Vibration/high frequency shudder under heavy acceleration in 1st and second

Hi Folks, my dealer ended up paying $1000 towards my timing chain and VVT repair, so it's booked in tomorrow to have the work done.
Unfortunately there still seem to be problems with the car, and I am posting here to get some advice on the next problem,
I have a vibration/high frequency shudder ( a bit like driving over a washboard), under heavy load/hard acceleration in 1st and second, particularly from 3200 to 4600 Rpm subsiding after that as the reves rise ( I am aware this is where the load would be greatest at it covers the torque curve peak) ,the car also has a similar vibration although much, much less apparent at around 2500-2800 Rpm while cruising and light acceleration. and yes the e-brake one click trick removes the vibrations. my car is still fresh from the used dealer, and he put a new set of Toee 225/40/18s ( not the exact size but same tyre : HAIDA / TOEE HD921 255/30R22 93W SUMMER TIRE | AWSIDE AUTOSPORT ) to go with the 70% worn Kumhos.
I have just had a rotation, balance and alignment, and if anything it is worse, I bought a meter rule and foot rule to measure actual tyre heights and with the 70% Kumhos on the rear now and the new Toees on the rear I ended up with 42psi on the front and 36psi on the rear to get close to the same tyre height.
Incidentally I do not have much if any diff whine
I have googled this subject to death for a week or more, and have read all the ozmps posts I can find, so this is my last ditch attempt to get some actionable feedback.
as far as my tire suspension place has told me my diff mount looks fine and is not loose or broken, although this car seems like a mysterious unicorn to my local mechanics.

Different rotation dimensions front and back causes the AWD system to chuck a hissy fit...

Quote:

---

Originally Posted by SarcasticOne

Different rotation dimensions front and back causes the AWD system to chuck a hissy fit...

---

I have read this, hence the measuring rule and tyre/ rim height check and tyre pressure adjustment I performed.

The fact it goes away when you pull the hand brake up one notch says to me it's the awd system not liking something...

And as the last thing to be touched on the car was tires, I'm still inclined to point the finger at them...

I'd consider getting the dealer to swap the other 2 tires as well...

I saw some cheap Chinese tyres the other day at a wreckers, plenty of tread but bulges all along the side walls.

I once had a FWD car with worn tyres on the back. When I moved them to the front the car became almost undrivable. I suggest swapping the Kumhos back to the front where all your steering and most of your power and braking is done.

As long as the tyres are the same specified width and profile I wouldn't expect trouble with the AWD. I have never had an issue with my CX7 as the tyres have worn out.

Quote:

---

Originally Posted by SarcasticOne

The fact it goes away when you pull the hand brake up one notch says to me it's the awd system not liking something...

And as the last thing to be touched on the car was tires, I'm still inclined to point the finger at them...

I'd consider getting the dealer to swap the other 2 tires as well...

---

I appreciate you feedback Sam & I agree the AWD system Is not enjoying something, the problem was definately there before the tyre rotation,it may just seem worse because I expected it to solve the problem,
If the dealer wasn't 200kms away I would be on his doorstep by now have no fear, but getting repairs under warranty with him has been a serious uphill battle, so any knowledge I can acquire before I approach him is paramount.
Tyres are not a warranty item, and I am already hundreds of dollars down, I'm not sure what the legal implications of supplying a car with different make front to back 225/40/18s when the standard is matched 215/45/18s. but all this is a waste of effort if it turns out to be a driveshaft/cv joint problem.

@shakespeare
I know you have been here, I had hope reading your posts over and over again might point straight to my major problem cause :(

A local car in Newcastle recently went to gearbox place for rear end vibrations, they sent him away and told him to get all the tyres replaced.

rule of thumb for all awd vehicles, rotate regularly and replace all 4 tyres at once.

Quote:

---

Originally Posted by MPS2NV

A local car in Newcastle recently went to gearbox place for rear end vibrations, they sent him away and told him to get all the tyres replaced.

rule of thumb for all awd vehicles, rotate regularly and replace all 4 tyres at once.

---

And this fixed the problem?

Don't know, the bloke doesn't have a job, good chance he doesn't have tyres yet either!

Might sound strange, but do you have a friend with a modern (BA, BF, FG) falcon?

If you do, and they have 4 (relatively new) tires the same size, see if they'll let you borrow their rims...

Offset will be wrong, so they'll stick out from the fenders, but it'll answer your question :)

And there is no legal issue with having different brand tyres front to rear.

However, just because they say they are the same size, doesn't really mean they are. Could be very minor differences due to shape or tread.
Also, you will want to measure the rolling diameter of the tyres, not height. And it would be quite difficult to do so accurately

If you're ever in Brisbane, you can borrow my track set of tyres (I'm that drunk prick on FB) 😊

As said on FB - even though your tyres all say 225/40/18, each different manufacturer will have small differences both in grip and in rolling diameter (different moulding machines). This will cause your AWD to play up - you may be up for higher cost repairs with the diff later longer term down the road if this does not get rectified soon - a few members can attest to having seen this scenario I think mainly on the mazdaspeed forums..

Quote:

---

Originally Posted by SarcasticOne

Might sound strange, but do you have a friend with a modern (BA, BF, FG) falcon?

If you do, and they have 4 (relatively new) tires the same size, see if they'll let you borrow their rims...

Offset will be wrong, so they'll stick out from the fenders, but it'll answer your question :)

---

So it'll have hella poke and there's a Downshift meet this weekend so you'll fit in... win/ win [emoji14]

I got a local quite for a set of 215/45/r18s Hankooks $840 fitted, so just need to raise the cash.
Thanks for the offer of a loan of tires/wheels, but whatever I still need to get matching boots or I'll end up with issues down the line even if I don't have diff problems yet.
Thanks for all the info and advice.

Jax has achillies ATR sport 2 - which i have heard isnt a bad tyre for price - 125 ish each..
try that if you like

Ok Folks update time. Thanks again for the support and advice.
Just traded my mismatched used tyres In for $120 and therefore paid $720 for 4 Hankooks fitted and balanced.
Results: 90% of the vibration is gone, road noise is much much quieter.
Next step will be to change out gearbox, transfer & diff oil with something decent. Can't seem to get the Motul oil so will have to look at alternatives for the dif and trans.

Latest update:
Still having vibrations at 50-55KPH, pull e-brake one click and gone, and mild washboard vibration feeling under hard acceleration in 1st and 2nd.
Went to my local Mazda service center and got them to test drive/hoist check it (out of desperation more than anything).
Their diagnosis was that the rear differential mount bushes were degraded & to blame although by their admission upon visual inspection they seemed fine, they had had this issue before (yes in my home town!) on another 6 MPS (although the vibration was at 100kph on this one) and they had changed diff components to no effect before changing both front and back diff mounts which seemed to 90% solve the vibration.
Quote for the mounts front and back is $635 and labor is $202.
Parts have been ordered from Japan, so it will be weeks before they arrive and I have to make a final decision on the work.
I have read (amongst a million posts about the diff mounts) that the Mazda diff mounts now supplied are a revised design, and are better.
I know they are not going to be as solid as an aftermarket mount kit, but as vibration (and to some extent a touch of diff whine) is already the main issue, I would rather not have a high duro bush setup.
In addition to this nearly every aftermarket mount/bush I've read about seems to have had failures or problem, so to me it seems there is no obvious aftermarket choice, especially for a lower duro one.
The mounts on the car have lasted 120,000ks so far and I will not be pulling over 170kwATW, so I am sorely tempted with the revised (if they really are) Mazda offering.
Any thoughts or advice at this stage would be most appreciated, before I spend more hard earned dosh on the car .

SOLVED.
Got new tail shaft from breakers, balanced at engineers shop.
Vibration under hard acceleration gone. Totally gone,
bibration at 55kmh gone.
old shaft was stiff at one of the unis,