ok my question is that my truck is a 1991 slivrado that used to be a v6 manual but i swapped in a mild built 350 and a th350 trans would the rearend from the manual trans have any bad effects on an auto trans? like the gear ratio? would it cause my truck to max out at like 70mph and and cause my trans to not shift into 3rd gear and run at high rpms when going down the freeway?

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manual transmissions usually run a lower ratio than automatics do. You will need to swap rear ends to make your truck preform properly. I once change a car from an automatic to a manual 4sp and I could run 90+ MPH in 3rd gear untill I changed to a posi 4:11 rear end.

 

No.

If it won't shift into third, it won't shift into third. Are you sure you've got the detent cable and vacuum set up right for that transmission?

Allan

 

Ya its all hooked up right, this is the third trans I have put in there because I thought it was the trans but this one is a fresh rebuild, also could it have somthing to do with the truck used to having an od trans? I seen somewhere that the rear is geared for the overdrive and swaping in an non od trans might have different effects?

 

And it just will not shift into 3rd?

The rear end has ABSOLUTELY NOTHING to do with that transmission shifting.

What rear-end ratio do you have? Maybe it is shifting and you just can't feel it? Like a 5:88?

Sure, running down the road, the engine speed is gonna be higher because you don't have that extra gear on top.

Allan

 

Not sure what gear ratio have not got into the rear yet all I know is when Im going down the freeway ill put the pedal to the floor and it seems to not go at full speed and im sure its not shifting into third I can feel it jump to 2nd but feel nothing after that and the rpms hit like 3500 - 4000 but does not slip or feel stuck can't really get an accurate mph because im in the process of installing mechanical speeding seeing how it was electrical

 

I agree not the rear gears. Look at things like the cervo or torque converter or vaccuum lines. Make sure you hard line the vaccuum line up to the intake manifold with only a short piece of rubber hose to connect. I'm assuming the other transmissions you've tried all shared the same torque converter. Did you go with an aftermarket stall converter? If so maybe it is not suited for your engine combination. Maybe I'm wrong but that is where I'd start.

 

They all had different tcs except this one has a 2800 stall but ill double.check the vac lines to make sure

 

checked all the vac. lines everything seems to be hook up right and getting good vacuum could maybe the carb not being tuned right have somthing to do with it? and i had somthing attached to my trans and have no idea on what the hell it is or fine any info on it but the speedo cable was hooked to it

 

I would have to agree with the others. The rearend has nothing to do with the trany shifting. The part you have in the pic is a ratio adapter. That will change your speedometer reading. Can you shift the trany manualy to make sure its shifting into 3rd gear?