71 LS5/TH400 shift points

[Dale P.]

We own a 71 LS5 automatic .. car shifts very nice and firm when pulling away from a dead stop (without having it to the floor) .. but if cruising say at 50 and want to pass the car in front of you .. you kick the pedal down to the floor AND ... the car does down shift .. but if sure seems to have no power (no RPM)... it does have a 3.08 gear and is an automatic but I was expecting a better passing gear .. am I expecting too much ?? OR can something be done by my local tranmission shop to "rearrange" the shift points

[Jim T.]

Re: 71 LS5/TH400 shift points

Is your 71 downshifting to 1st or 2nd when you are doing 50 and press the gas pedal to the floor?
Take off you air cleaner and have another person press the pedal to the floor with the engine off. Look at the front throttle blades and see if they are straight up and down.
There is some adjustment that can be made where the throttle cable attaches to the throttle cable support bracket mounted on the left rear carb bolt. I am assuming your cable and bracket are like what is on my 70 350/300.
It is also possible that your secondaries are not opening. Do you still have the Q-Jet on your 454?

[Dale P.]

Re: 71 LS5/TH400 shift points..more information

the QJet is still on the car and is in good condition .. the front does open 100% .. and the rear is free to open when suppied with vac.

the main issue is that I think it is only down shifting to second from drive

[Chuck G.]

Re: 71 LS5/TH400 shift points..more information

I'm NO expert, but I'll take a shot. The downshift to passing gear is controlled electrically in the THM 400. There is a switch under the dash...above the gas pedal. When you put the "pedal to the metal", this switch is pulled backwards. This switch is one of those that is self adjusting. Maybe it's out of adjustment...not hooked up, etc. I'm told that "low speed" shifts are controlled by the vacuum modulator on the side of the trans, while high speed (passing gear) shifts are controlled electrically. I would check this switch, and the wiring to the side of the trans. I know that on my THM 400, if I turn the car on...WITHOUT the motor running, and turn the radio on, when I depress the accelerator pedal, I can hear an electrical "click" through the radio. That tells me it's working. Hope this helps. Chuck

[Dale P.]

Re: 71 LS5/TH400 shift points..more information-re

well .. I tried that approach .. didn't hear a thing "from the radio" ... I see the switch you are talking about and when I move the gas pedal while watching the switch there "is nothing happening" in fact it looks like the gas pedal linkage should be depressing this switch so .. I used my finger and still nothing .. so it looks like I am into a search and destroy mission .. I guess what I'll do is break out the volt meter and start to see where I have power and where in ends .. I did find the fuse that feeds that circuit and it is OK so at least I am OK at the starting point .. do you know were there issues with the switch under the dash going bad ??