Drive train vibrations from Getrag 5-speed retrofit 280SL

[Berggreen]

Hello everyone

I recently had a 5-speed Getrag 265/6 gearbox and shortened drive shaft installed in my 1970 280SL (originally manual 4-speed).

I have now done a bit more than 1200 km with the gearbox and revised (shortened) drive train, and the gearbox runs and shift great - it’s like having another car, when driving at an elevated speed at now much lower RPMs.

However, I have recently noticed a vibration issue that slowly have become worse and worse, and it seems to originate from the drive train rather than the gearbox, when accelerating at high torque, thus especially in 2nd gear. But the deep vibrations from the rear, which can be felt in the chassis, can also be felt in  1st and 3rd gear, but are most pronounced when accelerating hard from stand-still going through 2nd.

I can almost avoid the vibrations, if I accelerate more smoothly and I don’t push/torque the car. But if I accelerate harder the vibrations are there again. But they can only be felt when accellerating from stand-still - not at higher speeds in 4th and 5th gear.

Just for the record: As part of the installation of the 5-speed Getrag, the special shortened front drive shaft was welded to a BMW star-fitting to match the Getrag 265/6 originating from a BMW, and then balanced together with the rear drive shaft at a drive shaft workshop. Also, a new BMW rubber flex-disc was installed. Likewise, the center drive shaft bearing and rubber housing was renewed too and the cross link bearing at the rear axle end was also replaced, before balancing of the drive shaft.

In the beginning the vibrations were not noticeable, but they have become increasingly apparent over the past 4-500 km.

Any clues what I am facing here?

Thanks,
Christian

[Jack the Knife]

How is the transmission mount?

[Cees Klumper]

Sounds like one of the driveshaft bearings, although new, is failing. Go underneath the car and check for any play / movement in the driveshaft.

[Berggreen]

Thanks a lot. I will start by inspecting the drive shaft for play and the transmission mount and get back to you. 

[DaveB]

Inadequately tightened fasteners anywhere in the driveline might cause vibration under load (as you've no doubt considered). And rubber mounts or bearings as suggested. If you have a gopro or similar you could try mounting it under the car on a test drive.

[Pawel66]

From my Gclass struggles experience:
1. Misalignment of the drive line
2. Misalignment of the drive shaft joints
3. Output or input flanges radial play (even small amounts, to be measured with attached micrometer, very small tolerances there)

I had a small uneven surface on the transfer case output flange that caused slight misalignment. Vibrations not felt while cruising, but under load the drive shaft started moving sideways causing vibrations. Getting flange through grinding on a lathe made it. 

[DaveB]

It’s interesting Pawel that such a minor deviation from true in one component caused vibrations. Given that, it’s  surprising that most drivelines run smoothly. I guess something like that may not be apparent on a GoPro camera either.
It sounds like an issue for the workshop who did the swap Christian (or did you do it yourself?)

[Berggreen]

It’s interesting Pawel that such a minor deviation from true in one component caused vibrations. Given that, it’s  surprising that most drivelines run smoothly. I guess something like that may not be apparent on a GoPro camera either.
It sounds like an issue for the workshop who did the swap Christian (or did you do it yourself?)

Thanks a lot for your input, and I have indeed an appointment the coming Monday with the workshop, who did the Getrag 5-speed installation. They will raise it on the lift and take a look what is causing the vibrations.

I will keep you posted, once I have news from the workshop. :-)

By the way, about the Getrag, then it is running smoothly in all gears (except reverse where I sometimes have to work it a bit in and out to avoid "teeth brushing" and make it engage) with ATF Dextron III, although with a slight bit of gearbox noise, also when warm at certain rpm levels.

In connection with the visit to the workshop, I will therefore also ask them to change the ATF again in the gearbox, as the gearbox had an unknown past history and was a bit of a gamble to install, and after 1300 km it may be good to flush the oil out and refresh with new oil. But I have also asked them to add some engine/gearbox add-on, which I have with succes used before in the engine oil in my other cars, and which reduces the internal friction between contact surfaces. It is not a Teflon based product, but it chemically works with the internal contact surfaces and makes them smoother. I am thinking that this may cure some of the slight noises, the gearbox makes and will extend the lifetime of the gearbox.

What are your views on this?

Cheers,
Christian

[Pawel66]

It’s interesting Pawel that such a minor deviation from true in one component caused vibrations. Given that, it’s  surprising that most drivelines run smoothly. I guess something like that may not be apparent on a GoPro camera either.
It sounds like an issue for the workshop who did the swap Christian (or did you do it yourself?)

Indeed! But the tolerances came from the book. Grinding the flange on the lathe fixed it. I saw the car on the dyno and I saw the shaft going sideways under load.

I have also learned many things about these shafts - angles, position of yokes vs. each other, etc.. I thought before it was just a question of balancing... well, it was not.

[Cees Klumper]

When I was 19 (1979) I drove a Triumph Spitfure that had a driveline vibration under load. I suspected one of the driveshaft U-joints - the front one is accessible from within the car once a tunnel cover is removed, so I put the rear on jackstands, let the engine run in gear, and sitting in the driver's seat held a piece of chalk closer and closer to the spinning driveshaft until it touched -  and it only touched one side, so the flange was not centered etc. By inserting a shim into one side of the U-joint fitting underneath the circlip holding it in, and grinding down the opposite side circlip, I was able to move the driveshaft to exactly 'centered'. Drove it happily ever after with no vibration.
Fast forwarding to 2010, a used 2002 Volvo S80 (FWD) I bought in Geneva with 30K miles also had a vibration under load. Turned out the passenger side driveshaft was just a slight little bit bent, likely from a fender bender the PO experienced (I also found a small bottle of Jagermeister tucked away behind the fuse box cover). I replaced it (the driveshaft) and it's still doing duty without any vibration today.

[Pawel66]

There is a natural question coming to mind when you read your post, but I do not want to sidetrack the thread...

[Berggreen]

There is a natural question coming to mind when you read your post, but I do not want to sidetrack the thread...

I am curious Pawel, what are you thinking of? Don’t worry about side tracking.

[rwmastel]

They will raise it on the lift and take a look what is causing the vibrations.

If they are looking at alignment of the drive train, keep in mind that the engine is mounted to the subframe and subframe to body.  If using a 2 post lift with arms under the body, subframe mounts may sag, lowering the engine to a position it would not be in otherwise.

Group, is this proper logic?  Check alignment of components on a 4 post lift?