Loss of reverse gear

[C420sailor]

Did plenty of searching and reading, just looking for a sanity check here.

4R55E in a 96 XLT

Symptoms:
-Suddenly lost reverse. No noise, just went out to the truck one morning and reverse wasn't there anymore.
-Manual 1 and 2 engage and accelerate fine, but provide no engine braking. Coasts.
-Flashing OD OFF light, getting the codes checked Monday.
-Truck can be pushed easily in neutral.

Wouldn't the truck not accelerate in 1/2 if the low-reverse band were broken or cracked? Does the lack of engine braking mean the band is cracked or worn?

Thanks in advance.

 

[PopRichie77]

If the band was broken, manual first would be gone. The low, reverse band is not used for manual second.

 

[C420sailor]

Okay, makes sense. Only code was P1701, reverse engagement failure or something like that. Hopefully it's just a leaking servo seal? Thoughts?

 

[greasemanicure]

I'll be watching this one. I've had no reverse on our 96EX for almost a year. Goes forward normally only WITH the OD turned off. At speed it will go in and out of OD manually but will not successfully downshift to third to accelerate. Pressure is solid in the 80's cruising but does not pass the stall test due to high pressure and no real engagement.

 

[C420sailor]

Dropped the pan today. Here's what I found:

-Approximately 60% of the valve body bolts seemed undertorqued. I torqued all to 8ft*lbs (~95in*lbs)
-I found the cooler bypass valve spring hanging out of its bore. I reinserted the spring in its bore.
-The o-rings on the reverse servo were intact with a smooth bore, but they seemed a little...small. Maybe like they shrank a bit? I ordered new ones.
-Tip of the reverse servo is pristine. No chips or wear.
-No metal filings, powder, or pieces in the pan or pan magnet.
-I used a long screwdriver to try to 'test' the reverse band. I felt a little spring action, but the travel was short and stiff.

Plan is to replace the o-rings on the reverse servo with d-section rings, button everything up, and hope for the best.

 

[4rd Xplora]

I'm having a similar problem. So I'm to see if that helped or changed the problem in any way. One other thing, mine has never lost reverse completely. I shutters like it's jumping in and out of gear, BUT it does it every once in a while. Maybe once out of every 15 times it's put in reverse.

 

[C420sailor]

Follow up...

I ended up tightening the valve body bolts to spec, replacing the reverse servo o-rings with d-ring seals, replacing the filter, and topping off with MERCON fluid.

Still no reverse. I'm pretty sure the reverse band is broken, or at least the part that the servo engages has broken off. That's as much work as I'm doing to that thing. My brother in law can live without reverse gear.

 

[DirtJunky]

I lose reverse every now and again in my 98 xlt. I can't figure it out either and been looking into threads for answers and found nothing. OD has not acted up and neutral, first, second, and forth have had no problems. Didn't have 3rd for about a week then all of a sudden popped back like nothing happened? Checked all and found nothing. No codes becides emissions leak and that was gas gap. Sitting back and watching what you come up with C420sailor.