727 reverse delays

[Huicho417]

I recently rebuilt the 727 transmission. All new seals and even finally stoped the leak after trying five different pan gaskets. Also opted for a new deeper pan in case the original was bent. After that I rebuilt the third member and axles. Car has been running great for about two months now. Only small issue was that it was slow to go into reverse. I did adjust the bands when I rebuilt it. In forward motion it shifts great from first to third. No issues getting up to 75 on the highway. This afternoon on a trip to the grocery store I decided to test the reverse and even accelerated on an empty street. When I did I heard a loud scraping sound and immediately went away. I stopped immediately got out and checked underneath and everything looked normal. Got back in it and again tested the reverse but went easy on it and no problem. Shifted to drive and came straight home. Somehow it seemed like the transmission was shifting even better than before and felt like a slightly different car in a good way. Is it possible the noise came from the gears in the third member? And maybe somehow adjusted themselves for a better drive?

 

[493 Mike]

No. Gears are set by the installer. How was the bore finish in your 727 rear servo? Any trouble installing the piston? You could check the servo pressure easily. Make sure your gauge has enough range to accommodate the pressure range.
Mike

 

[Lefty71]

I'd pull the pan now and readjust the rear band before you drive it anymore. Look closely at the adjuster and band strut while you can see up in there..... and have a peek at the servo as Mike said while its opened up. BTW, the $$ Moroso pan gasket has proven to be a reasonably efficient way to go.

 

[Huicho417]

I will be removing the pan tomorrow to inspect. What could have caused the rear band to loose adjustment? Does the locknut turn from vibration?

 

[493 Mike]

I will be removing the pan tomorrow to inspect. What could have caused the rear band to loose adjustment? Does the locknut turn from vibration?

Two things: lining coming off/excessive wear or adjustment lock nut not secured properly.
Mike

 

[Huicho417]

Well, I just finished removing the transmission pan. Nothing seems loose and did not notice any metal shavings in the pan. The rear band still seems like it has the proper adjustment. But just to be sure I will readjust. Only thing I saw that was weird was a little black plastic lodged into the bottom is the dipstick tube. Anyone have have any ideas as to what this is?

 

[493 Mike]

The transmission assembly plant used to put plastic plugs in the dip stick hole for shipping and occasionally the plug was rammed in with the dip stick tube (Fridays). It resembles one of those plugs. On the other hand the rear band adjusting screw appears to have a lot of thread showing so I'm wondering if there could be a issue with band linkage installation? Anyone else concur? Now you can pull the test port plug and check servo operation with compressed air (rubber tip air gun works fine). Don't worry about pressure, your compressor doesn't make enough to hurt anything.
Mike

 

[Huicho417]

Which one is the test port plug to check the rear servo?

 

[493 Mike]

Which one is the test port plug to check the rear servo?

Look on the outside of the rear servo bore, transmission exterior, small pipe plug facing the rear. It's shown in your photo.
Mike

 

[Huicho417]

Is this the plug you are referring to. If so do I just remove it and shoot it with compressed air. Am I just looking for it to move the rear servo?

 

[493 Mike]

Is this the plug you are referring to. If so do I just remove it and shoot it with compressed air. Am I just looking for it to move the rear servo?

View attachment 1203628

Yes. If everything is correct it won't move much.
Mike

 

[Huicho417]

Below is a link to the servo moving after I readjusted the band stud. Let me know if you think this movement is proper. Thank you


https://youtu.be/mqw2wa9f4LM

 

[493 Mike]

Below is a link to the servo moving after I readjusted the band stud. Let me know if you think this movement is proper. Thank you

What amount of turn out are you using? I'm assuming the screw was torqued to 72 in lbs. Is the readjusted play similar to the "before" play? Did you apply air pressure to the test port?
Mike

 

[Lefty71]

I think that plug (rubber piece) came from the top of the dipstick, under the metal cap that seals the top of the tube.... Look at your dipstick and see if the other half is still there or if its gone.... Maybe that has some relation, but I'd guess not. I can't tell much from the pix, but I'd say for a recent rebuild, there's a lot of friction material and burnt fluid showing in the pan, so somethings been slipping too much, whether it be a band problem or clutchpak issue, but why?? How much of a rebuild was done?, and who did it?
HTH, Lefty71

 

[Huicho417]

My apologies, I did not do a full transmission rebuild. I took it apart and replaced all the seals since my only issue at the beginning was that it was leaking badly from just about every area it could leak from.

I tightened it to 72 inch pounds and backed the stud out two full turns. I did it twice with two different torque wrenches. Just in case one was incorrect. Both were spot on, and the movement was very similar to do hay was there before.

 

[493 Mike]

My apologies, I did not do a full transmission rebuild. I took it apart and replaced all the seals since my only issue at the beginning was that it was leaking badly from just about every area it could leak from.

I tightened it to 72 inch pounds and backed the stud out two full turns. I did it twice with two different torque wrenches. Just in case one was incorrect. Both were spot on, and the movement was very similar to do hay was there before.

OK. Did you replace the servo piston seal?
Mike

 

[Lefty71]

My apologies, I did not do a full transmission rebuild.

This may explain the quality of the residual fluid in the pan then. I take it you dont really know the clutch pak or other clearances?? May have been really close to time for steels and frictions. That trans may have been close to needing a full rebuild. I personally cant be sure what the issue with slow reverse engage tho.... However, with any crud whatsoever, including a tiny chunk of that rubber you showed earlier, you could have just lodged a bit in the valve body and hydraulic pressure blew it through at some point. HTH, Lefty71

 

[Huicho417]

The transmission assembly plant used to put plastic plugs in the dip stick hole for shipping and occasionally the plug was rammed in with the dip stick tube (Fridays). It resembles one of those plugs. On the other hand the rear band adjusting screw appears to have a lot of thread showing so I'm wondering if there could be a issue with band linkage installation? Anyone else concur? Now you can pull the test port plug and check servo operation with compressed air (rubber tip air gun works fine). Don't worry about pressure, your compressor doesn't make enough to hurt anything.
Mike

I tested the rear servo with compressed air like you recommended vía the test port plug. Below is link to the video.

https://youtu.be/BD03uyfPbww


Also, I double checked the band adjustment with a new craftsman digital torque wrench and it seems like that also made a difference. I think it reduced the play slightly on the rear band. I don’t think my old torque wrenches are calibrated correctly.