5R55E low Line pressure, slipping while in gear

[blazing badger]

Hello all. I have a stock 99 Ranger 4.0L OHV 4x4 with 5R55E transmission. It currently has 202,000 miles and rebuilt the transmission back in 2010 when it had 150,000 miles. I did this because the reverse band broke, but when I rebuilt I also did the Sonnax kit on the valve body.

Recently I have noticed that when in reverse, if I was on an incline it would require higher engine RPM to generate enough torque to move the truck. This has been getting steadily worse over the past month or so, and now when backing up a hill into my driveway, I have to get to over 3,000 RPM to get the truck to move. I think I can also feel it in forward gears, too.

I bought a 300 psi gauge transmission tester and tested the "Line" port at idle. When it is in park and neutral, the pressure is rock-steady at 105 psi. When I shift into Reverse, the pressure will start out at 155 and then drop to about 115 (see video linked below).

There are no check engine light codes stored, and the transmission seems to shift just fine.

Any clue what could be causing this issue? I'm tempted to buy a remanufactured valve body on eBay to see if that fixes the problem.

 

[JK080]

Would be good to watch the gauge in each gear (except park and neutral) under stall conditions, pressure is a little low but lets see what the high end looks like.

Stall pressures in reverse should be up around 300 and in drive you should be able to get above 200.

You could also check your EPC pressure with around 17 in drive and stall around 135. Its test port is on the other side near the tail housing.

 

[blazing badger]

Would be good to watch the gauge in each gear (except park and neutral) under stall conditions, pressure is a little low but lets see what the high end looks like.

Hi James - thanks for the reply! I was going to test stall pressures, but I noticed that the specification for reverse is 282-350 psi, and the gauge I bought only goes up to 300 psi... so I was concerned that the gauge might get damaged.

I should also mention that my first guess at this problem a few weeks ago was a leaking reverse servo (even though I replaced it with double-lip seal during the rebuild 50k ago), so I dropped the pan and replaced the reverse servo o-rings. The oil color looked good and normal amount of friction material in the pan. I filled the trans with the same amount of oil that dropped out. I also thought that maybe it was low on trans oil (the dip stick is near impossible to determine the actual level while running in park), so I added an extra quart and drove around. After I observed the same slipping, I removed the extra quart with one of those electric pumps to pump it out through the fill tube.

 

[JK080]

If you are worried about damage to the gauge I would still do the stall test but maybe dont push it too hard, the important thing here is to know if you have sufficient line rise. If you can get pressures near 300 I wouldn't think the transmission is slipping.

 

[Paul Fithian]

Maybe the "O" rings on the reverse servo are degraded? See my findings in this thread: http://www.explorerforum.com/forums...55e-valve-body-sonnax-zip-kit-install.460623/

Installation of the new D-shaped "O" rings on the reverse servo completely fixed my delayed reverse issue

 

[blazing badger]

If you are worried about damage to the gauge I would still do the stall test but maybe dont push it too hard, the important thing here is to know if you have sufficient line rise. If you can get pressures near 300 I wouldn't think the transmission is slipping.

Hi James - I will run the test tonight and see what happens. But I'm not sure why it would matter if I can get higher pressures at WOT? I know the pressure gets high enough to produce torque when I rev the motor to over 3,000 RPM, but the truck used to be able to back up into my driveway at idle or with just a little bit of throttle - so I know it's slipping at low RPM. And even at 3,000 RPM it still feels like really low torque.

Maybe the "O" rings on the reverse servo are degraded?

Hi Paul - The reverse servo o-rings were my first thought, too, so I replaced them a couple of weeks ago and the symptoms didn't change.

 

[JK080]

Hi James - I will run the test tonight and see what happens. But I'm not sure why it would matter if I can get higher pressures at WOT? I know the pressure gets high enough to produce torque when I rev the motor to over 3,000 RPM, but the truck used to be able to back up into my driveway at idle or with just a little bit of throttle - so I know it's slipping at low RPM. And even at 3,000 RPM it still feels like really low torque..

I am starting to think that maybe the stall in your converter has changed, even with those pressures and especially if they rise under throttle I would think the transmission is fine.

The stall can change due to clearance problems in the converter. Sometimes when I deal with a customer that has a built engine they experience problems when the transmission is put into gear, it can pull the engine idle down too low and the engine cant idle at that RPM causing the engine to stall and gives them the impression the converter is locked up. Installing a higher stall converter in most cases can correct this. High stall converter can give you the feeling the transmission is slipping due to the higher RPM it takes to get them to start pulling.