727 Reverse problem

[Just Call Me B]

1973 plymouth satellite 340 727. Car shifted great. Forward gears still do. Reverse started to act like neutral until about 1500 rpm then brutally slams into reverse. I pulled the pan and the cup that holds the spring that i believe goes to the reverse piston had blown past its retaining clip and was hanging on the lever that activates it. I am obviously not up on correct part names. The lip on the cup was no longer flat. We flattened out the lip and reinstalled the cup. We were able to back out of the driveway twice and blew the cup out again. Lever bolt was set at 72 inch pounds and backed off 2.5 turns. Any thoughts would be appreciated. Thanks, Brian

 

[493 Mike]

Excessive reverse pressure? Check it with a 0-500 PST gauge. Service manuals always list pressures and procedures.
Mike

 

[Dave6T4]

The ONLY time I have seen this is when the client had no kickdown linkage, and was running the transmission with the lever tied back. Reverse circuit was seeing full pressure (300 psi.) all the time. His blew up the servo piston, too.

 

[forphorty]

https://www.coperacingtrans.com/?product=727-lowreverse-hd-spring-retainer

 

[Just Call Me B]

Thank you for the feedback and also the link for a stronger cup/retainer. The car acts/shifts and downshifts perfectly normal. It is a fun ride.

 

[R413]

They may have turned up the pressure adjustment too high, or too beefy of a spring on it.
This will happen, sometimes it breaks the band, strut, or the piston.

 

[oldkimmer]

U can’t just straighten the plate it needs replaced. 2.5 turns is too loose. It lets the band slam too hard against the drum and also over extends the rear servo. Kim

 

[Wietse]

What Dave6T4 said, check your kick down linkage.
Reverse pressure is normally bumped to 200-230 psi in an original transmission and will increase when giving more throttle.
If your line pressure is already increased by means of adjustment or shift kit installation and your linkage is tied to maximum setting there will be a massive pressure bump applied on the piston.
Installing a stronger retainer might hold it in place but does not solve the root cause.

 

[dvw]

Manual valve bodies run full line pressure all the time so that shouldn't bother it. I'd be making a pressure check. Maybe the pressure regulator valve is stuck. On the race stuff with even higher pressures some valve bodies bleed the feed pressure to the rear band servo in reverse. We've run trans brake valve bodies with 175psi with the stock rear servo.
Doug

 

[Just Call Me B]

U can’t just straighten the plate it needs replaced. 2.5 turns is too loose. It lets the band slam too hard against the drum and also over extends the rear servo. Kim

How many turns would you suggest backing It off?

 

[oldkimmer]

If it’s a stock build I go 1.5 to 1.75 turns as it won’t slam into reverse then. No more than 2 turns on one with the pressure turned up as in a shift improver kit or a shift kit. Kim

 

[Just Call Me B]

If it’s a stock build I go 1.5 to 1.75 turns as it won’t slam into reverse then. No more than 2 turns on one with the pressure turned up as in a shift improver kit or a shift kit. Kim

Thank you. The car was redone in 1984 and sitting behind a garage in Missouri since 1989 when the owner went into the service and did not return. Transmission looks shiny and new inside. I have changed all the fluids added new brakes and rubber and have put about a hundred miles on the car.

 

[493 Mike]

Did you remove the rear servo piston to inspect it?
Mike

 

[Wietse]

I think the fastest way to confirm is to hook up a pressure gauge on the rear servo test port and check what pressure you are getting. That retainer doesn’t just pop out for no reason. The book states a maximum of 270 psi, likely with the throttle valve maxed out, which could be your case if it is fixed/locked in max. position. If for any reason your regulator gives more due to modifications you could have over 300 psi on there and that would be simply too much for that thin retainer.
And it also would not serve you any purpose.

 

[Geoff 2]

I have had this happen TWICE with Transgo kits. The low/rev servo spring gets replaced with a stronger spring. The spring retainer is just thin, pressed metal; it bends with the extra spring force & pops the c'clip. I believe the aftermarket make a stronger retainer. With mine, I brazed a re-inforcing 'washer' onto the OEM piece & that fixed it.

 

[493 Mike]

I have had this happen TWICE with Transgo kits. The low/rev servo spring gets replaced with a stronger spring. The spring retainer is just thin, pressed metal; it bends with the extra spring force & pops the c'clip. I believe the aftermarket make a stronger retainer. With mine, I brazed a re-inforcing 'washer' onto the OEM piece & that fixed it.

Were you using the Transgo recommended band adjustment procedure? Not the OEM spec.
Mike

 

[Dave6T4]

A&A Transmissions offers a billet piece to replace the stamped retainer.

 

[Wietse]

I have had this happen TWICE with Transgo kits. The low/rev servo spring gets replaced with a stronger spring. The spring retainer is just thin, pressed metal; it bends with the extra spring force & pops the c'clip. I believe the aftermarket make a stronger retainer. With mine, I brazed a re-inforcing 'washer' onto the OEM piece & that fixed it.

Must have been a bad/damaged retainer to begin with then, because the spring pressure is nothing compared to the hydraulic pressure it will be facing.

 

[Geoff 2]

Everything was done per the instructions. It happened to a friend also. The hyd pressure is compressing the spring, which is now much stronger & that increased spring tension is what pops the retainer.

 

[493 Mike]

Everything was done per the instructions. It happened to a friend also. The hyd pressure is compressing the spring, which is now much stronger & that increased spring tension is what pops the retainer.

I have probably installed a dozen TF-2 kits and none had any problems.
Mike