so i have a 74 with a th350 tranny. i think the shift points are off because at higher speeds i am high in the rpm range. at 75-80mph i am at about 4k for rpms. if anyone knows anything it would be helpful. i would like to know at what rpm should i be at that speed. it is a 350 engine and bone stock. any help to diagnose this would also be appreciated.

 

Are you saying at 75-80 mph the trans is still in 2nd gear, or just that your rpm's are high (that would mean a low rear gear)? You can feel it shift, so what gear is it in at that speed?

 

it feels like it is shifting at very low speeds. i think it is in 3rd but i'm not 100% sure it feels like it shifts out of 1st at about 15 then out of 2nd around 30. what rpms should i be at. i am going to change the tranny filter, a seal, gasket and fluid this weekend. could that help or do you think it is a vac problem? thanks for the response

 

If you're driving the car like a granny, the trans is gonna upshift at much lower speeds and rpm's. But if you put your heel to the steel, the rpm's are going to get closer to redline before a shift. If you can feel it going into 3rd, and you're at the speed/rpm you say, then you must have some low gears...3.73, or even 4.11's? Does the car jump off the line like it has low gears? And do you know for sure your speedo is accurate?

 

yeah, i have gotten on it but it doesnt jump off the line right now because i need to get a new carb for it. it is the stock carb and it just doesnt seem to want to work properly. i dont know the gears in it, stock as far as i know. i do think my speedo is off a little. maybe 5 no more than 10. and i know that i am going faster than it reads. but even then it just seems like i am at too high of an rpm for close to those speeds. i will let you know whats going on with it more after i work on it this weekend. thanks for the help.

 

i have 2.73 gears in my 79. i manually shift it when i wana drive hard but other than that the TH350 will just about shift into third from first at 10mph if you baby it. i can hardly feel it go from 1-2 then it just silently goes into 3 for me.
i know this to be pretty accurate and i know for a fact i have the 2.73 gears

2.73 gears.

2,100RPM@55mph
2,300RPM@65MPH
2,450~2,500RPM@70mph

these are the main speeds i cruse at being most is freeway miles so that gives you an idea. what freeway gears look like compared to your 3.73 or 4.11s you most likely have.

best way to know being that back when people changed rear ends more than they do today i would open up the diff cover and look for the stamped # on the ring gear. and why your at it change the fluid im sure its over do.
hope i could help

 

thanks. i do think it is a stock rear end. and it does shift into all the gears. how much of a difference would the rear end make with the rpms? would it really be about 1k rpm difference? i didnt get a chance to swap out the fluid and filter in the tranny this weekend. could that also be a factor. the car has been in storage for about 5-6 years before now. even before it was in storage it was only driven for about 6 months. before then it sat in a yard for about 5 years. i know it is overdue a lot of stuff. could the carb effect this too?

 

Use this and it should tell you what gear you have roughly.

It says a 4.25 gear at 70 mph with a 25 in tire. You probably have 4.10's in there.

 

yeah i plugged the stuff in and it came out 4.16 so i do probably have 4.10. i will find out for sure this weekend when i hopefully change out the differential fluid. thanks for the link and the help.

 

No problem. Also, if it's stock and the gears are original you can check on the front of the axle tube on the passenger side. There's an axle code there close to the differential housing and it's stamped in the tube. You may have to take a wire brush to it to be able to see it though.