1987 V10 700r4 locks up immediately after 1-2 shift

[Gander]

So I got the truck a couple weeks ago. Been working on it since then. Had it at the exhaust shop on the rack yesterday and noticed the tcc plug on the trans was unplugged. It’s been unplugged a long time, connector is cooked. Got a new connector on the way and I’ll wire it in as soon as it gets here. Anyway here’s the problem.

I plugged the connector in and took the truck for a drive. With the TCC connected, it locks up immediately after the 1-2 shift. I can hit the brake and it’ll disconnect and I can punch the throttle and it’ll disconnect but then it’ll just lock up again.

Looking online, it seems like there are a couple easy things I can try, like changing out the TCC solenoid, checking the TCC solenoid screen, changing the pressure switch. There’s so many variations of this trans though. It’s confusing me on which parts I have to order. Is there one pressure switch in the pan to change or 2 or 3? How to know I’m ordering the right TCC solenoid? I dropped the pan on this truck the day after I got it and changed the filter, kicking myself over not looking up at the TCC plug and seeing it was missing, could have fixed this right then. Anyway, I’d like to order parts and have everything here before I drop the pan again and I’m going to stay driving around town while I’ve got the TCC unplugged.

Anyway, thoughts? Am I on the right track replacing these parts? Speaking of that, got some part numbers for me? Numbers on the trans look like 6tkm-y-00891496-050-a but they’re a little hard to read. Anyway, let me know what yall think.

 

[89Suburban]

@NickTransmissions

 

[Gander]

@NickTransmissions

 

[Sad Sack]

What they said...^

 

[Gander]

So since I never heard back from @NickTransmissions maybe someone else can help me out?

I think I’ve got this figured out but of course won’t be sure until I replace parts. When I got the truck the electrical connector was unplugged from the transmission. I cleaned it and the socket on the trans as best I could and then plugged it in. Driving down the road it locks up immediately after the 1-2 shift: that leads me to believe that the pressure switch is bad and no big deal I can access that by pulling the pan BUT I need to know part numbers. I’m seeing some info that says there’s 1 pressure switch to change for 4th gear, others say 2 switches for 3rd and 4th. I’ve even seen one diagram online saying 4 pressure switches total plus of course any part numbers associated with any of this is discontinued. O’Reilly’s has a single switch available but is that what I need?

6tkm-y-00891496-050-a are the numbers on the trans. 4 wheel drive truck trans built in 1986 from what I can tell online which makes sense since my 1987 model year truck was built in Oct 1986. What I need is to know how many pressure switches I’ll need to replace and part numbers before I pull the pan off because once the pan is off I won’t be able to drive over and get any parts I don’t have from the parts house. Can anyone help me out here?

 

[Bloodhound1981]

So since I never heard back from @NickTransmissions maybe someone else can help me out?

I think I’ve got this figured out but of course won’t be sure until I replace parts. When I got the truck the electrical connector was unplugged from the transmission. I cleaned it and the socket on the trans as best I could and then plugged it in. Driving down the road it locks up immediately after the 1-2 shift: that leads me to believe that the pressure switch is bad and no big deal I can access that by pulling the pan BUT I need to know part numbers. I’m seeing some info that says there’s 1 pressure switch to change for 4th gear, others say 2 switches for 3rd and 4th. I’ve even seen one diagram online saying 4 pressure switches total plus of course any part numbers associated with any of this is discontinued. O’Reilly’s has a single switch available but is that what I need?

6tkm-y-00891496-050-a are the numbers on the trans. 4 wheel drive truck trans built in 1986 from what I can tell online which makes sense since my 1987 model year truck was built in Oct 1986. What I need is to know how many pressure switches I’ll need to replace and part numbers before I pull the pan off because once the pan is off I won’t be able to drive over and get any parts I don’t have from the parts house. Can anyone help me out here?

You need this manual. http://bee.mif.pg.gda.pl/ciasteczkowypotwor/#samochody/Chevrolet/thm-700-r4-4l60.pdf

 

[NickTransmissions]

So since I never heard back from @NickTransmissions maybe someone else can help me out?

I think I’ve got this figured out but of course won’t be sure until I replace parts. When I got the truck the electrical connector was unplugged from the transmission. I cleaned it and the socket on the trans as best I could and then plugged it in. Driving down the road it locks up immediately after the 1-2 shift: that leads me to believe that the pressure switch is bad and no big deal I can access that by pulling the pan BUT I need to know part numbers. I’m seeing some info that says there’s 1 pressure switch to change for 4th gear, others say 2 switches for 3rd and 4th. I’ve even seen one diagram online saying 4 pressure switches total plus of course any part numbers associated with any of this is discontinued. O’Reilly’s has a single switch available but is that what I need?

6tkm-y-00891496-050-a are the numbers on the trans. 4 wheel drive truck trans built in 1986 from what I can tell online which makes sense since my 1987 model year truck was built in Oct 1986. What I need is to know how many pressure switches I’ll need to replace and part numbers before I pull the pan off because once the pan is off I won’t be able to drive over and get any parts I don’t have from the parts house. Can anyone help me out here?

Sorry, didn't see your initial posts. 82-86 did have a 2nd-4th TCC apply strategy however in 1987, they went from locking the TC in 2nd gear (some models) to only have it lock up in third and 4th. So it shouldn't be locking immediately upon shifting from 1-2. From what I can recall, everything is electro-mechanical in those earlier years so a bad pressure switch can certainly be a possibility. Here's a valve body diagram and legend which shows all the pressure switches found on your valve body. I believe you should only have the 3rd and 4th clutch pressure switch but there were a variety of configurations in 1987 as that was a big change-over year for the 700r4s in many respects.

In your case, I would purchase all of the pressure switches that the valve body takes and simply return the ones you don't need. This way, you're not stuck. Also grab a new filter and pan gasket (no rubber or cork) as well.

 

[Gander]

So I figure I’d let yall know my progress on this. Before I dropped the pan again and started replacing stuff I spliced in a new connector and did my best to clean out the TCC plug socket on the trans. Plugged it in and it works as it should. Locks up in 3rd, unlocks between 3-4 shift, locks in 4th, unlocks for downshift, unlocks when brakes applied, unlocks when I punch the gas.

My problem is it’s annoying as hell locking up in 3rd and 4th. I’m only around 30-35 mph in 3rd and 40-45 when going into 4th and I don’t have a tach but it sure feels like I’m lugging the motor doing this. I’d like to have it locked up in 4th on the highway but not around town. I’m thinking about wiring up a switch on the dash for the TCC. Is it as simple as just installing a switch on the brake switch since pressing the brake pedal unlocks TCC? There’s so much stuff online about this and kits sold and whatnot that I’m wondering if it can be as simple as wiring in a toggle switch off the brake switch. Anyway, let me know!

 

[gmbellew]

keep it in D around town. being locked up in 3rd at 40mph is a lot different than being locked up in 4th at 40mph regarding engine RPM and lugging. the only other option is an override switch or if it is like my 90, adjusting the lock speeds on the PROM via a tuner

 

[Ricko1966]

Why not just replace the 4th gear pressure switch and tcc solenoid and wire it for 4th gear only lockup?

 

[Gander]

Sorry, didn't see your initial posts. 82-86 did have a 2nd-4th TCC apply strategy however in 1987, they went from locking the TC in 2nd gear (some models) to only have it lock up in third and 4th. So it shouldn't be locking immediately upon shifting from 1-2. From what I can recall, everything is electro-mechanical in those earlier years so a bad pressure switch can certainly be a possibility. Here's a valve body diagram and legend which shows all the pressure switches found on your valve body. I believe you should only have the 3rd and 4th clutch pressure switch but there were a variety of configurations in 1987 as that was a big change-over year for the 700r4s in many respects.

In your case, I would purchase all of the pressure switches that the valve body takes and simply return the ones you don't need. This way, you're not stuck. Also grab a new filter and pan gasket (no rubber or cork) as well.

just need an answer. I have a 1987 truck, 350 TBI, built Oct 86. Trans is built in 86 as well. Numbers on the trans are 6tkm-y-00891496-050-a

Right now the truck has lockup in 3rd and 4th gear which is pretty annoying since this ends up with me lugging around all day in 3rd or 4th around town locked up. I want to eliminate 3rd gear lockup and keep it locking up in 4th when the ECM tells it to, but I can’t figure out how to wire this or which pressure switch to use. Right now there are 3 2-prong pressure switches, my understanding is that there’s a 3rd gear lockup switch, a 3-4 switch to unlock and then quickly lock again during up shifts or downshifts between 3 & 4, and a 4th gear lockup switch. What happens if I just unplug the 3rd gear lockup switch and 3-4 switch? Can I just eliminate them altogether? Do I need a new 2 prong pressure switches for 4th? If so what is the part number for that switch because I can’t find one at the normal auto parts store. How do I wire this up? Remember, this is a 350tbi truck so there’s an ECM telling the trans when to lock up. Answers to these questions please? I’m tired of dropping this pan and putting it back and refilling it and not being able to solve this. Already have replaced the male and female ends of the case plug, the O-ring was leaking, and installed a pan with a magnetic drain plug last time I was in there. I want to pull this pan one more time and solve this lockup thing and put it back together and forget about it so I need to know beforehand exactly what I’ll need to do it so I have all the parts here because once I take that pan off I’m walking until I get it back on and full of fluid. Anyway, please let me know and thanks!

 

[Ricko1966]

Why not just replace the 4th gear pressure switch and tcc solenoid and wire it for 4th gear only lockup?

This ^^^ use only a 4th gear pressure switch to control the tcc solenoid that's it. 12v in to pressure switch 12v out from pressure switch to solenoid. Other side of solenoid grounded. Or 12v in to solenoid solenoid to pressure switch pressure switch to ground. Depends on if you have a 2 prong normally open or a 1 prong normally open with switch casing being the ground. And no need for a brake interupt switch you aren't going to stop in 4th gear.