Mazda 6 MPS Differential problems and/or solutions

[nissanman]

Good post shakesspeare. Very interesting actually. I'm on me iPhone so won't post big but I'm running stock as stock driveline and with only 3,000km old Tyre s

[ManicMPS]

Howdy guys, although I'm not hugely experienced with the MPS6 but being an ex-Skyline owner, I am certainly aware of a number of issues experienced by some of the GTS4 and GTR's on the forums. The 4wd models are definitely sensitive to the rolling diameter of the wheels, particularly when there is any difference front to back. One poor bugger in Adelaide with a GTS4 was running 18" rims with out a problem until he punctured a tyre. He took out the factory space saver and put it on to get him home (as you would). Didn't get far before he did irrepairable damage to his front differential. Ended up having to replace the front diff/gearbox assembly. His space saver would have been fine to use if he was still running the factory rims and tyres (which were 16" on the GTS4 from memory).....a big trap for the unwary!
Even though this is slightly off topic, I just thought it would be worth alerting those of you who have never heard of such things before. If you do not have a full size spare, you may be better off getting the car towed. Anyone every tried putting a mismatched spare on an MPS6 and lived to tell the tale?

[kmh001]

It's a good point you make about non-standard wheel diameters.

Fortunately, if a significant F-R diameter mismatch occurred (eg when using the spare) the diff coupling temperature would increase until the temp sensor informed the 4wd control module to go into fault mode and disconnect the diff coupling, leaving the car in FWD-only and hopefully preventing any damage.

Those of us with an MPS3 switch can turn the rear diff off and it sounds like running non-standard wheel diameters is another reason to install the switch, in case of a flat.

[shakespeare]

Another update, I've managed to get a few kms down over the last few days and here are my findings:

1) Diff whine is still there but very faint, mainly in 6th around 120kph and you need a smooth road to hear this.

2) Resonant vibration is still there but again very faint around 90-100kph again need a very smooth road to feel and hear it.

3) Vibrations under acceleration at WOT are still there, but again they are significantly less than when I had the 225/45/18's on?

Overall I'm much happier, however will try and get back to Mazda soon and take the service manager for a drive and see what he thinks

[shakespeare]

And one more update from the man with temperamental diff!

Thought I'd play with tyre pressure and see what effect this has, so this moring changed from 38psi all round to 39psi front and 37psi rear.

The big difference with this is under hard acceleration the vibrations I felt from the diff seem to have diminished again - now only very slightly noticable, in fact I've been a little nervous about giving it too much lately (after all my diff woes) but this morning I took a differerent way to work with some good roads with 100 kph zones and I must say that I was extemely happy with the way she ran!

Will keep monitoring this and play around a bit with pressures to see if I can totally eliminate the vibration!

[kmh001]

Shakes have you experimented with matching the tyre height?

[shakespeare]

I've got 215/45/18 all round now, but haven't measured the tyre height yet, will do this with the current pressures and see what this is.

[shakespeare]

Checked height 632mm front and 635mm rear, will alter this tonight and see what how it goes, thanks Mal that was a great suggestion!

[nissanman]

Another update, I've managed to get a few kms down over the last few days and here are my findings:

1) Diff whine is still there but very faint, mainly in 6th around 120kph and you need a smooth road to hear this.

2) Resonant vibration is still there but again very faint around 90-100kph again need a very smooth road to feel and hear it.


Overall I'm much happier, however will try and get back to Mazda soon and take the service manager for a drive and see what he thinks

Yep sounds like my life Spot on

[shakespeare]

Hopefully Final Update!

Re-adjusted tyre pressures - 40psi front 36psi rear

Tyre heights using my simple measurement method of a flat object on top of the centre of the tyre and a measuring tape - 633mm front, 634mm rear.

Results, the vibration under hard acceleration has almost dissapeared, still slightly there in 2nd. I need a longer drive to test fully but resonant vibration at 100kph seems to be almost gone too.

I'll post some more findings in a week a two after I've managed to clock up some km's

[kmh001]

Good one. I was able to eliminate my vibes by matching tyre height, but the pressures were all over the place, something like 23, 44, 51 36. No vibration, but the car handled like a wet sponge so I resumed vibrating. Sounds like you got a good result.

[shakespeare]

Update!

Over the last month or so the vibration under acceleration has been there particlarly when the tank was less than 1/2, which I took to less weight over the rear wheels, when full it seemed to go away again. Anyway the last 2 weeks I've driven about 3000kms so my tyres now have 5000kms of wear and the new diff bracket has been on for around 6000. The vibration under accelaration seems to have all but dissapeared (it's there slightly but not enough to cause any major concern.) I'm actually quite annoyed as I'm due to take the service manager for a drive tomorrow to try and identify this. My only theory is with the wearing in of the tyres (front more than rear, though they're pretty close to being even) is that the difference in front to rear rolling diameter is now the same and therefore there is no cause for the diff to vibrate??? As I said, I'm annoyed it's not there anymore as I wanted to show Mazda, but happy it's gone too - confused Oh well I'll still take it in as it has the 6th gear resonant vibration still.

[shakespeare]

Update, installed new CP-e rear mount and Turbine Tech forward mount today, it's never felt better, full story here

http://www.ozmpsclub.com/forum/tech-...html#post84872

[IN4M3]

hey ppl
thank to the forum members and there wealth of information.
All ways reading though these threads to see what's going Notice the vib in the rear end,that obviously the bolts workiing there way out of the rear diff mout, then today a bit of clunkiing when accelerating, on pedal "clunk" off nothing on, thought that was a bit sus so i check out the thread's to see what's a likely cause.
GO down and check out the bolts and one has worked it's way out and the other has gone. i noticed one endlink is a bit dodgie as well. thanks to the community!! now i know bolt size and how to fix, no drama, except i carn't drive RIGHT NOW

[mazda6mps]

IN4M3 - what rim and tyre package are you running? (rim size and tyre size)?

I would be interested in what others have in terms of rim/tyre packages, who have also suffered the 'auto bolt loosening' of the diff bolts.

[shakespeare]

IN4M3 - what rim and tyre package are you running? (rim size and tyre size)?

I would be interested in what others have in terms of rim/tyre packages, who have also suffered the 'auto bolt loosening' of the diff bolts.

Hi mate, I'm running stock rims and tyres 215/45/18.

FYI

Forward bolts sheared with 225/40/18

Rear mount cracked with 225/45/18

since back on stock and new mounts no problems and driveline is smoother than stock

[Doug_MPS6]

I'm at a loss to understand why different tyre sizes between front and rear axles (within normal tolerances) would be related to any vibration issue, assuming tyres in good condition and balance, etc.

The purpose of any kind of centre differential is to equilibrate for such differences, and that role is common to all vehicles with AWD, regardless of the mechanism employed by the diff to effect the result (mechanical, viscous, etc). Every time you go around a corner, both differentials compensate for far more differential axle rotation across and between axles than is induced by a gnat's whisker of difference in wheel circumference. And I'd sure not be introducing tyre pressure differences across an axle, as I have heard of some doing, which is asking for trouble.

Further, I also don't really hold with building cut-out switches to isolate the vibration at the expense of also isolating the RWD component of the drivetrain which I'm sure Mazda engineers must have thought long and hard about and considered a useful thing to have, and with which I'm sure we all agree, else why are we all on this forum waxing lyrical about MPS's?

The reason, or at least one reason, I bought the MPS6 was for its AWD attribute which makes it so good a) in shit surface conditions b) on corners and c) in emergencies.

I can really see myself identifying a sudden on-road crisis with mere milliseconds to act and thinking, "Crumbs, I might need AWD to help me through this", then reaching for and selecting the RWD isolator switch while endeavouring simultaneously to, say, control an understeer slide, then dealing with the transition to oversteer right when I am already really busy!

Sure there are long fast bits of freeway or open road where the MPS6 can tool along happily without its back axle; soooo......why not buy a stock Mazda 6 and be done with it, as we know they will all work for hundreds of thousands of kms in FWD mode? Why burn juice just to keep that pesky back axle turning?

But I just finished a fast 600km trip on a variety of roads and surfaces, and reckon there wasn't one part of that trip where I would have wanted to NOT have AWD. Fast overtaking, gravel verges, surface transitions, tram-lining longitudinal seal joins, long fast sweeping bends, dodging trucks and fools hogging the outside lane, and so on. I'm sure I would have worn my poor little switch out if I had been selecting and deselecting the back end every 20 seconds.

Sorry, but my back end stays selected. Any minor vibration at 100kmh I have is easily solved by not sitting at that speed, and I have yet to hear a passenger comment, far less be aware of it.

[kmh001]

It's nice that you don't have a vibration problem Doug. But in my car, before the gearbox was replaced the vibration was unbearable and I had no intention of driving along at 80 in a 100 zone just to avoid the vibrations. That would have been so absurd that I would have been better off staying at home or catching the bus.

There's no rule that says you must install a diff switch. But those of us who have one have done it for a reason. For my part those reasons are entirely justified and the advantages outweigh the disadvantages... come to think of it, there are no disadvantages.

As for car control, with the the rear diff turned off I have an additional over steer correction method that you don't have.

[shakespeare]

I'm at a loss to understand why different tyre sizes between front and rear axles (within normal tolerances) would be related to any vibration issue, assuming tyres in good condition and balance, etc.

The purpose of any kind of centre differential is to equilibrate for such differences, and that role is common to all vehicles with AWD, regardless of the mechanism employed by the diff to effect the result (mechanical, viscous, etc). Every time you go around a corner, both differentials compensate for far more differential axle rotation across and between axles than is induced by a gnat's whisker of difference in wheel circumference. And I'd sure not be introducing tyre pressure differences across an axle, as I have heard of some doing, which is asking for trouble.

Not sure Doug but the service manager felt quite strongly that diff wind up from non standard tyre sizes was causing my issues. Not willing to keep taking it back to them to fix mounts I went back to stock tyres! and put some new mounts in - all good now

Actually front and rear tyre sizes were the same, just all round different to stock, if anyone can offer an explanation why my forward mount bolts loosened then sheared and then loosened again after having them replaced with the 225/40/18 tyres I'll be a much wiser person and why then when I went to 225/45/18 I cracked my rear diff mount and then to have no problems apart from vibrations with the new mount on stock tyres, I'll be much wiser again! Thanks

[Doug_MPS6]

KMH001, Hi, sorry if I narked you a bit, as I sense from your note, that wasn't my intention. I know you to be technically competent and would have explored most if not all possibilities to find a solution to your issue. I wasn't being critical but trying to open logic avenues to assisting.

That said, one of my implied greater points was that I see on these pages so much stuff being messed with, often a supposed solution looking for a problem (of which TB earthing has to be one example), that it seems to me that often more fundamental things are at play that are not being exhaustively tested or examined. MANICMPS also raises a valid point in that some causes or effects seem to come right out of left field and are usually the last things to be considered, often after vast expense and time has been devoted to trying to locate the problem.

In your (or our) case, the fact that a manufacturer goes to all the effort to stick another 160kg of machinery under a particular model, braces up the frame to take the additional stresses and expects it to provide some handling or performance advantage, tells me that, after millions of dollars of research, it most likely works as advertised or planned. That's not to say I'm a great believer in the infallibility of manufacturers, for we have all seen some awful things tried by them that should never have seen the light of day.

So it seems to me that if you are having this irritating vibration, them something is fundamentally wrong. I know you have explored this at length, with some competence, but if de-selecting your switch restores the problem, or you feel you can only comfortably do so outside certain speed ranges, then plainly the problem is still there and the switch is a mere band-aid. It might keep you happy and sane, but I bet you'd rather not have it at all.

I sympathise. I've been down this street before with my V12 Jaguar, and I replaced and/or rebalanced literally everything that rotated or hung off a mounting, from disc rotors to propeller shafts to axles, and all bearings and mounts, but could never eliminate the speed-specific problem which in an otherwise ultra-smooth, quiet car like the Jaguar, was very noticeable. After the expenditure of nearly $12,000 and in a last-ditch assault, I eventually tracked it down to an out-of-balance planetary gear in the GM400 gearbox, where a small face-mounted bolt had drifted loose and fallen out - further validating MANICMPS's point!

There are only three mechanical principles - the cam, the lever and the wheel. When assessing vibration sources, it comes down to examining any one or all of these, but usually the first two, plus one other issue - harmonics.

Thus your vibration seems to indicate, obviously to us both, that something (most probably the "wheel" of our above principles) is rotating out of balance, (and)/or it is (also) a harmonics issue, where a minor vibration from a rotating source is being amplified, and/or a mounting is intercepting a harmonic in the wrong position and not allowing an otherwise minor vibration to resolve itself naturally (think rifle barrel compensators).

After owning three cars with centre bearings in a split propeller-shaft setup, I've found that these can be a real problem area and is the first one I examine in cases of drive-train vibration.

However, it seems that Chris is possibly closer to identifying the problem, perhaps even unwittingly, in that he has really been dealing with a harmonics issue. By trying to fix his fracturing diff mounts he has effectively been playing with intercepting harmonics, by strengthening mounts and changing the vibration characteristics of the materials they are made from.

Without try to teach you how to suck eggs, if it were my problem, I think I'd initially have both shafts out and spin them up and balance them in their centre mount, and look at the diff and centre mounts. The fact that you cut out the vibration with your switch suggests that whatever is going on must be in your front end, or the way it is mounted, for the propeller shaft and back axle are still turning when on-road, albeit in trailing rather than driven mode, hence if there were any vibration in these components, it should still be there regardless of your switch.

Failing this, as with my GM400 box, and as a last resort, one might be forced to look inside the front axle assembly, which it seems that you have done (with your gearbox replacement) with some reduction in vibration. It's so often the last thing you expect or the most expensive option that get s left until last. Sooo...where to from here?

FWIW, I've tried the handbrake trick and my vibration, such as it is, doesn't go away when the rear axle drive is isolated by this means.

Further, just as a bit of info, when I installed my CP_e DP, at 42,000kms, I removed both top and bottom engine mounts to drop the motor and give me room to work. They were still at spec torques and had showed no sign of backing off.