87 700r4 lock up issues

[ClarkUsa1]

Alright here it goes, I bought an 87 r10 with the trans slipping due to trans Cooler in radiator leaking and filling trans with coolant. My plans were to rebuild this trans but case was busted. I got a known good trans from an 86. Trans shifts fine,but as soon as it goes to drive the torque converter locks up,then onto overdrive.. but no lock up in overdrive. I can tap the brake and unlock converter when it’s in drive.it shifts like this every time regardless of temp.my cruse doesn’t work either and I have no check engine light. Any help would be greatly appreciated

 

[Vbb199]

Does your speedometer work correctly?

 

[ClarkUsa1]

Does your speedometer work correctly?

Yes,it works fine.it maybe 10mph fast.im going to change speedometer gears this week

 

[84 M1008]

I went through this nonsense with a stock 700R4 in my military K30 that the previous owner swapped into it. The 6.2 quickly ate that transmission alive. I put the hated Monster 700R4 in it and deleted the controller. It would randomly hunt up and down, upshifting and downshifting, and yes the throttle valve cable was adjusted perfectly. I wired an old school dimmer switch on the floor to control lockup and never had a problem with it afterwards.

 

[gmbellew]

Yes,it works fine.it maybe 10mph fast.im going to change speedometer gears this week

on my 90, the speedometer reading factors into the lockup or shifts somehow. because when my speedo was off, the truck didn't behave right on the highway. it could just be a VSS thing, though....not sure.

 

[Vbb199]

on my 90, the speedometer reading factors into the lockup or shifts somehow. because when my speedo was off, the truck didn't behave right on the highway. it could just be a VSS thing, though....not sure.

90 and 91 use a VSS with a DRAC module, all electric.

All the other 700 driven trucks use a little module behind the instrument cluster for lockup, shifting and such.

 

[Vbb199]

When i regeared my rear end to 4.10 the trans was doing weird **** also and lockup was way off.

Correct the speedo gears.

 

[Matt69olds]

I don’t have a manual handy, so I’m going by memory with this.

Some transmissions use a 3rd and 4th gear pressure switch. If I remember correctly, the 700 transmission is hydraulically capable of locking the converter in every gear except first. That means the computer depends on the correct sensor signals to command converter lockup function.

Where am I going with this you ask??? If your transmission has a 3rd and 4th gear switch, the computer may be seeing a signal for 3rd gear (allowing lockup) but no 4th gear signal. Since it has no 4th gear signal, the PCM may be commanding to converter to unlock.

Put a test light in pin F of the CCC connector. That’s the test pin for the converter clutch. The test light should be on with the key in the run position. Push the brake, the light should go out. Once the PCM provides the ground to engage the clutch, the light should go off. If it comes back on once the trans shifts into 4th gear, you know it’s the PCM commanding the clutch to release. https://atracom.blob.core.windows.net/gears/2015/2015-03/2015_3_32.pdf

here is a diagram I found for a mid 80s F body. You can see power goes to the solenoid (and the TCC brake switch)on the pink wire, come out on the tan/black, and goes to pin F of the data connector and the PCM. The diagram doesn’t show a 3rd gear switch, but I’m almost positive some 700 used them. Depending on what the transmission came out of, you may just need to move a couple pins around on the connector.

 

[Matt69olds]

Crap, I just noticed I posted the wrong link. Try this one!

You must be registered for see images attach

 

[Bextreme04]

I think both the cruise control and TCC lockup use the optical VSS signal off the back of the speedometer housing. I would also check to see if that is working. It might be why your cruise doesn’t work.

 

[Matt69olds]

The speed sensor is a input to the PCM. If the PCM doesn’t know how fast the truck is going, the converter won’t lock. The fact the converter will lock in 3rd gear suggests the pcm is getting the signals it needs and likes, until the trans shifts into 4th gear.

 

[ClarkUsa1]

I put my original speedometer gears in today and adjusted tv cable properly,it still does same thing.conveter only locks in 3rd. I’m leaning toward the ecm

 

[Itali83]

I put my original speedometer gears in today and adjusted tv cable properly,it still does same thing.conveter only locks in 3rd. I’m leaning toward the ecm

I would lean AWAY from the ecm. If the ecm can lock the converter in 3rd, then you need to find out why it’s being TOLD to unlock in 4th. The fact that it locks up tells you the ecm is good.

Ben

 

[ClarkUsa1]

I would lean AWAY from the ecm. If the ecm can lock the converter in 3rd, then you need to find out why it’s being TOLD to unlock in 4th. The fact that it locks up tells you the ecm is good.

Ben

Should the converter lock in 3rd every time? When I take off from dead stop and mash on it,it even locks then

 

[Itali83]

Should the converter lock in 3rd every time? When I take off from dead stop and mash on it,it even locks then

the converter shouldn’t lock at wide open throttle. I guess I’d have to drive it to see exactly what it’s doing. Does it hit 3rd gear and instantly lock up? No matter what throttle position? And instantly unlock when it shifts into overdrive even if it was locked all the way through 3rd? I know for a fact that the 700’s are physically able to lock the converter in all gears except reverse and first. I have a manual lockup switch on my truck and sometimes I forget it and it locks in 2nd. It just sounds like you’ve got a bad 4th gear pressure switch or wiring in the trans pan that once it shifts to 4th, the pressure switch isn’t telling the ecm to stay locked. Even though it was locked in 3rd. Hope this helps.
Ben