Robert's new XM

[xmexclusive]

Hi Dean

If your list out the Autobox documents you have copies of in a PM then I will look and see what others I have.
A quick look found Pug "Principles of Operation" for 4HP20 and AL4.
Not sure there is an eqivalent 4HP18 one.

John

[robert_e_smart]

I was driving a 2.0 16V auto yesterday, and I noticed the shift points were different from the TD, but I can't recall if they are the same as the TCT one. I'll pay more attention the next time its round.

There was a XM 2.1 TD auto for sale a while ago that someone claimed they had the shift points changed when the car was new.

[Dieselman]

i wonder why a 2.1 derv would shift at later speeds?
More to the point i wonder what part of the valve block is responsable for shift points, if i knew that then some proper personalisation of the box could be done.

D

The governor springs and weights dictate the shift points.
The reason why diesels go faster before changing is they are higher geared so the speed of shift is set higher to keep the engine in a useful rev range.

[Dean]

The governor springs and weights dictate the shift points.

Thats what i always thought but these shift points are also ballanced by the load sensor which is under the Valve block along with the boost sensor if a turbo is fitted and these will adjust shift points.
Robert has proved the valve block has the main influence on shift points by swapping a tct one into his TD box.

D

[2point5XCL]

Hi Robert,
As I previously mentioned, the one thing that irritated me about the the 2.1 auto estate I had was the change points. The engine was busy as a blue assed fly around the 30 & 40 speed limits. To change up, if opportunity arose meant exceeding the speed limits by around 4mph in my car and it would hold that gear until the road speed dropped to about 1 or 2 mph below the speed limit when it would change down again. That often resulted in hunting up and down the gear changes in traffic. Ideally the torque of a diesel could easily cope with a speed differential of around 10 mph in the change up change down road speeds.
I know very little about auto boxes so when I put that point on XM-L,(I think), the reply was that as the change points were determined by hydraulic pressure and that was not possible.
Two other relevant points: Willie Johnston has fitted petrol autoboxes to diesel cars without any adverse problems and he also suggested checking the kick-down cable setting (as per Haynes) as that could affect the change points. Alas before I could investigate the latter, a prang deprived me of the car and opportunity to find out. I bought the 2.5 I now have as consolation, which is superb.

Roy.

[Dieselman]

The pressure cable will definitely influence the change points.

The business you describe was what put me off buying an auto 2.1. I tried one at WHM and it was quite infuriating having it suddenly change down for no reason.

[robert_e_smart]

I know little about autos as well, but I'm learning more, and want to learn a lot more.

The thing that annoys me most when driving the auto is not the auto box, its all the other arses on open roads who continue to drive at 45. I want to go at 50 minimum to be in top gear! Going faster in town to maintain 3rd gear wasn't a problem, as no one obeys the 30 limits anyway.

Is there a ZF Auto box forum? Perhaps we should all join

When adjusting the cable, you're increasing the sensitivity for the kick down, and making the lockup fucntion not work as long, as the box will think its time to kick down a gear when you're trying to keep it going along just above the change down speed.

[Dean]

Adjusting the kickdown cable just makes it,well, kickdown with less throttle applied which is ok in a petrol but ive heard its not good for the box, i doubt this is true other than too much changing gear can cause the box to overheat, hence why in the owners manual it states that it should be driven in 3rd if you are on a twisty road.

A ZF forum eh.................would probably just be full of all those BMW 5, 6, 7, and X5 owners with the new tiptronic box moaning that they have lost drive due to the design issue's with the reverse clutch poor souls, looks like the HP 18 is bombproof by comparison!!!

D

[Dieselman]

That's Beemers for you. Mind you I'd be surprised if the car went as long as the box giving trouble, the turbo's and swirl flaps normally give up before long.
The swirl flaps are real fun as they get ingested into the cylinders...

[Dean]

yes i remember reading that now in a bmw mag at the barbers, sounds like a fairly pointles setup as some owners have found a way of removing them with no change noticed.....

D