727 manual valve body-Reverse is slipping BAD, All other gears seem good - Pressure tested

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MobileCustoms

MobileCustoms

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OK, so my transmission performed really great when I pulled the drivetrain out 2 years ago to paint my car. I had previously overhauled it with all the good stuff and billet servos from Oregon Performance, etc.

Now, it slips real bad in reverse. Just drove to down to my friend's garage today and put it up on the hoist to run some line pressure tests.
Got 270 psi at the rear port, 90 psi at the front port and absolutely nothing at the middle line pressure port.
Any advice or tips would be much-appreciated! I've tried my best to look up old threads and info that points to the same symptoms. Hoping it's just something funky with the rear servo but baffled as to what could have happened while it was just sitting. The ONLY thing that is new or different now compared to when I pulled it out is that i have a new torque converter from PTC and a new but identical flex plate ( my old one was cracked) I'm heading out to dinner right now but will be checking back in this evening.

IMG_20150304_192952_719.jpg
 
Does it slip on first engagement into reverse after starting the engine? I and a number of others have experienced this on 904's. start cold engine, put in reverse and the trans acts like it is slipping really bad, put in neutral and give a bit of gas, let off and put in reverse again and it feels good. seems to be typical for 904 don't know if the other trans does same thing.
 
Dana67Dart said:
Does it slip on first engagement into reverse after starting the engine? I and a number of others have experienced this on 904's. start cold engine, put in reverse and the trans acts like it is slipping really bad, put in neutral and give a bit of gas, let off and put in reverse again and it feels good. seems to be typical for 904 don't know if the other trans does same thing.
Click to expand...

Nope. I'm aware of that issue and it's not that at all. I've let it run in neutral for a long time and checked fluid levels. Never gets any better.
 
MobileCustoms said:
OK, so my transmission performed really great when I pulled the drivetrain out 2 years ago to paint my car. I had previously overhauled it with all the good stuff and billet servos from Oregon Performance, etc.

Now, it slips real bad in reverse. Just drove to down to my friend's garage today and put it up on the hoist to run some line pressure tests.
Got 270 psi at the rear port, 90 psi at the front port and absolutely nothing at the middle line pressure port.
Any advice or tips would be much-appreciated! I've tried my best to look up old threads and info that points to the same symptoms. Hoping it's just something funky with the rear servo but baffled as to what could have happened while it was just sitting. The ONLY thing that is new or different now compared to when I pulled it out is that i have a new torque converter from PTC and a new but identical flex plate ( my old one was cracked) I'm heading out to dinner right now but will be checking back in this evening.
Click to expand...
Obviously the fluid level needs to be correct.

The VERY first thing I would do is pull the rear servo and check it for cracks and lip seal condition.
Then make sure the valve body bolts are down tight like they should be.
@fishy68 (Tracy) may have more on this.

The center test port needs to be checked while in forward gears, but these links should help you.
First one you put in the symptom and it tells you where to look (the valve body is one listed for slipping reverse)
A-727 Torqueflite Diagnosis Dial

This link shows where to test and under which conditions.
Note that the governor port says (should be equal to road speed)
This means as your wheel speed increases, so should the pressure, so at 50 on the speedo should show around 50lbs at the governor port. (exact match not a big deal)
Transmission Line Pressure - TCI® Auto
 
Thanks @TrailBeast for the links and insight! I will be checking into these more tomorrow. The center port never showed any pressure at at in any gears. But we never had the whells moving either while testing. Had my foot on the brake and brought rpm up to around 1600 or so.
 
I believe I have found the problem: the rear band adjustment seems really loose. I can move the lever quite a bit with my finger, as shown in the video clip. I will tighten it up to 72 inch lbs and back it off two turns. Will also check the front band adjustment while I'm at it. Hopefully, they are not too badly worn.

I checked all the bolts & screws on the valve body and all are tight. Can't see anything else right off hand. The filter had some junk stuck to the top side of it and the magnetic drain plug had some stuff stuck to it also. But the pan looks clean and the fluid looks good. This represents running it fairly hard for 2 years (Spring through Fall only).



IMG_20190324_141855251.jpg

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IMG_20190324_131118.jpg
 
Low 1 engine braking is a test of the low-reverse circuit; as long as the band apply hasn't been eliminated in manual low; common in some full manual valve bodies. Wind it out in manual low and see if the engine slows the car down when you let off the gas.
 
double wrap band on a v8 904 is 4 turns out....the /6 904 single wrap band is 2 turns out...
 
I pulled the transmission pan and did a thorough visual inspection of everything. The reverse/low band adjustment was extremely loose and the front band was pretty loose also. After adjusting both of those Andy follow-up test drive, it seems to be operating normally now! I am still curious about why the middle pressure port with showing absolutely no reading at all yesterday. I have not retested that.
 
Jeez Louise, how do you suppose the lever/band got so loose?

"...Line pressure and front servo release pressure tests must be made in (D) position with rear wheels free to turn"...54-60 psi in D (3rd) at about 1000 RPM with wheels moving?

Is 3 (red circle) test point for line pressure?
Drive.jpg
 
pishta said:
Jeez Louise, how do you suppose the lever/band got so loose?

"...Line pressure and front servo release pressure tests must be made in (D) position with rear wheels free to turn"...54-60 psi in D (3rd) at about 1000 RPM with wheels moving?

Is 3 (red circle) test point for line pressure?
View attachment 1715308837
Click to expand...

Thanks for that info. I have no idea how that rear band ended up so damn loose! Hopefully, things will be fine now but time will tell.
 
Dana67Dart said:
Does it slip on first engagement into reverse after starting the engine? I and a number of others have experienced this on 904's. start cold engine, put in reverse and the trans acts like it is slipping really bad, put in neutral and give a bit of gas, let off and put in reverse again and it feels good. seems to be typical for 904 don't know if the other trans does same thing.
Click to expand...
Trans-Go "No Yo-Yo" kit comes with 1 modded spool valve that stops convertor drainback in P that minimizes this AND potential compromised dipstick O-ring leaks. Negative effect (if any) is that starter fights full convertor on initial cold start, (This was a early design function so initial starts were spinning a lighter, half empty convertor) probably not even felt with today's high torque mini starters or none but the coldest climates. Its under $20 last time I priced one.

<<<<Good luck finding one, I just looked and did not see it on their website without a password....? >>>>
 
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I may have a couple of those No Yo Yo kits as I used to put lots in. Ami thinking right that this was a shift improver kit? It’s been awhile. Kim
 
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