I’ve been trying to do some research of what the purpose of a lock up switch is but can’t find a clear answer. I get that it’s used to lock up the convertor but what I can’t find a clear answer on is under what scenarios would you want to use a lock up switch? I know this is a newbie question but I just don’t know the answer to it ?

You either have the OD off so you know once it’s in third you can lock it and it won’t shift to 4th or have OD on and lock once in 4th.

So if i slow down with the od on or off, where it should be in a lower gear due to rpm, will it shift if i lay into the throttle in lockup or will it just lug?

 

I'm assuming if it starts lugging then you just turn the switch off, get into your preferred gear then relock it again...

When slowing (on my truck at least) it’ll hold gear until I left off the switch. It WILL downshift when locked if you mash the pedal. Obviously not ideal, and I didn’t think it would, but I found out it would lol. Typically if I was doing anything WOT or close to it I don’t mess with the switch until I’m ready for it to lock in 4th. 

Some of you worry far too much. I live on my lockup switch. Locked 3-4 daily. 

Well i spent 4500 on my transmission rebuild when i got the truck and I'm not going to do that again if i can help it...

2 hours ago, jlbayes said:

Some of you worry far too much. I live on my lockup switch. Locked 3-4 daily. 

That is cool ,how long you been doin that?

Edited January 5, 20187 yr by JAG1

3 hours ago, JAG1 said:

That is cool ,how long you been doin that?

 

Be a year in a week or two.

IBMobile, are you leaving yours locked from 3rd to 4th when hauling your fifth wheel?

3 hours ago, jlbayes said:

 

Be a year in a week or two.

 

Arent you on a built trans? I personally don’t worry about it but I’ve had it built so I wouldn’t need to worry. I just think it’s good for people to know the potential risks, not saying it’s for certain.

14 hours ago, jlbayes said:

I live on my lockup switch. Locked 3-4 daily. 

I love it when I'm towing my 5^er.

 

11 hours ago, JAG1 said:

how long you been doin that?

I've been using my switch set up since April 28, 2015

 

5 hours ago, JAG1 said:

IBMobile, are you leaving yours locked from 3rd to 4th when hauling your fifth wheel?

All the time

If you were towing with a 5 or 6 speed transmission you wouldn't be power shifting or popping the clutch. This would put undue strain on the driveline components and eventually causing a failure.  It stands to reason then that you don't keep the throttle peddle to the floor when up shifting from 3^ed to 4^th with the torque convertor locked.  

 

When I'm towing up a long grade I'll down shift to 3ed, lock out O/D, and lock up the convertor with the momentary switch.  When I reach the top of the grade with the convertor still locked I back out of the throttle, up shift to O/D and roll back into the throttle, like shifting a manual.

 

When going down a long steep grade I'll slow down to 50-55 mph then down shift to 3^ed  and then lock up the convertor with the foot switch option.  This will allow me to still use the foot brakes with out the convertor becoming unlocked.  Once at the bottom of the grade I'll unlock the convertor, up shift to O/D and relock the convertor with the momentary switch.  I don't like going over 55mph in 3^ed  because the rpm level is high due to the 4.10 rear end.

 

 

 

It seems so weird to me that you want a locked converter for enhanced engine braking. I would think it’s the opposite. 

 

I know that some gas vehicles purposely unlock the tq converter to enhance engine braking when the service brakes are applied. 

 

 

3 hours ago, AH64ID said:

It seems so weird to me that you want a locked converter for enhanced engine braking. I would think it’s the opposite. 

 

Try this scenario.  Pretend you are climbing a grade with a load using 5th gear in a 6 spd manual transmission.  You crest the top of the hill and begin descending the other side.  You like the feel of the engine holding you back a little..  You approach a curve and need just a touch of brakes to help maintain your speed.  Would you shift the transmission into neutral at this time?  I don't thinks so.

 

If you were driving the same scenario with an automatic transmission in 3rd gear (OD locked out) with the torque converter locked up, then you would not want it to unlock the converter when you stepped on the brake.  It would be kind of like putting the transmission in neutral.

 

- John

Edited January 6, 20187 yr by Tractorman
spelling

The 47/48’s drop to N while coasting? I didn’t think they did. 

 

The transmissions I have driven that unlock the converter while braking have a very noticeable increase in drag with an unlocked converter as the converter has drag when unlocked, and no drag while locked. You could coast with a locked TC easily, then tap the brakes the TC would unlock and you would slow down much faster. 

 

I know why you want it locked for EB use, but general coasting is odd. 

 

Just different transmissions I supposed. 

13 minutes ago, AH64ID said:

The 47/48’s drop to N while coasting? I didn’t think they did. 

 

The transmissions I have driven that unlock the converter while braking have a very noticeable increase in drag with an unlocked converter as the converter has drag when unlocked, and no drag while locked. You could coast with a locked TC easily, then tap the brakes the TC would unlock and you would slow down much faster. 

 

I know why you want it locked for EB use, but general coasting is odd. 

 

Just different transmissions I supposed. 

 

I know that the automatic transmission does not shift into neutral when coasting, but it gives a similar sensation when the converter unlocks.  Is it possible that you are feeling a programmed downshift when the brake is tapped in the circumstance you described? 

 

I believe that transmissions that have the "Tow / Haul" feature will automatically downshift on a downgrade when the brake is tapped if the "Tow / Haul" feature is turned on.  In this case the converter will unlock during shift but locks up again after the shift and it is the lower gear that you feel holding you back.

 

- John

It’s not a downshift. The ones that come to mind right now are the Toyota truck transmissions. There is Toyota documentation on them specifically unlocking the torque converter to improve engine braking. Not only from increased rpms, but from the increased drag of a unlocked converter, all of which is aside from any downshifts. 

I think you guys have it wrong because when my T/C is locked on down hill grades it holds me back better than if unlocked.

 

Going down hill watching the tachometer... it is so nice to NOTto see the T/C slipping and building heat.

 

Locked in going up or down long steep grades is wonderful to get a feeling of something that works for you instead of against you.

Edited January 6, 20187 yr by JAG1

1 minute ago, JAG1 said:

I think you guys have it wrong because when my T/C is locked on down hill grades it holds me back better than if unlocked.

 

Going down hill watching the tachometer... it is so nice to NOTto see the T/C slipping and building heat.

 

Locked in going up or down long steep grades is wonderful to get a feeling of something that works for you instead of against you.

 

 

I understand that, it’s just backwards from the auto transmission I’m more used to. They very specifically unlock while braking and it makes a big difference in engine braking.  It does warm up a little, but not too much. 

 

It could be as simple as TQ converter design, as one may create more drag while slipping than another. 

1 hour ago, JAG1 said:

I think you guys have it wrong because when my T/C is locked on down hill grades it holds me back better than if unlocked.

 

IBMobile and I are saying the same thing.  I hope we are not being included in the "you guys have it wrong" part.

 

- John

No John, not at all. The only thing I am saying is it engine brakes better with it locked and do not understand why some say otherwise.

23 minutes ago, JAG1 said:

No John, not at all. The only thing I am saying is it engine brakes better with it locked and do not understand why some say otherwise.

 

Because there is OEM documentation from at least one OEM that engine braking is better with an unlocked torque converter. I have driven multiple vehicles that also unlock the tq converter for enhanced engine braking, thou they were rentals and I don’t recall the make/model. I owned a Toyota that did it so I recall that info more specifically. 

 

I brought it up because it’s the exact opposite of what you guys are saying here, and I found that interesting. I trust what you guys are saying it’s just odd to me. 

 

It makes me wonder why. It honestly makes no sense to me that a locked torque converter can provide more resistance than an unlocked one. There should be more drag, and higher rpms, both of which should give better engine braking. That being said I’ve never driven a 47/48 trans and cannot provide any experience with those, I just my experience with other auto’s. 

Edited January 6, 20187 yr by AH64ID