Vibration assistance needed - Manual Transmission Related?

[R Leo]

Marlene's auto -> manual swap has logged about 1000 miles and, since day one with the manual, she's had a bad vibration in both third and fourth gears.

Here's the facts:

1)This vibration manifests isself in the 1400 to 1900 rpm range and only in 3rd and 4th gear.

2)The vibration only occurs when the the drivetrain is under load either accelerating or decelerating. If you feather the throttle to minimize/nullify the driveline load, the vibration goes away.

3)The vibration is (I'm guessing here) about 30-50Hz and doesn't seem to increase in frequency. If it does increase, it is only a slight change. The amplitude is significant; if you really have your foot in the throttle, it will blur the image in the rearview mirrors.

4)Driveline and engine support status:
— All new motor mounts (front and rear)
— Remanufactured driveshaft installed 10/03 (did not vibrate prior to tranny swap)
— Stub end of driveshaft shortened during swap using piece from donor car. End bushing has been checked for fit on the transmission output shaft and feels the same as the reman stub.
— Driveshaft was balanced when shortened. Has been separated a couple of times but has witness marks and has been reassembled correctly.
— Overall, I'd say the transmission is quiet. No apparent chipped-tooth sounds, no whining. The fluid was replaced during the installation.

I guess what I'm looking for here is other's experiences with the four-speed manual. Particularly failure modes and bad gear box experiences.

Danke schöen!

[leathermang]

As soon as you are ready to fund a dynomometer out here I will build it... and you will be able to get under the car with it under load and at the right speed and SEE what is vibrating....
Just let me know.... it will be great to have it here for future Get Togethers...

[boneheaddoctor]

and there is NO chance the driveshaft halves got seperated and reassembled in a manner that upset their balance? Sounds like a driveshaft balance issue

[R Leo]

Originally posted by leathermang
As soon as you are ready to fund a dynomometer out here I will build it... and you will be able to get under the car with it under load and at the right speed and SEE what is vibrating....
Just let me know.... it will be great to have it here for future Get Togethers...

Great! And, we'll use your MBZ-powered DC welder to build it with, right?

NO chance the driveshaft halves got seperated and reassembled

Seriously, the driveline is OK. Balanced at the time of alteration; always reassembled with the marks in the right place.

My past experience with driveline vibration issues was a rumble or a roar...sometimes a heterodyning rumble. This is a distinct BUZZ...this is like an oscillating sander.

[boneheaddoctor]

ok, hmmmmmmmmm need to think about that a bit.

[leathermang]

Ok, Randy, What do YOU think it is ?

[R Leo]

Originally posted by leathermang
Ok, Randy, What do YOU think it is ?

Dunno.

[leathermang]

If you " Dunno"... it seems illogical to rule out some of the things you seem to have.....

[R Leo]

Originally posted by leathermang
If you " Dunno"... it seems illogical to rule out some of the things you seem to have.....

I'm not following you.

The first entry in the thread states the conditions the work that's been done and, at least I think, a pretty accurate description of the vibration. Right now, I'm out of ideas about what is causing this vibration.

Short of spending a sunny, Texas afternoon laying on my back in your sandy pasture, performing a potentially avoidable transectomy on Jane Donor, I dunno what to do next.

Hopefully, Ridge, Grimgaunt, TomJ or someone else who has more experience with MBZ Standardgetribe than you or I will see this, think about it and pony up a new idea or two.

[leathermang]

You have assumed, because you did everything you could think of, and which anyone has said needed to be done , that those parts are not causing it... but something is missing from the equation... and I don't think those items should be ruled out until you can see them NOT vibrating at the same time you can feel the vibration in the car...very small things can either cause, or several small things can add up to something like this...
When people around me lose things... and I start looking all over... they often say ' it is not there I already looked".... but having found many things ' there'.... I ask them if they know where the item is... and when they admit they don't... then I keep looking all over...and I find the stuff....
Why don't you go to that dyno place, put a camera under it and get the vibration going... ?

[R Leo]

Originally posted by leathermang
Why don't you go to that dyno place, put a camera under it and get the vibration going... ?

Because, I'm not convinced that if you did put the car on the Dyno and buzz it, you could pinpoint the cause....we're talking about enough vibration amplitude to blur the image in the mirrors. Everthing on the car moves when it buzzes. How will you tell what the abberrant component is if the whole damned car is shaking???

...anyway, that's gonna cost me at least $50-60 just to ride the rollers. I'm going for the cheap (Forum) solution first.

One more thing, the DynoJet isn't a brake dyno. You can't very easily just load it up and run against the resistance at a given speed for any length of time.

[bkr]

just bought a 300TDT converted from a 230TE. Not total similar vibration pattern but very close. The engine mounts has a damper on the left side but not on the right side. I think diesels are supposed to have dampers on both sides.


-bkr

[rgp123]

I have a little vibration in my 240 around 35 mph (no tach) in 4th and 20 mph in 3rd. Larry Bible's suggestion about two flat washers under one side of the carrier support made very little difference for me but you might give it a try unless your bearing and support are new as well. I believe replacing all mounts next will fix my "buzz." I know what you mean about the mirrors!

[leathermang]

Ok,, all new motor mounts....
Did you make one of the homemade tools the shop manual says one needs to position the motor mounts correctly ?
If you did I need to borrow it... and won't make my own when renewing my motor mounts.... but I suspect you did not make one.... therefor have no way to know if the motor mounts are centered properly...

[R Leo]

Originally posted by rgp123
I have a little vibration in my 240 around 35 mph (no tach) in 4th and 20 mph in 3rd. Larry Bible's suggestion about two flat washers under one side of the carrier support made very little difference for me but you might give it a try unless your bearing and support are new as well. I believe replacing all mounts next will fix my "buzz." I know what you mean about the mirrors!

Bearing, support and all mounts are new. Buzz is bad but not as bad as it was.

FWIW—No tool is required on the 123.193 (wagon) with the OM617.952 engine and two engine shocks. The tool is only used to correctly torque the fasteners holding the rubber part of the front engine stop on non-turbo models (some 123s and all 115 chassis).