The tranny is mis-behaving on my 88 740, B230F with AW70L. Recently have experienced failure to shift into 4th gear or sudden unexpected down shift to third. This happens only after at least a half hour of driving usually at freeway speed. Sometimes at constant speed and throttle it will briefly shift back to 4th, then go back to third. Never happens when cold. Dowshift cable seems OK, tranny was flushed within last year. I have resoldered overdrive relay, OD light behaves normally and always toggles with pushing of the OD switch. I have even removed the relay and inserted a jumper into the relay socket between 87 and 15 (relay pin numbers). This applies 12V directly to the solonoid wire, but got same results.

So, problem would now seem to be at the solonoid. FAQ section seems to indicate that solonoid problems typically occur when tranny is still cold, my problem only occurs when hot.

Before I crawl down under my next test will be to monitor current flow through the solonoid at the above mentioned jumper point to see if I have an intermittent connection or open solonoid coil problem.

Looking for thoughts and suggestions. How do they fail, do they get clogged up, worth cleaning, does the coil go open? Should I just go and get one from a pick and pull and swap it?
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David Hunter