Potentially stupid question re Autos

[McClure]

Hypothetically speaking, how easy/difficult would it be to swap a 3 speed auto box for a 5 or 6 speed? (retaining the 3 speed for refitting on resale of course).

Thanks.

[ohtari]

Depends on the car, front or rear wheel drive? Did that model come with a 5/6 speed auto? Why not a manual conversion?

I'm guessing you're thinking of mating a modern gearbox to an older engine. Is the input shaft the same diameter, length, with same number of splines? Is the bell housing the same (and I mean, identical)?

In short, it'd be easier to do a complete engine and gearbox swap than what you're suggesting.

[davepoth]

Swapping an auto for an auto? Really quite tricky. Older 3 speed autos are generally hydraulically controlled, so they're pretty self contained apart from the kickdown. Modern gearboxes tend to be more electronical and will be expecting inputs from the engine ECU, which will have to be replicated.

[Timberwolf]

For a 5/6 speed auto? Very difficult, at a rough guess.

The problem is that a modern autobox will be expecting to talk to a lot of things around the rest of the car; ABS system for road speed, electronic throttle position sensor, engine ECU for load information and to request throttle overrides for changing gear, dashboard module for gear selection display - even 4-speed boxes from the '90s often want a connection to the engine ECU so they can retard the ignition to smooth upshifts.

I expect on a classic most if not all modern automatic gearboxes will be stuck in limp mode if they even move.

[McClure]

Right. Basically a no-go then.

Thanks guys.

[V10Mike]

However, if your auto is a GM TH350, it is relatively easy to swap it for a 700R4 with a lock-up on fourth (top) gear.

[McClure]

V10Mike said:

However, if your auto is a GM TH350, it is relatively easy to swap it for a 700R4 with a lock-up on fourth (top) gear.

No, it'd be a TH400.

[V10Mike]

Same applies -you just need a 700R4 that's been modified to take the extra torque. Available here http://www.bowtieoverdrives.com/index.shtml and elsewhere.

[McClure]

V10Mike said:

Same applies -you just need a 700R4 that's been modified to take the extra torque. Available here http://www.bowtieoverdrives.com/index.shtml and elsewhere.

Interesting... Thanks.

[lowdrag]

No mention of the car make, but surely it depends on the marque? Jaguars are relatively east to convert (classic cars that is).

[Motown Junk]

Put a TH700R4 in my Camaro, world of difference.

IF it's an American V8, TCI do a complete 6 speed auto conversion

http://www.tciauto.com/tc/transmission-packages.ht...

[Upatdawn]

seek out and ask PH's very own tame Hotrodder/Drag racer/Quickest street car in the world Mr Andy Frost, autos are his reason for living

while he is guilty of cutting up some nice Vauxhalls he isnt all bad

http://www.redvictor1racing.co.uk/index.php/penn-a...