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Torque Converter Not Locking P0740


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4 replies to this topic

#1 gruhfy

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Posted 04 May 2004 - 10:52 PM

I am working on a '98 Legacy Outback with a check engine light: code P0740. The dealer has $250 of mine and only told me that everything checked out OK outside of the trans (Brake relay, wiring harness etc). After code set, I only noticed the TCC lock once, that evening, and not since (3 weeks later). The dealer said I can either drive the car or pay to have them dissasemble the trans. I would like to remove the valve body and root around myself. Any tips on valve body removal for the advanced DIY person who has never been inside a trans? Is a valve body rebuild kit available? I found a diagram from the shop manual posted on the web, but I have no idea what to expect in the way of special tools required. Please help.
Thank you.

#2 Legacy777

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Posted 05 May 2004 - 11:33 AM

I would check to verify both speed sensors are working properly in the trans.


If you want to remove the valve body.....you could probably do so......there are different length bolts, and for this reason i highly suggest you have some form of manual to know where everything goes. You really probably won't be able to see much just by looking at it.

There is a rebuild kit, they are not for the do-it-yourselfers. Trust me.

I'd suggest dropping the pan, look at the oil, look and see if there's metal chunks around the magnet.

you could try running some sort of flush through there....but that may make it worse.....not sure.

#3 gruhfy

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Posted 06 May 2004 - 08:44 PM

Thank you for the reply. I am hoping that the dealer checked the speed sensors while they were poking around for 3 hours. My interpretation is that the computer is satisfied that the conditions have been met and is trying to lock the converter, but it is just not hapening inside the trans. I found a few pages of the manual on the internet which shows what bolts go where, and which valves operate the different shifts. (Illustrated as upper, middle and lower valve body) I work as a machine builder for a manufacturing company and feel comfortable using a micrometer and calipers and taking anything apart. I would really like to remove the lockup valve, check the spring free length and ensure it is working correctly. Only problem is that I don't have a benchmark of what is "correct". I assume that it would be sticking or show signs of a worn seal if it were bad. Any advice if this is a good idea or a really BAD idea for someone who has never been inside a trans. Worst that can happen: I need to buy a rebuilt trans and the problem would be fixed (This is the last resort, least desired result.)

THanks again.

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#4 opus

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Posted 13 May 2004 - 12:11 PM

Sounds like my problem, but mine still locks. I got the same code as you.
The dealer took my money too....must have been the same dealer...lol!
Curious to see what you do to resolve it.

#5 Hondasucks

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Posted 13 May 2004 - 01:29 PM

It could be a bad TCCC solenoid (Torque Conveter Clutch Control), your diagram should show which solenoid is the TCCC, and any transmission shop should be able to tell you how to test it, and replace it if necessary. If that all checks out, the clutch lining inside the torque converter could be shot, unfortunately the T/C is a sealed unit, and there is no way to measure how much cluthc material is left. If that is the case, best bet would be to replace the T/C and have the tranny and cooler flushed.


Ther should be a pressure tap somewhere on the tranny for the TCC, and there should be a procedure for checking the pressure of the TCC.. If it is getting pressure, then I would suspect the clutch itself.

Transmission Exchange in Portland (www.txchange.com) could help you with finding a T/C or parts if you need parts. They can also get you a repair manual which would help you in your diagnosis. I would not touch the valve body without a manual, improper torquing of the bolts will result in warping of the valve body, requiring replacement ($$$$$$$$$)

Last valve body I bought was for a AXOD (Taurus time-bomb) and it was almost $400...




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