To anyone who has had an issue with their Explorer transmission slipping on 2nd and 5th gear or even 2nd, 3rd and 5th. I have an '02 Explorer that now has 179,000 miles. With today's economy I really can't afford to buy a new vehicle so I was left with no choice but to fix my transmission (or die trying!). Fortunately my brother-in-law nudged me into pulling the trans and helping me do the rebuild. It is now finally fixed! Here is what I found.

My research into this problem was long and difficult since there isn't a lot of information on automatic transmissions out there. Plus very few repair manuals are willing to print anything on them due to their complexity. My main source of information and parts initially came from Lory Transmissions in Florida. They sell lots of parts and technical manuals. Get a manual. It has a lot of information packed into a few pages and is simply presented. It also will show you all of the possible computer error codes that you could get and what they are. The only code I ever got was a P0775, otherwise it was most often the dreaded blinking OD light. So what was the cause of my problem?

My problem was the slipping of 2nd and 5th gear and then eventually no 2nd and 5th. This is really only a symptom of the real problem, which is a serious leak of transmission fluid between the pin and bore of the overdrive servo. Eventually the mid gear bore will leak too, which causes the loss of 3rd gear. If you purchase the technical manual from Lory Tranmission you can find where to install a temporary pressure guage (be sure it can handle 500 PSI or more) and watch the line pressure from the pump to see if too much fluid is leaking. Mine was so bad it was nearly half the pressure of what it should have been. Once I understood that I had low pressure it made it a lot easier to search for the problem and eventually find the cure.

It turns out that the 5R55 tranmission is notorious for leaking in the servo bores of the mid gear and overdrive gear servos. The reason is because the bore is machined from the case of the transmission, which is soft aluminum. The pin of the servo is hardened steel, which has no difficulty in quickly wearing out the aluminum. So that's why so many folks are having transmission failures at 70,000 miles or even less! To fix the leak I recommend this tool from Servo Pin Bore Repair by Northland Transmission, which allows the bore to be accurately opened up so that a brass bushing can be inserted fixing the leak. Your other option is to find a tranmission shop that can enlarge the bore and insert a bushing. Either way that will fix the slipping of 2nd and 5th gear. So other than the replacement of all of the friction material in my transmission and the new brass bushings, my transmission has all of the original parts and is now solidly shifting through all gears. Good luck with yours!

Oh, and one more thing. The 5R55 transmission has 3 variations, 5R55W, S and N. This transmission is found in the Explorer, the Ranger, the Mazda Navajo and even a few Mustangs. So just because you hear horror stories about Explorers, realize there are other vehicles with this same transmission and its problems.

 

my friend is having issues with his 02' explorer tranny too. He took it in because of the OD light and the local Ford dealer said it was throwing a "torque converter slipping" code. They also said the fluid was dark and slightly burnt. He occasionally pulls a tent trailer and has about 120k on the rig. What do you think--replace the converter or is that darn servo pin bore leaking?? I'm no tranny expert--but form the sounds of your experience, it may need the same treatment as your's. thanks, Kevin

 

Kevin,

It may be that your friend's transmission is showing signs of low pressure due to a leaking servo bore. The fluid should be bright red and not dark. Dark fluid would seem to indicate that a lot of friction material has been burned off from various clutches. The dealer telling your friend that the torque converter is slipping is the torque converter lockup. The converter contains a friction clutch within it that is dependent upon enough force from a lockup servo in the trans to keep it from slipping. It is very possible the converter's friction material is worn away and therefore should be replaced, but this is merely a symptom of not enough force from the lockup servo.

To test for a worn out servo bore connect a high pressure guage (rated for at least 500psi) to a pressure tap found on the driver's side of the trans toward the rear. It is an 1/8 inch pipe thread plug with a 7/16 hex head (I think that's the size). If possible use a suitable hose that is 10 feet or longer to connect the guage. Start the engine with the vehicle on the ground and put it in forward and watch the pressure with the engine still at an idle. If the engine is a v-6 then the pressure needs to be 90 psi or higher. Next try it in reverse and look for the same pressure. If the engine is a v-8 the test is the same except that the pressure can be as low a 80 psi and still be considered ok.

If the trans fails the above pressure test there is a way to check for a worn servo bore without taking the trans apart, though it may have to be pulled from the vehicle. On the passenger side of the trans are two caps for the mid gear servo and the overdrive servo. With an appropriate snap ring removal tool or a persistant hand and screwdriver remove the snapring and the cover to the servo. Carefully observe how the snapring was oriented and set aside. The cover is next and can be a little stuborn. A big pair of pliers used gently should work. Finally you will see the servo. It may want to stay inside the trans without some persuation. A small enough screw driver can be safely inserted in the center hole to provide some grip on the servo as you pull to one side slightly and out of the case. It shouldn't take much to get it out. Once it's out partially reinsert it and push it from side to side in the bore hole. A worn servo bore will feel quite wobbly as you shake the servo side to side. If it's good there should barely be any wobble back and forth. Try testing both servos. This may be possible to do with the trans still in the vehicle if there's enough space between the trans and the tunnel. I don't have my vehicle in front of me right now so I don't know.

If it turns out to be worn servo bores the fix is not that difficult for a trans shop to perform with the Northland tool. I seriously doubt the dealership will take on the task of a repair like that. Your friend may be in for a mild search to find a shop willing to perform this very specific repair, plus the usual friction parts replacement and, yes, a torque converter replacement. If done through a shop he's looking at around $1,500 to $2,000 for this kind of job, but once done it will be bullet proof. Mine is now working better than when it was new and better than when first repaired.

Good luck to your friend Kevin!

 

Great story. Would you be of the opinion that keeping the tranny filled with fresh syn fluid might reduce the bore wear to an acceptable level?

 

thanks Dave, i'll relay this info to my friend and see what he wants to do. It seems that the exploder has quite a history of tranny issues--i almost bought an 02' a few years back--now i'm glad my wife talked me out of it

thanks again--

Kevin

 

Great review. I was already aware of the problem somewhat, but I have no experience with the transmission. I'm glad you found a fix. Someone out there needs to be offering rebuilt 5R55 transmissions with the bushings installed, and also some of the upgrade parts that are available, such as better bands and clutches. There is enough demand, and many people and technicians don't know enough about this problem to deal with it, all too many shops just swap trannies without really fixing the problem.

 

Boy! That's a lot of responses to my last post. I'll address each as best I can.

To srercrcr:
While I'm not a metallurgist I do know one important fact about the aluminum that the case is made of - it's soft! Much softer than the steel that the servo is made of. And while the best lubricating fluids slow down the loss of the aluminum where the steel rubs, it won't stop the erosion of the aluminum. Brass, on the otherhand, is almost ideally suited in a bearing application when paired with steel. So, no I don't think even frequent changes of synthetic fluid would help in this situation.

During my research, I found a publication for transmission technicians that reported that the 5R55 series of transmissions commonly wears out the servo bore by 70,000 miles. This is rediculous when compared to classic transmissions like GM's T-350 or the stout T-400 - and those trans didn't have synth fluid when they were developed. The only conclusion that makes sense to me is that the 5R55 should have never been built without brass bushings in the servo bores.

To Kevin:

While I'm relieved and glad that I fixed my transmission, I must admit that if I had to do this all over again I would have preferred not to have had to fix it.

To Bear River:

When I was first looking at rebuilt transmissions I found that the bigger volume shops did use Northland's repair tool or had a good machinist that didn't need the tool. So there are rebuilts that have this fix done. I just didn't have $2500 it would have cost me to replace my original trans with good rebuilt.

In any event there are mechanics out there that know about this repair to the servo bore. What appears to be lacking out there is this kind of information amongst car owners - and dealer service shops!

One more item. When my trans was finally pulled apart it had nearly 160,000 miles on it. Most of the clutches and clutch bands looked pristine. Only the overdrive band and coast clutch drum were ruined due to the worn servo bore. My impression of the gears and clutches are that they are very stout for a transmission that is intended to be behind a v-6 or a small v-8. That's why I'm saying that if the hydraulics portion of this transmission is made strong then this transmission is hard to break.

Thanks for the comments and I really hope this helps some folks out there to have a reliable transmission.

 

I have an 02 and a 93 Explorer, both with high miles and the transmissions have been OK so far and I tow a heavy boat a lot. I do some things that I think make a difference. First, I flush, not change the fluid every 20,000 miles or sooner. Second, I have the trailer package which comes with a separate fluid cooler besides the radiator. Third, I install a cooling fan on the fluid cooler and run it from a switch during hot weather. On the 02, there is another concern. Worn or mis matched tires can damage the transmission. All four tires must be the exact precise same diameter. If not, the system detects slip and begins to engage the various wheels and eventually begins to shudder. I was experiencing this, immediately changed the tires, and the problem went away and has not come back. Another friend with an 02 lost his transmission. I was checking out his tires, and they had very obvious uneven wear. Frequent rotations and alignments may help with with this concern.

On another note, I haven't figured out how to start a new post. I'm currently replacing the engine on my 93. I'm stuck on some Chilton instructions that say to remove the torque converter inspection cover to remove the flywheel bolts that must connect the transmission to the engine. I don't see any such cover. Perhaps the bolts have to be taken out through the starter area? Anyone know? 4.0L OHV motor. Thanks.

Oh, can someone tell me how new posts are started? I haven't been on this forum in a long time. Thanks.

 

Go up one level to the Explorer, Sport Trak forum, there's a NEW THREAD above the list of posts.