Team Chevelle banner

Status
Not open for further replies.
1 - 9 of 9 Posts

·
Registered
Joined
·
92 Posts
Discussion Starter #1
Okay, this may sound silly, but here goes,

My 72 chevelle has a 350 engine and TH350 trans. From a stop it accelerates very well, and when its floored you can hear the motor gets up to about 5000 or so rpm's before it shifts (No tach). But, if I'm already moving, say 35mph, and I floor it, it is extremely sluggish, and does not downshift to pick up speed like other cars I have driven. I know that most newer cars will downshift into the next lowest gear to accelerate faster if you hit the gas hard while already moving , but I'm new to old cars and I dont know if my chevelle should or not. This transmission was supposedly rebuilt not too long ago (approx. 5000 miles, but how long it took to put that 5000 miles on the car I dont know). It also has a small leak which has not been located yet, but I keep plenty of fluid in it. I've also been thinking of adding about a 2400rpm stall converter to get better acceleration. Any help or explanation would be great.

Thanks,

------------------
Joe Scott
 

·
Registered
Joined
·
3,752 Posts
Your TH350 sould downshift. It sounds like your downshift (detent) cable is missing or mis-adjusted. It's a simple fix. Although I can't tell you how to do it. Perhaps someone else can provide the details.

------------------
Pat Kelley
66 El Camino, daily driver
67 El Camino, STRIP/street
 

·
Registered
Joined
·
1 Posts
It should downshift but I think on the TH350 and TH400 it is internally controlled based on RPM and load. On other transmissions such as the TH700R4 it is controlled by a cable attached to the carb or EFI, called a TV (throttle valve) cable. When your transmission was rebuilt it may have been done incorrectly.


------------------
'66 Chevelle Malibu 4dr
in progress!
will have 350/4 sp 370 HP
 

·
Registered
Joined
·
433 Posts
That fluid leak may indeed be the culprit, but it's most likely a missing or maladjusted detent cable. They attach to the throttle and I _think_ the governor. To set it, hold the carb to full throttle. Then attach the cable so it's at its tightest. So when you release the throttle, there should be slack. But pull the pan off your tranny, remove the filter, and the valve body. Check the separator plate (it should be obvious what it is). If it has specific imprints that match the valve body passages, you're good. If you see something resembling a large red blotch, you need to take it to the shop. If there's a fluid leak where the tranny feeds a 2-3 shift valve, that's what's responsible. Also check the vacuum modulator with a vacuum gauge in the tranny end to see it's it's getting the righth vacuum at WOT.

------------------
"...it costs what now?" Lev
Team Chevelle Member #590
70 Malibu
350/300hp
Soon to be 396/325hp
 

·
Administrator
Joined
·
16,196 Posts
Joe, If everything else about the trans functions normally then you just need to see whats going on with the throttle valve cable. It is a black cable similiar in looks to the accelerator cable on your carb. There are 2 places it can possibly hook to, 1)To the carb right below the accelerator cable. If so the adjustment is at the bracket near the rear of the manifold. There is a plastic clip you lift from the fat part and while someone holds the pedal to the floor just slide the clip back in. 2) It could go thru the firewall just above where the accelerator cable goes in. If so the adjustment is made by sliding the retainer clip on the cable. At either location there is to much slack in the cable, you will have to adjust it shorter. There is also the possibility that it isn't even hooked up. Let me know what you find.

One last thing, it comes out of the trans on the passenger side just in front of the fill tube. Then is routed behind the distributer to one of the 2 attaching points.

------------------
Philip Valentine
Gold Member #42
"Perseverance is not a long race; it is many short races one after another."
[email protected]

[This message has been edited by 64elcamino (edited 02-16-2000).]
 

·
Registered
Joined
·
51 Posts
My Chevelle (Which I don't have anymore) Would downshift nicely at 40MPH. But only after I put the new 4-barrel Road Demon on it. With the original 2 BBL , it was considerably lower. I may have just been the adjustment of the kickdown cable..

------------------
Scott, 20
Denton/Dallas, 70 Chevelle Malibu
May the force be with you..
 

·
Premium Member
Joined
·
3,438 Posts
Sounds like the kickdown cable is not hooked up or adjusted wrontg..otherwise something is wrong internally with the valve body. Th350 trans does not have a TV cable, only a cable for the kickdown. Shift points are controlled by a mechanical governer and vacuum modulator. Find your kickdown cable and with it off the carb (if it isnt already) hold the case and pull on the cable, you should be able to feel it actuating the kickdown valve on the valve body. If the cable has no feel, it either isnt hooked up inside the trans (drop the pan to check) or the cable is broken, or the valve is stuck. If you can feel the cable working, hook it to the carb and adjust so when the carb is opened all the way the cable is pulled enough to work the valve.

------------------
70 chevelle ss396 conv
66 chevelle ss396 hdp/conv
55 chevy prostreet
69/71 camaros
 

·
Registered
Joined
·
92 Posts
Discussion Starter #9
Okay guys,

I took a look to see if I could find the throttle valve cable and sure enough it was diconnected!! I hooked it back up and and re-adjusted it and now it will downshift beautifully at speads up to about 45mph. It sure makes it a lot more fun to drive! Thanks for all the help guys, your advice was right on the money.



------------------
Joe Scott
 
1 - 9 of 9 Posts
Status
Not open for further replies.
Top