Solved 4R55E shudders & slips in reverse. All of the other gears are fine.

[Kamaaina]

Hello all. First of all I did check thru the forum looking for a similar problem but none exactly as mine. This is for a 1996 Explorer XLT, V6 4.0 ohv, 2wd, 4R55E trans. Trans overhauled 2 years ago (all clutches & bands changed) & ran fine but recently began shuddering & slipping in reverse only. ALL forward gears work good. Here's what I did so far:

- dropped valve body & changed separator plate gaskets (old ones were fine, no missing sections),
- changed low-reverse servo piston o-rings & cover plate gasket,
- checked all (6) solenoids on valve body for continuity (SAT),
- checked reverse band for broken ear (SAT),
- refilled with Dexron lll/Mercon fluid (owners manual specifies MERCON).

Took out for test drive and no improvement. Further troubleshooting: coasting down a hill in manual-low gives engine braking so the low-reverse band is engaging; first gear in drive position is normal so sprag one-way clutch is working. MIL is off.

It just feels like the low-reverse band isn't clamping the drum tight enough and shudders/slips. The truck will reverse on flat ground but if I try to back up a hill it will slip. My truck only sees highway driving and no off-roading, it's well maintained and I'm a light driver. I'm stumped! Need some input/suggestions to further my troubleshooting. Help is appreciated! Thank you all.

 

[JK080]

It would be interesting to know what the line pressure is doing in reverse, if there is no line rise it can cause reverse to slip like this.

This could be a valve body or epc problem and even the mlps can do this.

If the reference voltage is low from the MLPS it could cause the computer to think the shifter is in neutral and not create the line rise needed for reverse, reverse should read around 3.6 volts and neutral is around 3.0. I have had this happen more than once with these, you should be able to catch it with a scanner that can read transmission data.

If the MLPS checks out good I would suspect the valve body and or the EPC solenoid.

 

[Kamaaina]

Thank you "JK080" for the response. Interesting info about the Manual Lever Position Switch (MLPS) controlling pressure boost in reverse. I have to see if I have a gauge that'll go up to 340psi to check line pressure. I will check the switch first before doing anything else. Will also unplug trans electrical connector and flush out with contact cleaner. Want to check as much external items before I tear into the trans again. JK080 - your info makes a lot of sense, sounds like i'm not getting that pressure boost in reverse.

 

[Kamaaina]

Oops! Forgot to ask one more question: Where & what is this "SSA" solenoid in the valve body? A lot of websites refer to this solenoid for a loss of reverse gear but makes no explanation of what it does or where it's located. Thank you!

 

[BrooklynBay]

Refer to the diagram in this link: 4R44E valve body diagrams are needed.

 

[Kamaaina]

SOLVED!!! - First of all thank you JK080 & BROOKLYNBOY for your replies. Using your advice I asked myself "why is it that only reverse is messed up?" After googling a butt-load of websites I narrowed it down to the Manual Lever Position Switch (MLPS). I removed it and, being persistent, drilled out the (10) rivets to look inside. Sure enough, one of the sliding contacts was flattened out lower than the rest. It turned out to be Pin-6 which sends different voltages to the PCM to tell it what gear is selected. So I was never getting the boosted pressure to the reverse-first servo to hold the drum. I reshaped the contact, slapped in some dielectric grease and pop-riveted the switch together. After reinstalling and making darn sure that the alignment marks for neutral were spot on I tested the Explorer by reversing up my super steep driveway. It made it with no slippage or shudder. I ordered a new switch from RockAuto for a back-up just in case. Hope that this thread can help others who have a similar problem. Thanks again!!!

 

[JK080]

Glad to hear and good job on being persistent and figuring it out!

We've pulled transmissions back out and apart just to find the MLPS causing issues, lessons hard learned!

 

[BrooklynBay]

Thanks for the update. Your thread is now marked as solved.

 

[imp]

SOLVED!!! - First of all thank you JK080 & BROOKLYNBOY for your replies. Using your advice I asked myself "why is it that only reverse is messed up?" After googling a butt-load of websites I narrowed it down to the Manual Lever Position Switch (MLPS). I removed it and, being persistent, drilled out the (10) rivets to look inside. Sure enough, one of the sliding contacts was flattened out lower than the rest. It turned out to be Pin-6 which sends different voltages to the PCM to tell it what gear is selected. So I was never getting the boosted pressure to the reverse-first servo to hold the drum. I reshaped the contact, slapped in some dielectric grease and pop-riveted the switch together. After reinstalling and making darn sure that the alignment marks for neutral were spot on I tested the Explorer by reversing up my super steep driveway. It made it with no slippage or shudder. I ordered a new switch from RockAuto for a back-up just in case. Hope that this thread can help others who have a similar problem. Thanks again!!!

@Kamaaina

Good for you! imp

 

[transman304]

Always great when we get a follow up and hear of a successful repair. Good job!