88 chevy trans computer problem

rpage · 02-04-2004, 09:53 PM

I have a 88 chevy truck with a 355 engine and 3 speed auto trans. The problem is that the truck originally came with a 700r4 overdrive transmission. Do I need a different computer to make it shift at its correct shift points? Can I just get a chip? Or is it fine? 2nd gear seems very short at wide open throttle, it only goes from 40mph to 55mph. And it shifts at a low rpm. The motor is decked out and I know I need a chip but the transmission problem really concerns me. Any help or advice will be greatly appreciated and thanks in advance.

Robert Page
page@dmci.net

72 rs · 02-04-2004, 11:35 PM

the computer in your truck is designed to work with a computer. even though it only locks the tourqe converter it still comunicates with the trans. i would recomend puting a 700r4 back in the truck.

Thunderbolt · 02-05-2004, 12:40 PM

Do you have the kick down cable adjusted right. It is similar to the detent cable that was on your 700 r4 and they must be adjusted correctly. Why did you get rid of the 700 ?? They are a good trans when built right and would actually perform better than the 350 turbo.

rpage · 02-05-2004, 08:53 PM

I bought the truck with the trans already swapped, I didn't take out the 700R4 trans but I would like the trans that is in the truck to stay in. There is no kickdown cable either, (the one that runs to the bottom of the throttle I think), it has been disconnected before I got it. The problem is I bought the truck and am currently figuring everything I can out that the previous owners have done to the truck. The engine is a 355 and has a edelbrock performer tbi intake, dual exhaust, and I don't know about the bottom end of the engine. The engine has been bored so I don't know what pistons or rods or crank they used. The engine idles real rough and at wot it seems sluggish. The trans shifts at weird times and the trans looks new and its a different trans from stock so I think my main problem is the computer. If anyone has any more help since I've cleared things up I would appreciate it.

quaddriver · 02-05-2004, 09:14 PM

Quote:

Originally Posted by rpage

I have a 88 chevy truck with a 355 engine and 3 speed auto trans. The problem is that the truck originally came with a 700r4 overdrive transmission. Do I need a different computer to make it shift at its correct shift points? Can I just get a chip? Or is it fine? 2nd gear seems very short at wide open throttle, it only goes from 40mph to 55mph. And it shifts at a low rpm. The motor is decked out and I know I need a chip but the transmission problem really concerns me. Any help or advice will be greatly appreciated and thanks in advance.

Robert Page
page@dmci.net

the puter simply provided a ground for the TCC solenoid on the 700, and it used the VSS signal for other stuff.....you need the VSS - the pulse generator is either in the tail shaft or on the speedo.

the thm350 uses a kickdown cable and a vacuum modulator....are both hooked up?

rpage · 02-09-2004, 11:14 AM

I know the kickdown cable isn't hooked up, but I don't know about the vacuum modulator. And now when I go to a stop, I always stall the engine, reverse or forward. I think it is idling way too low but is there a way to adjust it?

TEXAS-HOTROD · 02-11-2004, 10:02 PM

Do you know what trans you have? Turbo 400s use a vacuum modulator and a kick down switch (electric) where a TH350 uses vacuum and a cable. I have seen some older TH350s that didn't use a cable.
The governor controls the main shift points where as the vac modulator compensates for varying engine loads. You can adjust a modulator to stiffen up the shifts, but that intern will also raise the shift points.
Sometimes a trans is harder to tune than an engine.
The 454TBI used a bigger throttle body. Scrounge the bone yards for an injector unit/adapter assy. and adapt it to your manifold, or stick it on top of a Victor Jr.
Good luck
---TEX---

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