_DAN_

Really simple questions here. I know NOTHING about autos and CBA to learn about them to find out some simple questions

When you put your foot down in an auto. Does the gear always change up at the same RPM regardless of throttle postion and load? Or does the change up point (RPM) change depending upon the throttle postion/load? In example, it'll change up at 4500RPM regardless of whether you're thrashing the shit outta it or cruising? Or does it vary the change point as I thought earlier? I'd hae thought it would be varying as people do thrash autos as well as cruise in them.

Also, what exactly is a stall converter with the RPM tag assigned to it mean? Ie, one of these. http://www.jegs.com/webapp/wcs/store...10002_70456_-1 What does it do also?

Finally, on an automatic gear gate in the car. I understand what the P, R, N and D mean. But when it says 1,2,3 etc. Does it mean you can hold it in 1, lift off, then bang it up in to 2 then put your foot back donw like a manual? Or if you leave it in 1 will it just sit there revving it's tits off? Likewise for 2, will it drop to 1 or just stay in 2 till the redline? Then once at the redline, what'll happen? Change up or keep revving to the limiter.

Sorry for all the questions, I'm a bit bored and curious and my mate who knows autos isn't around.

Stavros

About when it changes up and down gear when in drive, that depends on how the box works, some are better and more complex than others, and some are more sporty than others.
Some of them (when in sport mode) will kick down at the lightest bit of throttle and rev all the way to the limiter in each gear, giving max performance, so take a bit more encouragment.

Most cars if you in 1-2-3 etc and hit the top of the revs, you just bounce off the limiter like a normal car.
Tho ive driven some gay cars when it changes up, spoiling your fun.

Dont need to let off to change gear in a auto mate, full throttle shifts all the way!

The rpm thing on the stall converter is what revs the converter locks up and the car drives from.
Basically as standard most cars will drive (ie the converter locks up, like the clutch being lifted) from pretty much 1000rpm, which isnt exactly good for launching hard when you launching at idle!
So you buy a torque converter for the sort of rpm you wanna launch at, job done.

PS- Im still learining too tho, but gonna run an auto with the turbo v8, stall converter high enough so it launches on boost, and a manual valve body so i do the gearchanges myself.
Really looking forward to it TBH!

PPS- Jegs, good call, cheap as fook, ill be buying the Demon Blow Thru from there i think.

_DAN_

Ah yeah, I see what you mean Stav thanks. I was thinking of something like a C4 or a TH400 'box? So a fairly simple 'box in an old skool muslce car or whatever...

See what you mean about the change up point, it would vary due to infinite driving condtions/styles etc.

If you fit the manual valve body will it be totally manual? No kickdown etc, just the same as a manual 'box with no clutch? Could you still be gay whack it in drive and let it do it for you?

focusv8

No, it becomes a manual change box with no clutch.

.

Stavros

Some autos are controlled by ECUs meaning they are cleverer than others, more simple ones simply have a kickdown switch on the throttle somewhere and just change up at a set point.

There are ones where you can have it just in drive, or do it yourself, yeah, but manual valve bodys dont do that, you do it all yourself.

My only problem, ive noticed with the C4 is top gear is 1:1, same as a cossies 4th, a bit low for me in an ideal world

_DAN_

focusv8

If you drive very light footed it will change throught the gears very quickly, and you'll be in top gear in no time, doing plenty to the gallon

Floor it in each gear and it will hold off changing till it's upper design rev limit.
Some boxes, like my Ford AOD, you can get valve sets to allow you lift the revs it would normally change at, to whatever suits the power, but only by removing the box sump, not during everyday use.

.

Danny B

you can get manual/auto valve body so when you put it in D its auto but you can also run it manualy through the gears, C4 is the most compact box as Th400's are very long and heavy.

_DAN_

Cool, thanks for the replies. Reckon this could be an interesting topic.

Am I also right in thinking the change up point will vary because of the various driving condtions? Something with a governer or something?

Something I'm still not 100% sure on. Thinking along the lines of a C4/TH400 here btw etc.

Could you get an auto/manual valve body for a TH400?

Stavros

Can you get longer gears for a C4? 1:1 in top sucks!

lead_foot

iTrader: (1)

How about a O/D? Lowers it to 0.78

Stavros

I know next to nothing about autos still, i need more explanation than that

OD as in overdrive, and understand .78, but how/what/where/when

lead_foot

iTrader: (1)

I know fuck all as well TBH. OD is over drive.

http://en.wikipedia.org/wiki/Overdrive_%28mechanics%29

I found this:

http://www.drivetrain.com/new_overdr...o%20C46%203-Sp

HTH (it was a 2 mins search, nothing i really know anything about).

focusv8

It's simpler to change the diff ratio.

Ford C4 is 3 speed
Ford AOD is..4 speed, well 3 plus overdrive, it's a rather wide box, but went in my Focus o.k. ish.

http://www.ford-aod.com/

The 3 speed overdrive box in the link looks a bit expensive.

.

Stavros

Danny reccomended the C4, is a AOD much bigger/weaker/expensive?

C4s deffo are cheap, thats for sure.

focusv8

AoD is much bigger in width, length is the same.
Aod is weaker as standard but can be built to take high power, but costs a lot more to build for power than a C4 would for the same power rating.

.

dojj

iTrader: (3)

i'm sure that there will be auto's that have been fitted to beefier motors that will have longer gearing

having driven auto's for a while now i can safely say that no 2 will be the same

it all depends on the the torque the engine is kicking out as well as the box bolted to it so in the 24V granada it's nice and simple to get accelration with just a prop of the pedal without getting kickdown, whereas the mondeo needs the kickdown to get it going, otherwise you just raise the revs and don't go anywhere

with the bigger beemer's and merc etc, and not just with the newer models, you'll have the sports switch and econom switch as well as the normal setting but i'm not sure how these are controled other than there is some clever electrickery going on
eco mode gives you an upshift as soon as there is enough spin to change gears hgher, normal is the normal mode and sports holds onto the gears right up until the red line
so in the case of the skoda 6 speed autoi had, lifting off from rest would see you change into second gear at as low a speed as 2 mph, but even mashing your foot to the floor wouldn't see you hitting 60 before the box had changed up into 4th

can't see the wikipedi links but the auto works with a simple paddle wheel in the torque converter that sends fluid round other bits of the box that do the changing up and down (you have the torque converter which is a big bowl bolted to the flywheel and inside it indipendalty is a paddle wheel which is linked ot the gearbox, so you don't actually have direct drive from one to the other, but the fluid in the bowl siwshes about and turns the paddle which in turn turns the insides of the box, that's about as far as i need to know and the kickdown is in 3 ways, either manual when the selector is shifted, electic when you mash the pedal and it activates the kickdown or normal as in when the fluid speeds cahnge in the box

lead_foot

iTrader: (1)

The Wikipedia link is about Over drives.

_DAN_

Cool, thanks for the replies. Understanding it alot more, especially after speaking to my mate who runs a TH400.

Anymore anyone?