Hi all. Hope everyone is well. Although it shows I am a 'new' member, I have been a member for quite some time but had to create a new account as I lost my original work email/sign in. I pulled the trans pan to replace the lockup solenoid and discovered the attached photo, which was a bit more 'complicated' than I was expecting/familiar with, so I have a couple questions and I was wondering if a trans guy could help me out here in terms of what's going on here and simplifying it. The way it works now is power comes in, via a toggle on the dash, to one side of the 4th gear pressure switch (blue plug). That switch does whatever magic it does & feeds into one side of the 3/4 pressure switch, (yellow plug), the other side of 3/4 switch feeds the lockup solenoid. I don't know if this is factory, but it works so that's cool. But I feel like there's a simpler way to do this. Another wire in the plug harness (that I have not traced yet due to the unholy mess under the dash) feeds into the 3rd gear pressure switch (green plug). The other side of that switch feeds the switch on top of the converter solenoid (other green plug). Never seen this before-what does that switch/sender do covering the lockup solenoid?? All my checking online shows a plug in that port. My main questions are what does that switch do by the converter solenoid, and can I get rid of it?? Also, how can I simplify the lockup solenoid activation? All I want to do is lock this up in 4th gear via a toggle on the dash. Anyone care to share why whoever did what they did in here?? Thanks all, always appreciate the depth of knowledge here. John.
Why? Don't create a "solution" for a problem that does not exist. Leave it alone. You already have a 700R4 that can lock the converter in 3rd and 4th. They are not overly common, but there is absolutely nothing about this that needs to be changed. Make sure you have a good powertrain ground, and that 12V-IGN runs to the power wire, and you're done.
Hi sir. Appreciate your input. To answer your question, I am trying to simplify this so there is less opportunity for problems if a sender/switch fails. This particular off-topic vehicle, the trans gets far too hot far too fast without the converter locked due to a variety of unrelated inputs so I am trying to minimize the risk of a part failing by getting rid of anything unnecessary. I don't know how often those switches fail, but if they are prone to failure I'd like to eliminate whatever I can. I agree with you but I'd also like to better understand why it was done the way it was done. Any idea what the sender/switch is covering the lockup solenoid? Regards, John.
I have never had a switch failure. I have never seen or heard of a switch failure. I have rebuilt a few hundred of these, some that now have 500,000+ total miles, and have never replaced a switch. I never found any evidence of switch failures in the GM archive. That's not a sender. It is a ground switch. All of the single-pole switches are grounds. All of the two-pole switches are p***-through switches. If you are experiencing excess heat, put a cooler in the return line, after the heat exchanger in the radiator.
That looks like it's wired per the type 1 diagram, for models MD/MK/TK. That tcc signal switch is the final/only ( switch to close to ground ) None of the other switches close to ground. To complete the tcc circuit.
@gimpyshotrods , I was going to post the same thing, but don't have first hand experience like you do. I check with my transmission rebuilder friends, when I have questions, and they tell me the same thing.
Thank you sir. We are clearly not on the same page in terms of methods and/or the questions posed above, but I appreciate you taking a moment to share your expertise and experience. Regards, John.
Perfect, thank you sir, much appreciated- never seen that diagram so that helps me understand this better. Regards, John
There is some good info about actuating the lock-up solenoid here- Technical - 700r4... Run Without Lockup? | The H.A.M.B.
I believe the switch by the solenoid is in the throttle valve (tv) circuit so it locks and unlocks according to tv pressure. Probably wide open throttle.
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