Vibration at 15-20 mph

Hello, I would be grated if someone have solved a similar problem.

I have a vibration in my A108 at 15 to 20 mph and around 30-35 mph.

It's noticeable when accelerating normally or deccelerating normally, in gear.
No vibration when coasting at any speed, and no noticeable if you accelerate hard, perhaps because you pass those speeds quick.

It appears to be a driveline vibration, but I have measured the driveline angles and are 4° between transmission and driveshaft, and 4° between driveshaft and differential.
I don't know if they are the correct ones it must be, but they are the same.

Any help would be appreciated a lot.

Happy day for all.
Alfredo M.

U-Joints, drive shaft not balanced, those two will also cause a vibration.

here is some ideas, move the front tires to the rear, move the rears up front.
hopefully this would eliminate flat spot in the front tires, have you had the tires balanced??.
as mentioned above it can be the u joints. a lot of these are so tight you can't get to a grease fitting if it has one,
is this a automatic or 3 speed ???.you could try to jack up the back end on jack stands, and try running it, although it may not do anything with out the load,
if it's a automatic it could be a bad torque converter or lose bolts holding it in place, or the wrong one, is it a v-8?? the 318 and the 360 engines have a lot of parts that will work on both engines but the torque converter is not one of them, one engine is balanced internally and the other is balanced externally, i'm fairly sure the front damper on the crank shaft can not be swapped from a 318 to a 360 either, and could cause the same problem, the front damper is also called the harmonic balancer

Thank you all, for your answers and ideas to check. I appeciate much your help

I must to add some more details:
Engine 225/6, A-727 trans.
I got new tires, and balanced, as the old ones were a little hard. No change.
Fronts to rears swap. No change.
Renew the u joint and revised and repacked ball & trunion. The vibration was reduced but not eliminated.
Trans tail check for any play, but in perfect shape.
I have done the on stand test and no vibration at all without load.
It only appears under a medium load at the 15-20mph and 30-35 speed range.
If you don't accelerate or deccelerate, you don't feel any vibration.
Vibration is at the same speed in first, second or drive gear. Then I had eliminated the converter posibility. Anyhow, I have check the converter bolts and they are ok.

I have looking in the service manual, but only says, " check for paralelism".

I know, it isn't an easy question, but after all those test, the only thing I can say isn't perfect was the trunnion case, having a very, very little play in the bench (perhaps 0,4mm) but installed in his angle is totally firm. I doubt if this could be the problem....

Thank you all in advance....and happy vanning.
Alfredo M.

what condition is the tranny mount and the rubber motor mounts ??

The mounts are 5000 miles old, the old ones was smashed, but same vibration.

Did it vibrate since you got it or after some work was done on it,,,,,,,how about rotate the U Joint at the rear end 180 degrees and see if there is any difference,,,,,

Yes it vibrate from the first day I got it.
But, ...I haven't test the u-joint at 180° !!!!. I will test it as soon as possble.

Thank you all for your help.

Back to tranny bushing @ tailshaft & ball & trunion!1 Remember -after you greased ball & trunion vibes were not as bad!! yet still there-likely just replace that & do a tailshaft bushing !! are u-joints greaseable?? if not-replace them!

Thank you for your answers.
Yes, when I have cleaned and greased the ball and trunnion, the vibes almost gone, but they return to the same level in a short time.
I will try the 180° position, and if it don't feel better, I will try to get a new ball and trunnion unit.

Thank you for your help. I'm very pleasant.

could be the trunnion shaft is bent or moved,,,,,,a hint would be that greasing it did improve the situation temporarily,,,,,,,,you might try removing the driveshaft, and running the transmission through the gears and see if the transmission jumps around, you are just looking for clues,,,,,,,

,,another thing to try is to watch the ends of the driveshaft as someone holds the brakes on and shifts the trans through ALL gears,,,,,,,see if something moves out of place,,,,,,how does the pinion bearings feel in the rear end,,,,,,is there a lot of backlash in the ring gear?

Thank you donivan65. I will try those posibilities, but i have tested without any load and no vibes.
But really could be some thing jumps around....
I will try all this weekend...with help on the pedal.

Big thanks.

has this been resolved yet ???

Hello, after trying the past possibilities and without an apparent reason, Iwent to the trunion unit again....and...
After a carefull checking for looseness in any rotating position.....all was ok until... Repeating the procedure of turn a little and hand push check, In an only one position, I see "1/8 play" in that only position. A lot!!!! ...and only in a concrete location. The rest of the turn was perfect.

The trunion has a worn section detected only in the installed position and in a concrete rotating angle.

Greasing inside reduce vibration as donivan65 says...

I'm getting a NOS unit, and shortly it will be installed.

I will report the results.
Thank for all for the help in locating this phantom vibe.

Happy ride.

Glad to hear you found the problem, Good Luck!!:cheers