Converting Auto into Semi Auto

[RSmith]

Hi guys,

With some wiring and DIY bits and bobs could you convert an automatic gearbox into a semi auto? My reasoning is that surely the only difference between auto and semi is whether you or a computer chooses the gears. My little smart car has an option for putting the gearbox in semi or full automatic - so there must be a way.

Anybody done it / knows how to? Many thanks,


Richard.

 

[HDi fun]

Blimey - that's a difficult one. Older style automatics which use a mixture of brake bands and hydraulic valving to control changes will not be convertible.

Anything that's electronically controlled has more chance.

 

[RSmith]

Older style automatics which use a mixture of brake bands and hydraulic valving to control changes will not be convertible.

How old are we talking? What would be the year reg cut off point? I'm looking at a 1988 Merc... so that might be out of the question.

 

[HDi fun]

Probably, yes, to be honest although I don't have specific information for any vehicle.

I had a '98/R Nissan Primera with a Jatco 4 spd auto with O/D and that, although having some electronic controls for different shift patterns etc. still worked on the traditional epicyclic gears/bands/brakes/fluid principle.

They're incredibly complicated devices, at least to my untrained, eye and it's surprising they work at all.

However, if you could find a way of intercepting the flow of ATF and dirverting it via a series of electrically operated valves you might be able to do something. You'd possibly also need additional hydraulic pressure from an auxiliary pump as I guess that some operations you wish to 'force; might require more pressure than is available from the torque converter alone under certain operating conditions.

Anyone else know AT's?

 

[lutonmatt]

first i would say no dont do it or think about it

as semi autos are controled but many parts and some ecu's thats why you dont find them on older cars

not many people know to much about autos i have been a working at my garage for 10 years and have been a fully trained mecanic for 6 years yet i sort of know how auto boxes work as most run on hydraulic pressure but more and more are running on bands like the old fiestas and escorts

i can strip and rebuild any manual box as easy as anything as long as i have the time
but a auto box i would say go to a auto box shop

 

[HDi fun]

first i would say no dont do it or think about it

as semi autos are controled but many parts and some ecu's thats why you dont find them on older cars

not many people know to much about autos i have been a working at my garage for 10 years and have been a fully trained mecanic for 6 years yet i sort of know how auto boxes work as most run on hydraulic pressure but more and more are running on bands like the old fiestas and escorts

i can strip and rebuild any manual box as easy as anything as long as i have the time
but a auto box i would say go to a auto box shop

I was afraid that would be the case. If hydraulic pressure controls all the planetary gears and brake bands then it's too much to consider.

I'm still a fan of automatic xmission though; once there's enough torque to tear the wheels free of the tarmac then who cares if there's a couple of bhp lost in trnasmission

 

[marti5]

You would require a valve control body with various solonoids and the wiring to and from the EGS & ECU....very very complicated...as everything has to fit perfectly...it only costs approx £30million to design and manufacture an automatic/tiptronic gearbox...

 

[RSmith]

Hi guys,

Okay, the main reason I asked (I should have been more specific in my post) is because I'm trying to build a budget track car and I hate automatic gearboxes but love the big 5L V8 in the Merc 500SEC. I think that engine has a lot of potential but I don't know what to do about the transmission.

I really can't spend a lot to be honest (about £1500 max) - would anybody have any suggestions? I'm hoping to bring the engine up to about 380-400 hp and pulling roughly 450 lb/ft torque.