transmission problem

[greg s]

97 explorer 4wd 5r55e trans. I finally got the time to work on my transmission, and installed the new seperator plate, shift kit, filter etc. But I am still having a problem with a delayed reverse. The shift kit came with a new reverse servo seal that I installed and the rest of the trans was spotless inside. I cleaned the valve body and looked at the solenoids and everything looked fine. The transmission shifts great, no codes, no flashing overdrive light and I measured how much oil came out and made sure that much of the Mercon v went back in. It is not a consitent problem, maybe happens in about 1 out of 10 shifts to reverse. Basically what happens is you put it in reverse and when you give it a little gas it makes a mild bang noise and begins to back up, it seems worse if you are trying to back up a hill. When it first happened about 6 months ago it was so loud that I thought I had hit something. I have to drop the pan again to replace the servo because it has hit so many times that it has fractured the tip of the servo rod. Any thoughts would be apprecited.

 

[Glacier991]

Did you have any of these symptoms prior to the VB rebuild? If not, I think we can safely assume it is a VB issue. (Otherwise there are PCM input issues to address).

Looking in the FORD Factory manual for the 5R55E, for HARSH reverse only, it lists as possibles:

Screws out of torque specification

Gasket damaged, off location

Separator plate damaged

EPC, SSA solenoid stuck, damaged, O-Ring damaged or out of bore

Reverse modulator valve (205), Pressure Boost Valve/main regulator valve (208), check ball B, springs damaged, missing, misassembled, stuck, bore damaged

That's a start. If you need anything more, let me know.

 

[Glacier991]

FWIW, I'm thinking one of the 2 valves. It seems unlikely if you did not have this problem pre rebuild, it is a solenoid. Focus on what might have changed in the rebuild. Also the intermittent nature strongly suggests something sticking.... I can send ya another EPC solenoid and SSA to swap out if you want to see if either of those is the issue.

re-reading, maybe I should ask how long between rebuild and now? How long between rebuild and this issue showing up?

 

[greg s]

Thanks for the replies. The problem was there before the work. I was hoping that the seperator plate and shift kit would solve the problem. It is very intermitent as I might use reverse all week and have no problems then it will happen out of the blue. The shift kit had me change some things in different bores but I dont have the paperwork with me to see what number they where, but they where very clean with no signs of damage. I did not take all of them apart, only the ones that needed a part or spring changed. I am wondering if one of the solenoids could be bad but it is so intermitent I dont know how I could test it to be sure. I also think it sounds like something sticking because its not until I give it some gas that it does it. If I am on the flat and shift it to reverse and let off the brake it will roll and back up smoothly. It never makes a clunk when I shift from Park to Reverse or Drive to Reverse. It only happens after the truck has moved a few feet.

 

[Glacier991]

let me send you an EPC and SS and try replacing them... just for grins... might rule out something intermittently wrong in them....this is where a NGS tester would be nice.

ps. and see what I get for assuming. Now the entire range of issues, including inputs, is in the game. Now my $$ is on the solenoids, if for no other reason that something that intermittent is more likely electrical than mechanical.

 

[greg s]

I might take you up on the solenoid offer. After thinking about what is happening and with my experience with hydraulics I think it is a problem with the solenoid or reverse modulation circuit. Is there some type of schematic that shows the fluid paths during different operations? Since there is no return spring on the reverse servo piston I would assume it operates like a double acting cylinder and requires pressure to apply and unapply it. Here is what happens, with my foot on the brake I shift it to reverse (no noise made) the engine loads a little and you can tell it is in gear. I let off the brake and it starts to back up (servo must be engaged and band tightened somewhat), it moves a couple of feet and makes a loud thump/bang noise and continues to back up after I give it a little gas. Shift it to drive and everything is fine, no codes, no flashing O/D. I think something is sticking in the bore or one of the springs is broken and allows some pressure to apply the servo but then bypasses and unactuates it for a second until I give it a little gas and increase the pressure which overcomes the unactuating pressure and slams the servo into the band. That would be what caused the tip of the servo to fracture where it contacts the band. But the ASTG manual does no show any type of fluid paths to figure out exactly what applies and unapplies the reverse servo. I see in the parts diagram that there are two valves and two springs in the reverse modulation bore, so I think depending where the shift spool is located and whether the solenoid is powered or not it applies pressure to one side or the other. Any thoughts are appreciated.

 

[Longjohn119]

I had a similar problem with OD after an A4LD VB rebuild....

Make sure to properly torque the valve body with a good inch pound torque wrench ...

I also changed the the soleniod even though it wasn't plugged but I still think it was not having the VB torqued properly

Sure works good now ....

 

[Glacier991]

Standby, I took some pics of the hydraulic circuits in the manual.... Do you have a trans pressure gauge? That might be helpful. Anyway let me post the pages I took pics of....

Entire page here..

Now another view of the entire page

Now the lower right

lower left

upper right

I hope this helps. If you need the manual let me know, we can arrange a loan or something.

 

[greg s]

Thanks for all the help Glacier. Looking at the diagram it appears that the reverse servo is only a single acting. I dont see where there would be fluid pushing it back. I guess it is only the spring pressure of the band that pushes it back, since there is no spring under the servo. (though the diagram sort of looks like there should be). I know it would be a big leap of faith, but I would be intersted in borrowing your manual and copying the pages and return it to you. I might be able to borrow a pressure gauge or rig something together from the stuff I have laying around. I would like to trouble shoot the problem better and not have to keep pulling the VB apart. Thanks again,Greg

 

[greg s]

After looking at the diagrams a little closer I noticed it's the diagram of the circuit shifted in reverse, and that it looks like there is an opening for pressure to unapply the servo (making it double acting). And when it is in drive it should apply pressure to the opposite side of the servo. Thanks

 

[greg s]

Glacier would you still be interested in loaning your manual? I can copy the pages at work and return it to you asap.

 

[Runnin'OnEmpty]

Greg, in looking at Glacier's flow diagrams, a possibility might be (like Glacier mentioned) that the reverse modulator valve is occasionally sticking. Since it's referred to as a "modulator valve", that would lead me to believe it's supposed to modulate the pressure when reverse is selected, and smooth out the shift. If the modulator isn't 'modulating', then you might have a harsh reverse engagement......?

Does that make any sense?

EDIT: One other thing: Have you tried adjusting the low/reverse band? Maybe it's the band that isn't fully releasing...?? That's something that can be done without taking a Mercon V bath.....

 

[Glacier991]

ROE, I think you are thinking of the interrmediate.. the low reverse is not adjustable.

 

[Runnin'OnEmpty]

Indeed. Thanks for correcting me, Glacier.

That's what I get for posting when I'm sober......

 

[Brian_B]

Glacier: Are those color pics out of the same book? Those are so much better than the ATSG ones. I want one. I know...keep looking. I am.

 

[greg s]

Thats what I am thinking as well. I got a new reverse servo piston to replace the cracked one but am trying to trouble shoot and get every thing ready before I drop the pan and vb again. But from the way its acting it seems like a piston sticking from wear or contimination. Or it could be one of the solenoids sticking as well. Everthing was very clean and the bores that I took apart to put the various parts of the kit in looked good, but I did not take all of them apart including the reverse so thats what I am leaning toward. I might buy a new EPC and shift solenoid to have on hand and replace because there is no one local that I can pick one up from the same day if I find I need one. I hate just blindly throwing parts at a problem, but to fix something you need to know how it works so I am trying to learn as much as I can so I can systematiclly test some things. Thanks for all the replies and help so far