transmission noise

[castr]

I have a 97 Explorer w/auto 4WD and the SOHC V6. Lately when I've been going around 60-70 mph or better on the highway and I let my foot off the gas to decellerate I get a loud buzzing or rachet noise as its dropping out of overdrive. The tranny shifts fine, and it doesn't hesitate, buck or heave, etc. Once the noise starts, the pitch will rise or fall depending on how much gas I give it, but will stop when I suddenly tap my foot on the gas a couple of times. It is not a problem at lower speeds, and it doesn't even happen every time at high speed. I thought maybe I should stay out of OD, but when I shut it off while decellerating, the gas pedal trick wouldn't stop the noise. Recently, the noise started when I was parked and shifting to reverse. I put it back in park and the noise stopped, then reverese again and it was OK.

I do not get a transmission or engine light. Also the fluid is fine, the color is right, and there is no burning odor.

The truck has 148k on it but I just had a new torque converter, fluid control body (modulator) and all new soft transmission parts replaced last December. I'm hoping I'm not in for another $2,600 tran job.

Any advice??!!
Thx!

[wcgirling]

I think I am experiencing the same problem. Have you had any success with finding probable cause?

[castr]

This is a reply I got from someone at www.ford-trucks.com. I coudn't have gotten a more thorough explanation! I still haven't gotten it fixed, but its OK around town. I was going to order a rebuilt (http://transfercases.com/) but I think I'll try to get an "as is" from a local yard. Not sure yet. I'll report here when I fix mine. Let me know how you make out. Anyhow, good luck!

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Answer from Ford Trucks.com:

You have a bad transfer case. If you look around on this board you will find a complete explanation but basically the helical cut gears in your Borg Warner 4405 transfer case are trying to separate when you lift your foot off the gas and coast and the noise you hear is the gear teeth sliding over each other. This is caused by wear in the aluminum case halves and can only be repaired by taking the case apart and using a new case half or machining the case and inserting a bushing. See this link for the case halves http://www.omegamachine.com/html/BW4...se_repair.html.

My 1997 EB started this problem a month ago with 150k miles. For now I just try to avoid putting reverse load on the transfer case by feathering the gas pedal when I want to slow down over 50 mph or putting the truck in neutral. I bought a 1999 transfer case but it doesn't have a speed sensor hole and I am trying to figure out how to adapt it. If I can't I may take mine apart.

It sounds like you don't work on your own car so I will base my reply on that assumption.

I would say taking the car to the dealer and getting a new transfer case would be the most expensive option, probably way over $2000 and a waste of money for a 1997 truck.

Next would be buying a rebuilt unit, I have seen them on the internet for around $700-850. (http://transfercases.com/order.htm). Just look on google and type "4405 transfer case" and you will see several vendors that sell rebuilt cases, but you need to return your core. These things weight over 80 lbs but you can send them UPS.

Another option is to use a local service to rebuild your transfer case. They would have to understand the with the gears separating, which is unique to this transfer case it seems. They would either machine your case halves or they can buy already machined halves from Omega for around $140 each ($280 total). I probably wouldn't go to a transmission shop but would either use a local mechanic you trust or go directly to a place that rebuilds differentials and transfer cases. See your yellow pages. What you don't want is a transmission shop that doesn't understand the problem and rebuilds your case without fixing the case halves. It will just start grinding again after a few thousand miles.

Finally, you can just buy a used case and hope it lasts until you want to sell the truck, which could be years. You have to be careful because the 1997 Explorer needs a 4405 case with a speedometer hole and cases from 1998-2000 don't have this hole. I called a junkyard in Texas and got a price over $800, which is way too much. If you can find one with low miles for around $300 I would buy it. Mine went to 150k before it had this problem and it seems other people having this problem have relatively high mileage trucks so getting one with under 75k miles would probably be ok.

I've done a lot of work on cars so installing the transfer case is something I would do myself. It doesn't look like a particularly difficult job but if you don't work on cars I would have someone do it for you. Installing the case is probably around a 2-3 hr job on the garage time sheet, although with a lift I guess it could be faster. I would imagine a mechanic would charge you at least $200 to install a transfer case. (It's a LOT easier then installing a motor or transmission in an Explorer).

So there is your answer. I would say the price could be as low as $200-300 if you bought a used part and did it yourself up to around $1000-1400 if you had a garage install a rebuilt case. If I didn't work on cars and had this problem I would probably go with a local mechanic I trusted or look in my local area for a 4x4 speed shop and ask them to recommend an honest mechanic who works on 4x4 trucks. If you're lucky you might find someone who can both rebuild your case with the new case halves and install everything for around $800.

[wcgirling]

Actually I had a private mechanic tell me exactly what you had described so I guess I know what I am dealing with now. Thank you for the very comprehensive answer.

FYI - My problem started with a different symptom; I was getting a loud "clunk" on acceleration at about 2000 RPM. I was told it had to do with a loose output shaft from my transfer case. . I had a local specialist repair shop that deals only with transfer cases
replace the gear and the clunk went away but not the buzzing at high speed.

My private mechanic's assessment agreed with this; i.e. he thought the clunk was due to the output shaft but the buzzing symptom was a seperate problem associated with the transfer case halves as you described.

AAAAAH! 4X4's aren't all they are cracked up to be!

I'll let you know how the drama plays out.