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I recently picked up a 1972 cutlass 442 clone. It's got a 455 in it and has had engine modifications, but what exactly I do not know. It has aftermarket headers and pretty sure it's cam has been changed but I don't know what else has been done. It seems to shift right at 4k RPMs, which seems too low. I've also noticed that when going about 20 mph if I slam on the gas it doesn't down shift. It down shifts fine going 30-40 mph though. I've seen a couple threads that say a built 455 would shift between 5k-6k. Is shifting at 4k a a bit too low and if so, any thoughts on why it would be doing that?
I hate that I don't know this, but I don't know.
This is the only tag I could find on it, It's a turbo something... I also don't know how many gears it has. I think 4, but it could be 3. I should probably know this...
Last edited by Byron; April 12th, 2023 at 11:42 AM.
I hate that I don't know this, but I don't know.
This is the only tag I could find on it, It's a turbo something... I also don't know how many gears it has. I think 4, but it could be 3. I should probably know this...
This is a 1975 TH400 out of a Pontiac with a 400 engine.
Thank you Joe! I'm curious, how did you figure that out?
I can confirm, thanks to Fun71 and the chart he posted, that it's a TH400
The stamped "75" on the tag is the model year. The "PX" code designates the original application. I use the application list from the Ron Sessions TH400 book.
If the detent system isn’t functional, the trans will tend to short shift.
There is an electrical terminal on the drivers side of the case. Is there a wire connected to it? If not, you need to collect a few parts to make the detent system functional. You need the switch and mounting bracket on the gas pedal. I believe the wiring under the dash is already there, you just need to add the wire in the correct spot in the engine harness connector.
If the wire is there, unplug it, put s test light on it. With the ignition on, push the throttle wide open. Does the light come on? If so, then the problem is inside the trans. If not, check the fuses, check the switch under the dash for proper adjustment, throttle actually opening all the way, etc.
Whatever you do, DONT mess with the vacuum modulator. The modulator controls part throttle shifts only, and has a very narrow window of adjustment. At most, you can raise or lower shift points 2-4 mph.
The modulator controls part throttle shifts only, and has a very narrow window of adjustment. At most, you can raise or lower shift points 2-4 mph.
That's not entirely correct. The modulator controls controls trans line pressure in response to manifold vacuum (which is a surrogate for engine load). Lower vacuum indicates higher engine load, which causes the modulator to raise line pressure, delaying upshifts.
If the detent system isn’t functional, the trans will tend to short shift.
There is an electrical terminal on the drivers side of the case. Is there a wire connected to it? If not, you need to collect a few parts to make the detent system functional. You need the switch and mounting bracket on the gas pedal. I believe the wiring under the dash is already there, you just need to add the wire in the correct spot in the engine harness connector.
If the wire is there, unplug it, put s test light on it. With the ignition on, push the throttle wide open. Does the light come on? If so, then the problem is inside the trans. If not, check the fuses, check the switch under the dash for proper adjustment, throttle actually opening all the way, etc.
Whatever you do, DONT mess with the vacuum modulator. The modulator controls part throttle shifts only, and has a very narrow window of adjustment. At most, you can raise or lower shift points 2-4 mph.
So this bad boy here? Wire is connected and goes to metal box and then what I am assuming is the kickdown cable running out of it. There is a small wire the same size as the wire going to the transmission, that is going towards the engine bay/cab. Could this be what connects to the pedal switch?
Matt, are you saying that shifting at 4k is indicating there is a problem?
The stamped "75" on the tag is the model year. The "PX" code designates the original application. I use the application list from the Ron Sessions TH400 book.
Joe, this is awesome to know. Thank you for teaching me something!
So this bad boy here? Wire is connected and goes to metal box
Metal box? The wire should just run directly to the switch on the accelerator pedal. Of course, that plastic terminal isn't the factory connector, so who knows what was done to the car. And 4000 RPM upshift at wide open throttle is low, but may not be unusual for a 1975 trans.
Metal box? The wire should just run directly to the switch on the accelerator pedal. Of course, that plastic terminal isn't the factory connector, so who knows what was done to the car. And 4000 RPM upshift at wide open throttle is low, but may not be unusual for a 1975 trans.
So this bad boy here? Wire is connected and goes to metal box and then what I am assuming is the kickdown cable running out of it. There is a small wire the same size as the wire going to the transmission, that is going towards the engine bay/cab. Could this be what connects to the pedal switch?
Matt, are you saying that shifting at 4k is indicating there is a problem?
Really? Wow, someone spent a bunch of money they didn't need to. FYI, improper adjustment of that cable can be a primary cause of your kickdown problems.
I'm guessing your car was originally a TH350 car, which used a cable kickdown instead of electric. Apparently whoever swapped in the 455 and TH400 was clueless about how Olds accommodated the kickdown switch on TH400 cars. The wires were even already in the harness from the factory, just taped up out of the way on TH350 cars. Who knows if they are still there now. This is what the factory kickdown switch looks like, mounted to the accelerator pedal.
Note the switch on the righthand side of this diagram vs. the second cable on the lefthand side. The accelerator pedal is different due to the tab for the second cable getting in the way of the switch.
That's not entirely correct. The modulator controls controls trans line pressure in response to manifold vacuum (which is a surrogate for engine load). Lower vacuum indicates higher engine load, which causes the modulator to raise line pressure, delaying upshifts.
Another way to put it, once manifold vacuum drops below a certain point, the modulator has zero influence on shift points. By that time, line pressure is maxed out.
So this bad boy here? Wire is connected and goes to metal box and then what I am assuming is the kickdown cable running out of it. There is a small wire the same size as the wire going to the transmission, that is going towards the engine bay/cab. Could this be what connects to the pedal switch?
Matt, are you saying that shifting at 4k is indicating there is a problem?
I person have never used one of those boxes, I have seen them in the JEGS catalog. As expensive as the factory kickdown switches have gotten, you could almost buy 4 for the cost of that kit.
Beside the point: I’m guessing one of the 2 wires going into the box will have power. The other wir should have power with at WOT.
This looks to be exactly how my setup is. And I must have the same Lokar carb bracket as well.
What is the point of this kit? Does this bypass the switch at the pedal?
Last edited by Byron; April 12th, 2023 at 04:32 PM.
I recently picked up a 1972 cutlass 442 clone. It's got a 455 in it and has had engine modifications, but what exactly I do not know. It has aftermarket headers and pretty sure it's cam has been changed but I don't know what else has been done. It seems to shift right at 4k RPMs, which seems too low. I've also noticed that when going about 20 mph if I slam on the gas it doesn't down shift. It down shifts fine going 30-40 mph though. I've seen a couple threads that say a built 455 would shift between 5k-6k. Is shifting at 4k a a bit too low and if so, any thoughts on why it would be doing that?
Thank you for the advice!
to be clear, are you talking about full throttle RPM upshift in drive?
Really? Wow, someone spent a bunch of money they didn't need to. FYI, improper adjustment of that cable can be a primary cause of your kickdown problems.
I'm guessing your car was originally a TH350 car, which used a cable kickdown instead of electric. Apparently whoever swapped in the 455 and TH400 was clueless about how Olds accommodated the kickdown switch on TH400 cars. The wires were even already in the harness from the factory, just taped up out of the way on TH350 cars. Who knows if they are still there now. This is what the factory kickdown switch looks like, mounted to the accelerator pedal.
Here's what the TH400 pedal assembly looks like.
Hey Joe, unless my beer goggles are kicking in, I have a TH400 pedal? I have a TH350 pedal and no kickdown switch.
Last edited by Byron; April 12th, 2023 at 04:24 PM.
I have the Lokar Electric Kickdown Kit. This is from the description on their website "This design eliminates mounting unsightly electrical switches on carburetor, manifold, or near throttle pedal." So I'm reading that as it bypasses the kickdown switch at the pedal and since I seem to have a pedal assembly for a TH350, this kit is eliminates the need to replace the pedal and kickdown switch assembly when changing out the trans for a TH400. Am I wrong?
If I am right (for the first time in my life) then back to my original question, if the transmission is shifting too early at 4k RPM, what could be the cause?
This looks to be exactly how my setup is. And I must have the same Lokar carb bracket as well.
What is the point of this kit? Does this bypass the switch at the pedal?
Yes. As I said above, whoever installed this apparently didn't know about the factory switch on the accelerator. This Lokar kit is designed for street rods. Nearly $200 for a cable-operated switch vs. the factory style seems like a waste.
Hey Joe, unless my beer goggles are kicking in, I have a TH400 pedal? I have a TH350 pedal and no kickdown switch.
As I said above. Your car came from the factory with a TH350. The kickdown cable for that trans would have been attached to that second hole in the accelerator pedal arm. The Lokar kit will work, it's just a ton of money and waaaay more parts than needed.
As I said above. Your car came from the factory with a TH350. The kickdown cable for that trans would have been attached to that second hole in the accelerator pedal arm. The Lokar kit will work, it's just a ton of money and waaaay more parts than needed.
Definitely seems like a lot of extra parts. Thanks for helping me piece this all together!
I have always wondered if my setup is correct and this discussion is leaving me still wondering. My 455/400 was a swap from a ,350/350. We installed a cable actuated electric switch at the carb. The car will downshift into 2nd up to about 55 mph. It has 323 gears. After 55 the car hauls *** if you open up the secondaries, but no downshift. I've had many small block stock highway gear cars that downshifted to about 65 to 70 and not nearly the response of the 455 without the downshift. Is this normal or should my car downshift above 55 mph?
I have always wondered if my setup is correct and this discussion is leaving me still wondering. My 455/400 was a swap from a ,350/350. We installed a cable actuated electric switch at the carb. The car will downshift into 2nd up to about 55 mph. It has 323 gears. After 55 the car hauls *** if you open up the secondaries, but no downshift. I've had many small block stock highway gear cars that downshifted to about 65 to 70 and not nearly the response of the 455 without the downshift. Is this normal or should my car downshift above 55 mph?
I'll try and compare that with how my car performs, just so you have a comparison. It will be a few days until I can go play around though. From my spotty memory, I think my car behaves similar to what your describing. I have commented on how well it pulls at 50+ mph, but not sure if it was downshifting or not. Do you know what RPMs your car is shifting at?
Like on 700R4 you adjust shift points by adjusting the cable.
[QUOTE=Byron;1491610]I recently picked up a 1972 cutlass 442 clone. It's got a 455 in it and has had engine modifications, but what exactly I do not know. It has aftermarket headers and pretty sure it's cam has been changed but I don't know what else has been done. It seems to shift right at 4k RPMs, which seems too low. I've also noticed that when going about 20 mph if I slam on the gas it doesn't down shift. It down shifts fine going 30-40 mph though. I've seen a couple threads that say a built 455 would shift between 5k-6k. Is shifting at 4k a a bit too low and if so, any thoughts on why it would be doing that?
Thank you for the advice!
Last edited by oldsmobilejim; April 15th, 2023 at 06:02 AM.
I'll try and compare that with how my car performs, just so you have a comparison. It will be a few days until I can go play around though. From my spotty memory, I think my car behaves similar to what your describing. I have commented on how well it pulls at 50+ mph, but not sure if it was downshifting or not. Do you know what RPMs your car is shifting at?
It will be interesting to see what you find. Haven't really noticed the rpms at which the car shifts. Tach is a bit small and my eyes aren't what they used to be when I installed it. If I am not pushing it, it's hard to tell when it shifts since I don't have a shift kit.
I have always wondered if my setup is correct and this discussion is leaving me still wondering. My 455/400 was a swap from a ,350/350. We installed a cable actuated electric switch at the carb. The car will downshift into 2nd up to about 55 mph. It has 323 gears. After 55 the car hauls *** if you open up the secondaries, but no downshift. I've had many small block stock highway gear cars that downshifted to about 65 to 70 and not nearly the response of the 455 without the downshift. Is this normal or should my car downshift above 55 mph?
For comparison, my unopened OG-code 79,000 mile TH400 readily kicks down up to about 72-3 MPH in a '69 4-4-2 convertible with 3.08 gears.
Like the Bang Man said, the proper response of a turbohydramatic, at highway cruise in drive, when floored, is to downshift and stay in that gear while you are still on the kickdown switch (ie floored) until the RPM approaches some point, usually around 4500, then shift back into high. Depending on tire size and rear end, this can be anywhere from 70-90.
If I am right (for the first time in my life) then back to my original question, if the transmission is shifting too early at 4k RPM, what could be the cause?
Joe P already answered it. ( He answers questions correctly and concisely even when he seems to say something in passing ...)
Originally Posted by joe_padavano
And 4000 RPM upshift at wide open throttle is low, but may not be unusual for a 1975 trans.
Byron the 1975 PX coded transmission was intentionally calibrated and paired to a performance dog. A Pontiac with a 400 4BBL producing 185 HP and a 2.56 rear gear while weighing 4000 + LBS curb ...
For reference, Road Test Magazine March 1975 tested a 1975 Pontiac Trans Am 400 4BBL THM400 with 2.56 rear. It weighed 4035 LBS curb and needed 11.2 seconds to hit 60 MPH and 18 seconds to cover the 1/4 mile at 79 MPH...
Bottom line you need to get the shift points to exceed your HP peak rpm but obviously stay below the engines redline. WOT shift RPM must exceed HP peak in order to see max performance.
For example, the Trans Am's 400 CID engine HP peak occurred at 3600 RPM. The transmission shifting at 4000 RPM is ideal.
April 12th, 2023 | 10:10 AM
