Auto keep stalling???

[Jonny Boaterboy]

I seem to have developed a problem this morning on the way into work... when pulling up at a set of lights I put it in Neutral to find the tic over wont settel and is cycling between 1000rpm and 600rpm and then when you engage drive it stalls?

Any ideas what might be causing this?

Thanks

Jonny

[Bowie]

Sticking idle stepper motor, almost guaranteed :)

[SteveGoodz]

I think Bowie is right .. sticking stepper motor. Easily cleaned with some brake cleaner.

I did wonder though why you put it into neutral at the lights anyway? Was it running rough before that?

[Jonny Boaterboy]

Perfect I knew you would have the answers...... just a minor point what's a stepper motor and where is it and what does it do, and how do I get it out!! ? Do I need to get a new one or will just a clean up be ok?

I have always put it into neutral when pulling up at the lights as that what it advises in the hand book? I guess it takes some of the wear of the clutches in the gear box box. It makes me look like a good driver to the car behind as well!  :D  (i.e. brake light goes off indicating I have applied the handbrake)

Tar

[SteveGoodz]

Ah, well telling you where the stepper motor is would take all the fun out of this wouldn't it? It's located on the back of the plenum chamber and sticks out towards the drivers side (assuming it's a right hand drive vehicle). It has an electrical plug on the end and is screwed into a removable boss. When you unscrew it you'll see a plunger with a conical end that the motor moves in and out of a tapered hole in the boss. They tend to get clogged up and can be cleaned using brake cleaner or petrol. If cleaning doesn't work it usually needs replacement but they can, sometimes, be set to work on a different part of the range. Needs a suitably equipped garage with computer equipment to do that.

My question about using neutral when stopped at lights comes from a discussion on another board. My old BMW 7 series (e32 model) had exactly the same gearbox and the owners manual was very specific about not putting it into neutral at lights/junctions/etc. ZF - the manufacturer - also used to give this advice on their web site ... something to do with the loads induced when going from N into gear being greater than simply leaving it in gear and oil pressures being lower when N is selected. Can't find it on their site now though :-(

Of course, you can still put the handbrake on and take your foot off the brake if you want to (appear to) be a good driver. The handbrake should hold it ... I do it all the time ... and you can get some wickedly quick pull-aways by hitting the accelerator as you release the handbrake :-)

Enjoy your driving :-)

[Jonny Boaterboy]

Stevegoodsz that's great, I should have learnt by now there are far more knowledgeable and smarter people out there than me , what that saying, "no one knows your a fool till you open your mouth" (in reference to putting the hand brake to appear to be a good driver!) will be trying you idea out at lights from now on as it does sound like a good way to pull away from lights.... especially if there a "init" in a nova or corsa next to you at the lights  :twisted: (nothing wrong with novas or corsas or inits though, each to their own!)

It would be interesting to know which is better for the gear box, as you have pointed out there is quite a thud when you put the box into drive, more noticeable if you select D without the handbrake on, with the hand brake on it is quite smooth. I was assuming that the clutch plates could wear out if left to slip in neutral all the time allthough I have never heard of an auto box having the clutch plates wear out?

Thanks for the advise on the stepper motor will be doing that first thing in the morning

Thanks Mate

Jonny     

[SteveGoodz]

I should own up ... advanced driving is a kind of passion for me. I'm the Chief Observer (like the head instructor) for the Institute of Advanced Motorists in Bristol. Makes me a kind of anorak when it comes to driving techniques and skills - doesn't make me perfect though. Far from it. I try to learn something each time I drive the car.

The ZF autobox doesn't have clutch plates, by the way. It uses something called Sprag clutches ... whatever they are  :-k

My wife's been telling me I'm a fool for more than 30 years ... and I haven't dared open my mouth in all that time  :dance:

[Range Rover Blues]

Sprag clutches are a sortof free-wheel mechanism that allows drive in one direction only, they are used in many things including those nice click-free ratchets and jet engine starer motors, amongst others.  Also used in the original S1 gearbox and Willys overland JEEP to provide permenant 4WD.

I doubt there are no clutches though, the sprag clutch is what allows the car to overrun in 1st unless postion 1 is selected, then you get full engine braking.

They do still have brake bands for sure.

[clbarclay]

The ZF gearbox (ZF4HP22) does have clutch plates, about 58 of them including the friction discs :shock: arranged in 6 multi plate clutches. These multi plate clucthes are in principal similare to the clutch on manual gearboxes, but use many smaller diameter plates and are typically oil immersed, with an hydraulic ram in place of the thrust bearing. The workshop manual has a lovely exploded diagram stretching over 5 pages :lol:

This shows a typical multi plate clutch assembly

[SteveGoodz]

Nice one Chris, I stand (well sit anyway) corrected. I've never delved into the automatic gearbox part of the manual before ... too scared ... and now even scarederer  :D

We live and learn  :D

[Jonny Boaterboy]

What a wealth of information you guys have  :shock:  I would have to confess I have never tried to work on a gear box, Manuel or auto, both seem to need there own expertise and specialist equipment! I just change the oil a little more often and try and treat it well, so after that all that which is better, to put it in neutral or leave it in drive when you get to the lights?

I sorted out the stepper motor, it was quite gunked up. I used carb cleaner as I had no brake cleaner (probable the same stuff!) and it is now ticking over beautifully so thanks very much for that

Jonny

[Range Rover Blues]

I was testing mine with it plugged in whilst not fitted, it sprang apart and I had to fit a new one