Another 700R4 question

[Bloodhound1981]

Yes, another 700R4 question.

As I have worked out nearly all the bugs in my truck since finishing it, this one now pops up not too long ago. In 4th gear, in lockup cruising on the highway, I occasionally get this thing where the best way to describe it is it feels like the transmission is popping out of gear for half a second. Yesterday I went on the highway for a half hour with no issues. Then on the ride home, it happened about 4 times. Just cruising along and then this thing happens a few different times. It never happens in 3rd or any other time. It is a 1989 Corvette 700R4. About 30k miles on the tranny (never rebuilt). Precision Industries Vigilante converter with about 3.500 miles on it.

I had a previous 700R4 that lost 4th gear at some point, I'm wondering if that is where this is headed. I had the pan off to fix a leak after this started and the fluid and pan looked all good. I of course will tag the guru @NickTransmissions for any advice as well.

 

[Ricko1966]

How is your TV cable set up,factory carb? Factory brackets? Tested pressures. TV cable is NO1 killer of 700r4s and 4th gear is always what goes first.

 

[Bloodhound1981]

How is your TV cable set up,factory carb? Factory brackets? Tested pressures. TV cable is NO1 killer of 700r4s and 4th gear is always what goes first.

I have an aftermarket fuel injection intake that is designed for 700R4 TV cable geometry. I tested the line pressure on initial setup 3,500 miles ago, all was good. It still shifts perfectly/appropriately in all gears. Just this popping out of gear feeling thing. And it's not consistent which is equally frustrating. Might go for a 40 min 80mph highway ride with no issues, then the next time it happens several times.

 

[Bloodhound1981]

I figured I'd go for the ChatGPT diagnosis.....

Worn or sticking TCC Apply Valve (VERY common 700R4 problem)​

This is the #1 cause of violent lockup dropouts.

Inside the pump, the TCC regulator valve bore wears.
When it suddenly vents fluid, the converter clutch drops out instantly, not gradually.

Symptoms exactly match what you’re describing:

• Only in 4th
• Only in lockup
• Intermittent
• Feel like the trans “mis-shifts” for half a second
• Pan looks clean
• No codes
• Randomly worse some days, fine other days

Fix:
Install the Sonnax TCC Regulator Valve 77805E-K.
This is the cure for 90% of “violent dropouts.”
It requires removing the pump cover or using a reamer kit.
Most shops can do this with the trans in the truck.

 

[Ricko1966]

I figured I'd go for the ChatGPT diagnosis.....

Worn or sticking TCC Apply Valve (VERY common 700R4 problem)​

This is the #1 cause of violent lockup dropouts.

Inside the pump, the TCC regulator valve bore wears.
When it suddenly vents fluid, the converter clutch drops out instantly, not gradually.

Symptoms exactly match what you’re describing:

• Only in 4th
• Only in lockup
• Intermittent
• Feel like the trans “mis-shifts” for half a second
• Pan looks clean
• No codes
• Randomly worse some days, fine other days

Fix:
Install the Sonnax TCC Regulator Valve 77805E-K.
This is the cure for 90% of “violent dropouts.”
It requires removing the pump cover or using a reamer kit.
Most shops can do this with the trans in the truck.

You need to tag @NickTransmissions

 

[Bloodhound1981]

You need to tag @NickTransmissions

I did in my first post. I'm sure he's a very busy guy. Maybe if I say it 3 times like Beetlejuice he will appear.

@NickTransmissions @NickTransmissions @NickTransmissions

 

[gmbellew]

My TCC on the 90 burb is electronic lockup and had some issues like that bc of a cracked TCC solenoid. Serviceable with a pan drop on mine. It also caused some idle jumpiness after a highway run bc it also wouldn’t fully unlock.

 

[Trucksareforwork]

I wonder if this is related to gearing and your vacuum kick down switch.

I have a 700R4 in my 85. It’s behind a 305 that is reliable but not strong, and it has the added indignity of 2.73 gears in the rear end.

If I’m in OD on the gear selector, and get into a sustained uphill slope and I’m easy on the pedal, the trans will jump between 4 and 3 often in a quick rat a tat tat as it hunts for the right gear. My truck has a close to stock vacuum hose routing, which I believe has a delay valve to the trans kick down switch…I have wondered if that delay is the issue.

My solution is to just drive most of the time in “D” not OD, which keeps the engine in its power band under 60 mph.

Your comment that it didn’t happen one direction but did happen on the way home is what struck me. I have a road to my house that has a 55 mph hill where I get this 3-4 hunt if I’m in OD, but it’s only in one direction (of course, the uphill direction).

 

[NickTransmissions]

Yes, another 700R4 question.

As I have worked out nearly all the bugs in my truck since finishing it, this one now pops up not too long ago. In 4th gear, in lockup cruising on the highway, I occasionally get this thing where the best way to describe it is it feels like the transmission is popping out of gear for half a second. Yesterday I went on the highway for a half hour with no issues. Then on the ride home, it happened about 4 times. Just cruising along and then this thing happens a few different times. It never happens in 3rd or any other time. It is a 1989 Corvette 700R4. About 30k miles on the tranny (never rebuilt). Precision Industries Vigilante converter with about 3.500 miles on it.

I had a previous 700R4 that lost 4th gear at some point, I'm wondering if that is where this is headed. I had the pan off to fix a leak after this started and the fluid and pan looked all good. I of course will tag the guru @NickTransmissions for any advice as well.

Likely 3-4 clutch pack going out. Falling out of 4th is a common initial symptom. Falling out of TCC lock up is a different story and it’s usually caused by failing TCC solenoid but pump, valve body or converter are also suspects.

 

[Bloodhound1981]

Likely 3-4 clutch pack going out. Falling out of 4th is a common initial symptom. Falling out of TCC lock up is a different story and it’s usually caused by failing TCC solenoid but pump, valve body or converter are also suspects.

This is a violent quick thing, for falling out of fourth would it be more of a slipping?