Technical 700r4... Run Without Lockup?

I have a 700r4 in my '26 T coupe. The lockup is wired so that it automatically locks up as soon as the trans shifts into 4th gear. No brake switch involved. The 4th gear change and lockup is just too much of a gear change all at once. I'm not a big fan of the 700r4, but I use it for the OD, so I can run a decent rear gear, 3.89:1. Last night I installed a switch on the dash to interrupt the power going to lockup.
My question is, how does this affect the trans. Will I burn it up if I don't use lockup in 4th gear?
With lockup power on, when the trans shifts to 4th and lockup, I get a little shudder and hesitation.
This morning, I took it out for a test drive. With lockup powered down, the shift is just right and no shudder. To me it is a much better geared trans without the lockup. I would like to just leave lockup out of the picture until I hit highway speed, 60 or so. Is this going to hurt the trans?
Thanks for any insight!

 

Not using the TCC lockup will cause more heat in the trans fluid which can be a problem.
If you add a good trans fluid cooler it will help.
Just delaying lockup with your switch will have little negative effect....... as long as you don't forget altogether.
There was a good thread recently about using a time delay to postpone lockup after hitting 4th gear (OD).
From memory, it was posted by @rockable .

 

Yep, here it is.....
https://www.jalopyjournal.com/forum/threads/700r4-torque-converter-control-tcc.1321352/

 

I have a 700R4 installed with a non-lockup converter. The trans has functioned fine over 60k miles.

Yes, I would prefer the converter to lockup, but it was put together before I owned it.

 

I once had an OT vehicle with a TCI built 700. They gave me the option of an external manual switch to control the lockup converter. Worked great, so you should be fine.

 

The amount of heat it gets will depend on how much the converter is slipping. GM started using lockup converters in the late 70s when they went to really tall rearend gear ratios, such as 2.29, to get really low engine rpm, to save gas. Problem was a stock converter would slip a lot, so they introduced lockup. Then they went to overdrives in the early 80s, but still kept the rear gearing such the converter would slip a lot if they didn't have lockup.

Since you're running 3.89 gears, you might or might not have an issue with converter slip, but it depends what the stall speed of the converter is. You didn't say, so we can only guess.

So, what is the converter stall speed? And what RPM does the engine turn at highway speeds in OD?

 

YES...you can.
This is from Art Carr who builds T-200-4R's and T-700-R4's for a living.

BUT, you need a GOOD radiator (cooler, heat transfer device...whatever !)
A flat tube design like this -
The bigger the better.
https://www.summitracing.com/parts/hda-687

Mike

 

It is a Freakshow converter. I ordered a 2500 stall, but I'm not quite getting 2500 stall. Closer to 2000. Probably should have ordered a 3000 stall. At 60 mph, rpm is right at 2000.
The trans is not hooked to the lower radiator tank for cooling, but I have one of those tube type coolers on it. About 15" x 3" with a lot of fins running the length of the cooler. It gets plenty of air flow. It's been plumbed that way for almost 35K miles now.
Lockup gives about a 350 rpm drop from 4th gear.

 

Probably the best/easiest thing to do is to just use a toggle switch to engage lockup once you're up to speed, if you don't mind the extra work that involves (flipping a switch is a lot of work!)

 

Does your TCC circuit include a coolant temp switch and/or a manifold vacuum sensor? The convertor shouldn't lock up until the engine reaches operating temperature. The vacuum sensor should keep the converter from locking up under higher engine load, low vacuum conditions. It also sticks in the back of my head that some versions of the 700R4 locked the converter before shifting into overdrive instead of after.

An A/T fluid temp sensor probably isn't a bad idea.

 

Without the 4th gear lockup the 700R4 torque converter functions just like a TH400 or TH350. I have a couple friends whose cars have had a 700R4 without lockup wired for decades and never a problem. Both use auxiliary coolers to make sure the little extra heat doesn't do any harm.
I have lockup on mine, and don't find it objectionable at all. My rear gears are 3.73 and my '39 Chev weighs about 3500 lbs. and the SBC is 430HP. It shifts into 4th and locks up, and just has a solid shift, but not abusive at all.

 

It can be very bothersome. Driving a customer's O/T F-Bird I couldn't wait to get out of it

 

Do you know what year your 700r4 is ? 81-86 ( possibly to 89 ) you can control the lock up. Hydraulicly/mechanically in the valve body. Iirc.

Ideally you should have a delay timer or vacuum switch installed. Along with a proper brake switch. So that it currently operates more seamlessly.

 

Short answer to your question; Yes, you could damage the transmission. The realistic answer, very doubtful.
By eliminating Lock-Up you allow the torque to slip, the slipping torque converter creates heat. I know
nothing about a 700r4 transmission so here is a table with a make-believe transmission and range ratios;
Driveshaft
Engine Spd Ratio Range Speed
2000 4.0 1st 500
3.0 2nd 667 Driveshaft Driveshaft Driveshaft Driveshaft
2.0 3rd 1000 Speed Speed Speed Speed
1.0 4th 2000 0.95 1900 0.90 1800 0.75 1500 0.50 1000
0.6 OD 3333
The first four columns show a perfect world, no converter slipping. 4th range engine and output speed are
1:1. Remember what I am calling output speed is the driveshaft speed (rpm). Since you already know your
differential ratio, with your tire size, and an online mph to rpm calculator you could calculate your driveshaft speed.
To the right of 4th range I listed different output speeds, each different/slower output speed gives a different
gear ratio. The difference in the lower output speed ratios and the perfect 1:1 ratio is called slip ratio. So, 4th range
2000 engine speed with an output speed of 1500 gives you a slip ratio of 0.75. Or 25% slip. Anything around 0.9 will have minimal effect on temperature. Anything with a slip ratio of 0.5 or lower your driving a mechanical microwave.
If you wanted to see this in real time, the next time you are cruising at 60mph (minimal throttle), have someone video the speedometer and tachometer. While videoing, give 100% throttle, see if the engine speed climbs faster than the output speed. The torque converter slipping allows the engine speed to accelerate faster than the output speed. If you are a part time nerd like me, take the video home and jot down the tach and speedo readings to calculate your slip ratio.
You could also put an engine oil temperature sensor and guage on your trans-cooler return line. 80-85c (180f) is what we try to maintain where I work.
As others have said, we had automatic transmissions with torque converters long before we had lock up.
ras

 

You'll be fine. Its's gonna act like every traditional C4, C6, 904, 727, T350 and T400 out there and even if you have a stall convertor, the slip on the highway isn't going to be extreme.

A converter stall is a function of HP and resistance. Take a build and add HP or Weight and you'll end up with higher stall rpm. Tiny amounts of HP load result in less slip.

You don't need but 30 to 50hp at part throttle to keep a car going 65 mph on a flat road. You're not going to be at full stall levels of slip while you're just cruising.

I'd put a switch in for the highway because why not, but as long as you have a good cooler hooked up, you'll be fine.

My 69 Plymouth weighed 3850#, had 3.23 gears, tall rear tires, and a 3500rpm stall converter and didn't even come close to running hot on the highway.

-rick

 

If you have $700 burning a hole in your pocket, you can get one of these
COMPUSHIFT Mini – HGM Electronics
I installed one in my PU with a 46RE, works like the factory intended. The link should direct you to the 700R4 product, on the right side of the page.

 

I use the 200-4R because of the size and gearing advantages, but principles are the same for the 700 (me thinks). I run tranny cooling lines through the radiator tank and added on an extra cooler attached to frame rail (passenger side). Running without powering up your pressure switch will be fine as long as you have sufficient cooling. As others have stated….slip equals heat.
I’m a control freak, so here’s a pic of how I addressed my particular wants.
4th gear obviously means O/D and the Power On light gives me a quick glance indicator of whether or not I have lock up engaged (cause I’m old and have CRS).
Once I was satisfied my shit was working the way I wanted, I removed the gauges (too busy and take up too much space)…. and yes, I am that fussy.
.

 

I have ended lockup shudder many times when nothing else worked with a product called lubeguard .Its a friction modifier ,not snake oil

 

I have installed a variable vacuum switch on my T700, but I can't tell when/ if it has locked up . If the trans is in O/D and then the converter locks up, does it drop the RPM of the engine? The trans has an external cooler, and shifts up and down (including into O/D) smoothly. I want to temporarily install a toggle switch and tacho to engage it so I know that it is "on" and I know it's working , but how do you know if it's doing it's job?

 

Revs will drop a couple of hundred rpm (give or take) when the convertor locks up.
If it is set up to lock immediately when the trans shifts to O/D, you won't see the lockup rev drop.
Wire in a switch temporarily so you can engage and disengage lockup while cruising in 4th and see if the revs change.

 

I run mine through the 4th gear pressure switch and then through this manual override push/pill knob and dummy light.

 

Yeah, that's the way mine was with 4th gear change and lockup stacked right on. With my new switch I determined that the lockup on mine was worth 350 rpms.

 

sorry double post

 

I looked it up. Specially made for converter shudder. Never heard of it. I might try some of that, but I think I will call Freakshow first.

 

There is the possibility that your line pressure is a little low, but try that first.

The TCC controls flow to the converter clutch. It is a hydraulic wet clutch, that is dependent on pressure to lock quickly, tightly, and firmly.

 

If you mean the heat-sink style transmission cooler, most manufacturers recommend those as an auxiliary cooler and not a primary. If you're pumping excess heat into your transmission by not locking up your converter, you may end up too hot.

Derale (link below) says:

https://derale.com/choosing-a-heat-sink-cooler

 

Yep, that's the right style for a transmission cooler. The tube heat sink ones are meant as an auxiliary.

I think the mental gymnastics of remembering to flip the switch are more of the issue.

B&M makes a controller with adjustable vehicle speed engagement, many many times the cost of a toggle switch.

https://www.holley.com/products/dri...Mant9z7og7CqrSL-Zk8vWEvqDVff3h6SDILm7sK95pUVB

 

I will not install an on/off only TCC switch, even if the customer demands it.

I will only install a disable switch in-line with the 4th gear pressure switch.

I know three people that had accidents when they forgot to unlock the converter. Two rear-ended the car in front of them. One got t-boned when they unintentionally entered the intersection. Two of three were injured. All three people they make contact with were injured.

ALL THREE were found at fault!

All you need to do is forget, just once.

There is a very sound reason why GM engineers restricted TCC operation to 4th (and yes, in some rare cases, 3rd, too).

 

that's what I had in mind, was to install a switch in line with the wire that feeds power to the 4th gear switch inside the transmission. I should have made that clear.