Is there a sure fire way to tell if the trans is going into lock up?

Is there a sure fire way to tell if the trans is going into lock up? I’m on my third Roadmaster and it gets a bit less than desired mpg. My previous cars were a 91 and 94, this is a 95. The trans going into lock up was obvious on the 94, I can’t tell if it even is on this 95. I read that for model year 95 they made lock up more smooth, but I don’t know. I bring this up because on my 94 I could easily feel when it would go into lock up, and I barely notice any change on this car when I’m at cruising speed and I apply the brakes or throttle/ I never notice the sort of shifting feeling you get when it would lock up on my older Roadmaster. The car shifts great, and has plenty of power. The only other thing is that it is slow to shift into reverse.

Is it possible that I could get the air con unit to tell me if it is going into lock up? Or a scan tool? At this point I’m thinking that for some reason the car is not going into trans lock up which is why I’m getting a little worse mpg. Thanks for any help in advance! These are the only cars I’ve ever owned, I fell in love with my first one, so I’m keen to keep them running in tip top shape.

If you can probe the wire that the computer uses to lock the TC, you can measure the voltage, or existence of a ground. That would tell you if the system is working, but you can not determine if the converter is actually locking unless you can read an RPM drop. A tach (in the HVAC control) can give you an RPM readout. During acceleration you can read the RPM, then when you reach sustained speed for a short period, it should read a lower figure if the lockup works.

"" it should read a lower figure if the lockup works.""

Also, if the convertor is locked, the RPM will not flare if the gas is "blipped" under constant speed.

Drive at 50-60mph on flat ground. Note RPM. Stay at the exact speed, with your right foot on the gas. Use left foot, apply brake very gently while staying on the gas. RPM go up? Lock up working. No change? Lock up not working.

I should have thought to just read the tach in the air con unit. I’ll check and come back. Thanks.

In case it's busted...it's probably a worn valve in the valvebody. '95's and '96s will eventually wear out the TCC regulator valve. Sonnax sells a kit to turn it into the '94 style on-off, or you can buy a reamer and a sleeved valve to restore original operation. I had absolutely no lockup on my dad's '96 SS and with that valve and reamer, it now locks up like factory. The reamer isn't cheap but you can always sell it on ebay after you're done.

I don’t suppose the reaming is something you can donjust by dropping the pan? I don’t want to have to drop the tranny or torque converter...

Check this video:

https://www.youtube.com/watch?v=YK46XJbAJqg

Super helpful; thank you!

If you watch the tachometer in the video, the RPMs dropped about 500 when the TC locked up.

I know I'm off topic at this point - hopefully you've been able to test and find that your TCC is indeed locking up, and you can ignore the rest of what I wrote below. Otherwise...

Yes, you can ream it out just by dropping the pan and valvebody.  You do not have to remove the transmission.  The sonnax kit I used was 77754-04K.  Do be sure to use cutting fluid if you do it; ATF is not cutting fluid.

I would stay away from that Teckpak/Fitzall A74741Q valve - it's not a valve it all, it just allows full line pressure into the converter, which will balloon it. GM setup the converter to never see more than 60-80psi;  4L60E line pressure can go up to 140psi during lockup.  You will hurt your engine's thrust bearing and possibly break the transmission pump if you balloon the converter like that.

You can read more about 4L60E TCC modifications here..

But if you have the valvebody out, now's a great time to add the 4L60E-HP-01 shift kit, the heavy duty 2-3 shift valve, the o-ringed end plugs, and pinless accumulator pistons.

So I was able to determine with pretty high certainty that the torque converter is locking up fine by looking at the tach on the air con. I’m constantly baffled that they went from having a tech, volt meter, oil pressure, etc on the dash to just a speedo and coolant temp. I really miss having a tach.

Contrary to what people have told me though, it seems to stay locked up pretty well. If I depress the brake, it doesn’t jump in Rpms like it’s unlocking, though increasing throttle when going uphill does keep the rpms steady when locked as expected.

All of the silencing components on the engine make it a little too quiet for me to tell the difference between the rpms. And man, if our speed limits were lower like they were when the car was made it would get much better mpg I think based on the rpms it sits at locked when you’re going 65 (it drops from like 2000 to 1400) compared to 70-75 (where it goes from 2200 to 1900 or so).

Thanks for the help. Pretty confident everything is working as it should.

Also, tangentially related story. I was having some sort of sluggish shifts into second especially when the car was cold. Gave her the old Italian tune up and every shift seems tonjust glide right in like the trans is new. Must have thrown off some shavings in the gear teeth or something. This was a few weeks ago before I started wondering about the lock up issue. The car seemed to like it. Anyways, a trans fluid change is in order, but besides that I’m satisfied.

I learned A LOT about torque converters and the 4L60E and automatic transmissions in general through this experience and my research and you fine folks.

Thanks again.

Quote :

was having some sort of sluggish shifts into second especially when the car was cold.

Go back into the data on the HVAC head. With the car up to operating temp, let it idle, and keep watching the coolant temp. You will actually see the thermostat open and close. If the thermostat is sticking open a tiny bit, the trans fluid will be too cold on highway driving in cold weather, and that causes delayed/weird shifting issues. The coolant will get hot with the car just sitting there, but will be over cooled when moving and the stat not closing all the way. You'll see the temp drop, and not come back up to 200ish.