Technical Drive train angles on ..an option to correct??

hi guys, I bent my trailing arms on my 41 buick. So made the repair and added a torque arm. here is the way things sit at the moment.. the trans points down 6.3 degrees, the pinion on the rear end 2.0 degrees up. If my memory serves me right the angles need to match. the drive shaft is at 1 degree.

The way the car drives "now" I get a bad vibration at 50 +. This is not a new build. its been on the road for a few years now and never had the issue. During the repair I noticed the yoke that goes into the trans was not as much engaged as I would like it to be, so since I had everything apart I had a new drive shaft made by a shop in town. they did balance it too. I also needed new tires so had new tires installed too. looks to be in phase too,

so my two options I believe is remake the brackets for my trailing arms and torque arm to move the rear end to 2 deg up to 6 degree up..which is a bit of a pain. or...raise the the trans up 4 deg up. (to note..the carb is not level, but leaning back 3 degrees) so raising the trans helps out both angles. I never had any carb issues though. My question to you guys out there, is if I raise the trans 4 degrees, how much can that exhaust tube tweak?

 

You also need to consider the operating angle of the u joints. The operating angle needs to be at max 3.5 degrees or you will experience premature wear of the u joint and possibly a vibration. The joint will work at a greater angle, but will cause problems. Looks to me like you need to use both options. Raise the trans to 3 degrees down and the pinion to 3 degrees up and see what that does for the operating angle.

 

It's kind of difficult for us to see your exhaust system, to be able to guess at whether or not it can take that much misalignment. If it's a good exhaust system, it probably can't. If it's just some bad fitting junk, maybe it can. pictures?

 

To maintain correct angles and minimise strange harmonics it's best to stick to a well proven formula. The exhaust if moved up with the rear transmission mount will put it under tension at the engine flange(s). With the domino affect it will impact on clearances close to engine / frame etc and the mounts. The other end won't be affected as much. What engine transmission combination are you running? Get your critical drive train alignment issues sorted and then tweak the exhaust to suit.

 

What he said...

 

My engine is a 254 buick nailhead with a 700r4 behind it. My exhaust is a good solid one(s) duals.
the more I thought about it today I might just try first remaking my mount bracket. The car ran awesome for thousands of miles with the old set up, but my rear end was matching the trans out put shaft. never any vibration. To be clear is operating angle the same as working angle?

 

And doesn't operating angle of u joints depend on the u joint type?

Sent from my LGUS991 using The H.A.M.B. mobile app

 

I'd guess they did a poor job balancing the new driveshaft. I'd correct the engine/trans angle for lots of reasons but every 4wd pickup with raised body has worse angles than yours.

 

I also had a vibration to troubleshoot and found it had a needlebearing against the inside face of the cap from when they reused existing universals on a new yoke. It was really hard to spot because of the rubber seal, but when I loostened the universal the cap popped out from the universal itself. They must have used a 'c' clamp to draw the caps tight. It was an odd one and looked normal.

 

I suppose it would not hurt to have them recheck the drive shaft

Sent from my LGUS991 using The H.A.M.B. mobile app

 

you need to match the angles, not send the driveshaft back to be tested. Your angles are not compatible as they differ too much. A very slight difference is acceptable.

A cross type u-joint, running at an angle: The input rotation is a stable "velocity", but the drive shaft is not "constant velocity".

The driveshaft is actually speeding up and slowing down during a single revolution. So, you have the driveshaft's "un-constant velocity" trying to fight the other U-joint that has a different velocity than the front u-joint. There is your vibration.

ask the driveshaft shop, they will tell you the same facts.
.

 

This is good stuff guys. Thanks to you all who replied. Im going to try to get the new bracket made this week. See what happens i guess.

Sent from my LGUS991 using The H.A.M.B. mobile app

 

Another good thread to bookmark!

 

Tremec has an app for smartphones (at least an iPhone) that I used to to set my rear end up, what that really means is I thought it was right and then after everything was welded up I found that I had erred. I learned how to fabricate a wedge shaped lowering block to fix my error.

The app works pretty good, good luck.

 

You don't need to be concerned with critical speed but driveshaft angle is important for longevity.

 

Firstly, with consideration to vibration issues, here's a user-friendly example of illustrating the importance of having the engine/trans. output shaft center-line parallel with the diff's third member pinion center-line.



Another thing to consider with the above is that ideally your universals don't like to have big angle variations between the input/output, typically most prefer to operate with a number between 3-6 degree's, so if you can imagine the center-lines of your engine, then the driveshaft, then going into the diff, whatever number you come up with at the front, ideally needs to be the same at the rear, and also somewhere between 3 and 6. The sky won't fall if it's a bigger variance (although service life of your uni's will be reduced), but it will shake the crap out of everything if they're not close at their typical service position.

With regards to your combination, I'd try to do a balance between tweaking the rear, as well as raise the trans. up a bit, the carb will be fine as it should have a decent scope in it's fuel bowl (after all, you don't typically have fueling issues going up or down hills do you). if you can adjust the angle of the m both, and get them the same, that will minimize the effects on other components such as exhaust.

Cheers,

Drewfus

 

Can some one add to this discussion regarding the use of a constant velocity Carden joint as in my car?
Engine in negative 4 degrees downhill.
Both driveshaft and rearend rest at zero degrees ( both in the same plane ).
What should I adjust the rearend to minimize a vibration at 50 - 60 mph.

 

Follow the info from mgtstumpy. The operating angles of the u joints should be 3 deg or less & within .5 deg of each other ideally. Your comment about raising the trans 2 deg & rotating the pinion 2 is a good plan. I would watch for floor pan/ trans clearance. I had to do all this on my 40.


Sent from my iPhone using The H.A.M.B. mobile app

 

Just my opinion, but even if a true CV joint is used at the front, the rear joint running with zero angle will wear out very fast. It needs some rotation of the needles to move grease under them. A joint running at zero, makes straight grooves in the cup and cross stud.

 

In case you're wondering about vibration....if you get a hum that you can feel in your ass at speed, it's driveshaft related, either a u joint going, or poor driveline angles. Personally, I don't care what 4x4 trucks run for angles, these are not 4X4 trucks. My 36 ford pickup has been on the road 17 years, trans three degrees down, rear yoke three degrees up, still waiting for a u joint to wear out. LOTSA miles on her.

 

Generally speaking if it don't look right it ain't! So start there, forget all the mumbo jumbo and make it "look" right! Then make sure you have enough yoke engagement and make sure the "U" joints are not "outta" phase. Common sense will help a bunch in these situations...

 

Shim the axle to put the pinion up 4º. If you have soft leaf springs, and/or a lot of torque, go with 3º.

 

1941 buick = coil springs?

 

Stock, sure, which this car clearly is not. We would not be talking pinion angles here if it were stock either, as it would have a torque tube.

 

the trailing arms and added torque arm threw me off.

 

Probably been said...correct term is driveline phasing....on high performance applications you want a little rear axle negative phase for launching...traction bars are a great cheapo solution...keep it a few degrees max and balance the driveshaft for sure...built a bunch of custom chassis stuff..never had a problem..keep it simple...

 

The top example below says it's OK (both angles equal but not parallel).



But this one says no (bottom example). Which is correct?

 

Top illustration has angles the same, bottom one has different angles. What is critical is the angles between the shaft and the yoke at each end. they should be very close to the same. Doesn't matter what angle the components are, as long as the angles between the components and the shaft are close.

 

The bottom looks to have equal angles to me since the red lines intersect at the halfway point of the shaft.

 

Look at the angles between the yokes and the shaft, that's what is important. Not a great illustration.......