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700R4 TCC locking up early

anwat

anwat

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It would seem I have an issue with my Bowtie Overdrives 700R4. I've noticed I don't seem to get to enjoy a 4th or OD gear. When it shifts into 4th, it immediately locks the TCC. That's not the way it's supposed to work, is it? In 3rd, I will get to around the 1950 rpm range, it will shift into OD, and the converter will lock, which is dropping the tach down to about 1100. Completely takes me out of the powerband of the engine. I feel like if I could accelerate a little more before the TCC locks, I would be in a better place...I never get to use 4th gear, which I know is OD, but still, seems like I should get to spend a little time in 4th before it locks up. There's no ECM control on this trans, it's all self contained with the exception of a manual lockup switch. I've asked the local tranny shop guys about it, but I feel like I probably know more than they do from the blank stares I get when I explain the problem. Is this normal, and if not, can anything delay that lockup a little until the engine gets into a little higher rpm range?
 
4th gear (OD) is still 4th gear even with the converter locked. The converter being locked keeps fluid temps down and puts as much power as a slush box transmission can to the ground.

Your low RPM issue is a function of the gears in the axle. If you want to run in OD at a higher RPM, axle gear changes are needed.
 
I don't remember one locking up immediately like that when they were stock. But it seems like when the pressures get bumped up, which most builders do anymore, then lock-up happens faster. The 700R4 needs to be locked in OD for proper oil cooling and flow, but it doesn't have to happen immediately. Several seconds of delay is fine. But mine usually locks in less than 2 seconds.
Can you adjust the TV cable more? I usually have no more pull available at WOT on mine. Even if you only have a tiny bit left at WOT, maybe getting that last bit would help delay the upshift and lock at part throttle.
I knew a truck that had 2:73 gears in a K10, with a 700R4. It was a dog with a 305. But I would think that you have some room with the axle ratio. I can't remember how much input the governor weights and springs have at lower throttle input. Possibly not enough to make a difference.
I would think that you should be able to help it out a little, but I don't know how much you may have to change.
Maybe BTO can give you some help?
 
I have noticed that it's holding on to 1st a little longer than it used to, especially when it's cold. Maybe that cable has stretched a little, I'll check that. But from what you're both saying, it sounds like it's supposed to lock up right after the shift to 4th. It seems to be quicker now, like I can't even tell it's two drops in rpm, and before it was two or three seconds after it shifted. I was thinking it should run all the way up to about 1800 or so before the TCC locked, kind of like it does with all the other gears. I'll try tightening up the cable a touch and see what that gets...and a call to BTO is probably the best insurance.
Sounds like maybe I should just keep it in 3rd in stop and go driving and enjoy the taller gearing on the highway since it's surely saving me a little gas there. Part of it is me not being used to a big block, too...Not a lot of room to work with there, seems like idle is at 800-900 and I've never seen it about 2400...takes some getting used to after years of smaller engines.....
 
ktmoutfront said:
4th gear (OD) is still 4th gear even with the converter locked. The converter being locked keeps fluid temps down and puts as much power as a slush box transmission can to the ground.

Your low RPM issue is a function of the gears in the axle. If you want to run in OD at a higher RPM, axle gear changes are needed.
Click to expand...
So, if I'm understanding right, the 4th or OD isn't really there to contribute to building speed, it's just there to keep things moving once you're up to speed? As in this is more of a three speed trans with OD? And the TCC should pretty much always be locked while in OD? There isn't a rpm/speed/load combination that would leave the trans in 4th without the converter locked?
 
anwat said:
So, if I'm understanding right, the 4th or OD isn't really there to contribute to building speed, it's just there to keep things moving once you're up to speed? As in this is more of a three speed trans with OD? And the TCC should pretty much always be locked while in OD? There isn't a rpm/speed/load combination that would leave the trans in 4th without the converter locked?
Click to expand...
Correct. I never put the 700r4 in OD around town. No need. 55mph and under does not need it. It will increase speed in OD with a light throttle peddle increase. Down shifting into 3rd should be common.

What gears and tire size are you running?
 
If it's holding 1st longer than it used to, then it should be slightly delayed with the other gears, but not greatly different.

There's no situation where it should be in OD without locking the convertor after a few seconds.

I use OD all the time at speeds below 55 mph, BUT my transmissions have enough pressure to keep the convertor locked at low RPM. I have 2 with toggle switches that allow me to lock in any gear except 1st, and both will hold lockup at 1100 rpm. But I only pull them down that low on flat stretches of road, and they will downshift with appropriate throttle input. It's part of why I can get 12 mpg in town with a carburetor in a big block K10.

If you just went to a big block and you never see more than 2400 rpm, then I would expect what you described. The smaller engine took more throttle to get the truck moving, once you get into the higher gears. The torque band is lower and it probably just pulls with less throttle.
 
I drive my Jeep around with the o.d. Button turned off everywhere. I only turn it on once I hit the freeway and am like 70 mph+. You should drive that 700r4 the same way.
 
I didn't like my 700r4 with 4.10's and 33"s. in over drive. Mine also locks in 4th as soon as it shifts. It will shift into 4th between 36 and 46 mph depending throttle pressure, with 4.88's, 33"s and a mouse motor.
 
@anwat I think that you should call BTO. They can tell you what the transmission will take. The engine will tell you what it likes.
I have never been nervous to use mine in OD, and my big block truck has almost 50K on it.
 
Man, the age of this group is showing. The BTO comment was understood by all of us....To answer the question, I'm running 4.56 gears with 37" tires, a 7.4 and a Atlas 2.

6872xtc said:
There's no situation where it should be in OD without locking the convertor after a few seconds.
Click to expand...
And there is the answer I was looking for. the 4th gear is pretty much just an OD, and the TCC locking is just a more efficient, cooler way for the 4th gear to do it's job. Nothing wrong, I just need to spend more time in 3rd when driving around in traffic.

And yes, it will hold 4th locked at 1100, but it doesn't like it...it wants to be around 1500, but if I'm gentle on the pedal, it will slowly pick up enough speed to where it sounds ok...but that's my error, I should be doing is keeping it in third until I have enough speed and space to allow it to go to OD and stay there comfortably.
The fine band you referred to also said that it should lock up within a few seconds at most. They, of course, told me I need to check my pressures and adjust the TV cable according to their specs. Which I did about a year ago. Then I left the gauge sitting on the tire, got distracted, and went to move the truck out of the driveway. You'd be surprised what a mess a couple quarts of trans fluid spraying all over the driveway and underside of your truck can make.

Thank you guys for the help...I guess I'm right where I'm supposed to be, I just need to learn to drive a little different and get used to the big block.
 
Sounds like you have a good plan and feel for it then.
Mine has 4:56 with just 35s, and the cam in mine dies off about 4700 rpm. So mine pulls ok at a lower speed and rpm, I am guessing. The PF4 on the small block in my Jimmy doesn't seem to have the same pull at lower rpms as it did with the TBI on a dual plane intake. So that factor may play into it as well.

Now I have to get that song you guys brought up, out of my head...
 
Wes Harden said:
time for 5.38s that get you to 1430ish at 42mph
Click to expand...
Leaving it in 3rd is way cheaper...I'm sticking with that plan....plus, now that I fixed that exhaust leak right in front of the o2 sensor, my mileage has improved significantly, so maybe I won't even notice the lack of OD around town.
 
I like the idea of driving it in 3rd, you are doing the trans no favors by lugging it down in lockup as you have been. It is common practice with builders to wire the trans through a 4th pressure switch to bring on the converter clutch with 4th gear as a means to keep the converter and lube charge oil cool to save the trans.
HGM sells a product called the Compushift Mini which allows the user to adjust the MPH in which lockup is applied. It will also release the clutch under hard throttle and also when the throttle is released, just like a vehicle with computer and TPS would.
 
Very nice...and they're right down the street. I'm going to go by and talk to them next week. While I don't like the idea of computer controls that can go haywire and strand me, this looks like something that if it broke, I could just take it off and go back to the mechanical control that was already there. Thanks for the idea!
 
anwat said:
Very nice...and they're right down the street. I'm going to go by and talk to them next week. While I don't like the idea of computer controls that can go haywire and strand me, this looks like something that if it broke, I could just take it off and go back to the mechanical control that was already there. Thanks for the idea!
Click to expand...
I'm interested as well, let us know what you think. I know my performance would be better if the converter didn't lock p right away.
 
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