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The 5R55E and the infamous 2-3 shift flare issue

Glacier991

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Well by now, if you are either a loyal reader of this sub forum, or possibly have an Explorer with a 5R55E, you are used to hearing complaints about the so-called 2-3 shift flare. Simply put, many folks experience a situation where, at the time the transmission is shifting from 2nd gear to 3rd gear, the rpm's jump a little before the actual shift occurs to completion and they are fully engaged in 3rd gear. Sometimes this problem can get SO bad that it is needing to be addressed. I usually recommend a VB rebuild, and a replacement of the EPC solenoid. In most cases this works and fixes the problem.

Yet, in the 5R55's we are seeing this problem becoming a major one at relatively low mileage... sometimes as low as 60-70,000 miles (and in the case of the 5R55W - another thread soon - more so). What gives?

Let's take a look, and I'll solicit some expert views from a new member on the subject.... WAYYYYYY smarter than me.

First off let's examine what all happens on this shift.

The Coast Clutch (OD clutch) "May" be applied - One thing
The Front Servo (OD band servo) "IS" released - Thing number 2
The Intermediate Servo (Intermediate band servo) "IS" applied - Number 3
The Forward Clutch "IS" Applied. (No change it stays applied in all F gears - no big deal)
The Reverse Servo "IS" Released - Thing Number 4.

The main 4 things that happen, are all interrelated and have to happen in a timed sequence.... a neat trick, controlled by the computer. Key to all this is line pressure control exhibited by the EPC solenoid, and the computer controlling how it all comes together - a nice dance if you will.

Why is all this so tough? Well remember that in the 5R55, the 5th gear on a 4 speed was derived by overdriving first gear to get a 2nd gear (effectively making it a 5 speed). Now, in one felled swoop, we drop the OD and Reverse and add the Intermediate Band to make the 2-3 shift.... a LOT going on more or less all at once. Often a problem child. Without computer control? Nearly impossible.

Wanna see what happens in the typical shift? This graph, provided by "new" member Allbert, shows the "flare" in the normal, or at least not unusual, operation of the 5R55:

Outlook.jpg


See that little obvious blip? It is about 250 RPM's in the "normal shift". Compare that to the 3-4 shift (next drop on the chart - where only ONE thing happens, the application of the intermediate band... see?

The question becomes - why does this ultimately become a HUGE problem (BIG RPM jump) for some folks and how can it be fixed?

My typical answer is, when the RPM jump becomes a large one and is a problem...is: change the fluid, rebuild the VB and upgrade it, and very importantly, replace the EPC. And most of the time, as I have said, it DOES fix the problem (and avoids a quoted $2000 bill for an unnecessary rebuild!)

At the end of the 5R55E Valve Body Rebuild Diary new member Allbert posted some highly technical and very interesting info about the design of the 5R55E EPC solenoid. Long story short? It is so highly precise in its tolerances and operates in such a fashion that it is terribly unforgiving of any contamination. Here is a cutaway look inside the solenoid, but what is more important than the precision, is the way it operates - for that you have to go read Allberts post on page 13 of the 5r55E VB Rebuild Diary. Here is the solenoid in cutaway view:

viewofsectionedBoschEPCfrom5R55modulewithnotes.jpg


MORAL? In the 5R55E, filters, even additional filters, are a crucial key to their longevity. Frequent fluid changes are a MUST.

Maybe someday someone will come out with a new design EPC that is more tolerant to contaminants.... hmmm.... I bet the new one might have a "normal" 2-3 flare that looks something like this:

file000.jpg


Now if that EPC could be more tolerant of contaminants, it would beat the pants off the stock one!

Stay tuned, this might be a fun ride guys. More to come...really exciting stuff.

Glacier

ps. All photos and graphs compliments of Allbert - I thank him.
 


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dogfriend

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Interesting Post -

I had a thought - It would be interesting to see a plot of EPC pressure vs. time overlayed on top of the turbine shaft speed vs. time plot. It seems to me that if you knew what "normal" pressure should be during the 2 -3 shift , then you could check to see if the pressure is correct - that could confirm (or rule out) a bad EPC solenoid.

My scan tool has the ability to output EPC pressure but I don't have any ability to graph vs. time.
 




Glacier991

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Good idea Dogfriend. Maybe someone with a multichannel scope might derive just such a graph for us. It WOULD potentially be very informative - or at least interesting.
 




frickea86

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woot...at least i know i'm doing something right by changing my fluid every year...nice
 




Glacier991

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Dogfriend... I had an insight about what you posted. I think what you are seeing on your scan toolis the COMMANDED EPC pressure, not the actual pressure. There are no transducers, and in the pinpoint tests you still are required to connect a pressure gauge to readout the actual vs. commanded pressure.
 




dogfriend

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Dogfriend... I had an insight about what you posted. I think what you are seeing on your scan toolis the COMMANDED EPC pressure, not the actual pressure. There are no transducers, and in the pinpoint tests you still are required to connect a pressure gauge to readout the actual vs. commanded pressure.

Doh! You had to let reality get in the way of a convenient theory. ;)

So you really need a line pressure gauge that can plot pressure vs. time and somehow sync to the TSS sensor on the same time base.

Or just buy another EPC solenoid and hope for the best. :p:
 




Bent Bolt

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Think Canadian ,eh !!!!
Hohoho from The Great White North!! Nowhere near the north pole but just as white!!

Glacier991 has put to print what is going on in a 5R55e much more clearly than I could. There is alot going on on that in that trans than most people realize.

First off, it is my opinion that the 5R55E is a very very good trans especially concidering that it's based on the somewhat weak and not-so reliable A4LD. The valvebody gaskets and EPC solenoid are the worst part and I can honestly say that I do not overhaul 5R55E trans very often. Keep in mind that I deal with stock vehicles that are mostly still under warranty or relitively low KM's -- less than 200,000 KM.

When the VB gaskets fail, it can cause many differant symptoms in addition to the famous 2-3 flare. I have seen almost every symptom from manual 2nd gear or reverse only to no movement at all. Why ???? Because the gasket failure usually happens right near the EPC solenoid which controls the main line pressure of the trans. A major leak there can cause a loss of pressure so great that the trans simply won't move.

I might sound like a broken record but it is my opinion that a VB overhaul along with installation of the service kit and a NEW EPC solenoid will correct about 90% of all problems with these transmissions.

Another problem that crops up once in awhile is a physical failure of the EPC. Sometimes the tab that is machined into the solenoid breaks off and allows the solenoid to move from the VB-- and a huge pressure loss. A similair failure is caused by the metal retaining bracket that bolts onto the VB and holds the shift ,TCC and EPC solenoids in place.
 




Glacier991

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Now, it's ME that couldn't have said it better. Thanks Bent Bolt.

Dogfriend.... adding a pressure transducer ought not be that difficult, in fact iif you culd rig up an oil pressure sensor to the EPC port and capture the output you'd be part way home.
 




whoathere

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Is the EPC solenoid located in the transmission? I still have not had the codes read on mine yet, I'm gonna try it tonight. Either way, if the EPC solenoid is easily accesible, it might be smart to have it replaced when I get the tranny flushed and fluid changed, would it not?
 




BrooklynBay

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Lets take another approach to all of this. The EPC is only computer controlled. What if you had a transducer to provide a feedback signal to the computer to monitor its output, and compensate for the flare? As soon as there is a pressure drop when there is a demand for more pressure, the computer will compensate, and build up the line pressure to the correct amount. Isn't it interesting that this problem is only on the 5R55, and not on the 4R55E? There is more computer control going on in the 5R55 than in the 4R55E. The EPC is also different in the 5R55 (inductive signature).
 




Glacier991

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BB.. the computer more or less already does that. Except instead of reading pressures it looks at ratio variances to determine slip. It "tries" to compensate for the flare as it is.

The problem in a failure mode is that the EPC just isn't capable of changing things that fast anymore because of wear and or, apparently, contamination.
The inductive signature will only be of real value in a partial or total failure of the solenoid in my opinion.

The fact the problem is not in the 4R is pretty simple - no complicated "computer generated" 2nd gear. Just a simple A4ld APPLY SEQUENCE.

And to WHOA THERE...the EPC is located on the valve body...you might check out the 5R55E Valve Body Rebuild Diary thread in the stickies for more info. Automatically replacing the EPC is a pricey proposition, but if the mileage on the old one is over 75,000 miles or so it "might" not be a bad idea.

Let me suggest something. Wait to do this if you can. I may have an interesting proposition for you and others with the 5R55E in the near future in regards to EPC replacement.
 




CDW6212R

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Happy Holidays Chris, etal. Do you still have a want for a 5R55W, Robert has his 7k model for sale? Regards,
 




BrooklynBay

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Glacier991

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Let's just say at this point that it has nothing to do with a new boost valve OR (NEVER NEVER EVER) adjusting the set screw, but something far more interesting. I don't mean to be mysterious but there are few final details that would need to be worked out before I can go public with it.

DON, I am still interested in a W, depending on price and location. I'll be completely disassembling the one I get to make comparisons on various parts. I'm not expecting any great "strength" changes as it is still a 500 ft lb torque limited tranny.... but maybe some failure points addressed... and maybe upgrades to a Frankentranny II.
 




whoathere

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Glacier, I'll get those codes tonight and post them in my thread. Well, in regards to the EPC, the only reason I had suggested it was because if I have it in, they will have the pan off anyway, but if it's gonna be more involved than, I'll just wait I suppose. The tranny does have ~70k miles on it currently, and the 2-3 flare has only been happening for the last ~5 miles. I haven't driven it for a few days. I am going to drive it today, about a half mile away to get the codes read, so I'll be able to post them later on tonight.

I'll have to check out the valve body sticky again, i skimmed it once already, but didn't look to fun so I closed it. Thanks again for all your help, hopefully soon I'll get this solved...
 




Glacier991

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Your idea to change out the EPC is not a bad one, do not misunderstand me. I'm just saying that in the next week or two I might have some alternatives for you to consider when you replace the EPC.
 




zhanx

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Hey Glacier, I might be the test dummy for ya. I just blew a soft line to my cooler and had to put in crap fluid and drive home 8 more hours. Now I replaced the fluid new cooler and new fluid. Non synthic fluid I have the 2-3 flare. When i rebuilt the VB last time i didn't replace the EPC. So when i get home from the holiday vacation. I am gonna pull and replace the vb gasket, EPC, and refill with royal purple again.

Normaly i would just replace and flush the fluid but i want to check the reverse fluid paths. (shudders slightly in reverse, so i think i fuber'd something when i rebuilt it last) I am gonna grab an extra vb from a junk yard and upgrade it. Then just swap it and see if that fixes it.
 




mferdin

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What do you think about the possibility of the 4x4 module causing the shift issues?
 




whoathere

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Not all of the Explorers experiencing this problem have 4x4, mine for instance does not have 4x4, but I still have the shift flare problem.
 


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mferdin

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ahhh.. good point :)

I am taking mine in to Ford tomorrow (not under warranty) to have them look over the 4x4 not engaging and after reading a couple of other threads hoping that if the 4x4 mod is replaced ..maybe it will correct the issues shifting from 2nd to 3rd ( fingers crossed)
 




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