Gearbox Decel noise.

[bazeng]

I had the shims after trying to order the rubber grommets from mitsu (they gave me the wrong stuff). Suprisingly, it allowed me to find out that if mitsu sell these shims for the carrier bearings, it must be a common problem for them to provide a solution to cure it.

I too have the poly engine mounts. I found that they cause the engine to sit at a certain angle causing the xfer case to point if looking from the drivers side door at around 8ish oclock fixed, therefor the angle that the tail shaft entering the xfercase is somewhat off. I believe the RWD V8 guys aim for about 4 degrees. I loaded my first bearing with about 10mm of shims and it got rid of some vibration, I then loaded up the second bearings with about 5mm of shims and it once again changed the harmonics.

Another thing to keep a lookout for guys is the yoke cover. There is a metal sleeve that sits outside of the yoke which can get loose. Mine was spinning and caused a nasty noise which I thought was the twin plate. To fix it I just pressed it / knocked it back onto the shaft.

Also, look for any loose bolts / nuts that may be located under your carpet.

 

[JAP63]

I too have the poly engine mounts. I found that they cause the engine to sit at a certain angle causing the xfer case to point if looking from the drivers side door at around 8ish oclock fixed, therefor the angle that the tail shaft entering the xfercase is somewhat off. I believe the RWD V8 guys aim for about 4 degrees. I loaded my first bearing with about 10mm of shims and it got rid of some vibration, I then loaded up the second bearings with about 5mm of shims and it once again changed the harmonics.

So your saying in your case, the output of the xfer pointed down to the ground too much? and you then shimmed the bearings down to meet it and take away the angle you would have had?
I though the best scenario would be a straight shaft right through, from head to tail..never gonna be perfect though is it..

 

[bazeng]

Yes that is right.

I think it is somewhat aimed down to compensate for when the engine revs which will then cause the motor to lean forward causing the angle to flatten out.

It is also considered bad to have it straight.

It is all trail and error. Every car will be different.
Somebody give it a shot and confirm if it works or not.

 

[mrcyborg]

think ill give it a go, i have had some nasty noises since my evo conversion in the cyborg, lucky i only have one hanger bearing.
but i to also have solid poly mounts and only three of them at that, so might be worth giving it a go i think.
could you just use some washers you think baz? or you think i should use the mitsi shims?

 

[JAP63]

Yes that is right.

I think it is somewhat aimed down to compensate for when the engine revs which will then cause the motor to lean forward causing the angle to flatten out.

It is also considered bad to have it straight.

Jeez, now i think about what ur saying it makes sense, if it was flat and you had torque twist, it would just invert the shaft the other way.......maybe if everything was solid, you could align it closest to level and get away from all these angles to compensate for movement in things..though the other issue is, when u tighten the mounts up with a more solid composition of rubber etc, you end up increasing the NVH, so everything sound louder anyway and more vibrations are felt...
Where did you get the 4 degrees figure from, wonder if mitsu have specs on this?

could you just use some washers you think baz? or you think i should use the mitsi shims?

Essentialy, washers will work like shims, but if you need finer adjustment, ull need shims (as theyre alot thinner)

 

[bazeng]

the 4 degrees was from a old V8 modder I know.

He usually went for 4 degree's down / 0 degree's shaft / 4 degree's up (based on 2 piece shaft).

Some guys go for much lower angles. ie 2 down / 0 shaft / 2 up.

What you dont want is something like 5 down / 0 shaft / 0 up.

The uni angles are meant to cancel the noies / harmonics.

For race use though, this rule somewhat changes due to the shaft being constantly on load @ WOT.

As for the single piece (front) shaft for our cars, there is a guy in HONGKONG who has one and he tells me that it vibrates like crazy!

 

[JAP63]

Absolutuely rubbish drawing

But is this what u mean?

I can see something like that flattening out to close to 0 deg as the engine rocks, eg at WOT

 

[bazeng]

You would probably want to match the angles up and down.

But your drawing is pretty much correct.

So 4 up / 4 down with the centre flat.

 

[mrcyborg]

hey was just thinking mine is completely different!! i have only one hanger, but i also have a solid diff!! so mine would move the back section more with the squat and lift of the rear axel.
any ideas on this one tech gurus?

 

[JAP63]

hey was just thinking mine is completely different!! i have only one hanger, but i also have a solid diff!! so mine would move the back section more with the squat and lift of the rear axel.
any ideas on this one tech gurus?

A solid diff as in you have a solid rear axel, not a floating rubber mounted IRS setup?

One centre bearing, known as a two piece shaft i think would be similar but with no flat centre section, might be say 2 or 4 down, then the same up. Then again, it would depend, as you said on how much torsion your diff offered to the shaft....The rubber around the centre bearing should flex to some degree to accomodate for the changes in angle id assume.

 

[mrcyborg]

yes exactly, solid rear axel, with single bearing. i guess its mainly the input angle to that center bearing that i could change, so the back would varie quite a bit normally with the axel, i have also put in coil overs and changed the height with this conversion also, so may have affected it.
but i am leaving towards the transfer to center bearing more so being whats causing noises.

 

[JAP63]

yes exactly, solid rear axel, with single bearing. i guess its mainly the input angle to that center bearing that i could change, so the back would varie quite a bit normally with the axel, i have also put in coil overs and changed the height with this conversion also, so may have affected it.
but i am leaving towards the transfer to center bearing more so being whats causing noises.

Do the centre bearing first then see..

What car is it?

 

[mrcyborg]

we have another tail shalf coming into work in jan, so will try that one to see if its any diff, its a low km one.
its a ca model mirage cyborg awd. but its getting quite modified now from standard.