Datsun Roadster Forum-311s.org

I seem to have a driveshaft vibration. Worst about 45 mph. I have recently replaced U joints and had driveshaft balance checked. Out of the car, everything checks out fine. I suspect I have it installed out of phase, but cannot locate a reference mark. Please advise.

Thanks

Just a thought, how are your transmission and motor mounts? Are they in good shape?
If you had the driveshaft balanced, they usually stamp the pieces where they should match up - I had mine done this summer and had new U-joints installed by them at the same time. It's just a small punched line that goes across the two pieces.
You can look at the two u-joints, and if there are not any marks, just make sure that the two "fixed/bolted" points of each universal are in the same plane. I.E - the floating ends are the driveshaft only ones, and the fixed/bolted ones are on the differential and the transmission side of the two pieces of the driveshaft

If no reference marks are found, you may have to resort to re-installing the shaft 1/4 of a turn at a time "out of phase" to see if/when a new clocking position helps. Sorry.

I have a pickup with a bunch of slop in the rear yolk bearing of the transmission and it sometimes will vibrate when decelerating. I too have had the driveshaft balanced and replaced the U-joints.????

The 5 speed drive shaft has zeros or circles stamped on the yokes from the factory; I'm not sure about the 4-speed shaft. In any case, the yokes should be aligned with each other. A u-joint drive shaft uses the u-joint pairs to cancel out the varying velocities. The shaft itself will accelerate and decelerate but the overall velocity of the driveshaft remains constant. In order for this to work, the yokes have to swing in exact oppisite directions so the cross axis must be in the same plane. If the yokes are out of phase, the driveline all the way to the rear wheels will be feeling this rotational inconsistancy. Obviously on the 5-speed, you have to make sure the slip yoke spline is engaged correctly also.

I hope this makes sense.

Steve.

Motor mounts are new. Trans mount is a modified urethane mount from the list. I tried aligning the yokes, that seemed to make it worse. Guess I'll just make sure flanges are in same plane. Will look more closely for any stamped or other marks indicating alignment. There is a factory tacked balance weight.

Any other ideas?

I believe another poster had an issue with vibration and the urethane mount. They also tried new U-joints and balanced the driveshaft to no avail. It seems the urethane mount may just be a bit too ridgid, to cushion small vibrations actually exacerbating any imbalance. That individual went back to a OEM mount and the problem went away - IIRC. If you have the old mount, it might be worth swapping that out to see if the problem gets any better.

I would make sure the yokes can be moved by hand with there new bearings installed. I had to use a hammer a few months ago to get one of mine to move. Yes it got replaced. I replaced a u-joint once and one of the needle bearings came out of the cups and as I pressed the cap in to its seat it crushed the bearing.
Just some thoughts here.

Richard

I had this same problem - I ended up going back to the factory mount on the trans to test to see if it cured the problem - it did.
By chance are you running urethane motor mounts? I have wondered if the combo of hard motor mounts with the hard trans mount (that is what I had) may have contributed to the problem.
There is a Chevy mount that can be adapted (I think the number at Advance Auto was Pioneer, Inc 2268) for a 69' 396 Chevy 4 speed that needs similar modification to the urethane units - not hard and its a cheap mount.
Worked for me....

Mark
70 SRL
-Ohio

Thanks to all for your seasoned advice.

I was able to find the factory marks (stamped 0s) as described and align everything properly. Vibration is still there, though not as severe. I do have a urethane trans mount. I replaced both motor mounts (stock) at same time. That was about two years ago. I haven't driven it that much and had also redone the rear axle bearings.

I think the urethane mount is the likely source. The old factory mount was shot. I think I'll try the alternative Mark described above. Will let you know if that's the fix.

PM me if you have any questions, but the changes are just like the urethane requires....

Mark
70 SRL
-Ohio

Something else to consider is whether the U-joints are assembled correctly. I've done lots of joint replacements on my Z car. I learned that if the bearing caps are not perfectly centered in the yoke, it will cause vibration. I have urethane motor and tranny mounts. Even with a balanced engine, I get a lot engine vibration transmitted to the car. But I feel it the most at idle. The vibration doesn't seem to be car speed dependent. In your case, it seems to be speed dependent which usually indicates imbalance or the driveshaft not running on center.

45 mph is the "classic" speed for driveline imbalance if you look at a diagnostic chart. I have the urethane mount and it's a bit harsh. I may go to the rubber chevy mount.

A few things that can affect the driveline you may be able to check. As mentioned above, a tight u joint bearing cap can be an issue. As far as phasing, if you put the driveshaft on a Vblock or lay it on a bench and put a bubble level across one set of yokes and level it, you can compare it to the other end and they should be exactly the same.
Another thing is the angle of the pinion shaft vs the angle of the output shaft in the transmission. They should both be parallel to each other, so the angle of the front and rear joints will be equal. You can measure how many degrees from level each of the mounting flange faces are, they should be equal. Essentially, if you extended a line from the trans output shaft centerline back and from the pinion centerline forward, they would be parallel. Flanges on the transmission, pinion and driveshaft also need to be clean and flat, a piece of rust can cause alot of misalignment

So lots of talk here... a simple question: I've had my drive shaft out many times and always just put it back so that the two sets of ujoints are "aligned", i.e. if the back one was straight up and down and moved up and down, I made the trans one the same way... I assume this is correct? Am I making sense as I try to visualize this from my desk?

I would just use as you have it if doesnt vibrate. Trans seal isnt leaking. Differential seal isnt leaking.

Rich