700r4 Intermittent Lockup or None at all...

[Boone83K10]

Please read entire post..sorry it is sort of long.

About 8 months ago, I tried to take off my factory cruise control. I lost converter lockup even though I am not sure if I knew it was doing it before that. I put it back in, but the shift points changed. They went from 15,25,35 and engaged lockup at 45...... then it went to 15, 35, 50 and no lockup. I know it isn't locking because you can tap the brake pedal and the RPMs don't change.

About 2 weeks ago after messing with a bunch of wires under the dash while fixing my brake/backup light problem... it started working. Now it did get a lot cooler around then. It wasn't driven for about 2 weeks. It went back to lockup shifts I listed above.

It then went to only locking up when the truck was "cold" It would cycle a couple of times after shifting into 3 and 4 then smooth out. It would stop after braking when warmed up or if I had to engage kick down. It hasn't come back since about a week ago. There is no slipping, it shifts real good. I don't go faster than about 55-60 since 55 is the highest speed limit around here. I don't know if lockup occurs at a higher speed when it does this.

I confirmed that the brake switch is functioning. the vacuum switch is hooked to full manifold. the TV cable is adjusted just fine. Also, this truck has a swapped in 350 from 1970.. the LE9 305 is long gone. The ESC is still there but every wire is cut at firewall. I don't know if this truck was EGR bleed transmission or not. The RPO is MX0 with K34 cruise control. Vacuum diagram code is DFH which I can't find anywhere online...

Does that sound like a bad 4th gear pressure switch? Converter going out? Vacuum switch is failing? any help is appreciated.

 

[Boone83K10]

I got up under the truck dash again.

I have this switch

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It has an ORANGE wire that is hot all times. It has a WHITE wire that is hot when the brake is pressed. This plug is closest to the plunger. (I thought the brake plug was suppose to be furthest away from plunger?)

I also have a plug that has two GRAY wires into one side of the plug. There is a GRAY/BLACK wire into the other side of the plug. GRAY/BLACK is hot all the time. The two GRAY wires are HOT when the brake pedal is at rest. This plug is furthest away from plunger.

I also have this switch

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It has a LIGHT BLUE and a BROWN wire running into the plug. It also has a vacuum hose out the back. This switch is to the right of the brake switch.


On the other side of the column I have this white plug.

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It has a LIGHT BLUE wire, 2 WHITE wires, BROWN wire and 2 LIGHT GREEN wires.

 

[Boone83K10]

After studying the wiring diagrams all day (at work :LOL I am wondering if things are plugged in wrong.

this pic shows the LT BLU and BROWN wiring on the same switch with the brakes. This pic is in a thread on this forum. That clear plug is on the other switch with the red plunger in my truck.

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Wiring diagrams show LT BLU and BROWN to brake switch with reference to stop lamp. It shows 2 GRAY and 1 GRAY/BLK to "brake switch". I assume that this means the release switch with the red plunger and not the black switch since the diagram says REF STOP LAMP for the LT BLUE and BROWN.

Do you think it will make a difference if I switch them around. Could I have switched them around when I tried to take off the cruise or maybe it got messed up when PO made the engine swap?

 

[Boone83K10]

After reading over my posts, I noticed and remembered that I did not test the LT BLUE and BROWN wires. Gave them a test and both were hot with pedal pressed and at rest. So the switch must not be doing its job. BTW, they plugs don't interchange.

I took off the switch and you can open it up. The contacts inside were not touching (just barely apart) when the plunger was pressed in. This probably explained why it worked when it was cold outside. metal would shrink and they would touch, then go away when I would heat up the inside of the cab.

I cleaned up the contacts, bent them some and put it back in the truck. I cleaned the brake switch too while I was at it. I drove around for about 15 minutes and it works like a charm. WOOHOO...

and since no one responded to this...yay to me for figuring it out on my own.

 

[austinado16]

Wow man, impressive job in diagnostics, obtaining and reading the wiring diagrams, and sorting it all out. Seriously, you've got skills.

Can you imagine the bill had you dropped it off at a shop? Whatcha gonna do with the money you saved?

 

[Boone83K10]

I try to never take my vehicles to the shop. Usually the simplest answer is always the right one. I spent it on more parts lol.

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[MrMarty51]

Thank You for the updates as You went along with the diagnostics and the pics. too.

 

[89Suburban]

Good job and thanks for reporting everything. Sorry for the lack of quick help. Reps added.

 

[Boone83K10]

Hey thanks. You guys help a lot.

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[HotRodPC]

Great Job Dude !!! Kudos and Rep Given !!! Sorry I missed it. Been so damn busy with the new job, my own drama and now my daughter has major drama going thru a bad divorce, I'm doing good to keep up with subscribed posts, let alone any new posts.

Honestly, I wasn't aware of that relay though. I used to the Vac Switch or the ECM lock up. So I'll be looking all this over and seeing what I can make of it and learn something myself.

Usually when you see a little box you speak of, and it has contacts in it that barely touch, that's a relay switch of some sort. Usually operated by powered magnetism aka electromagnet to draw the contacts together when they get power, and shut the magnets off which lets the contacts separate. Of course are different type relays too.

 

[89Suburban]

My lockup has been acting up lately. Like slipping, and randomly skipping and making the truck shudder at a certain speed sometimes. It is not the transmission clutches, it is definitely the lockup clutch in the converter acting up. Only started doing it during this 6 degrees ********.

 

[HotRodPC]

My lockup has been acting up lately. Like slipping, and randomly skipping and making the truck shudder at a certain speed sometimes. It is not the transmission clutches, it is definitely the lockup clutch in the converter acting up. Only started doing it during this 6 degrees ********.

Might be the converter clutch itself inside the Torque Converter.

 

[89Suburban]

Might be the converter clutch itself inside the Torque Converter.

That's what it feels like. Got to do some homework on the topic.

Not trying to hi-jack Boone83K10, just trying to keep the related topic convo together so it's easier to find.

 

[v2500burb]

Thoughts on a 700r4 in my 3/4ton Burb???
It has a th400 now
The lack of over drive kills me...
No HWY speeds


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[bigcountryguy19]

Might be the converter clutch itself inside the Torque Converter.

I agree with hot rod, I had this problem in a truck I had, I replaced the converter and the O ring on the imput snout and it fixed the problem


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