5R55E Stuck Reverse Servo Piston

[ve7fet]

Hi,

First post here, but spent the last few days running the search engine and taking a crash course in the 5R55E.

Here's the story...

'05 Sport Trac, 174,000km, runs like a top. Until the other day when the wife is backing up and hears/feels a bang. Gets out to see what she hit, nothing there, drives off.

Next day, she goes to back in to her parking spot at home, throws it in reverse, nothing there... just like neutral.

So, I then spend the next few days (mostly here), trying to figure out what has happened.

I've got the factory workshop manual, and the ATSG manual for this transmission, yes it is a 5R55E, they used them in the ST right through to the '05 production year (last production before switching to the new body style in '07).

Still shifts up through all forward gears fine.

Have manual 1st gear, but it appears to not have any engine braking.

My research points to either a bad reverse/low servo, or broken reverse band.

Did a line pressure test, all line pressures are good.

At idle we've got 220psi in reverse, so no blown reverse servo gasket or valve body gasket.

Tried the stall test in the workshop manual for reverse, fails (figured it would). Exceeded the RPM's listed in the test (>~3100), obviously because there is no apply pressure to the band/drum.

So, time to drop the pan and have a look at the reverse servo and check the band... or so I thought.

Oil's out, pan's dropped, got the cover off the reverse servo, gasket is good, but I cannot for the life of me get the servo piston out.

I can move the outer part of the plunger/piston (the aluminum part) around, so it would appear to not be wedged on the o-rings too bad, but no matter how hard I pull and wiggle with a pair of vice grips on the piston (on the raised aluminum casting), it will not come out.

Of course all the manuals, and every one else, says "remove piston", implying that it should just come right out.

Mine, not so much.

Anyone got any wise words of wisdom on how to get this piston out?

My theory right now is that the tip has mushroomed, or somehow the piston shaft has become bent, and is jammed in the upper part of the bore, preventing it from sliding out.

The only thing I can come up with is to drill and tap the aluminum plunger part of the piston, stick a slide hammer on it, and try and pull it out. Not sure what other damage this will do the upper bore, but I am running out of ideas.

Has anyone else seen this problem before, and got ideas on how to correct it?

I picked up a 5R55E and transfer case from an '01 ST for cheap, hopefully it works... but at least it is a backup and an option I can go with if I need to.

I really want to check this reverse band before I go and re and re the used one in. If it is just a piston problem (hopefully), and the band is still good, that would save a whole lot of headache.

I look forward to your wisdom.


Thanks!


Lee

 

[JK080]

Thats unusual for sure, most of the time they fall out. I think you are going about it the right way. The only thing I can think of you might try is to remove the valve body and try to blow it out with air pressure. I think there is a bleed hole that goes into the servo passage, maybe blowing air into that hole it will blow the piston out. Other than that it might be slide hammer time.

 

[ve7fet]

Thats unusual for sure, most of the time they fall out. I think you are going about it the right way. The only thing I can think of you might try is to remove the valve body and try to blow it out with air pressure. I think there is a bleed hole that goes into the servo passage, maybe blowing air into that hole it will blow the piston out. Other than that it might be slide hammer time.

Thanks James, was afraid you were going to say that.

Well, not much to lose now, so I may as well beat on it some more while it is securely mounted in-frame and see if I can get it out. With luck (not likely), that is the root of the issue, and I won't damage the bore getting it out.


Lee

 

[BrooklynBay]

Welcome to this forum! Did you try to heat the servo? Sometimes expansion & contraction will break it loose. There is something called a freeze spray that is used on servos, pistions, and seals inside the transmission which makes assembly easier by causing these parts to contract when they get cold.

 

[ve7fet]

Welcome to this forum! Did you try to heat the servo? Sometimes expansion & contraction will break it loose. There is something called a freeze spray that is used on servos, pistions, and seals inside the transmission which makes assembly easier by causing these parts to contract when they get cold.

Yeah, could try something like that.

I can see if I can sneak a heat gun up on the side of the case to heat up the bore... or maybe a torch.

I can also try freezing the shaft with some freeze spray (got some cans of 'air duster' that conveniently will become freeze spray when inverted). I don't think this will help much, since the shaft of the piston is such a small area that I can get to.

Can't quite see how the piston shaft is attached to the plunger part of the piston... must be a c-clip or similar, but it must be tucked in the end of that shaft.


Thanks for the input.


Lee

 

[ve7fet]

Well, here's the follow-up.

Got the piston out.

Ended up going the slide hammer route. Drilled and tapped the piston for a 1/4" bolt for the slide hammer, and was able to ease it out.

Not sure why it was stuck, must have got ****ed in the bore somehow.

Piston looks fine, so it isn't the issue.

Stuck a screwdriver up in the bore to poke the band... I can feel the band there, and with the screwdriver in the right place, you could be fooled that you feel the band with it.

However, if you look close up in there, there is no pocket for the piston to push on... just darkness.

Found the broken band piece when I looked closer up in there and poked around a bit with a screwdriver.

So, transmission is coming out, and the used one is going in, for the time being.

Glad to know what the issue is for sure now, that puts my mind somewhat at rest.


Lee

 

[BrooklynBay]

Thanks for the update. Let us know how the next transmission works. Maybe you could rebuild the old transmission, and save it as a spare.

 

[ve7fet]

Thanks for the update. Let us know how the next transmission works. Maybe you could rebuild the old transmission, and save it as a spare.

Hah, yeah, that is probably what will happen.

Looking again at the date codes, I think this one I bought might actually be an '04 and not an '01. That makes me feel a bit better, as my valve body has been solid in my '05... think they might have worked out the bugs by then.


Lee