Rebuilt M12 changing quick and not kicking down

To my knowledge all the V8 Shift Commands will do an automatic 2 to 3 upshift at 5000 rpm or so, even if the selector lever is left in "2". However the down side is that the tranny will drop back to second as soon as the rpms drop back. This is very hard on the front band.

As far as the vacuum modulator and the corresponding rod length goes, I can't give you an answer. I can say though if you can adjust the modulator you have currently installed to get the shift points in the normal range then you should be OK. If not, you may need to put the original modulator and rod back assuming the modulator is good. If you were sucking tranny fluid through the modulator into the engines intake manifold then it was bad.

Thanks for all your help guys !!!

My Hornet went back to the Mechanic this week and your tips were passed on regarding the Tranny.

The word is it's now stretching its legs through the gears before changing up and I am getting kick down .

Motor was in for it's first service after rebuild, so cant wait to get it back and give it some "Proper" driving !!

Regards
Craig

Good to hear! Nothing more pleasant than a good running, shifting drivetrain...nothing more disappointing and worrisome when it's just rebuilt and still not right.

Craigie wrote: Had a list of things for the mechanic (my cousin Mark) to run through and sort out, including lights/wiring, door locks and some fluid leaking from the Tranny. Most of it is all sorted except for the leak. Was not sure what to make of fluid leaking from the freshly rebuilt tranny when it did not leak before the rebuild ?? Didn't start dropping fluid until the last 6-8 weeks. The first few weeks of driving around were issue free after the rebuild. Mark has taken a close look and seems to think on a cold start up, there is a puff of oil coming out of both the breather and dip stick tube. The tranny fluid level has been checked and is not overfilled. Obviously tranny fluid spilling into the engine bay is not ideal so any solutions would be most welcome ?? At the moment we are not sure how to tackle the problem. Regards

Craigie, what size tires are on your SC/360? It looks just like mine, except I have blackwall tires. I hope you get everything sorted out on your car. You have had the worst luck of anybody so far. 

From your description it sounds very much like your transmission is over filled. You may very well not have the right dipstick. The oil level should not be so high that you're expelling oil or oil mist out of the trans. vent or the dipstick tube. I cannot speak with certainty about this but on my both my 69 AMXs, the one I bought new and one I bought when it was 5 years old, had 343 stamped into the metal handle of the transmission dipstick. I understand that there never was a dipstick that was stamped 390 or 401. Are there any markings on your dipstick or do you know of anyone that has the proper "343" dipstick that you can compare to yours for the overall length and the position of the level markings? For now I'm going to assume that all the AMC M-11 and M-12 transmissions used the same dipstick until they were phased out at the end of the 1972 model year.
I just check the dipstick of my 67 Ambassador with the 343, 4V and the M-11. It too has 343 stamped into the dipstick handle.