300 TDi Auto gearbox query

[ydna-renrut]

Hi Folks,
I have a 300 TDi with approx 100k on the clock. The auto box is the 4 speed one and I want to bounce off a few thoughts for clarification and a question at the end.

The car seems very slow until it get's in top (which I believe is an overdrive on these boxes). The engine has oodles of power but the gearbox doesn't seem to be transmitting all the power to the wheels in gears 1-3. I don't think there is anything majorly wrong with it and maybe nothing at all but it seems to rev higher than i would expect. Does that sound about normal or indicative of a fault.

Fimally my other question is that the gearbox appears to change into top gear by way of of a switch or similar which I presume is fed from the speed sensor somehow. At the moment it changes into top at an indicated 52 mph and also when slowing down it changes into 3rd at 52 MPH so as you can imagine when driving between 50-55mph the garbox is constantly switching from 3rd to 4th. Is there anyway this could be changed (eg change into top at 45mph or even 40mph and use the kickdown facility if required to accelerate). Am I missing something??

Any advice.

Many thanks in advance

AndyT:)

[Rangienut]

I dont know if you can alter it but it changes at the same speed as my V8 with ZF 4 spd, and yes, it is annoying! :rolleyes:

[StrangeRover]

There are other things going on down there. The ZF box has a lock-up mechanism that is activated by road speed. Below that speed the box allows some 'slip' and engine revs can rise and fall giving a smooth take-up of power.
I think what you are detecting as a gear change is the lock-up engaging and disengaging. Try using the gear selector to get a feel for what the revs equate to in MPH in 3rd then in 4th.
My 300 series 3.9 Disco will still kick-down to 3rd at 70+ mph but my 3.9 RR Classic is set-up not to kick-down anywhere over 60 mph. Not sure how the Diesels are set-up.

[swag298]

Sound's about right.
Tdi and 3.9 auto's lock up at alot higher speed than the 3.5 version.
3.9/Tdi is in 4th by around 40mph and it locks up at around 50mph.
3.5 hits 4th at 30mph and lock-up at 40.

I presume it's all down to the valving inside the box.

Personally I find 3.9 valving a pain. I prefer the lower revving 3.5 set-up if your not doing any towing. If you do any towing the 3.5 has difficulty remaining in the power. 60mph drops you well below peak power and torque, meaning you get slower and slower, until you kick-down, then it's revving it's heads off in 3rd.

Any difference in kick-down between 2 similar vehicles will be down to kick-down cable adjustment.
A RR is more aerodynamic so will tend to require less throttle for a given speed. Less throttle means less tendency to reach kick-down.
It also depends on tyres, weight, terrain and such.........anything that will mean you have to apply more throttle.

swag

[ydna-renrut]

Thanks for the replies guys. Good tip about using it in manual to get a feel. Is there anyway I can change the speed that it "Locks up" as you put it as it goes into 4th at 52mph accelerating or decelerating and if driving at 52mph is up and down constantly which can't be write surely??

Many thanks

AndyT

[swag298]

Might be worth talking to Ashcofts or some such place.
There should be a small hysteresis loop designed into the shift pattern.........it changes up at a higher speed than it changes down..prevents hunting between gears.
But your looking at changing the point at which the torque convertor locks up. I believe that point is the same accelerating or deccelerating.
Maybe it could be re-valved to suit. Quite common over here to re-valve auto's for different uses, or on electronic 'boxes they can be "chipped" to alter shift points.

swag

[ydna-renrut]

Thanks for your posts - I did as suggested this evening and drove with the gears in manual. I also noticed that although its a 4 speed there is also another shift up at 52mph and this I presume is what you are referring to when you say "locking up". What exactly is locking up??

Anyway at 2500 rpm this is the speeds through the gears.
1st - 20 mph
2nd - 34 mph
3rd - 37 mph
4th - changes up again (Locking up :confused: ) at 52mph which is 2300 rpm.
Once in this overdrive gear 2500 rpm gives 75mph.

Does this sound about right?? If so It would be nice to have the box locking up around 45mph. How is the locking up initiated, road speed, torque??? and can I get that changed easily without any sort of intervention to the box.
I will have to find a web site that explains how an auto box works as its baffling me.

MAny thanks for your understanding with this.

regards

AndyT

[reedrider]

The speeds and gear changes sound just about the same as mine and like you I get p**sed off with it kicking down a gear everytime it slows a bit when I'm towing
I have just had it in and the auto box refurbed the clutches had burnt out so it was a costley rebuild
Now it pulls just the same as when I got it but without boiling the oil in the box
If you off road and do some deep wading see piccy left always your front grill and wash out the oil cooler I didn't and it has cost the cooler blocked and the oil boiled and then the clutches started slipping so it cost about £1,200 al together to repair

[ydna-renrut]

your not wrong. 52mph which is the point it "locks up" is a nice speed on the lanes round here so its very very frustrating. Surely this set point can be adjusted in the software from the speed sensor???

Any thoughts anyone??

AndyT

[swag298]

Dunno about the 3.9, but the 3.5 version was completely non-electronic. The valving sets what point the TC locks up at.
When you get lock-up, basically the fluid in the torque convertor on the flywheel gets pressurised to the point where it's virtually locked up, usually by means of some type of clutch or brake band.......output speed into the gearbox is virtually 100% of engine speed.
At all speeds below that 50-ish figure the torque convertor allows slippage of varying percentages depending on gear, speed, load etc..

Less slippage means less heat generated by viscous friction in the torque convertor, better economy etc..but less "get up and go" in the 40-50mph range. Maybe the 3.5 valving would suit the Tdi better, although you may find yourself dropping out of the turbo's best operating revs range

Why they raised the lock-up point for the 3.9 is anyones guess. More torque and power should cope easily with the 40mph lock-up, especially if you're not towing. Maybe something to do with the low rev, high power, lean running causing cylinder liners to slip, giving the porous block symptoms.....

swag

[lynalldiscovery]

On the rave cd there is a complete test procedure for the zf box and a list of faults and its a bloody big list.

The lock up is just that, the torque convertor becomes solid and allows no slip.

My last TDI was an auto and the best cure is a chip for the engine.

Admittedely this does not stop the 50mph shunt in the 50mph roadworks but it goes like hell!

Box only went elec control on the D2 models.


Lynall

[jetfiremuck]

One other thing to note that the torque converters are looser(slip more) before lockup behind the diesels than the V8 due to engine torque characteristics. Lockup speeds below the numbers quoted can result in engine power pulse vibration and resonance when under way as there are no clutch springs in the torque converter as in the clutch in a manual box to absorb this shock.The zf with the hydraulic valve body is a four speed (3 shifts) and lockup in top which feels like a shift . The electronic valvebody has pressure controls from the pump to soften shifts, allow lockup in some of the lower gears, controls kickdown(no cable).

[ydna-renrut]

Thanks guys - I have a copy of the Rave disc but can't get it to run. I am using Windows XP and I think thats were the problem is as its for Win 95/98???


I'll have another go tomorrow.:rolleyes:

Andy

[lynalldiscovery]

My old rave disc is for 95/8 and will mot run on my xp so got another from e-bay for 2.00ish.


Lynall

[ydna-renrut]

My old rave disc is for 95/8 and will mot run on my xp so got another from e-bay for 2.00ish.


Lynall
Doh - I just bought this one from EBay so obviously bought the wrong one.... looks like I will be bidding again in a few minutes:o . Thanks for the tip

Andy