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Torque converter lockup

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goochieman83

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Just curious, the blazer I just got has a manual torque converter lockup switch, which I have no idea which way is locked up and which isn't. Question is what doe it actually do, tried reading up on it but what is the point of the manual switch and how do I tell the difference with it being on/off?
 
What year is the truck? Is this a carb or TBI? Manual switch is basically a hack to get the thing working. Somebody probably had problems with it and gave up or swapped the trans and couldn't make it work. The best setups are the factory ones, really. For TBI, the ECU controls lockup. For carb, there is a vacuum switch and an extra valve in the valve body to manage lockup. There are also aftermarket kits that can lock based on vehicle speed.

If your switch is working, you will notice the engine speed dropping a 100 RPM or 2 when it locks. Alternatively, if it is locked, the engine speed should raise when you tap the brake pedal. With the TBI trucks, it's possible to maintain lockup at all times, which is very bad. If you come to a stop with the TCC locked, it will stall the engine. Plus you'll wear it out.

If it's a 700R-4 trans, it's possible your switch is only controlling the option of lockup in 3rd gear, with it always working automatically in 4th gear (mine is set up this way). You don't want to run in OD without lockup - too much heat.
 
Wow, that's a lot if info. It's an 86 with a 6.2 diesel and a 700r4, I just didn't really understand the point of the switch and if it was even necessary. I also was trying to figure out to tell when it was locked or not, to no avail. I was basically told that it didn't matter when I got the truck but wanted to look into some more regardless.
 
It is important that lockup works - the switch may or may not be important. Try tapping the brake pedal at highway speed to see if the engine speeds a bit. If you have a tach, it's easy to tell. With the TCC locked and cruising at a steady speed, the engine speed is fixed. If the TCC is open, the engine will speed and slow as you climb hills and such.
 
Will give that a try and report back. What is it wired to anyway, and if it was unhooked do you think it would cause any issues?
 
Ok driving home, had the switch in the down position and the blazer shifted great drove normal, no increase in engine idle while braking, even with some throttle. Switch in the up position, from a stop acted like it wasn't getting fuel, very sluggish, full throttle, down shifted and accelerated after some hesitiation. Just cruising I could slowly give it more fuel and rpms stayed the same. So basically with the switch down it drove and shifted perfect, switch up lots of hesitation when giving throttle and didn't want to shift. No rpm change at braking on either though.
 
The stock stall speed of a diesel 700 converter is about 1250 rpm, so you might not notice the big rpm variance you might in a gas applications between locked and un-locked operation. Having the converter locked kills torque multiplication which sounds like what you had going on there with the sluggish response and later shift speeds since you were having to apply much greater throttle to try and accelerate.
 
So it works but due to the sluggish 6.2 it seems as if it is just demolishing the tranny. But is it worth having the switch or no?
 
The trans and converter will certainly run cooler with the converter locked. You don't need it locked in lower gears but having it locked in overdrive really helps.
 
Ok, so having the switch off, shifting normal, is fine for short drives. Having the switch on, sluggish feeling from stop and slow shifting, is good for long highway drives. Just trying to clarify.
 
Ok, I was wondering what the purpose of it was for and how to tell whether it was locked or not. I appreciate all the help. Was so confused about the purpose of the switch in the first place. Thanks guys!
 
Well Mr. Brian Wafer if you don't mind one more question, my 6.2 starts kind of rough for being in florida in 95 degree heat. Takes about 15-20 seconds to start. The injection pump is rebuilt and the glow plugs are good, what do you think? Not trying to bombard you with questions.
 
does it turn over fast! a starter that turns over slow will not help. usely a healty diesel should start quick in warm weather. is it on the first start of the day or all the time. does it smoke unburnt fuel,dripping injectors. fuel filters, air filters ok!
 
Yeah it turns over good and it is the first start of the day or after I've been letting it sit at work for 9 hours. It does blow whitish grey smoke when it finally initially starts. Has the fuel filter upgrade and an electronic fuel pump, mechanical fuel pump deleted.
 
It probably needs glow plugs--several might not be working,or maybe they are not coming on..6.2's need the glow plugs,even in warm/hot weather to get them lit--the first start of the day is usually when they are most needed..
 
Copy, it has a manual glow plug override and I usually hold it for about 10-15 seconds before trying to start. P.O. said it has Bosch Duraterm plugs in but, no clue how long theyve been in for.
 
They might still be OK,you can test them by un-plugging them and putting a test lamp between the positive battery post and the glow plug tab where the wire plugs on--this may not always be a sure fire test though,sometimes they'll test "good" this way,but not heat up enough...some guys take them out and hook jumper cables to them for a few seconds to see if they actually glow..

It could be they aren't getting power too--someone rigged a ford starter solenoid & push button to the glow plugs on my '85 Suburban,and it always was a bear to get started,even in summer..
Sometimes the solenoid would not energize when I pushed the button,and I had to push it several times before it would "click" on...the truck sits a lot and I figured the solenoid was rusting up inside..

One day I couldn't get it to activate when I went to start the truck to move it,so I jumped the large studs where the glow plug harness and battery positive go,for about 10 seconds..

I got in it and it fired right up,faster than it ever has--usually I had to crank it till the batteries would almost die,this time it spun over about 4 times and vroom!..(with old stale fuel thats been it it for 5 years!).....so I assume the solenoid wasn't letting much juice get to the glow plugs..
I had replaced at least 5 out of the 8 on it with new AC 60G ones too..
 
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