Oyoyo - Now Chicken Coupé

[Andrew]

I am trying to get rid of a very loud vibration when this G is lugging - typically when changing gear upwards at sub ideal revs it sounds like the engine is lying directly on the chassis as if high torque loads makes something misalign and rub. I have hunted all the usual suspects and as far as i can see the enitre drive train is very well isolated from the chassis.

I seem to remember on later 460's that there was a brace introduced between the back of the gearbox and the transfer case. Can anyone please shed some light on its function and perhaps include a picture?

 

[Van]

Hi Andrew, it is probably the brace in the picture below. It connects the gearbox and transfer case with an adjustable link (picture from the internet, not mine, credit to its owner). Trevor has these brackets in stock (I asked him earlier this year). Not visible in the picture is a bracket on the gearbox which connects to the adjustable link, I will take a picture of my 300GD's gearbox bracket for reference if needed.

 

[Andrew]

Many thanks Van. I wonder whatit does?

 

[Alan]

AFAIK, it's supposed to counter the torque forces from the engine.
I recently swapped out my engine mounts with genuine MB ones and the difference to the worn out SY mounts was astonishing. Just putting it out there.

 

[Andrew]

My issue is only under load. Cruising is very quiet and smooth. Someting twists and touches and resonates to chassis. If only i could work out what sort of movement that grasshopper leg is meant to catch.....

 

[Alan]

I, think it will be exactly that ... On pull away and when accelerating or going up a hill, that's when the forces are strongest.

 

[Van]

I will venture a guess that the gearbox mounting is at fault, allowing too much play and causing misalignment.

Not to labour the issue, a nice video on vibration in drivelines is this: https://www.macsmotorcitygarage.com/video-driveshaft-angle-and-phasing/

I will be trying out that 'grasshopper leg' soon on my wagon - just to tick that box in persuit of solving all vibrations.

 

[Alan]

Cool, please keep us posted on results.

 

[Andrew]

AFAIK, it's supposed to counter the torque forces from the engine.
I recently swapped out my engine mounts with genuine MB ones and the difference to the worn out SY mounts was astonishing. Just putting it out there.

Re your first point - if i look at that device in Van's photo, perhaps it can resist a little vertical movement even though it has a gimbel as if it constrains the engine - gearbox unit into a radius around the output flange (as per arrow and circle). This movement is compensated in the centre prop slip joint but as far as i can see there is no constraint horizontally??

I have three brand new mounts - the engine are SY (plot-rat economy) and the rear (gearbox) is MB. I pulled out the lhs mount and looked for steel on steel rubbing evidence but could see none. I will pull the rear mount and check it, but I really hope Van is wrong as that thing has become pricey. I then hope Van will not suggest that it could be the rhs mount as this one sits in such a place that you first must grow a long ponytail and a pinky fingernail and then rub a crystal ball and say OMMMM for a long time before it comes out.

 

[Dikfrik]

Andrew I would try the "tie-rod thingy" between the boxes and see if it works - the torque moments on the drive train under full load can make the boxes move in unexpected ways considering the complex support arrangements. Trial and error is an acceptable problems solving if theory lets us down...

 

[Andrew]

I

Trial and error is an acceptable problems solving if theory lets us down...

You dont by any chance build road bridges?

But yes you are right - i will try and work out where to connect this “sprinkaanpoot” to my non standard 711 gearbox.

PS why do you think it has that adjustable vertical gubbin on it? As if it adjusts how much mass can press on the rear mount?

 

[Alan]

As far as SY mounts go, see my video attached. From the bottom up: MB White (turbo/RHD Driver side), SY RHS after 60kkm, SY LHS after 60kkm.

The SY RHS mount sagged around 15mm and was touching the chassis. With both SY engine mounts vehicke was really vibrating and had a "touching" noise obviously coming from the engine mount.

 

[Alan]

With regards to the bracket, it seems they were also changed with models.

Early 240GD

"96 290 GD

290GDT

OK so the actual triangular bracket is the same, just the mounting slightly different between the 290's

463's did not have it anymore.

 

[Andrew]

Thanks Alan. Useful info.

Can you guess as to why the adjustable turnbuckle?. The bracket makes me think of an engine hoist - ie it suspends the back of the gearbox

I am going to try and make a bracket to suit the 711.113 gearbox i have in there.

Those SY mounts dont look fresh at all!

 

[Alan]

No idea, maybe to get everything aligned when installed and no load?

 

[Dikfrik]

I

You dont by any chance build road bridges?

But yes you are right - i will try and work out where to connect this “sprinkaanpoot” to my non standard 711 gearbox.

PS why do you think it has that adjustable vertical gubbin on it? As if it adjusts how much mass can press on the rear mount?

Mmmm Bridges i have designed simple ones.. if you pay me a lot i will divulge where they are so you can avoid them with any vehicle heavier than a Jimny..

On a serious note - we do simplify the bridge structures intentionally with joints and special bearings so we can more accurately predict the forces to design for..

I will slip underneath my 290 to if i can figure our what that adjustment is for ..

 

[Dikfrik]

Looking at that "sprinkaanpoot" assembly on my 290, adjustment of the length of the link will alter the angle between the transfer box (it will tilt the transfer box) and the main gearbox but will also alter the load on the main box rear mounting. How much it will rotate the transfer box will depend on the stiffness of the main box mount and the weight of it. I think it could have an influence on the vibrations caused by high torque situations..

 

[Andrew]

Many thanks my friend. So its like a little derrick crane suspending the rear of the gearbox? And would the adjustable gimble be some sort of pre- load?