727 Servo Leak?

[jar84203]

I'm rebuilding a 727 and am to the point where I am checking the servos for leaks with air pressure and it seems like the low/reverse servo applies much harder than the kickdown servo. Is this normal? I've replaced the sealing rings and checked their fit and they were fine. Any suggestions? Thanks.

 

[fishy68]

Since the reverse servo uses rubber seals and the KD servo uses steel sealing rings one would assume that the rear servo should seal up somewhat better. Even with that in mind I've never noticed much difference in how hard they apply when air pressure testing but I never use high pressure. Usually about 40 lbs is all I use. Do you hear air leaking from the KD servo when applying air to it? A very slight amount of leakage is normal but you don't want much leakage. How much air pressure are you using?

Also keep in mind the springs used in each servo. If there's much diff in the spring rate that will affect it.

 

[jar84203]

I had the pressure regulated to 30 psi and noticed it leaked a lot. There is a hole at the bottom of the bore that vents to the inside of the case where it seems to leak and also just above the hole used for the test. Both can be seen in the picture. I've tried the original and new rings and get the same results. Would Teflon rings seal better?

 

[oldkimmer]

........as fishy68 says...................dont worry, b happy..............kim.........

 

[jar84203]

........as fishy68 says...................dont worry, b happy..............kim.........

So it should leak through these holes? This is my first transmission and I'd prefer not to screw it up. Thank you :-D

 

[bOb shingler]

don't worry, be happy but hone the bores.

 

[djwhog]

If I were you I would upgrade to a billet rear servo piston. They are wider, stronger, seal better, less issues with binding and breakage and overal a best investment to a 727.

I have broken dozens of stokers over the years in a trans that has had a shift kit, even in mild use.

It is one of the weakest links next to the over running rear clutch.

 

[trannyguy14]

scotch brite the servo bores and try using teflon rings. Or get a unpgraded servo with dual sealing rings. Performance automotive and tranny center makes these. No leaks

 

[jar84203]

Performance automotive and tranny center makes these. No leaks

Have a website?

 

[trannyguy14]

www.transmissioncenter.net/727/transmission.htm

 

[rumblefish360]

trannyguy, bad link, page not found.

 

[fishy68]

Here's the right link I think. Weird thing is it's spelled out the same but it works for me where the other one don't. Go figure??

http://www.transmissioncenter.net/727transmission.htm

 

[jar84203]

Thanks guys