Automatic Transmision Question

[ToNkA]

Drove a blokes car from work the other day off road.

Its a Turbo Diesel Prado (i think)

Anyway I don't drive to many auto's and noticed that when you put it into reverse (for example) it would roll forward like it was in neutral, until you put your foot on the accelerator to reverse. It felt like the transmission wasnt gripping, if that makes sense.

In other auto cars I have driven I always feel the car trying to move when in gear (forward or reverse).

So is this normal, or is the transmission slack or something?

Its done 40,000k and in good condition with no tough offroad work etc donw.

[TuffRR]

The torque converter in an auto will only engage fully above a certain RPM. If in gear, it should still require a reasonable gradient to make the vehicle roll as the torque should still be somewhat engaged at idle. Similar to riding the clutch really.

[awill4x4]

Tonka, this is how with some of the really strong auto's you can put them in reverse when going down a steep hill forwards and slowly push the throttle down to try and drive the car back up the hill even as gravity is taking you down the track. It's an unreal sensation where you use the accelerator to slow you down but it's hellishly hard on auto temps.
Regards Andrew.

[ozrunner]

...this is how with some of the really strong auto's you can put them in reverse when going down a steep hill forwards ..............

Going down a slippery steep hill with sliding locked rear wheels doesn't sound like my idea of a controlled descent.

[awill4x4]

I've tried it and it works far better than anything apart from crawler gears but it is very hard on auto temps. The torque convertor acts like a giant elastic band but the trade off is heat.
You just need to get it in your mind that to go slower accelerate more and to go faster use less throttle.
This technique only works in high range though, the engine will stall if used in low range.
Regards Andrew.

[ozrunner]

.....This technique only works in high range though, the engine will stall if used in low range.
Regards Andrew.

Andrew, I won't bore you with the inner workings of a converter but you answered it yourself "low range will stall the engine" = locked rear wheels.

If you are using high range then you must be referring to your driveway

[stuee]

http://auto.howstuffworks.com/torque-converter.htm

This site is great for stuff like this. I don't know how many assignments I did for physics at school just using this site.

awill4x4 your idea sounds workable but like you say very dangerous on trans temps. I would'nt do it for fear of destroying my tranny - maybe on a work car but thats something else altogether - either way I don't see it as being a good practise. Would be better off learning and/or using the apropriate braking techniques.

[robbie]

Unfortunately Ozrunner you wouldn't know shite from clay. I've tried it and it works far better than anything apart from crawler gears but it is very hard on auto temps. The torque convertor acts like a giant elastic band but the trade off is heat.
You just need to get it in your mind that to go slower accelerate more and to go faster use less throttle.
This technique only works in high range though, the engine will stall if used in low range.
Regards Andrew.

awill is right, I have tried it in my patrol SWB GQ auto..

[Gwagensteve]

I use this method often in my G. However, I NEVER use it when descending forwards as the consequences of stalling the motor an an inopportune moment don't bear considering.

If I fail a climb, and i'm trying to edge back down, I will often leave the car in drive and use the accelerator as a brake. This avoids the horrible "drop" you get when you go from D to R, and then fighting with the brakes to hold the car.

I'm sure it's hell on temps, but I don't have a gauge so what I don't know wont hurt me.

[A12]

I use the brake with the transmission....step 1, put foot on brake, step 2, rev engine against brake to 1500rpm, step 3, release brake and regulate speed using the brake. Works really well if you have ABS as well as the ABS will pulse the brakes if you lock only 1 wheel......bodgy traction control.

Mind you, had to have front disks machines at 40k and new pads were requried.

Greg

[TuffRR]

The technique mentioned above (ie high range D when reversing down a hill) does work and is actually part of the advanced driver trainer syllabus of the Victorian DTU.

It is an advanced technique and as such should not be attempted by inexperienced drivers. It will put extra pressure on your torque converter and should only be used on slippery slopes where there is buggar all traction.

[ozrunner]

Original comment

"Tonka, this is how with some of the really strong auto's you can put them in reverse when going down a steep hill forwards"

Later clarified to:

"This technique only works in high range though, the engine will stall if used in low range."

Which is what I was referring to, ie stalled engine means locked rear wheels downhill means YIKES.

But no problems its high range so whether to use this method to do a steep descent in high range versus normal low range would be a personal choice and no problems my end. The concern was using low range should someone try it !!!!

Others initially seemed to agree with this concept but maybe not entirely .........

"However, I NEVER use it when descending forwards as the consequences of stalling the motor an an inopportune moment don't bear considering."

and

"The technique mentioned above (ie high range D when reversing down a hill) does work and is actually part of the advanced driver trainer syllabus of the Victorian DTU."

Good for them but have a second bite at the cherry as the original comment was about now using high range reverse when going down a STEEP hill, not reversing

So which is it ....

[awill4x4]

As I said in my original post, it's going down a hill forwards (in high range) with the auto in reverse gear
I was taught this technique by an accredited VIC DTU driver trainer. He showed me how it worked in his 360 cubic inch Mopar powered 78 Jeep Cherokee. The technique comes out of the USA and is particularly suited to Torqueflite auto's as you couldn't break em with a sledgehammer. I've tried it in both his car and my GQ and I'll stand by my comment that it is a technique that is second only to crawler gears, used correctly your car can go down the most insane hills slower than a diesel. But (and it is a big but) it is hell on auto temps, it's fine on something like a torqueflite but I think that the current crop of 4 speed auto's probably wouldn't like it too much without some extensive work. Personally I use the left foot braking and accelerating at the same time technique also taught by the DTU but that is hell in brakes, but it's cheaper to change pads than rebuild a GQ auto. If I had a V8 engined 4x4 with a strong turbo 400 or torqueflite behind it I'd use the original technique on "oh shyte" hills as it works so well.

[DamTriton]

Someone correct me if I am wrong, but if you stall the engne in an auto going fowards downhill in reverse gear, then with the engine not providing the power to the torque converter and therefore no oil pressure to the various actuators, wouldnt the output shaft of the transmission effectively be disconnected from the engine? Wouldn't this put you in the "angel gear" scenario?

I can see the reasoning behind doing it only in high ratio to avoid this happening

[ozhumvee]

I've found that while it will work with most of the older auto's, don't try it with modern vehicles with EFI and electronically controlled auto's. The vehicle senses that you are in the wrong gear for the direction of travel and shuts the engine down which leaves you without any control, brakes or steering.

[ozrunner]

..........If you don't want to believe the technique works ozrunner, fine, but unless you've either tried it or been in a car driven by someone who knows the technique .

"As I said in my original post, it's going down a hill forwards (in high range) with the auto in reverse gear[/b]

Sorry but you DID NOT say that in your original post. If you did no comment would have come from me.

I made a reference to locking the rear wheels because I like probably most others first assumed you were referring to using low range, which would be too dangerous and cause rear wheel lock up due to stalling the engine and you yourself later confirmed this and indicated use of high range.

And where did I say it didn't work

[-Scott-]

I made a reference to locking the rear wheels because I like probably most others first assumed you were referring to using low range, which would be too dangerous and cause rear wheel lock up due to stalling the engine and you yourself later confirmed this and indicated use of high range.

Of course, if you're in 4wd (NOT fulltime 4wd) you'd need a wheel on each axle to lock...

Scott

[rOd]

Ive tried this technique on my auto SWB GQ and it works very well I thought. It wasnt a very long descent, but I dont think I would like to use it all the time .

[RaginRover]

Ok guys,

Lets keep this On Topic and play nice

I am sure you both know what each other mean and Tonka has the answer to his question

Tom

[BabyGodzillaGTi-R]

I'm confused why would u want to engage reverse and decent down hill?

So what happens if u start to drift slightly? How would u correct the car then?
Coz currently when doing decents on an auto car i'm still sticking to left foot braking.

Hope u guys could enlighten me.

[V8Patrol]

Flames extinguished ( thread cleanded )


And .... I have a question too !

My experiance with autos, cars only as I dont trust em in a 4x4 at all but thats just me ......

When the engine STALLS and your in "D" or "R" the car continues traveling in the direction it was moving in and as if "ANGEL GEAR" ( neutral ) has been selected...most likely gravity would be the controling factor in this case ....
Therefore driving forward down a hill but with the auto in reverse and the engine stalls then wouldnt the likely outcome be a runaway rig rather than a stalled motor and locked up rear end ????. Perhaps the stalled motor and locked up rear end may exist momentarily but then there would be the sudden downhill run as gravity took hold...... that run would be fun too...
No power assisted brakes One heavy pedal with no real braking
No power assisted steering Armstrong steering under pressure !
No control because of the above....yep it would be fun ride for sure


Kingy

[awill4x4]

Kingy, all I know is that the technique works. I don't know why it doesn't stall in high range but it doesn't seem to. It will stall in low range though. It's a bit of a balancing act where you are trying to drive the car back up the hill while going downwards at the same time. For those in auto's who have tried it, it is an absolute eye opener and the control is 2nd to none. Want to go slower, then accelerate, want to go faster, take your foot off the throttle. I guess it's a little like riding a clutch while waiting for the lights to change on an uphill stop at the lights in a manual car.
Regards Andrew.
ps, I'm not trying to advocate that this technique is the perfect answer.( I would love to have a set of crawler gears but I can't see me being able to afford them any time soon) When I was told about it, I was like everyone else "What a load of bulltish" but the instructor got me in his car and showed me then he had me do it in his car as well and it changed my mind quick smart. I have NEVER EVER had an auto go down steep hills with so much control and slow speeds.

[BabyGodzillaGTi-R]

But my question is when i'm going down hill and when i get into a drift i try to correct the car by giving it a slight gas depending how bad the slide is.
But what if u're doing it in reverse?
How would u correct it then?
I know that your descent in reverse is much slower but what if it gets sideways?

[V8Patrol]

I dont doubt that it does work at all ... infact .....

I can now say I've done it succesfully in both high n low range

After a visitor droped in yesterday in her yota ( one of the missus horsey friends ) and both her n Julie took off in the statey and left that yota POS in my way ....had to move it didnt I ...its kewl as she always leaves the keys in it and allways tells me to take it if I need to duck down the street for something.....

So i needed to duck UP the street for a test

Went to the steepest hill in town......
Pool hill is damn steep but is sealed and has a good runaway area, ok so its not the perfect OFFROAD enviroment but for the test it will do.....

I did the drive down in Hi range/reverse easilly and it worked a treat, straightup for a novice beginner at this style of driving..... 3 attempts later and I recon I had it mastered well enough to do it in low range....

Low range takes a hell of a lot more skill to do this trick I can tell ya !

1st attempt = started to actually reverse back up the hill

2nd attempt = reversed it again

mmmmmmmmmmmm

3rd atempt = moved my driving line to the gravel sides of the blacktop this is where it became interesting...... at first it was a real balancing act on the throttle to get that fine control of engine revs versus traction versus actual auto hookup and yes I did the spin the wheels and slipped a tad sideways and then I did the stall thingy and the rig just took off down the hill with no locked up rear end which was what I was trying to actualy do......

attempts 4,5, & 6 were much the same and its obvious to me that if this driving style is to be used its not the sort of thing one could do without PRACTICE.....and heaps of it !

Around atempt 10 I did actually do what I would call a controled decent in low range reverse...... in fact I'd go sofar as to say it was more controlled that just using the brakes and leaving the auto in "D".
As for speed of decent I found I could slow it down that much that "crawl" is an understatement, but DAMN its difficult to get it right, it certainly takes alot of practice to get it right and my last 'attempt' may well have been an absolute fluke but the style DID work.

Now .... before ya all get upset about me doing this to a rig ( tow rig for a horsefloat really and thats all ! ) let me tell you a few things.....
1/ I drove it for 3 kilometres between each run to allow the auto to cool down & return to normal operating temp
2/ the auto in this tow rig HAS duel auto oil coolers fitted.
3/ I used a certified hand held TEMP reader ( I have one due to my business ) for the taking of the autos temp after each run.


So..... the temp questions......
I took a temp reading at the top of the hill and then again once the rig was at the bottom and could be left idleing over in NEUTRAL with NO handbrake on...... the hill is a 100 metre decent around 40 degrees incline

The runs in Hi range produced a very slight temp increase an average of a 6 degree increase over the normal operating temp ... thats all

the runs however in LOW range increased the temp by an average of 21 degrees, with the highest temp recorded being 24 degrees above "normal" operating temp .

"My" summary.....
1/
The style WORKS....no question there, but its damn difficult to master and certainly not a style for the "novice driver".

2/
A Novice driver WOULD loose control without question and I would recemend that a lot of practice be done before hand to get any real idea as to how this all works and to get it to work well even for the more skilled drivers within our ranks.

3/
Dont do this without an OIL COOLER being fitted to your auto, the temp readings I recon could double easilly enough on a non cooled auto, and even with one cooler they would be hotter than I'd like to see.

4/
A good style to use under "certain" conditions and I recon they would be few n far between, but if used more regularilly then I'd strongly suggest that a more regular servicing of the auto be performed.

Kingy

p/s
The owner knows I drove her POS.......... up the street

[ISUZUROVER]

Pool hill is damn steep but is sealed

the hill is a 100 metre decent around 40 degrees incline

Very cool tech and very comprehensively performed.

I doubt very much the hill is 40 deg. though (if it is a public rd.). If you measured it you would probably find it is less than 30 deg.

[GRIMACE]

Pool hill is damn steep but is sealed

the hill is a 100 metre decent around 40 degrees incline

Very cool tech and very comprehensively performed.

I doubt very much the hill is 40 deg. though (if it is a public rd.). If you measured it you would probably find it is less than 30 deg.

if you look right into it you will discover its only 26.2 degrees

[V8Patrol]

mmmmm ya might be right........

But its phuken steep for a public road

Might get a pic and let you lot be the judges

[Allan Mac]

Was also taught this technique & works very well. A couple of things to remember though;
Only advantageous on slippery surfaces. If you can left foot/drive through brakes, no real advantage on dry surfaces using opposite gear.
Be careful on long hills; anymore than 100mtrs or so, tranny will suffer.
When using this, always in high range.

It takes some practise, but IMO should only be used on slippery surfaces.


Cheers
Allan Mac

[awill4x4]

Kingy, I think the most difficult thing is to get your head around the fact that if you want to go slower you have to use more throttle. But it's an interesting sensation going down a really steep hill so slowly in an auto by accelerating rather that relying on the brakes. I never bothered with persisting with low range as I was advised of the difficulties and after stalling a couple of times reverted to high range.
Regards Andrew.

[V8Patrol]

I dont really think it was that hard to do in hind sight, the problem I had really was trying to get it to do what I WANTED to do ..... the stall n lock up thingy..

Other than that I spose really my test was a waste because it wasnt on a super steep slippery hill cut up by heaps of other 4x4's and shrouded in panel crunching trees along with all the other distractions we encounter whilst out wheelin.

I recon if those with autos wanted to do this then they should do as I did n get a tad bit of practice before the real thing happens.
Over all its is a good style but not for the novice and not for those that find emselves in a situation where its a choice and they have never attempted it before.

I've driven heaps of differant vehicles over the years from Porches through to a "cut n half mini " ( paddock hack ), from a B double to a old 4x4 Acco cab over sh.. box,...... rear wheel steer is the hardest thing to come to grips with, even found it easy to convert to a left hand drive garbo truck here in aussie and had no dramas driving in the states.

Just a matter of co-ordination really

Kingy