Auto won't hold on hills

[mikemoss]

My new (to me) 1999 E320 estate auto refuses to 'hold' on hills, leaving me the choice between rolling back alarmingly or attempting to hold the car using my left foot on the brake. Its predecessor, a 1990 300TE, had no such bother.

Tick-over is a tad over 500 rpm and I'm just hoping this isn't a 'feature' of the electronic gearbox. Any clues anyone?

 

[fgaffney]

My electronic box will only hold me stationary up to a certain incline.

Anything too steep and the car gently rolls back but still feels like it's being held to some degree.

I assumed this was normal?

 

[nickmann]

If the box is in "S", or any of the numbered gears then it will not hold (except by accident on a slight gradient). If the box is in "W" then it will (or at least should) hold.

 

[Brian WH]

If the box is in "S", or any of the numbered gears then it will not hold (except by accident on a slight gradient). If the box is in "W" then it will (or at least should) hold.

I agree as W is second gear, but bear in mind that the Torque Convertor is not a Brake and isn't intended to hold you on hills. It only does it on slight gradients by default. You can overheat it if used too long for this purpose.

 

[nickmann]

I agree as W is second gear, but bear in mind that the Torque Convertor is not a Brake and isn't intended to hold you on hills. It only does it on slight gradients by default. You can overheat it if used too long for this purpose.

Agreed, but I believe this is true of any lever position. If you are stationary for too long in gear then the fluid is getting heated.

I'm not sure "Hold" holds because it is second gear or because there is additional control in W mode, but I believe it is the latter.

On mine it feels as if there is additional control as when I come to rest on a hill, the car will roll back about an inch, then stop hard. It's the same feeling as when you use P, or the parking brake. This is true on any gradient. I think it makes for an easier take-off on snow as there is no rollback when you go to set off.

The EPC/WIS talks about different change-up tables, and about the hold feature, but doesn't provide any data on how the hold feature actually operates. I use it for a 300m drag where there is always crawling traffic on the way to work - makes life much easier. The car is probably only stationary for a minute or so in total, across 5 or 6 stops, so prob. not too much of a worry. I don't think I'd use it for the traffic lights though.

 

[GordonTarling]

Not entirely sure that there is a specific 'hold' feature at all - I always thought that it was the natural autobox 'creep' balanced against the weight of the car that gave the 'hold' on hills. On shallow hills, mine still creeps forward. On steeper hills, it can roll back a bit when I take my foot off the brake.

 

[Brian WH]

The only true Hold is in P and is described as follows: -

In addition to the parking brake, the parking lock prevents a parked vehicle from moving.

Construction
The parking lock mechanism consists of the parking gear (9), the parking lock pawl (8). the cone (7) with spring (6) and the guide bushing (5).
The latch lever (4) and the connecting rod (2)
form part of the shift interlock mechanism (see section Shift Interlock).

Function
If the parking lock is engaged, the cone moves between the parking lock pawl and the guide bushing. This presses the parking lock pawl against the parking gear. If, with the vehicle at a standstill, the tooth of the parking lock pawl does not engage a gap between teeth on the parking gear, but rests on lop of a tooth, the cone is pretensioned by a spring (6).

In this case, the eerie is in a standby position.
Further turning of the parking gear will cause the parking lock pawl to engage the next gap between the teeth.

In order to prevent damage due to misuse, the gaps between teeth are designed to engage the pawl only it the vehicle is standing still or creeping slightly.

If the vehicle moves faster, the parking lock pawl will not engage due to the taper on the tooth flank.

2 Connecting rod, parking lock
3 Detent plate
4 Latch lever, parking lock
5 Guide bushing
6 Spring
7 Cone
8 Parking lock pawl
9 Parking gear

 

[nickmann]

That's a pretty flimsy bit of metal to be holding a car with!

How do you reckon the W 'hold' works? I guess the forward force could be balanced against the backwards roll by using the speed sensor on the box to detect roll, but only if there is some way of modulating the forward power without changing engine revs.

That would explain why the car rolls back an inch before the 'hold' engages, but the engagement has no effect on the engine revs, so the power modulation must be handled by changes in fluid pressure perhaps?

 

[mikemoss]

Oh eck, I wish it worked the same way as the old 300TE. Have to practise those old heel-and-toe manoeuvres from Mini days. I've booked the car into the main dealer for a look-see, but it sounds as though there won't be much they can do. Thanks for all the amazingly quick responses so far. Any more?

 

[nickmann]

Oh eck, I wish it worked the same way as the old 300TE. Have to practise those old heel-and-toe manoeuvres from Mini days. I've booked the car into the main dealer for a look-see, but it sounds as though there won't be much they can do. Thanks for all the amazingly quick responses so far. Any more?

Have you tried pushing on the parking brake just far enough to stop any rollback, but not far enough to click it 'on'?

 

[stwat]

Left foot on the brake?

 

[jimmy]

Sounds to me like your idle speed is a bit low, if you increase the rpm slightly to around 800-100rpm does that help to hold the car?

Mine will hold on quite steep hills and on the flat you have to use the footbrake or parking brake to stop it rolling. I have gotten into the habit of shifting to N and applying the parking brake in traffic, saves dazzling the driver behind too.

Yes the autobox 'Park' mechanism is very flimsy, do not rely on it on steep hills, always use the parking brake too, thats what it is for!