibration-analysis/angle-analysis/measuring-and-correcting-angle-problems/

I will throw this in, most vehicles have a 2-4 degree angle Engine/transmission, by lowering the trans more you are also angling the engine. When I slipped a late 360 magnum into a 67 Dodge van the original thick engine isolators (motor mounts) caused the engine/trans to have almost 8* of angle, too much. I used later model isolators, modified the brackets ended up with 4* down at the intake which is the same angle at the trans output and 0* at the top of the carb. The Ford 9" that I put in the van had a hair over 3.5* up angle measured at the pinion, that is parallel, no vibration.

To much angle creates a whole new set of problems, you may now have gear oil flooding the rear seal possibly causing it to leak at the same limiting the amount of gear oil splashed on the front bearing, not a good thing. Now for the engine, same thing, motor oil flooding the rear seal, excess crank splash due to deeper oil at rear of pan, frothing. Carb bowl no longer level so float not right, either starvation but in most cases flooding. Check your tilt that you have not caused the cooling fan to strike the radiator.

Thanks for this info all. I understand it now. I did lower the transmission mount with bolt-on brackets I made from 3"x3/16" plate with 1/2" angle brazed to the edges to make a channel. See pic below. It lowered the back end of the trans by about 1". I used my magnetic angle finder and found the engine/trans to slope down towards the back at 5 degrees. the u-joint yoke at the differential slopes up at 5 degrees, and the shaft's angle is 5 degrees. I test drove it. No vibrations. The engine seems to run fine and I don't see any leaks from seals, so I think I'm OK.

I'm glad you got it worked out.

Btw, if you ever want to return the trans to the stock position it looks like the 2 degree shims I used on my rear end would fix yours as well.

A lot of good information in this thread.  Had a friend who did an engine/trans and rear end swap and had everything finally dialed in correctly.  Still had a vibration.  Removed the driveshaft and took it down to have balanced.  Fixed the problem.

Wolfster wrote:A lot of good information in this thread.  Had a friend who did an engine/trans and rear end swap and had everything finally dialed in correctly.  Still had a vibration.  Removed the driveshaft and took it down to have balanced.  Fixed the problem.

I thought about that with mine, but the guy built it with all new parts for me. It had 3 little weights welded to it, so he did balance it.

I skippped a lot and browsed here and there in this thread,,, 1st off you have the less desirable and known as the crash box early 61'62 non 1st gear synchro 3 spd ,,, which is okay?????? however it uses also the weaker sliding yoke in the transmission. No offense meant here,, but most people replace that one with the 63/64 full synchro SOLID OUTPUT YOKE TOP LOADER trans. It has a ball bearing and a solid yoke that supports the drive shaft better,, just saying,,,,,,,,,,Next,, when you change the engine angle, you ALSO CHANGE THE CARBUERTOR INTAKE ANGLE,,,, Ford set an angle in the intake manifold to keep the fuel level in the carb,, ALL ENGINES have that angle built into on purpose,, for a purpose,,,,LOL
In 64 when they put in the automatic, they DROPPED THE FRONT OF THE ENGINE DOWN 2"s to match the 2" drop in the back using the one year only donut mount C4 solid ouput yoke. They did this on purpose on both sides to keep the fuel level correct in the carb,,,, SO,, dropping the rear of the engine has now screwed that all up.... If it wasnt vibrating BEFORE you put the 9" in there why would it now vibrate unless it is out of balance?? also,, you can use angled wedges to turn the axle which is very common,, YOU SHOULD NOT HAVE TO nor DO YOU WANT TO,, drop the transmission height. I have installed an easy 100 of these in the last 50 years and no issues like yours.....Not picking on any transmisisons, or people,, just telling it like I see it,,,

Old Skool

Here is an example of how Ford dropped the front of the 64 AUTOMATIC engine support arms to also match the 2" drop the donut mount dropped the rear of the engine...
Old Skool

With a 63/64 top loader 3 spd manual, you could swap out the small yoke for a matching 9' yoke,, OR used a small six 3spd manual HD drive shaft. It would have the small front u joint and the matching 9" rear u joint,, came stock in ours...cant find my pictures of small sixes right now? clearly showing the angle in the intake,, this is a 250 with an aluminum head, but it does show the angle also... The trans is a 65 to 67 top loader but shows the solid output yoke,,, drive shaft slides not in the transmission and stronger also...
Old Skool