727 Rebuild Blues

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80fbody

80fbody

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It's a BB 727. My first build. I assembled the trans & have tried to air check it but no luck. Front pack bleeds down as quick as I put air to it. Somethings amiss.

Specs:

1. 1971 BB core - purchased as a supposed running core but when apart it had some water inside & needed alot of cleaning.

2. Changed all sealing rings, thrust washers & bushings. None were really out of spec. Added 5 thin clutches to the factory 4 clutch front drum.

3. Both lips face down on the front pack. Replaced them twice now.

4. Check ball moves freely in the drum

5. Replaced the pump with a rebuilt unit just in case.

6. Tried to prime the air port with some ATF but no change. Could here the fluid pushing out from the air now.



I know there were some changes at the 70-71 model year. Are there any sealing rings, etc that could be screwing me up here. Maybe this has some factory 70 pcs inside. I'm stumped & really want to get this off my bench so I can get to some other work done.



Thanks,

Jason
 
Go back thru it; the only thing you have to take off is the front pump and the input shaft and what it's attached to, check piston rings and sealing rings.

At least you air checked it, more than I did my first few rebuilds. I had a hard road; in and out from under the vehicles. Yeow.

Keep your head, take your time, don't rush, you'll get it done.
 
Oh, I've had it apart several times now. Getting pretty good at that. Really starting to think I've got something mismatched due to the 71 model year. Just not sure what to mic up.
 
you said you are using 35 psi....what is the line pressure inside a 727?

I would turn up the air ...and yes..they bleed down
 
Ok. Could this input shaft be junk? It's about 10 thou smaller in the sealing ring area versus where the bushing rides below. I mic'd the new pump & it's the same size in the bushing as the the sealing ring area of the pump. Basically I think there's about 10-12 thou clearance at those sealing rings. You can certainly feel the step on the shaft just don't have another to compare right now.

 
80fbody said:
Ok. Could this input shaft be junk? It's about 10 thou smaller in the sealing ring area versus where the bushing rides below. I mic'd the new pump & it's the same size in the bushing as the the sealing ring area of the pump. Basically I think there's about 10-12 thou clearance at those sealing rings. You can certainly feel the step on the shaft just don't have another to compare right now.
Click to expand...

That has nothing to do with your front clutch. The front clutch gets it's fluid through grooves cut in the stator (the part that bolts onto the back of the pump). The 2 sealing rings on the stator that slip inside the front clutch are what seals fluid (or air in your case since your at the stage of just air testing it) to the front clutch carrier. 30-35 psi is fine to use for testing. The trans. does run at a higher fluid pressure but air will escape much easier than fluid so any pressure higher than that will usually leak past. I assume you used atf or seal lubricant on the front clutch seals and sealing rings? If not you should have. Like Poisiondart said you don't have to install the pump and clutch packs to test them. Clamp the front pump down in a vise (with a cloth to protect surfaces) stator side up and stack the front clutch first then the rear clutch. Then you inject air into the proper port on the pump that leads to each clutch pack. Be warned that when the front clutch seals up the clutch packs will want to "jump off" the pump so hold them down. Sorry I don't have a chart that shows what ports on the pump lead to what clutch pack but just try each hole until you find the one that leads to the pack in question. These ports/holes I'm talking about are the ones that contact the trans case. Pressure is fed from the valve body through the case and the front pump to the clutch packs. As far as a possible parts mismatch, it's easy to tell if their not right because a 70 and older trans. used a 1/2" wide front clutch bushing and a 71 and newer used a 1" wide bushing. Measure the bushing in the front clutch pack that rides on the stator and compare it to the stator bushing surface. Should both be 1" wide since you said it's a 71 trans.
 
Chk the pump stator rings off the pump and put them inside the front drum to make sure they fit the diameter ok. (Not to small to seal)
If I remember right there is a lip seal that can be mistaken for the right size inside the drum and if it's the smaller one, it will leak air pretty bad.
Assembling it on the pump and air testing like Tracy said will tell that quick enough.

Here's a pic for the rings and bushing topic, and the rings should be cast iron with interlocking ends.
 

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  • drum rings.jpg
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Ok, All that really helps narrow it down. Now I understand how the front clutch is fed. So those two rings fit great in the bore. That's a good check. This time I just installed the front clutch on the pump & can now see what's going on. The clutch is working but seems to be really leaking at the inner piston seal. Guess I pickup a new one tomorrow & see if that cures it.

Is the vasaline type assembly ok to use on those piston seals? Or could that be why it's leaking past so bad?
 
I used Vaseline and it seemed to work just fine.
I treated it like Franks Red Hot and put that stuff on everything. :thumblef:
 
I cleaned the front piston seals & just used ATF this time. Really feels better. Going to get brand new lip seals tomorrow for both drums & just use ATF on them.

Also realizing I can just place the front clutch on the pump & air check it is a big help. Much easier to see/feel what's going on with that pack.

Also learned tonite that the front drum is just a little lazyier than the rear when air checking. My in-experience thought that was a problem thus I kept tearing it apart looking for an issue.

I think it's going to be ok. We shall see.
 
Early on when I started rebuilding them I used Vasoline for a number of yrs. and had no trouble. Been using stuff specially made for transmission seals for about 15 yrs. now but to be honest I have no way of telling it works better since the Vasoline always worked fine. The trans. lube seems to last longer and is cheaper in the long run so that's a plus.

The front drum appears to engage slower and softer compared to the rear clutch because all the rear clutch has for a return spring is the Belleville spring. Doesn't take much to compress it.
 
Hello guys. Don't want to hijack the thread but I cant seem to find anyone with this much knowledge on the 727. I'm also rebuilding one for the second time and this time around I don't have the book with all the specs. Do any of you know the end play and the clutch pack clearances? Keep in mind this will be for street/strip use so if there is tighter clearances that should be used for that application what are those also?

Any help is greatly appreciated!
 
Sal_Detroit1 said:
Hello guys. Don't want to hijack the thread but I cant seem to find anyone with this much knowledge on the 727. I'm also rebuilding one for the second time and this time around I don't have the book with all the specs. Do any of you know the end play and the clutch pack clearances? Keep in mind this will be for street/strip use so if there is tighter clearances that should be used for that application what are those also?

Any help is greatly appreciated!
Click to expand...

Hi Sal,

Take a look through this thread... Lot's of good information here.

http://www.forabodiesonly.com/mopar/showthread.php?t=245164

Have fun.
AlV
 
Sal_Detroit1 said:
Hello guys. Don't want to hijack the thread but I cant seem to find anyone with this much knowledge on the 727. I'm also rebuilding one for the second time and this time around I don't have the book with all the specs. Do any of you know the end play and the clutch pack clearances? Keep in mind this will be for street/strip use so if there is tighter clearances that should be used for that application what are those also?

Any help is greatly appreciated!
Click to expand...

I shoot for .015~.020 end play. Sometimes you'll end up using the thickest selective washer (the one on the back of the pump) to get it tight enough.

.035~.045 clearance for the rear clutch pack. Some guys claim they go as tight as .030 and I tried that on 2 and both wanted to creep in neutral a little until the clutches wore in a little.

.060~.085 for the front pack. If your front clutch pack has 8 springs or less and the front band apply lever ratio is 3.8 or higher you may want to set the front clutch clearance on the loose end of that range otherwise it may have some 2-3 shift overlap.

Make sure and air pressure test things before you button everything up and install it. Air pressure testing can save a lot of future headaches.

BTW: here's a link where you can download the ATSG rebuild manual for torqueflites for free

[ame]http://apicdn.viglink.com/api/click?format=go&key=508e022f256315a50e8e5af8c001704f&loc=http%3A%2F%2Fwww.forabodiesonly.com%2Fmopar%2Fshowthread.php%3Fp%3D1970171343&out=http%3A%2F%2Fwww.mymopar.com%2Fdownloads%2FTorqueflite_A-727_A-904_Service_Manual.pdf[/ame]
 
Sal, you've come to the right place. These guys were a great help with my trans. Unfortunately my car won't be ready till spring to test it out.
 
Thank you so much guys! This info is everything I needed. I'm not used to getting in touch with knowledgable people on other forums I've been on... Haha so this all really helpful!
 
Hi A-bods,
Old thread I know but I'm also looking for 'lip seal' info.
I've seen you can fit 71-up lip seals into pre 70 front drums.
Is this correct?
As I have a pile of 71-up rebuild stuff and very little earlier parts.
Best wishes from John
 
STRorange said:
Hi A-bods,
Old thread I know but I'm also looking for 'lip seal' info.
I've seen you can fit 71-up lip seals into pre 70 front drums.
Is this correct?
As I have a pile of 71-up rebuild stuff and very little earlier parts.
Best wishes from John
Click to expand...
I doubt that'd work because each piston is designed with a groove that's either for the narrow seal or the wide seal
 
oldkimmer said:
U sure can. I’ve had to do it a few times. New style seal in old drum. Kim.
Click to expand...
Thanks Kimmer!

Its a lot of work changing out drums if they don't work!
I've been converting my transmissions to wide band 71'onwards DRUMs due to ring seal failures (and worse).
I've also been using the same input shafts but noticed an extra oil-hole in the pre 71 shafts?
Will this have any effect inside the LATER STATOR?
 
STRorange said:
Thanks Kimmer!

Its a lot of work changing out drums if they don't work!
I've been converting my transmissions to wide band 71'onwards DRUMs due to ring seal failures (and worse).
I've also been using the same input shafts but noticed an extra oil-hole in the pre 71 shafts?
Will this have any effect inside the LATER STATOR?
Click to expand...
I haven’t noticed a problem, but I have changed the input assambly with the front drum and pump. Kim
 
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