- Joined
- February 8, 2003
- Messages
- 9,824
- Reaction score
- 84
- City, State
- Sacramento, CA 95827
- Year, Model & Trim Level
- 1992 XLT
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:
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:
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:
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.
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:
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:
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:
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.