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Old 04-11-2010, 10:08 PM
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727 reverse band problems

hello i am looking for some help diagnosing a problem with my 727 transmission in my 68 charger. I rebuilt this transmission last winter and it is mostly stock with the exception of b&m shift kit and a billet reverse servo piston with solid bushing and heavy duty return spring. I am running type f trans fluid. the transmission seemed to work fine for about 50 miles with the exception of when shifting from manual low to second at low speed there was a lot of hesitation but it would shift fine in drive or when i was getting on it. then when driving down the highway one day in drive at 60 mph it seemed that the transmission was locking up then it released later that day after backing out of drive way and starting down road when it made 1-2 shift the transmission locked again then broke loose 1-2-3 all worked but no reverse the sprag was holding in forward gears but it broke the stock servo piston and the band was very loose replaced servo and adjusted band and tried it again today. worked great for a while then on way home it started to act like the reverse band was applying in high gear again so i parked it reverse still works but i really need help figuring this out before the band is shot or worse any ideas would be greatly appreciated

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Old 04-12-2010, 06:21 AM
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If the band adjustment is correct, I suspect a crosss leak if the valve body sections were not flat sanded to level them.

I adjust the band by visual , rather than turns on the strut. I like just under 3/8 inch gap as i pry up the band arm with a good sized screw driver.

Next , drill a relief hole of .045 - .055 diameter in the valve body casting right at the hole in the case that feeds the rear band.

This hole does a couple of things: Mopars tend to build very high pressure in reverse. This hole reduces the pressure slightly and also relieves any cross leak oil. The hole also allows the band servo to retract quicker for a cleaner manual 1-2 shift
Dont worry how old you are... it is the mileage on your body that adds up.

Last edited by Crosley; 04-13-2010 at 10:39 PM. Reason: spelling stuff
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Old 04-12-2010, 07:43 AM
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thanks I will try the hole and check valve body for warping I set the band with pry-bar to 3/8 the first time and did it by turns the last time
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