I finally got my th400 installed and actually ran with it Saturday. Minor vibration felt in my seat. I suspected driveline angle,since this is kind of a hybrid install. I used a BTO 200r4 tubular crossmember,since it's designed for a C-3,and has the right mount location.(th400/200r4 mount to bell housing length).

When I had the driveshaft out of the car,I rigged up a laser pointer that I mounted to the pinion flange,and was able to pin point the pinion centerline on the output shaft of the transmission. It was about 3/4" low,and to the left of center about the same.As luck would have it,the battery in the laser died when I needed it to check the transmission centerline.
I just installed the driveshaft,and test drove the car as it was.After having felt the vibration I looked at the tranny yoke,and noticed the angle between the yoke and driveshaft seemed off. I removed the tranny mount bolts and jacked the trans up till the agle looked better,installed washers and test drove the car again. Much smoother this time. So I cut a piece of 1/4" plate steel to replace the washers and checked the angles.

I rigged up a protractor and string with a weight,and used a carpenters square to get angle measurements off the crank pulley,and installed drive shaft. I got 91 degrees off the crank,93 off the shaft,for a difference of 2 degrees.

Since I could not figure out a way to use the "angle finder" I built on the pinion,but was able to get a measurement with the laser,I used a trig function (Tangent) to figure the angle,based on the length of the driveshaft,and measured 3/4" distance plus my 1/4" plate from the centerline of the tranny output shaft.The tanget of 2 degrees times the 30 inch driveshaft equalled one inch. (aprox)

Can somebody follow along my thinking here,or confirm mount height to tranny output shaft centerline measurements comparing a th400 to 200r4?

Who ever thaught after 20 years I'd acually use Trig for anything?

 

Follow along?...... you lost me on the 2nd paragraph
but for driveline angles, here is the cliff notes version:
The relationship between the tailhousing, center of the driveshaft and the pumpkin CANNOT vary by more than 3 degrees. The angles should not exceed 5 degrees individually and the tailhousing and pumpkin need to have equal but opposite angles to perform correctly.
Hope this helps.


Richard
Tech Support
Keisler Engineering

 

Richard,
What's the best way to adjust the pinion angle on the pumpkin? Cutting the bushing or shimming the 4 mounting bolts to the rear crossmember or is there another technique. Also, does the pinion angle change much with weight on the frame? (I'm trying to get my TKO 600 right with the body off). I can't tell how much I can raise the rear tranny mount until the body is back on and I see how much room I have in the tunnel, so I'd like to get the front of the pinion up to decrease the amount I need to raise tranny. Any suggestions? Thanks.

Jim

 

So how do you measure the pinion angle if you can barely fit your fist in the tunnel where the pinion flange is,much less get your face in to where you may be able to see any type of guage mounted to the pinion?

The laser I rigged up was a pointer you'd use for a lecture or slide show,that shoots a pinpoint up to 50 feet or so. I drilled a piece of 1/2" lexan with a hole for the laser and holes to allow bolting up to the pinion flange. In theory,the beam would be dead centered on the pinion,and would indicate on the transmission tail shaft a relative position.(As if I had a driveshaft installed with a zero degree angle. (Compare this to a laser sight on a rifle. The bullet is supposed to hit where the laser dot is on the target.

Anyway,with the laser dot on my tranny output shaft,it measured 3/4" off the center of the output shaft. If my thinking is right,it means in order for the driveshaft to actually be installed,there would have to be an angle of two degrees. This was calculated by using the driveshaft length of 30 inches,times the Tanget of the angle(2 degrees) equals my one inch of measured height.(original 3/4" off center,plus the 1/4" plate) The formula I used was from a site that showed how to calculate the height of an object based on distance and inclination angle.

I know this sounds way more complicated than it really is,but that's what I did.

The real question if someone could confirm,is the distance from the centerline of the output shaft on a th400 to the mounting pad the same as a 200r4?I'm trying to check my math by getting actual measurements,but I can't find this info anywhere on the web.

 

I always install the tranny as high as I can get it. The tranny always points down anyway so I feel if I can get it to the point of just touching the tranny hump when it settles on the poly mount it will self clearance itself.
I then measure this angle with a protractor.
I then raise the pinion nose by removing shims from the front or the bolt that holds the pinion nose up. I again use the protractor to get this angle equal and opposite to the one I got on the tranny output..
I don't use trig. I try to honestly measure all angles using the protractor

 

The Money Pit, it sounds like your math/trig is right. can't see your rig, so assuming that your setup is dead on then you would need to basically go about it as norval described. get the tranny set, measure, then move to pumpkin and measure back. if you have to change the pumpkin, then you have to start over since your first target has moved.

i would still check using a bubble. look in machinist tool supply or even some quality woodworking tool suppliers for bubble gauges that are graduated in degrees . . . somebody might chime in on a tool supply store with tool that works well

 

Money Pit:

I think you are on the right track. Ideally you want the pinion and trans/engine to be parallel, but offset, so each makes an angle of one or two degrees to the driveshaft. Here's the dirty little secret though:

The engine/trans points down at roughly 2 degrees on our vettes, that means you would ideally want the pinion pointing up at 2 degrees. From the factory, the pinions are more like 0 degrees and it would be pretty tough to get them pointed up 2 degrees. So the factory setting was less than ideal, but certainly good enough.

The one thing you said that bothered me was you were off left to right as well as up and down. I'd certainly fix the left to right mismatch, then hike the trans up as high as you can get it, and try that. BTW, I have a T-56 in my vette, the pinion is at 0 degrees and the engine/trans is 2 degrees down.

 

Here's a shot of the shaft installed. The problem I have is getting anything in the tunnel to measure the pinion angle.

http://www.finitesite.com/markwallas/shaft4.jpg

http://www.finitesite.com/markwallas/shaft1.jpg

I test drove the car around the block with the 1/4" plate and it's quite a bit smoother than it was originally. I know I'm on the right track,but I'd like to confirm my settings somehow,before I put the hammer down and twist my new 3" shaft to pieces.

 

Sorry Moneypit, not trying to hi-jack your thread.......

The way we do it here is to add washers to the snubber bushing. We haven't had a vette yet that the bushing needed to be cut thinner, theoretically(sp?) is sounds like it would work just fine.
Will the angle change if the full weight of the vehicle is NOT on the wheels...yes. How much, not sure but it will definitely change. Typically, you would not want the pumpkin going in the positive direction. Since your rear end housing is fixed, you don't have to worry about rap-up when torque is applied but I still wouldn't go very far(if at all)in the positive direction.


Richard

 

I raised the transmission tail another 1/4",and now the yoke to driveshaft angle is 1 degree. Joint looks much better up front. I took a spin last night with the wife,put her sideways hitting the gas in first from about 25 mph. She was not impressed......I was.

I have exhaust issues to deal with,having moved the pipes around,they'll need MIG welded to keep them in place,but all said. I guess I'm back on the road again!

Thanks to everyone that provided tips!

 

So is the vibration you experienced gone? What did you end up with for angles at the tail, center of driveshaft and pumpkin?


Richard

 

I need some smooth roads to see if the vibration is all gone,but it does feel better/smoother than before. The yoke to drive shaft angle is now one degree,I haven't checked the pinion.

Originally the yoke/driveshaft joint looked like a swayback horse,meaning the shaft tipped down when compared to the yoke. Now it's almost straight. I ended up raising the extension housing 1/2",and using my home brewed angle finder,measured off the crank pulley for reference to the yoke angle,and of course the driveshaft for the shaft angle.

Short of pulling the driveshaft,and buying some sort of small angle finder,I can't see how else to check the pinion angle. It takes a half hour with a 1/4" 12 point wrench just to get the rear joint apart,so I'll chase that only if I have to at this point.

 

Glad to hear it may be solved. Pulling the driveshaft and investing in an angle finder is the only way I know of to check the pinion angle.


Richard

 

I drove to work this morning,hit 65 or so and on smooth highway(well as smooth as can be expected around here),still feel a bit of vibration. It's been so long since last I drove the Vette,I forget how harsh it rides.Got spoiled with the Lincoln I guess.

I'll have to get an angle finder and pull the shaft down to check. It's those little nagging things in the back of your mind,that just won't go away till they're set right.

 

keep us posted.....


Richard

 

I use a 7/16th socket, a few long extensions and the impact and the rear universal joint is out in about 2 minutes.
Try a few extensions and a socket and go from the front near the tranny.

 

This is an interesting thread.

But, I'm not understanding this. If you have the driveshaft level, why would you want the pinion to point up. Wouldn't that give you 2 degrees at each end of the driveshaft. If you mount the differential so the pinion is level then there would only be 2 degrees at one end of the drive shaft. Seems like less chance for vibration.

I think the whole rule of thumb where the diff should point the same as the trans but opposite only holds true for a live axle rear end where the differential moves up and down altering the driveshaft angle and amplifying the angle between the driveshaft and trans.

The way I see it having a constant drivshaft angle is one of the benefits of a solid mounted differential, you just point the pinion at the trans and call it good.

Maybe I just lucked out when I installed my T56, I have no vibration up to the 100+ MPH I have been.

 

What boggles my mind is what I measured with a laser indicated the pinion set at two degrees pointed down. Using the protractor on the engine crank pully,with the car on the ground,it also points down one degree,which can't be right. What makes matters even stranger is I realized the differential must be higher than the engine.

I talked to Rossler's this morning,and the skinny he shared is all that really matters is that the centerline of the tranny,and centerline of the pinion are parallel. The working angle of the U-joint really doesn't matter,as long as it's not extreme.(Try to stay under three degrees)

Norval suggested the best advice,and I did set the tranny up in the tunnel as high as I could. With the tranny up this way,my shaft working angle is now only one degree. Now I guess I'll need to mess with removing pinion shims to get a negative one degree angle,or less there.

I started Googling for angle finders,and from what I see of them,the accuracy can't be all that great. The needles look fatter than the gradiants.When I mentioned my home brewed angle finder,I used a printout of a protractor about six inches acrossed,and sewing thread with a small washer for weight. I then held a square on the crank pully,with this Rube Goldburg protractor and could easily see to fractions of a degree. The gradiants on my protractor are about 1/16" apart,and sewing thread is only a few thousandths thick.

 

The industrial applications that i've seen so far (i know it's a little different animal) have called for an offset with small tolerance of the drive and driven yokes so that the driveshaft makes the same angle on each end. in these cases the yokes at each end were essentially stationary. the reason given was to extend the life of the u-joints. the rpms are generally constant and not as high as an auto can reach, so am not sure how a zero or very small offset can affect vibration ????

 

You need an angle at the u-joints for them to perform correctly. They were designed to work with an angle, not straight.
As I posted before, in an ideal setting, you want between 1 and 3 degrees positive at the tailhousing and the exact opposite but equal angle at the pumpkin(1 to 3 degrees negative). This will create the desired angle for the u-joints to perfrom correctly. You don't want any of the angles to exceed 5 degrees of either positive or negative. Ideally that number should be closer to 3. If the angle exceeds 5 degrees, you end up putting un-necessary "stress" on the u-joint and will wear it out pre-maturely.
Hope this helps.


Richard