P38 car jerks over when reverse selected.

Hi guys.

Get a lot of good info from this site, try to give back when I can.
My car is 2001 P38 Diesel autobox 130,000 miles.

This problem came on suddenly, so it's not a sort something wearing out slowly thing.

When selecting reverse from any position. There is a click from under the car, the engine slows abruptly, and the torque from the slowing engine is enough for the car to heel over.

It doesn't always do it, there isn't a pattern hot or cold. The car seems to drive okay, I do hear some noises when driving but I may just be noticing them now.

I don't suspect play in the drive line, as it does it if I go from R to N then back to R, and play in the driveline would be a slow wear kind of thing.

I could only find one thread with the exact symptoms, but the guy didn't report back.

I haven't had time yet to check gearbox fluid, or change fluid/filter. I will try these things next. I will have some time shortly to have a look so I'm just looking for other ideas.

I did think of engine mounts, but it doesn't do it in D, though I will have a look.

I don't suspect an idle problem. If the engine is suddenly loaded by other things it's fine. Like sudden steering input, or full beams and heater blower.

The Car is driving and pulling well, and the convertor is locking up disengaging normaly

Any ideas anyone what else it may be?
Thanks.

As the driveline takes up the torque from the box, the vehicle will heel over a tad....

Usually more noticable in Low box....

Does it metalic clunk or just engage and lean....???

I wouldn't quite call it a clunk, but it almost is.
But it really grabs the engine for a moment.
It's a fairly rough mechanical event, if you know what I mean.

Oh just remembered. If I select Reverse with my foot off the brake, the car moves away perfectly normaly without any effect on the revs, albeit immediatly.

sovereign said:

I wouldn't quite call it a clunk, but it almost is.
But it really grabs the engine for a moment.
It's a fairly rough mechanical event, if you know what I mean.

Oh just remembered. If I select Reverse with my foot off the brake, the car moves away perfectly normaly without any effect on the revs, albeit immediatly.

Click to expand...

You should never engage a drive gear without your foot on the brake...

The reason the revs dip and the car leans is because the engine is trying to drive the torque convertor and subsequently the gearbox, but as you have your foot on the brake, the torque of the engine trying to turn is hampered and as such it twists on its mounts which twists the car relative to the axles....and is nothing to be worried about.

Maybe a closer inspection of the negine mounts and the gearbox mounts could be in order....it has also beeb known that worn suspension bushes can cause a 'clunk' and excessive lean as they are less able to resist the torque moment from the engine/gearbox when they are worn...

sovereign said:

I wouldn't quite call it a clunk, but it almost is.
But it really grabs the engine for a moment.
It's a fairly rough mechanical event, if you know what I mean.

Oh just remembered. If I select Reverse with my foot off the brake, the car moves away perfectly normaly without any effect on the revs, albeit immediatly.

Click to expand...

What's it ticking over at?

Yes, I always put my foot on the brake when selecting gears from stopped.
Just tried it as a test.

Engine Idles at about 750 to 800 rpm warm, little higher cold.

If you do not get the same when you select drive and the engine slows and the car heels when selecting reverse, I'd get it on diagnostics PDQ. It sounds like the torque converter is locking momentarily.

It would be worth draining the oil, dropping the sump and looking at the colour of the oil. New oil and filter may help.

On mine there is no noticeable drop in revs when selecting D or R and it needs a few revs to start moving although it will creep just a little on the flat.

Datatek said:

If you do not get the same when you select drive and the engine slows and the car heels when selecting reverse, I'd get it on diagnostics PDQ. It sounds like the torque converter is locking momentarily.

It would be worth draining the oil, dropping the sump and looking at the colour of the oil. New oil and filter may help.

On mine there is no noticeable drop in revs when selecting D or R and it needs a few revs to start moving although it will creep just a little on the flat.

Click to expand...

Yes as the tickover speed is not excessive torque convertor being locked is a possibility. Diagnostics may show a cause. Bit of a strange one.

The torque convertor locking or jamming, sounds like a possible idea alright, as I imagine the fluid coupling at tick over wouldn't have much resistance.
I will change the fluid and filter and have a look around.

I've really been hoping it's not a problem internal to the gearbox.
I think those hopes may be dashed.
It's my daily driver, and it will be a week before I get a look at it.
Hope it lasts that long.

Thanks guys.
I'll get back to ye on it.

Here's a quick update.
No time to investigate the poor car yet, still driving, but definitly getting worse.
Selected reverse the other day and the engine almost cut out, also d is engaging harshly now.
When slowing to a stop the last downchange is becoming very harsh.

For a little while I was thinking of throwing the towel in, and getting a manual Disco.

check colour of the oil

It's going to be another week before I even find time to investigate this, just flat out at the moment.
I am driving the Rangie very gingerly. who decided to take away the dipstick?
The worst part is, I have to pick up a car with the trailer on Wedensday next too. Hope the old girl rewards me for all those oil changes.

if you go from p to r you get a click ?

Yes most movements of the gear stick, produce a click, followed by the engine revs dropping, enough for the vehicle to heel over.
It's still generaly driving fine and pulling well. But there is some vibration at motorway speed.

Used to be a very smooth drive.
My gut reaction is still it's not something serious, stabbing in the dark though. I need a day off to look at it.

first off id check ujs ,viscous coupling ,then oil

Ok I think I had a bit of a breakthrough tonight.
Drove the last seven miles home, on full beams and heater full on as it's freezing here.
Pulled up at the garage, jumped out to open the door, full beams and heater blower still going cabin lights etc.
Car in P handbrake on.

Jumped back in, put my foot on the brake pedal. Lo and behold the engine cuts out. Starting to think it is an idle issue now.
Have to look into this more.

A bit more info on this.
The symptoms have developed a bit.
When cold, the car starts up and idles around 900 rpm, pressing the brake pedal causes the rpm to drop to about 700 rpm the idle becomes very lumpy with the engine shaking. Releasing the pedal it stays lumpy.

If the brake pedal is not touched the idle is fine.

The car stays stuttery when driving around 2000 rpm, and slowing down to a stop the lumpy idle takes over and it stutters to a stop. Only when really warm the symptons more or less dissapear, after 40 mins driving.

I have resistance tested the lift injector (king injector) and got 100 Ohms, so that seems fine.
I connected an air line up to the map sensor, the resistance does change but only by about 3 Ohms, 3500 to 3503 Ohms. Seems like a very narrow range.
I have a pressure gauge on the turbo, it reads steady doesn't seem to be a leak.
I remade and checked all the main body earths.
Disconnected the alternator, to see if this was dragging the engine,( it wasn't)
Cleaned and tested egr valve. Ok.

The only thing I did find, was nestling among the glow plugs seem to be 3 water temp sensors, they are not mentioned in the manual.
Why are there 3 and what do they do?

Interestlingly 2 of them read between 200 and 900 Ohms. the one in the picture read open circuit, could this be the problem.

I can't understand why the revs drop when the brake pedal is pressed, it's not an engine vacuum driven system.

So I'm still stumped, I'll replace that water sensor. Could a temp sensor cause all this trouble?


sensor by Sovereign125a, on Flickr

Check the rubber damper on the prop if its getting perished .

1 sensor drives the gauge
1 sensor tells the ECU the temp
1 sensor is for the HEVAC system to tell it the coolant temp

If the sensor to the ECU if duff you will get difficult starting and odd running

Saint.V8 said:

1 sensor drives the gauge
1 sensor tells the ECU the temp
1 sensor is for the HEVAC system to tell it the coolant temp

If the sensor to the ECU if duff you will get difficult starting and odd running

Click to expand...

Ah. I see, thanks.