No reverse??

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Mark Benson

1975DodgeDartSwinger318
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I just rebuilt a 78' non-lockup 727. The problem is when i put it in reverse it will move backwards then all of a sudden in will stop almost like it goes into park and i can not even push it forward or backwards.It will start in park and neutral but in neutral it will take off forward?I ruled out the gearshift linkages by removing the arm to the braket on the tranny(valvebody) and had someone get in and start the car while i was under it and put it in reverse, same thing, reverse would lockup. Also it would still move forward when in neutral. Just to note it had reverse before i rebuilt it. All other drive ranges work. I was thinking maybe something on the valvebody got bent?
 
what kind of clutch clearances did you have? If they are too tight you'll burn the clutches up pretty quick. There are selective snaprings to adjust clutch clearance.
 
Mark Benson said:
I just rebuilt a 78' non-lockup 727. The problem is when i put it in reverse it will move backwards then all of a sudden in will stop almost like it goes into park and i can not even push it forward or backwards.It will start in park and neutral but in neutral it will take off forward?I ruled out the gearshift linkages by removing the arm to the braket on the tranny(valvebody) and had someone get in and start the car while i was under it and put it in reverse, same thing, reverse would lockup. Also it would still move forward when in neutral. Just to note it had reverse before i rebuilt it. All other drive ranges work. I was thinking maybe something on the valvebody got bent?
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have you properly adjusted your shifter linkage? sounds like your VB is getting caught in between gears PR <---- close together, may be engagin the park rod, ND <----- close together, possible fluid flow continuing due to valve not fully engaged in either position, but in between.
 
To answer 66dartman i didn't check my clearances but in each clutch pack i put in the same amount as i took out. For racedodge,I will check my linkages but why does it do the same when i shift it on the transmission with the linkages disconnected?
 
Mark Benson said:
To answer 66dartman i didn't check my clearances but in each clutch pack i put in the same amount as i took out. For racedodge,I will check my linkages but why does it do the same when i shift it on the transmission with the linkages disconnected?
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it is common for new rebuilds to have a forward motion while in neutral until the clutches get properly worn in a tad. that is just a byproduct of a new overhaul, but it will go away eventually.

I would pull your rear tailhousing to see if something is causing the spring on the parking lock mechanism to move forward engaging the parking sprag. did you take that apart to clean it when you overhauled the transmission? if so, did you put the spring back on?

secondly, check your rear band adjustment. 72" lbs, then back off 2 turns. make sure your rear servo piston is not cockeyed. you can do this by removing your valve body and doing a air pressure test. if the piston moves and engages the rear band lever appropriately [i.e. straight and snug] (after you readjust your band) then that is fine, but sometimes the lack of proper band adjustment may cause the piston to not engage the fulcrum/lever appropriately due to it being cockeyed in the servo.

Lastly, did you put the rear band strut in right? right is lengthwise, wrong is widthwise between the band and the lever.

let me know.
 
The fact that it drives in neutral says the rear clutch assy. doesn't have enough clearance. It sounds like the constant engagement of the rear clutch is causing your reverse problem because the rear clutch assy. should never be engaged in reverse. If they are both locked up at the same time you have the same effect as a trans. brake which won't allow it to move either direction. Did you keep the selective snap rings for each clutch assy. seperated so as to put the respective snap ring back in the proper clutch pack? If not you may have mixed them up causing the excessively tight rear clutch assy.
 
Mark Benson said:
I just did the 72 in. lbs. thing and i am still having the same problem.
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did you do an air pressure test to see the rear servo piston engage the rear band? you will need to remove your VB to do this. let me know.
 
For racedodge's question I did the air pressure test for the front and rear clutch assemblys and i could hear a thud when i applyed air and the rear servo piston did engage the rear band.
For fishy68 i did keep each snapring separated with each clutch pack.
 
Have you checked the low reverse servo piston? This is a very common point of failure, the piston could be binding in the bore or broken. It is used for reverse and low band apply breaking. If it is cracked or stuck in the bore will cause your problem too.
 
something is binding on that park sprag, somewhere, somehow. I would remove the tailhousing and inspect the parking break mechanism.
 
Forgot to mention one thing the whole time. I busted the plastic vent on my origional transmission pump and a guy at work had a new pump out of a 97' or 98' Jeep or Dodge truck (not really sure of the vehicle). Visualy looking at them they are identical. I did end up pulling the tranny back out and every thing was in order. I didn't start having problems until I put this pump in it. Rekon I'll just try to find the right pump and just maybe that will fix it?
 
Mark Benson said:
Forgot to mention one thing the whole time. I busted the plastic vent on my origional transmission pump and a guy at work had a new pump out of a 97' or 98' Jeep or Dodge truck (not really sure of the vehicle). Visualy looking at them they are identical. I did end up pulling the tranny back out and every thing was in order. I didn't start having problems until I put this pump in it. Rekon I'll just try to find the right pump and just maybe that will fix it?
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That sheds a new light on the subject. It's quite possible that the reaction shaft on the pumps are slightly different causing it to route fluid incorrectly.
 
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