Chevy Dave Posted April 20 Share Posted April 20 1970 SS 454, 2.56 axle ratio, 225 70 R15 tires When flooring the accelerator above 50 mph it does not downshift to 2nd. At 50 mph it does. Is there any way to get a downshift up to at least 70 mph? Quote Link to comment Share on other sites More sharing options...
Scott S. Posted April 21 Share Posted April 21 Hi David, Have you had anything rebuilt ? Assuming that you're running a stock engine, I'd look for some type of a vacuum leak. Might even be in the modulator or the carb. I've also read that an open element air filter can affect engine vacuum at high rpm's, Another factor is also the rear axle ratio...... Once you're up in that speed range, there's not much left to dig into. Just a couple ideas. Hope you get things figured out. 2 Quote Link to comment Share on other sites More sharing options...
rsorg Posted April 21 Share Posted April 21 check out the switch by the gas pedal ,not sure what it is called but is tan ,plugger type ,that was happening on my car a while back replaced it all good now Quote Link to comment Share on other sites More sharing options...
Glen Posted April 21 Share Posted April 21 4 hours ago, rsorg said: check out the switch by the gas pedal ,not sure what it is called but is tan ,plugger type ,that was happening on my car a while back replaced it all good now Funny… I thought mine was bad (help me out here… “kickdown modul(ator)” ???) on the ‘70 a while back. Turned out the Dynamat + new carpeting + existing carpeted floor mats = restricted gas pedal travel. Switching over to the original-type thin rubber mats cleared that right up. 2 Quote Link to comment Share on other sites More sharing options...
Scott S. Posted April 21 Share Posted April 21 3 hours ago, Glen said: Funny… I thought mine was bad (help me out here… “kickdown modul(ator)” ???) on the ‘70 a while back. Turned out the Dynamat + new carpeting + existing carpeted floor mats = restricted gas pedal travel. Switching over to the original-type thin rubber mats cleared that right up. Is that why you don't let the dog sleep at your feet while driving too ? Quote Link to comment Share on other sites More sharing options...
Glen Posted April 22 Share Posted April 22 5 hours ago, Scott S. said: Is that why you don't let the dog sleep at your feet while driving too ? Precisely why😂 Quote Link to comment Share on other sites More sharing options...
Chevy Dave Posted April 24 Author Share Posted April 24 With the ignition on, I don't have any voltage at the detent switch. The wiring diagrams in the shop manual do not show the wiring for this circuit. Does anyone know where the power is fed from? Quote Link to comment Share on other sites More sharing options...
jft69z Posted April 24 Share Posted April 24 1 hour ago, Chevy Dave said: With the ignition on, I don't have any voltage at the detent switch. The wiring diagrams in the shop manual do not show the wiring for this circuit. Does anyone know where the power is fed from? I can't find any diagrams or schematics that show the T-400 (M40) trans wiring either. One place suggested that the feed wire came from one of the 12V switched stabs on the fuse block and goes to one side of the accel. pedal switch. I can't verify that though. Maybe I'll go up in the attic and see what my old harness shows. Can you trace any wires from the switch connector back? Quote Link to comment Share on other sites More sharing options...
jft69z Posted April 24 Share Posted April 24 After looking at my old harness, it appears that the power for that switch goes thru the Radio/TCS Solenoid 10 Amp fuse, thru the power bulkhead in the engine compartment, and then to a short pigtail harness that goes thru a hole in the firewall to the Accelerator switch. From there, it would go to the transmission mounted switch. Dave and I were on the phone a few times and were both using multimeters at the same time, on our perspective harnesses, figuring out the circuit, lol. He doesn't appear to have power coming thru the engine side wire, which could be as simple as a poor connection at the bulkhead mating halves, or as bad as a broken wire. He tried to move the bulkhead connection a bit, but its location, plus it being bolted together produced no favorable results. We decided, If later attempts to re-seat the bulkhead don't work, a short jumper from a switched fuse block stab will work to power up the circuit. None of the diagrams or manuals I have showed that accelerator pedal switch. 3 Quote Link to comment Share on other sites More sharing options...
rsorg Posted April 24 Share Posted April 24 hi, a while back i was also having issues with this same problem ,but mine was not electrical so when i would put the pedal to the floor while driving sometimes it would shift down into passing gear and sometimes not,because the pedal was not engaging the switch so after not being able to adjust the switch ,i got some 3/8ths or 1/2 inch fuel line hose split it down the middle and put it on the switch part that touches the gas pedal and all is good now. Quote Link to comment Share on other sites More sharing options...
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