Correcting Speedo's?

[VX L67 Getrag]

well here goes for this 1 again...

I still can't get my head around it, although I haven't been changing the PPK for diff gears just leave PCM ppk alone & let them know all they need to do is change the relation between speedo at trans to cluster!

But someone else has complained & I really can't explain it well enough to argue, is there a simple diagram or something to show why the speed shifts don't need to be changed for diff gears?

I know I'm a d/w now & I believe all of you but I really just can't explain it well enough to argue the point!

Thanks in advance VX L67 Getrag

[yoda69]

Speedo into PCM is back of gearbox, what happens after this the ECU doesn'r care about, ie. the diff ratio and tyre size.
If the PCM was using the ABS wheels speed sensors for vehicle speed, then would need to redo all thye gear change setting as this is taken post diff.
Holden used the same calibration in anything from a V8 with 15" wheels to an SS with 17" wheels, and changing the PPK in the speedo to correct it rather than a separate calibration for each tyre size.

yoda69

[VX L67 Getrag]

So is it purely for if gear set's are changed in the auto or g/box?

Thanks for the clarification, I thought it may have been that simple but not 100%

EDIT: just thinking out loud, which probably will make me look even dumber, if that's the case why does the cluster speed go out as they use the same sensor don't they?

[yoda69]

If you change the diff ratio from a 3.08 to a 3.45 this is a 12% reduction so speedo will read 12% higher than true speed. ie. 100km/h vehicle speed wil show 112km/h on the speedo.
From an ECU point of view, the engine speed into the transmission to the output speed of the transmission stays the same, although the data in the ALDL will read 12% out. This data is then outputted to the speedo and the error remains which is why the speedo is wrong.
If you fix it on the ECU by correcting PPK from speedo input, you will then need to update every table/scalar that references vehicle speed, 1-2, 2-3, 3-4 up/down shifts, power/normal/cruise, TCC lock/unlock max speed in gears, etc to correct them, easiest way would be to multiply the whole table by 0.88 to lower all the speeds by 12%, but typically not all tables/scalars are in the xdf, so you may have now created a new problem. Looking at the $11 XDF which is well defined for the trans, with a quick look there nearly 50 Tables that would need to be adjusted.

yoda69

[VX L67 Getrag]

Oh Der...

sorry yeah total blonde thing, thinking logically & not literal... all obvious now!

Thanks for clearing that up!

[VX L67 Getrag]

Just to follow this up.....

For VY V6 which is the problem child a.t.m. It looks like the speed sensor wires to the PCM are blue/white @ D1 & brown or light brown @ D2! Then from documents I got the speed sensor comes out of PCM @ C1 & is violet/white!

Maybe a stickie could be made if confirmed & for other models speed signal to dash only wiring locations?

Cheers VX L67 Getrag

[VX L67 Getrag]

Not sure how it's possible but with speed corrector only now going to dash cluster it still isn't right?

It's most noticeable in 4th gear shifting into it too soon & then kicks back to 3rd & tries to hit redline????

How is this possible if everything between is fairly stock, it does have a 2800 stall converter too?

[TTVN]

did u change the ppk type settings back to stock settings

just changing diff gears has no effect at all on the trans shift points

the pcm still thinks the car is exactly the same a sit was before the gear swap

the issue your having has either been created by fiddling so go back and try stock tune or start again

or the issues were always there with stock tune but the vehicle was never going fast enough with tthe stock gears to notice eg on limiter in third

also are you sure your hitting rpm limiter not speed limiter as speed limiter is lowered proportionally to the percentage of the ratio swap

[VX L67 Getrag]

Thanks for the reply TTVN,

Unfortunately I just re-hashed the thread as it was same topic I was talking about, so yeah ppk & all assoc. parts are stock & even tried stock bin completely & still doing the same thing?

[Jervies]

Tech 2 worked for 3.5s in my vt, took all of 2mins no dramas