TH350 shift point question

[MagmaJct]

I have a 1971 C10 1/2 pickup. As far as I know it's all stock except the carburetor and larger tires.

Problem/Question: When accelerating from a stop, or when accelerating out of a turn, I ease into the accelerator. When you only get 10 MPG you do all you can. As the I ease into the accelerator the transmission with up shift (into 2nd?) too soon and the rate of acceleration decreases.

As I continue to ease into the accelerator, the transmission will then downshift again continuing the acceleration I had before. It has been an annoyance for some time, but now I'm concerned this will lead to excessive wear and tear on the transmission.

Details: As far as I know stock 350. Tire size 235/75 The carburetor is a Carter AFB equiv. to the Edelbrock 1405 with the add on electric choke. Engine vacuum is a little low, but I can't find a vacuum leak and engine compression is in spec according to my Chilton's.

Ideas?

[JimKshortstep4x4]

The vacuum modulator controls the shift points and your low vacuum could be causing your issue. The other item to check is th governor. If you cannot fix the vacuum then try to adjust the vacuum modulator. Also, make sure the kickdown cable is free and adjusted properly.

Jim

[stroked69]

Its either the vac module or the hose that runs from the module to carb.

[Roadmarks]

I had the same problem and a new modulator and vacuum line fixed it. Make sure ALL your vacuum lines are clear and not leaking. Also, use metal lines where ever you can.
They won't age, soften or crack later.

[fastwillie 696969]

sounds like the kick down is out of adjustment to me just sayin'

[MagmaJct]

Thanks everyone for the response!

I'm thinking the low vacuum would delay the shift point. Having said that, however, I will inspect the hose to the modulator. Also, the modulator is adjustable? I didn't know, I'll look into it. Thanks again!

I'll post updates as I have time to work on the truck.

--Mike

[wwotr]

Originally Posted by MagmaJct

I have a 1971 C10 1/2 pickup. As far as I know it's all stock except the carburetor and larger tires.

Problem/Question: When accelerating from a stop, or when accelerating out of a turn, I ease into the accelerator. When you only get 10 MPG you do all you can. As the I ease into the accelerator the transmission with up shift (into 2nd?) too soon and the rate of acceleration decreases.

As I continue to ease into the accelerator, the transmission will then downshift again continuing the acceleration I had before. It has been an annoyance for some time, but now I'm concerned this will lead to excessive wear and tear on the transmission.

Details: As far as I know stock 350. Tire size 235/75 The carburetor is a Carter AFB equiv. to the Edelbrock 1405 with the add on electric choke. Engine vacuum is a little low, but I can't find a vacuum leak and engine compression is in spec according to my Chilton's.

Ideas?

Magma,
I'm running a pretty stock 350 with a Turbo 350.
From a stop, my Tranny will hit 1st, 2nd and Drive by the time I'm just about to the other end of the Intersection!
Its alway's shifted that way.
Now if I get ON IT, it'll hold 1st gear much longer.
As with you, if I ease on the gas and it shifts into 2nd, and I give it a little more Gas, it will downshift back into 1st.

As far as I know thats the status Quo.
My Tranny doesnt slip at all.
Been that way for 2 1/2 years.

Maybe someone else can shed some light, but sounds like you OK to ME.

I had a 96 Chevy Tahoe, with a shift Kit.
That S.O.B. would hit 2nd, SO HARD (out of 1st) that it would spill a 1/2 full Soda Can, sitting in my Cup Holder!

[MagmaJct]

wwotr,

Maybe your truck isn't supposed to do that. :-D Maybe the same thing that fixes mine will fix yours. Ultimately I just want it to hold 1st longer, or at the least, stop going back into 1st 100 feet later!

[wwotr]

Originally Posted by MagmaJct

wwotr,

Maybe your truck isn't supposed to do that. :-D Maybe the same thing that fixes mine will fix yours. Ultimately I just want it to hold 1st longer, or at the least, stop going back into 1st 100 feet later!

Nah...I'm happy with mine.
When it goes out then I'll just get a 200R4 or a 700R4.
If it aint broke...don't fix it.

But please feel free to tell us how you proceed ,
what (if anything), you replaced, and any problems (if there are any), and what the final solution is.