[70chevyc10]

Im new to this so im hoping someone can give me some help - Ive spent a while browsing through previous threads...

I recently bought a 70 chevy c10 that had a supposedly "rebuilt" 350 motor with th350 tranny. The motor was rebuilt the tranny not, both are from a 1982 pickup.
I just got the engine prof. rebuilt with larger valves, mild cam and domed pistons - it has roughly 350-370hp. Needless to say its a new strong motor.
My problem is the tranny, it wont downshift no matter how far the gas is pushed. Ive replaced the detent cable and adjusted it, the fluid is at its normal level but it just wont shift. If I shift manually first is great it pulls strong, shift into second and its really soft and doesnt pull worth a damn until it reaches a fairly high rpm, third seems to work alright. How do I tell for sure whats up with it? Ive changed the fluid, what came out smelled slightly burned. Ive read in here that second gear can be somewhat burned up, can it be the modulator or do I still have a cable problem?

 

[Siggy_Freud]

The detent cable isn't going to affect how the tranny runs. It simply controls the downshifting upon WOT.

The modulator will control when the tranny shifts and its possible its shifting into second too soon or too late and your hitting a drop in your powerband.

However it is most likely that your tranny is on its downhill journey. The burnt smelling fluid is not a good sign.

 

[70chevyc10]

I understand the basic operation of the detent cable and thats one of the main problems Im having is downshifting at WOT.

I would like to adjust the modulator valve but have to research that a bit so I dont make things worse than they already are.

The whole time I may have assumed the worst (a new tranny) I just wanted to postpone the inevitable.

 

[musky2]

350 turbo problem

Ive read that you can adjust the modulator by putting a thin screwdriver through it ; I dont know if you turn to the right or left to make it shift sooner or later. I dont know much about trannys and I havent looked inside the tube you hook the vacuum line to but if thats what they are talking about it must be a small screwdriver. I dont even have my kickdown hooked up yet because Ive been having carb problems ; I think the carb I have on it now is going to work good so Ill hook it up. 750 Holley that came on the truck back on it now , I had replaced it with a 600 but it ran like crap , when I put the 750 back on it ran like crap too! but after blowing it out with air hose and tapping on it with a wrench the trash broke loose and runs fine. Thats all I know but someone else will give you the info you needeventually.

 

[70chevyc10]

I have to look into the direction I need to turn the screw in the modulator - If anyone knows please enlighten me. I also have to check the vacuum at the modulator, ive been told a partly clogged line can cause similar problems.

musky2 - what kind of symptoms did you have with your carb before you swapped it out?
I have recently developed a problem with mine which I was told was either a lean bog or a rich bog when the gas is punched quickly. I just rebuilt the carb (quadrajet) and have adjusted the idle mixture - seems to happen more when its cold than warm but most of the time nonetheless. Should I just ditch the old quadrajet for a new carb or has anyone else been able to fix this problem?

 

[Robinson Robin]

If you engine does infact make 370hp then chances are it has a fairly agressive cam and larger port heads which is a bad combination for low rpm torque hence why your engine doesn't pull well untill higher in the rpm band. In order you redidy this you will need some shorter gears in the rear end and possible a higher stall conv.

 

[70chevyc10]

I had considered swapping out the th350 for a 700 so I can get a low first gear and overdrive but dont have the time to get the drive shaft shortened or a place to get it done in my area. Seems this swap is fairly popular. As far as a higher stall converter what is a decent rpm, I dont drag (I guess that depends whos at the light). Im all for the steeper rear gears but I drive 1 hr round trip to work every day. I had almost the same 350/350 combo in my camaro with 353's and it was a monster , it was hard to drive even in the rain. If my 350 bites it should I stay with another 350 or go for the 700? any opinions?

 

[musky2]

350 turbo problem

My problem was just trash ; stopped up something. Im not good at carbs either so I stick with Holleys , easy to work on. Ive heard the Quadrajet is a fine and fuel efficient carb , they just scare me to open them up. The same for the overdrive trannys (700r4s etc.) Im old fashioned and like simplicity so Ill stick with my Holleys and 350 turbos. How do your plugs look? wet and rich or white and lean? On the Holleys the accelerator pump will cause a bog if not adjusted right. Someone still needs to explain the modulator adjustment to you for a firmer shift and maybe replace it , they are cheap and easy to replace . Blow through the vacuum line with an air hose and make sure someone feel a good stream of air come out the other side. the 700r4 is great but you better set the cable perfect ; it will burn up , you can bak on that ; but thats another story !

 

[70chevyc10]

tranny

Well, Ive concluded the tranny is pretty much on its last legs, so Im just biding my time until then.
I havent had a lot of time to mess with it - so im going to replace it next month.
Im now having a problem with dieseling, ill post that in another area.