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73-87 Chevy _ GMC Trucks => 73-87 Chevy & GMC Trucks => Topic started by: afran on January 02, 2013, 12:56:55 pm
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I am new to the site and fairly new to the older Chevy world. I recently purchased an 84 k-10 for the ranch and dropped in a remanufactured 350. The old engine had a 600 edlebrock on it, which is what I reused. Truck fires up and idles great. When driving highway speeds, the truck is constantly downshifting/upshifting. It is like it cannot find the right gear to be in. I searched the forum, but did not know what to call this issue, therefore, did not find an answer. I am not sure is this is a carb issue or a tranny problem. Tranny is a 700r4. Any help is appreciated.
Aaron
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Without seeing a picture....I would have to say the the TV cable is not hooked up correctly or at all. Because the 700r4 is a mechanical overdrive it has a special cable (TV cable) that helps the truck know when to shift in and out, all others models TH350 and TH400 just have a kick down cable that helps it "kick down" gear when you stomp it.
IT IS REALLY BAD to drive a 700r4 without the TV cable hooked up and adjusted properly to your carb. So I would recommend you do not drive it until it is fixed or drive it straight to a shop.
This should help:
http://forum.73-87chevytrucks.com/smforum/index.php/topic,24994.msg208296.html#msg208296
http://forum.73-87chevytrucks.com/smforum/index.php/topic,23815.msg198923.html#msg198923
http://forum.73-87chevytrucks.com/smforum/index.php/topic,15601.msg122052.html#msg122052
http://forum.73-87chevytrucks.com/smforum/index.php/topic,7133.msg41219.html#msg41219
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Thanks. This will give me something to do on my next day off.
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Although the TV cable could be all or part of your problem, the 700R4 transmissions are known for excessive 4-3-4 shift cycling at ~1/2 throttle and TCC disengagement/engagement cycling.
Absolutely verify TV adjustment first. Then...
TCC is disengaged with brake application. If the brake switch is right at the edge of its adjustment, pedal vibration at cruise can cause the switch to make and break contact and TCC will drive you nuts disengaging/engaging. Same thing can happen if a driver hovers the brake pedal with a foot, using it like an ottoman. Additionally, the brake switch can be easily knocked out of adjustment if a driver catches a foot under the pedal by accident and lifts slightly.
To determine if the TCC is the problem, try this: at road speed, slightly depress the brake pedal, but not enough to apply the brake. You should "feel" the TCC disengage. Releasing the brake pedal you should "feel" the TCC engage. Sometimes it's subtle - helps if you have a tach. TCC disengagement/engagement should occur within ~1 second of depressing/releasing the brake pedal. With the TCC forced to disengage by applying the brake as described, do your symptoms go away? If so, adjust the TCC switch (located next to the brake switch under the dash).
If the problem persists after defeating TCC as described above, and you verify that the trans is actually dropping out of OD, you may need to upgrade to the Corvette 3-4 throttle valve sleeve...
http://www.summitracing.com/parts/bmm-70237 (http://www.summitracing.com/parts/bmm-70237)
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If you dont have your TV cable hooked up the transmission thinks you are at WOT and this will work fine for about 10K miles and then your clucthes will start to slip and the transmission wont shift. Ask me how I know. Also your geometry has to be correct when the carb pulls the TV cable. Heres a good youtube video that shows proper TV cable adjustment and explains the geometry needed.
http://youtu.be/0jiSIoks7Jw