Auto-box question.............

Auto-box question.............

Author
Discussion

triple7

Original Poster:

3,851 posts

166 months

Thursday 20th January 2005
quotequote all
When I'm sitting in traffic jams, I slip the car into neutral, save holding on the brake. When the traffic moves I engage Drive.

If I continually slip in and out of gear, does this screw anything up?

Boring question, but I was thinking about this today.

Answers on a postcard...............


G

groomi

9,132 posts

172 months

Thursday 20th January 2005
quotequote all
My old XJ40 didn't like it much, the belts started making a bit of noise after a while on a longer jorney if I did this.

I Dare not do anything 'out of the norm' with the XJR due to the problems I had when I bought it. Still haven't got out of that 'wrap it up in cotton wool' feeling yet.

In theory, any modern auto should be designed with this kind of driving in mind and therefore not suffer as a consequence... how good is your warranty though?

triple7

Original Poster:

3,851 posts

166 months

Thursday 20th January 2005
quotequote all
Thanx Iain, didn't know what would be best, holding it on the brakes the whole time or releasing the strain on the box each time.

G

banny

58 posts

169 months

Thursday 20th January 2005
quotequote all
I do this ( slip it in to Neutral at light ect) Generally to reduce wear and gearbox oil temps??? Or so i thought. ?

triple7

Original Poster:

3,851 posts

166 months

Thursday 20th January 2005
quotequote all
Exactly Banny, must be better than not?

G
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GavinPearson

5,710 posts

180 months

Friday 21st January 2005
quotequote all
For what it's worth I would recommend just staying in Drive. What you are doing as you engage gear is engage the forward clutch, so it is getting wear every time you engage. If you stay in drive, you only get one engagement plus you actually get very little loss in the torque converter.

The later transmissions - the ZF 5HP24 and the Mercedes W5A580 are EXTREMELY durable, having been responsible for running them at Jaguar on the dynos I'd say they can survive a far greater thrashing than most people reading this could dish out.

In addition the ZF5HP24 went to a wavy plate clutch design in 1998 MY which gave about 0.5 MPG improvement through less drag. The Merc is a more efficient transmission than the ZF.

triple7

Original Poster:

3,851 posts

166 months

Friday 21st January 2005
quotequote all
Thanx Gavin, v interesting. I will hold it on the brake in future.

G

800

1,931 posts

165 months

Friday 21st January 2005
quotequote all
Mine's always held on the brake in drive, over 100K miles of London driving - seems fine......famous last words.......if I ever get her back!

356Speedster

2,241 posts

160 months

Monday 24th January 2005
quotequote all
I meant to dig my owners manual out last night and forgot..... but I seem to remember reading in there that Jaguar recommend putting the auto box into Neutral or Park when in traffic. I'll try to remember to dig it out tonight and check!!

Mark

triple7

Original Poster:

3,851 posts

166 months

Monday 24th January 2005
quotequote all
Aaarrrrrrrrrrgh, now I'm confused!

I'll go get my manual out now if you reckon its in there.

G

shadowninja

66,819 posts

211 months

Monday 24th January 2005
quotequote all
there's a thread somewhere else in PH that recommends keeping autoboxes in D and using the handbrake for prolonged moments, as it causes less strain than changing between D and N.

GavinPearson

5,710 posts

180 months

Monday 24th January 2005
quotequote all
356Speedster said:
I meant to dig my owners manual out last night and forgot..... but I seem to remember reading in there that Jaguar recommend putting the auto box into Neutral or Park when in traffic. I'll try to remember to dig it out tonight and check!!

Mark


I'm genuinely surprised. I used to do mechanical development work for the transmission systems at Jaguar. I used to spend a fair amount of time driving with other people in the department, I honestly can't remember anyone who did this. The transmission should last for the warranty period either way - it will benefit fuel economy in traffic (minimally, but technically it does), however, my concern is one of really long term durability. If you follow the owner's manual the car will last 100,000 miles, from what I have seen an XJ8 (ZF 5HP24) transmission is capable of lasting 250,000.

356Speedster

2,241 posts

160 months

Monday 24th January 2005
quotequote all
I knew I'd seen it somewhere.... section 4-42 in the owners manual states:

"When stopping for traffic lights, junctions etc, either select P or apply the handbrake and select N"

Just to confuse further ;-)

800

1,931 posts

165 months

Monday 24th January 2005
quotequote all
yup, but remember that this is is health and safety/nanny state stuff, nothing to do with engine/transmission dynamics. That is to say, if you have a shunt at the lights, once you release the brake in drive, the vehicle will creap forwards, ie., manufacturers attempt to limit liability........."warning contents of coffee cup are hot".......yeah, I should bloody hope so, that's part of the concept!

triple7

Original Poster:

3,851 posts

166 months

Monday 24th January 2005
quotequote all
The case deepens..................................

356Speedster

2,241 posts

160 months

Tuesday 25th January 2005
quotequote all
It looks like the answer is to get a manual ;-)

dave_3d

39 posts

160 months

Wednesday 26th January 2005
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Gavin: You seem to be just the guy to answer a few questions !

I have always had a snatching lurch as I come to rest in my 2002 4.2 S-Type, 16k with the 6sp ZF box. This is variable. And can lurch the car VERY noticeably when cold.

This lurch can occur after a few hundred yards, or after 4 hours at speed on an Autoroute and then LURCH as I stop at a Peage.

Do you have any experience of this Lurch ?

I also have a strange "WHHooooop!" noise under acceleration (acceleration that makes the gearbox drop a gear - not full kickdown but a quick change down of a gear). The whoop definitely comes fom under the car from behind the front seats.

I have had every available software upgrade (probably about 10 now), loctited diff flange, bush inserts and no change. The gearbox always runs like silk for a week or so after a software flash before the lurch returns.

I have been in contact with other owners who have this problem.

Are Jaguar aware of this ?

Dave

GavinPearson

5,710 posts

180 months

Thursday 27th January 2005
quotequote all
dave_3d said:

I have always had a snatching lurch as I come to rest in my 2002 4.2 S-Type, 16k with the 6sp ZF box. This is variable. And can lurch the car VERY noticeably when cold.

This lurch can occur after a few hundred yards, or after 4 hours at speed on an Autoroute and then LURCH as I stop at a Peage.

Do you have any experience of this Lurch ?

I also have a strange "WHHooooop!" noise under acceleration (acceleration that makes the gearbox drop a gear - not full kickdown but a quick change down of a gear). The whoop definitely comes fom under the car from behind the front seats.

I have had every available software upgrade (probably about 10 now), loctited diff flange, bush inserts and no change. The gearbox always runs like silk for a week or so after a software flash before the lurch returns.

I have been in contact with other owners who have this problem.

Are Jaguar aware of this ?

Dave

The lurch you describe is called a "Roll out" shift. I should imagine Jaguar know about it, but I would suspect that the torque signal the transmission is seeing from the engine management is inconsistent. What happens is that the engine calculates engine speed, load, throttle opening, fuel quality (inferred by spark advance, dictated by feedback from knock sensors) and calcules that the engine at that moment is putting out x Newton metres of torque. The transmission calibration then works out the rate at which to feed in the clutches. I would suspect that the torque signal is showing higher than actual on some occasions, possibly due to a "dashpot" effect. This is now electronic, but on old cars (90s with cable actuated throttle) you would lift off the throttle pedal but the throttle would not shut, it was controlled by a dashpot - this delayed response gives good emissions. So I would wonder if the torque signal was being affected by electronic dashpot, a electronically controlled decay of throttle angle from the throttle motor. I doubt it would be a harness issue because if there was resistance on an analogue signal the signal would read low, and the can bus is digital. So communication is there.

The bottom line is that you could have all the gearbox reflashes you want but what you need is an engine reflash with software that gives the correct torque signal. That is if it's available. I don't know.

As regards whoop on 3/4 throttle accels it may be the transmission mount needs adjustment to stop it 'earthing out'.

I telephone your dealer and ask he gets the Jaguar Service Manager to come out. These guys are very experienced at dealing with these issues and often take the subject matter expert Engineers with them. I'm sure they can do whatever is necessary - it may take another visit or two but at least your car should be right.

triple7

Original Poster:

3,851 posts

166 months

Thursday 27th January 2005
quotequote all
GavinPearson said:

The later transmissions - the ZF 5HP24 and the Mercedes W5A580 are EXTREMELY durable


Interesting. What gearbox is on my 2002 4.0ltr XKR?

Thanx.

G

dave_3d

39 posts

160 months

Thursday 27th January 2005
quotequote all

Thank-you very much Gavin for what must be the best answer I have had about the workings of this gearbox. Your insight about the workings of this box are exactly what I had expected to hear from my dealers but they just hum & haw.

I have worked for many years previously as a mechanic, and my Father and Brother are still in the trade (Garage in the family for over 75 years) and I have NEVER experienced this type of behaviour from a modern automatic - not even in other S-Types or BMWs with the same ZF box.

The main trouble is that my Jaguar dealer and Managers do not accept that there is a problem (I have had my car independently tested by the AA and other motoring organisations with written reports that DO find it) and Jaguar continue to maintain it is normal. The best Jaguar have come up with is "Well, we have tried all the updates and it is an adaptive gearbox you know".

I expect a Jaguar to glide to a halt - not jump/snatch/lurch as it comes to rest. My previous 2001 S-Type, with the older ford automatic didn't lurch.

I have become dis-illusioned and frustrated with Jaguar's whole "handling" of this issue over the last 2 years of constant complaining by myself (From 1 week after buying the car). I have put it in the hands of my lawyer (Many, many other mechanical issues/faults).

Again thank-you for your time and answer.

If only everyone in Jaguar was this way.

Dave