I have just completed a basic rebuild of a 727 transmission. New clutches seals and gaskets. Every thing looks good and no leaks. : ) Problem is the 3rd gear shift never happens.. The trans shift 1,2 and reverse no problem. 3rd looks like it wants to go at 40 or so then slips into neutral. Slow down a little a back to 2cd. The Valve body is a older Trans Go oddly missing one of the check balls when I inspected. So I begged the local trans shop for one and replaced it. all 5 check balls in plus one the spring and large one. I don't know if the VB controls this function. I can only guess. I am thinking of replacing VB with a stock unit to see if this may fix this. Also the Toque converter is super tight. NO stall engine runs in park and in drive with brake. But it runs like a stick. 1,2 shift is hard and strong almost no tire spin. This car used to spin the tires all the time with old trans and Torque converter. I am just guessing at where this build when wrong. I think the pressure to the converter is way to high. Again I am wondering what controls this. VB? Post any thoughts Thanks.
727 no 3rd
- Thread starter Caxey1
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KickDown
Just a Brit in Germany
Did you air pressure check the operation of the servos & clutches before you refitted the valve body?
Well the front drum is high gear, so it's probably a seal problem with all new parts.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Well if reverse works; they share the high drum. So if reverse works, the high drum is working.That means the issue is most probably in the VB.
There are three main pressure circuits in the tranny; 1)line pressure, 2)throttle pressure, and 3)governor pressure. These three are always changing and doing their little dances. If they get out of whack you get crap happening.
-So as usual, the first question is; is the KD system hooked up, correctly and with the correct ratios? At what road speed does the 1-2 shift occur with minimum throttle and does it vary with heavier throttle inputs?
-Did you replace the convertor?
-Did the tranny work fine with the one ball missing?
-"3rd looks like it wants to go at 40 or so then slips into neutral." This is a really big clue. It tells us that the VB is commanding the 2-3 shift, cuz the same oil circuit the engages the hi-drum also disengages the KD band. Since the KD band is releasing and the tranny drops into neutral,this means the hi-drum is not engaging. But since the hi-drum works in reverse, this seems to indicate that there is a problem with the oil-routing,or oil-pressure. So either the ball you put in, is not supposed to be there, or there is a problem in the VB casting,or that circuit is just not receiving enough oil-pressure to get the job done. That speaks to a faulty line-pressure adjustment, or insufficient throttle pressure. See, in reverse, the pressure to the hi-drum,is maxed out somewhere around 230plus psi . But in drive, that clutch might only receive between 50 and 90ish psi, depending on the throttle pressure(controlled by the KD mechanism).
In any case the VB has to come down,for inspection. While it is down, you can perform an air-pressure test to verify the front clutch packs are working.
-What does this mean:"Also the Toque converter is super tight. NO stall engine runs in park and in drive with brake."?
There are three main pressure circuits in the tranny; 1)line pressure, 2)throttle pressure, and 3)governor pressure. These three are always changing and doing their little dances. If they get out of whack you get crap happening.
-So as usual, the first question is; is the KD system hooked up, correctly and with the correct ratios? At what road speed does the 1-2 shift occur with minimum throttle and does it vary with heavier throttle inputs?
-Did you replace the convertor?
-Did the tranny work fine with the one ball missing?
-"3rd looks like it wants to go at 40 or so then slips into neutral." This is a really big clue. It tells us that the VB is commanding the 2-3 shift, cuz the same oil circuit the engages the hi-drum also disengages the KD band. Since the KD band is releasing and the tranny drops into neutral,this means the hi-drum is not engaging. But since the hi-drum works in reverse, this seems to indicate that there is a problem with the oil-routing,or oil-pressure. So either the ball you put in, is not supposed to be there, or there is a problem in the VB casting,or that circuit is just not receiving enough oil-pressure to get the job done. That speaks to a faulty line-pressure adjustment, or insufficient throttle pressure. See, in reverse, the pressure to the hi-drum,is maxed out somewhere around 230plus psi . But in drive, that clutch might only receive between 50 and 90ish psi, depending on the throttle pressure(controlled by the KD mechanism).
In any case the VB has to come down,for inspection. While it is down, you can perform an air-pressure test to verify the front clutch packs are working.
-What does this mean:"Also the Toque converter is super tight. NO stall engine runs in park and in drive with brake."?
Sorry you are wrong sir. Low and reverse share the drum. Not high and reverse.
KickDown
Just a Brit in Germany
In high & reverse the front clutch is applied. The difference being in reverse the apply pressure is much higher.
I get all that. We are not talking about reverse here. We are talking about why high gear is not applying.
TrailBeast
AKA Mopars4us on Youtube
You sure your not thinking of the Low/Reverse band instead of a drum.
I think it's a VB issue also, like springs mixed up or an out place check ball because of the mention of it feeling like it goes into neutral and back to second.
It might be trying to go to third and not able to engage it could cause a freewheel momentarily till it kicks back to 2nd.
Hard to tell without actually feeling it in person.
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