Hot Rods 700R4 w/o lockup when warmed up.

Hey there, the 700R4 in my avatar recently stopped locking up once the car is warmed up (say 10-15 miles down the road). It’s worked fine for about 10,000 miles. It’s has a TCI lockup kit, normally locks up as it shifts into 4th at about 40 mph under light load, and has 12-v power from the oil pressure switch feeding power to an electric fuel pump (it was nearby and seemed like a nice idea). Vacuum is fed off the distributor advance line.

Again - it still works great for the first few miles, but stops locking up when warmed up. I’m stumped.

Ideas?

Thanks,

John

 

the 700r4 does NOT have a vacuum modulator.

 

And if it did, it would be supplied with manifold vacuum, not ported advance vac.

 

First things first. Is the trans fluid level correct? Don't just assume, check it.

 

The TCI kit uses the vacuum signal to drop out of lockup under load (about 8 inches or so of vacuum).

John

 

I believe so, but will recheck to be certain. Report back tomorrow.

John

 

Warmed up, in park, engine idling............ but you already knew that.

 

AD -

Again..... Have you...maybe...called TCI ?
It's THEIR product ! Don't you think that just...maybe, they will have good questions to ask you, then provide the best answers ?

Mike

 

That's what I would be doing. They will be able to point you in the right direction.
Transmission diagnosis on the internet can be a costly exercise if the info you get is not correct........

 

Isn’t there a solenoid for lock up?

 

Not saying this is your problem but there is a small oring on the input shaft. That seals the fluid that’s pumped in the converter during lock up. If that orings gets damaged it can leak fluid and cause problems during lock up. But anything causing low pressure to the lock up section of the converter will cause problems.

 

solenoids go bad....recently discovered if the 700r4 doesn't lockup it will not self destruct...at least you can still drive ....what's the rpm difference at 65 mph ?

 

If I recall, my RPMs dropped 250 or so.

 

I'd suspect the vacuum switch has failed.

 

I would get a simple toggle switch and begin by wiring it across the vacuum switch connections. Once warmed up and it doesn't lockup just flip the switch and see if that locks it up. If it does then replace the vacuum switch. If it doesn't, then move the toggle temporarily to the hydraulic pressure switch and wire it in. Try it again, and if that locks it up then the pressure switch is the culprit and needs replacement.
I keep a test switch in my tool kit with long leads and alligator clips on the end just to use when testing switches and need to jumper them out to test.

 

A way of checking the vacuum switch is in the instruction sheet. (Looked it up, but have no personal experience with this kit)
Q: What do I do with the extra green wire on the external wiring harness?
A: As mentioned in Step 5 the green wire is a supplemental ground for the electric circuit and it is
strictly optional. By routing this through a dash mounted toggle switch you can override the fourth
clutch pressure switch and the vacuum switch and force lockup in second, third or fourth gears
manually. One example would be if you were towing in drive (third) and would like to utilize the
torque converter clutch. Remember that this is on the ground side of the circuit. Putting 12 volts on
this wire may short out your solenoid


https://www.tciauto.com/amfile/file/download/file/2299/product/40090/

 

Thanks for the suggestions.

I called TCI a couple weeks ago. Their tech said there must be a problem with my vacuum signal. He didn’t seem to consider it may be their switch, so there’s that. Checked vacuum lines, etc. and they’re fine.

Trans fluid was slightly over filled - I’ll address that this weekend and test before going further.

As some have suggested, I will then put in a switch to manually enable the lockup and see what that tells me.

I replaced the o-ring on the input shaft about 5,000 miles ago when I had the trans out to upgrade the converter for a higher stall (which was built for me and has had 5,000-ish miles of trouble-free operation since).

I’ll report back in a few days.

Thanks again,

John

 

Does the new higher stall converter have lockup functionality?

My 700R4 has a converter that does not have the lockup function.

 

Yup. Been great for about 5,000 miles.

More info from here by the end of the weekend….

John

 

I had exactly the same issue sometime back. But I'm not saying that what my problem was is the same as yours. It shifted fine as long as it's still cool.. The warmer it got the higher the shift point to fourth gear. Whenever it completely warmed up I had no fourth gear nor lockup. After all kinds of BS related to trying to keep the transmission cool I decided to check the governor. Strangely enough The problem was not related to fluid viscosity or anything in the valve body. Apparently due to a manufacturing defect and the very close tolerances of the plunger/slide valve inside the governor due to a difference in expansion rates of the two parts, the inside plunger would bind before closing off the last port that works against line pressure, which is controlled by the TV control valve. A new governor completely fixed the issue...

To check it, however, You have to cut the ends of the pivot points for the weights and remove the weights. You may not be able to see it if you just depend on holding the governor with the weights at the bottom to look at the clearance on the ports. I believe you can purchase the tiny long pivot pin replacements if you find that it's not the governor. On the other hand if you find it's the same issue I had then a new governor is in order...

Here is a short video of what I'm talking about.
https://www.49fordcoupe.com/The-700R4-Chapter-2/i-BM2mTVb/A

 

On the other hand if you are sure that you're getting into 4th but it won't lock up then I would be highly suspicious of something electrical. The only time that the 12 volt electrical part of the transmission comes into play is after it goes into fourth gear, the fourth gear pressure switch closes and puts power to the hydraulic solenoid which then opens the port to allow hydraulic pressure to apply to the TC clutch.

However, generally speaking, temperature doesn't necessarily affect electrical circuits in this temperature range.

Are you absolutely certain that you are shifting into fourth, and not getting lock up? Or is it possible that you're not getting into fourth?

 

Nobody said a word about a modulator. Some recommended control circuits have a vacuum switch to drop out lock up when the accelerator is pushed.

 

The OP already said that it's been working fine until recently. Pay attention.

 

That is only if the transmission has a two-pole fourth gear pressure switch. Some transmissions had two pole and some had single pole. The single pole versions grounded on the switch base.

 

Didn't some of these valve body's have a temperature switch that would keep lockup from happening tell the transmission got to temp?

 

Yes, the thermostat locks out lockup until the fluid reaches the set point, but that isn't the symptom here.

 

Then if the wire operating the lock up is just controlled from the outside it should be easy enough to test it from the outside.

 

There are usually two wires with an aftermarket lockup kit. Switched power and ground. You can externally trigger the lockup solenoid easily with these wires to check it. If this fails, it means the problem is inside the transmission, most likely a faulty tcc (torque converter clutch) solenoid. It could also be worse. It could be that the tcc circuit is not holding fluid pressure due to worn seals or valves.

Start with the easy stuff, one thing at a time. Hopefully you will fix the problem before needing a trans builder.

 

I would bypass all the pressure switches and vacuum switches and just run a toggle switch. Flip it on when you want lockup. If it still doesn’t work it’s either the solenoid, converter lockup valve or the converter/input o ring. It’s a process of elimination. Some times they can be tricky to figure out.

 

I am not sure what you mean by "pressure switches", but if you are talking about the pressure solenoids, they are in the valve body and you would have to drop the fluid and pan to be able to bypass them. If you are going to that much trouble just replace them (they are not that expensive), new filter and fluid, stitch it up and see how it goes.
I would be trying the other external stuff before getting to this point.