Calling 727 Experts!!

[408 swinger]

Working with a pushbutton trans. At operating temp, trans in Drive, under "normal" driving conditions, functions as it should. Getting out on the road, say about 40 to 45 mph, floor it, it kicks down as normal. Just about the time it goes to shift into drive, it breaks away/freewheels. Let off the gas, apply throttle to dive "normal", and it's right there. No slip anywhere. You have to be quick on letting off the gas!! I've air checked the direct pack(both for that matter), both seem normal. No excessive air leaks. Removed trans and visually inspected clutch packs and lip seals, all look perfect. Pump gears and clearances are good. Haven't disassembled valve body yet. The PR is cranked. Would a convertor give this issue? My experience with bad convertor is usually lots of slip or no movement at all. It is still the 19 spline input. About a 3000 ish stall behind a healthy stock stroke 440 with Maxie top end. I don't claim to be a Torqueflite expert, but, I know my way around them. This one has me stumped. Any and all suggestions welcomed!! Thanks FABO-land!!

 

[Murray]

I tend to think it is valve body related.

 

[408 swinger]

I tend to think it is valve body related.

Could be? I have not had a valve body do this. There is ALWAYS a first time! I have done a few "modded" stock valve bodies with the PR valve cranked way in. How much does the rear pump contribute to the overall line pressure? If at all?

 

[moparlvr166]

Does sound like fluid pressure bleeding off, if so, where, why? Just to understand, when warmed up, passing gear 3-2, are you still at WOT when condition occurs or are you letting up on throttle and wanting an upshift. just for test what would happen if you manually down shifted and up into 3rd in same type of speed related scenario?

 

[408 swinger]

Does sound like fluid pressure bleeding off, if so, where, why? Just to understand, when warmed up, passing gear 3-2, are you still at WOT when condition occurs or are you letting up on throttle and wanting an upshift. just for test what would happen if you manually down shifted and up into 3rd in same type of speed related scenario?

Yes, WOT. You feel it just hit third, then breaks away. When you let off the throttle, then roll back in easily, third is there and not slipping. When stepping down like you're getting up to highway speed, it functions perfectly. I did not try it manually.

 

[71Demon540]

Stupid question, but did you check the trans fluid level? I had a customer have same thing happen with a RMVB (I know, totally different than a push button with rear pump), but his fluid was low. Added fluid accordingly and it was back to normal.

But yes the valve body could be the issue if one of the governor valves are stuck.

 

[408 swinger]

Stupid question, but did you check the trans fluid level? I had a customer have same thing happen with a RMVB (I know, totally different than a push button with rear pump), but his fluid was low. Added fluid accordingly and it was back to normal.

But yes the valve body could be the issue if one of the governor valves are stuck.

Yes, fluid level was spot on. Std pan too.

 

[moparlvr166]

Question: current trans or new build?
If you haven't tried already try lower line psi some, possible front band releasing faster than direct drum applied due to band adjustment servo and/or ratio of lever your using?
Gov psi to low.
Try driving manually shifting for a test.

 

[408 swinger]

Build is an older build. And kudos to the previous builder/parts installer. All parts, and I mean ALL parts, look fantastic. No burnt bands or friction plates. Fluid doesn't even smell ill. Lever is a good question. To me, it does look like a 4.2. I have not compared yet. I should have tried to manually shift. I did not before removing trans. I'm sure I can safely clean and reassemble the trans, minus valve body. After some more inspection of small parts. Thank you to everyone thus far!!

 

[Bewy]

I agree with others, probably valve body. Since the problem occurs at WOT, I would be looking at the kick down valve circuit, because that is what 'tells' the trans a WOT shift is reqd.

 

[RustyRatRod]

So you have it apart already. I was gonna recommend you get everything adjusted properly as per the FSM before you did something big, but I guess you've done it. Hope you find the trouble!

 

[408 swinger]

So you have it apart already. I was gonna recommend you get everything adjusted properly as per the FSM before you did something big, but I guess you've done it. Hope you find the trouble!

Info I forgot to mention. I did check kickdown and band adjustments.