Transmission questions

[Architex_mA8tey]

Originally Posted by Mugzee

I forgot to mention that he said the 5HP boxes are generally very reliable. He also said a lot of premature failures are caused by MAF sensors giving readings that are slightly out of tolerance (wouldn't throw a fault code or CEL) and cause the transmission to shift at the wrong times. The only way of testing is by logging data and comparing to correct values.

I have read something about that before and that most people would change the MAF after fitting a new or rebuilt transmission. . . .

Interesting as I've always said that my MAF failing caused my perfectly fine box to fail and I replaced the MAF when I changed the box. My advice is to regularly scan your car for MAF codes etc even if the car is driving fine

[Delboy]

Could someone please explain to me how a faulty MAF can destroy a gearbox?

[notorious]

By the way, for ECU it is very difficult to catch MAF not working precisely. Most MAF inaccuracies are not noticed by ECU.

[Mugzee]

He was saying that as the ECU and the TCU both communicate with each other, when there are even slight deviations in MAF signal it can cause the transmission to shift at the wrong times. This in turn can pass too much torque through the box whilst in the wrong gear and cause excessive wear.

I would guess each gear has a designed operating RPM range and if operated outside those tolerances damage can occur.

[Delboy]

I suppose thats possible, but surely the ecu would communicate rpm etc too.

gearboxes are all about rpm and ratio so rpm would be a more logical signal to be sending to gearbox, but i guess load could be something to do with maf/ tps etc.

Just seems weird imo that the maf would screw a gearbox, if you said it killed an engine I could understand that quicker.

So how does one keep an eye on ones Maf? any links to what a good ones like and test procedures?

[ainarssems]

Originally Posted by Delboy

Could someone please explain to me how a faulty MAF can destroy a gearbox?

MAF values are used for load calculations and torque reduction during gearshifts. If it does not read correct it can cause extra load, stress and wear to gearbox during gearchanges.

That being said lot of failures are caused by faulty seal which fails due to age and thermal cycling. Oil contain conditioners for rubber parts but with age additives in oil wear out and stop conditioning them. Regular oil changes help to keep seals in good condition and last longer.

[Mugzee]

The only way you can monitor in that depth is with diagnostic software.

This guy used to work at Audi. He was saying that RS6's had a massive problem with the MAF signals and people were replacing the MAF's periodically as preventative maintenance to help avoid gearbox failure. He knew of somebody who's RS6 box failed, had a new one fitted and within a couple of thousand miles it failed again due to the MAF's as they were overlooked.

[Delboy]

Originally Posted by ainarssems

MAF values are used for load calculations and torque reduction during gearshifts. If it does not read correct it can cause extra load, stress and wear to gearbox during gearchanges.

That being said lot of failures are caused by faulty seal which fails due to age and thermal cycling. Oil contain conditioners for rubber parts but with age additives in oil wear out and stop conditioning them. Regular oil changes help to keep seals in good condition and last longer.

That makes total sense, cheers for that.

So any further info how to check a MAF?

[Mugzee]

If you have VCDS:

http://www.ross-tech.net/vag-com/adv...AF_TechTip.pdf

[Sir WIll]

Gents,

If you replace the MAF is it also worth pulling the ECU fuse to reset everything so it can learn again?