727 slipping in reverse when hot

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Miszny

Miszny

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Hi

I have a problem with 727, just like in the title it all works normal when cold, but when car gets hot, reverse slips like crazy, I need to give it 5000 rpm for the car to move at all. Can someone point me in the right direction? All forward gears work normal.
I tried swapping servos as I had aftermarket one billet one in there, I was sure it’s gasket issue, but different servo with new seal didn’t help at all. Band adjustment is also good. No signs of burning on the band as well.

Help!
 
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Air check the reverse apply servo with compressed air see if it leaks down. If so its a seal issue ...
 
Do you have engine braking in manual low?
How is the 2-3 shift on hard acceleration?
 
moparlvr166 said:
Do you have engine braking in manual low?
How is the 2-3 shift on hard acceleration?
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Yes there is engine braking in manual low and car shifts good in all gears. The only problem is reverse which works great when cold and gets worse with trans temp. I tried two servos, the steel one from transgo and factory one. There is zero difference.

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Have you tried adjusting the reverse band? "band adjustment is good" is pretty vague.
 
RustyRatRod said:
Have you tried adjusting the reverse band? "band adjustment is good" is pretty vague.
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Yes I tried 1 turn out, 1,5 turn out and 2 turns out on adjuster. This is not my 1st 727 and frankly I hit the wall here... I keep wonderking what did I screw up.
 
Braking in manual low & no slippage in high gear means the mechanical parts are good... I would try swapping in a different valve body... 727 & 904 interchange.. Just an easy swap that will give you a quick answer..
 
Miszny said:
Yes I tried 1 turn out, 1,5 turn out and 2 turns out on adjuster. This is not my 1st 727 and frankly I hit the wall here... I keep wonderking what did I screw up.
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From "WHERE" did you count the turns? I think the spec on it is to tighten the center bolt to 8 LBFT. I think the spec is given in INLB, but if I remember right it converts to about 8 LBFT. In other words, tightened "pretty good" but not stripping the thing out.
 
RustyRatRod said:
From "WHERE" did you count the turns? I think the spec on it is to tighten the center bolt to 8 LBFT. I think the spec is given in INLB, but if I remember right it converts to about 8 LBFT. In other words, tightened "pretty good" but not stripping the thing out.
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From 72 inch punds. I have torque wrench for this.
 
1WildRT said:
Braking in manual low & no slippage in high gear means the mechanical parts are good... I would try swapping in a different valve body... 727 & 904 interchange.. Just an easy swap that will give you a quick answer..
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I need to get one 1st, I am in Europe which makes things more compilcated.
 
When tightening a band the spec is 72 in/lb but in reality you can take a 5/16 wrench & the torque remains low till the band wraps tight around the drum from 72 in/lbs to 250 in/lbs won't amount to 1/4 turn of the adjuster....
 
Miszny said:
From 72 inch punds. I have torque wrench for this.
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Ok cool. Just trying to help narrow it down. Some folks tighten it down "a little" and that usually doesn't get all the slack out.
 
1WildRT said:
When tightening a band the spec is 72 in/lb but in reality you can take a 5/16 wrench & the torque remains low till the band wraps tight around the drum from 72 in/lbs to 250 in/lbs won't amount to 1/4 turn of the adjuster....
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What I usually do is overtighten it, apply the servo, loosen it and then go with spec.
 
RustyRatRod said:
Ok cool. Just trying to help narrow it down. Some folks tighten it down "a little" and that usually doesn't get all the slack out.
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I know, I'm frustrated here because I did a few of these transmissions and this one is giving me pain and I'm out of ideas. I try not to make threads without exhausting my options.
 
Manual low has the L/R band applied, same as rev, so it does not slip there, band adj should be ok.
Otherwise, probably a valve body/stuck valve problem.
Pretty sure the TF requires additional line pressure for rev operation. If so, a worn pump maybe the cause.
 
Bewy said:
Manual low has the L/R band applied, same as rev, so it does not slip there, band adj should be ok.
Otherwise, probably a valve body/stuck valve problem.
Pretty sure the TF requires additional line pressure for rev operation. If so, a worn pump maybe the cause.
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Pump has new rotor gears and bushing. I need to look into valve body problem I guess.
 
Bewy said:
Manual low has the L/R band applied, same as rev, so it does not slip there, band adj should be ok.
Otherwise, probably a valve body/stuck valve problem.
Pretty sure the TF requires additional line pressure for rev operation. If so, a worn pump maybe the cause.
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Manual low has the band applied but if the band slips you still have low gear because the sprag with prevent the rear drum spinning in one direction... But engine braking reverses rotation of the drum so that is when you'll see the band isn't doing it's job... Well, engine braking... And reverse...
 
man besides air checking the servo application and seal what else changes under heat? the fluid may be more viscous is there a warped servo bore and the piston is sticking...? or is there another valve sticking in a bore...? IMO do all you can diag and troubleshooting without pulling the trans. Valve body can be dropped and worked on the bench etc.
 
Did u hook up a gauge to the reverse port on the tranny to see what kind of pressure u have? Could be a broken or wrong spring in the valve body. Or the valve sticking. Or the torque converter pressure regulator valve sticking not letting the pressure build up. One other scenario I had back in the 80s was the inner lip seal leaking when warm. I pulled the tranny twice and couldn’t see anything wrong. I had the front drum apart both times. Seals looked good. Second time I replaced them. I found a small pin hole in the inner seal after I removed it. New seals and problem solved. Kim
 
oldkimmer said:
Did u hook up a gauge to the reverse port on the tranny to see what kind of pressure u have? Could be a broken or wrong spring in the valve body. Or the valve sticking. Or the torque converter pressure regulator valve sticking not letting the pressure build up. One other scenario I had back in the 80s was the inner lip seal leaking when warm. I pulled the tranny twice and couldn’t see anything wrong. I had the front drum apart both times. Seals looked good. Second time I replaced them. I found a small pin hole in the inner seal after I removed it. New seals and problem solved. Kim
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Kim,
My initial thought was a front clutch issue til I read he’s having no issue with 3rd gear. However, anything is possible ‍♂️ be curious to find out the end result.
 
71Demon528 said:
Kim,
My initial thought was a front clutch issue til I read he’s having no issue with 3rd gear. However, anything is possible ‍♂️ be curious to find out the end result.
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I had no issue with high get also way back then but I knew it had to be something. Wasn’t the vb either cause I had changed it from my other car and my other car worked fine with the vb from the tranny with no reverse. That’s why I mentioned the front drum. I have been wrong b4. There is only so many things it can be. Kim
 
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Thank you for response, I gave the car away a week ago for some registration paperwork to be done and once I get it back , I will dig into the transmission. My 1st idea is valve body swap. This will narrow things down. In the mean time I had time to play with IFR on my tunnel ram carbs so its all time well spent anyways! Will keep you posed for sure about this, I always try to finish thes threads so person with similar problem has a ready solution. The worst thing on forums is threads that dont show final solution to reported problem!
 
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