GM180 gearbox and a 1:3.45 axle - bad marriage?

Jasper M · Post by **Jasper M** » Mon Sep 01, 2014 9:35 am

Hi all,

I've got a GM180 connected to a back-axle with 1:3.45 ratio.
On full throttle I got the feeling that the engine wants to rev passed the 5500 rpm limit so I back-off on the throttle. I don't know if that is correct English

I thought the gearchanges happen on pressure but aparantly the gear ratio on the axle have got something to do with it?

Anyone got any experience with it? Thanks!

Cheers Jasper

DaveEFI · Post by **DaveEFI** » Mon Sep 01, 2014 10:28 am

The auto box has no idea what rear axle ratio you're using.

kiwicar · Post by **kiwicar** » Mon Sep 01, 2014 7:35 pm

Hi
the control of the change points is controlled by fluid pressure in the system, however that in turn is governed by manifold depression, throttle position, the "governor" on the back of the box, oh and how hard the torque converter is working. You can get kits to modify the change points of many autoboxes, they contain loads of springs, a new vacuum modulator, valves and a fortunately . . . and a set of instructions.
Best regards
Mike

Jasper M · Post by **Jasper M** » Tue Sep 02, 2014 9:28 am

Thanks for the fast replies guys, another thing learned!

DaveEFI · Post by **DaveEFI** » Tue Sep 02, 2014 9:55 am

My EFI with GM 180 box is still pulling very hard when it changes up on full throttle. You'll not break a standard engine anyway by going over 5500 rpm - the lifters will limit the maximum revs to just over 6000. And the car rev counter isn't very accurate anyway.