Torque Converter Lock Question

[Shaggy]

Didn’t really find what I was looking for online, so I figured I’d ask the BARFs.

I recently bought a 2006 Dodge Ram 3500 with an 4-speed auto with OD trans. The truck came with a BD Diesel Exhaust Brake and with the exhaust brake activated (toggle on/off for towing), the converter locks at like 25mph instead of the 50mph in standard Drive.

It got me thinking..... Is there any drawback to having the converter lock up so early for regular driving (other than rougher shifts). It obviously protects the trans from running hot with the converter slipping all the time, but is there a risk at all to having it lock early? Why don’t auto trans just lock up early all the time?

There’s gotta be something I’m missing.

 

[Mike95060]

Because when they lock they don’t multiply torque when you need it maybe?

 

[msethhunter]

I was a Diesel tech for Dodge when I was a wrench. I got out when your generation truck was being produced. There was a lot of problems with them burning up pistons when they went to the common rail system. Anyways, the speed when the converter locks was set as a compromise between NVH (noise vibration and harshness) and fuel economy. If memory serves correct, the set it where they did to keep the transition smooth.

Personally, I'd leave it be. Your truck makes gobs of torque and the transmission is the weakest link in your drivetrain. If memory serves, it's a 48RE. The 4 is for 4spd, the 8 is for 800ftlbs capacity, R is for rear wheel drive and E for electronic control. The weak link in your transmission is overdrive and the converter. It's not usually hard parts that fail. It's usually the clutches.

 

[Shaggy]

I was a Diesel tech for Dodge when I was a wrench. I got out when your generation truck was being produced. There was a lot of problems with them burning up pistons when they went to the common rail system. Anyways, the speed when the converter locks was set as a compromise between NVH (noise vibration and harshness) and fuel economy. If memory serves correct, the set it where they did to keep the transition smooth.

Personally, I'd leave it be. Your truck makes gobs of torque and the transmission is the weakest link in your drivetrain. If memory serves, it's a 48RE. The 4 is for 4spd, the 8 is for 800ftlbs capacity, R is for rear wheel drive and E for electronic control. The weak link in your transmission is overdrive and the converter. It's not usually hard parts that fail. It's usually the clutches.

So early lock is better for the trans or worse?

 

[msethhunter]

So early lock is better for the trans or worse?

I generates less heat, but is harder on hard parts. Heat is usually what kills an automatic transmission. But diesels break hard parts with their massive torque.

It's not a simple question with a simple answer.

 

[Shaggy]

Makes sense. I’m not beating on the truck hard at all. I did the fast diesel thing with my 6.4L Powerstroke. I’m just interested in longevity and reliability.

 

[stangmx13]

Because when they lock they don’t multiply torque when you need it maybe?

I was thinking this exact thing. Torque multiplication can be very useful. Id probably be unable to pull my boat with my tiny truck without it. But I'm pretty much guessing.

 

[KWeezyXB12]

if you do need a trans ever i recommend suncoast or make the trip to randys transmission. ats is ok but i hear people having issues but ats is pretty good about warranty stuff and replacement. i had a 06 with a suncoast and it was great. if you get the bug for bolt ons go banks as its all carb legal. i did their complete intercooler kit, intake and 6 gun tuner.

 

[msethhunter]

Makes sense. I’m not beating on the truck hard at all. I did the fast diesel thing with my 6.4L Powerstroke. I’m just interested in longevity and reliability.

Keep it cool then. I'm not sure you'll gain much by locking the converter earlier in terms of efficiency, and you may be dissatisfied with how it drives, but it's worth a try. If you do end up going to a manual control of your TCC, look into a kit that will also raise the line pressure as well. Line pressure = greater clamping force for the clutches. It'll probably shift a little harsher, but quick shifts reduce heat. Hard shifts break stuff.

 

[Shaggy]

Keep it cool then. I'm not sure you'll gain much by locking the converter earlier in terms of efficiency, and you may be dissatisfied with how it drives, but it's worth a try. If you do end up going to a manual control of your TCC, look into a kit that will also raise the line pressure as well. Line pressure = greater clamping force for the clutches. It'll probably shift a little harsher, but quick shifts reduce heat. Hard shifts break stuff.

I’m pretty sure the exhaust brake came with trans tuning. With the brake activated, it shifts much harder. I was wrong about converter lock though. It locks at 35mph, not 25mph.

I towed our 40’ toy hauler around a little bit today and the trans stayed right around 215°F the entire time.

 

[msethhunter]

I’m pretty sure the exhaust brake came with trans tuning. With the brake activated, it shifts much harder. I was wrong about converter lock though. It locks at 35mph, not 25mph.

I towed our 40’ toy hauler around a little bit today and the trans stayed right around 215°F the entire time.

215° is pretty good, especially towing something that size. A little on the high side but still well within an acceptable range. I'd start to worry once temps got above 250°. At about 265° it's time to shut it down and let it cool, and change the fluid.

 

[scootergmc]

I’m pretty sure the exhaust brake came with trans tuning. With the brake activated, it shifts much harder. I was wrong about converter lock though. It locks at 35mph, not 25mph.

I towed our 40’ toy hauler around a little bit today and the trans stayed right around 215°F the entire time.

Is your temp sensor inline precooler or in the pan? I'm assuming it has a double deep pan as well as the exhaust brake? Who built the tranny?

Are you a member of the TDR? The same information can be found on cumminsforums, etc., but it's worthwhile ($35?/yr.) for the forum plus the magazine:

https://www.turbodieselregister.com/forums/

 

[TheRobSJ]

Is there any drawback to having the converter lock up so early for regular driving (other than rougher shifts). It obviously protects the trans from running hot with the converter slipping all the time, but is there a risk at all to having it lock early? Why don’t auto trans just lock up early all the time?

There’s gotta be something I’m missing.

Because when they lock they don’t multiply torque when you need it maybe?

Exactly that. This is why the big boy drag racers have high stall speed converters. This is why converters go into lockup at light throttle/cruise conditions, but immediately disengage as soon as you feed in even moderate throttle.

Also they stay disengaged at slower speeds to maintain driveline smoothness and of course not stall the engine when you come to a stop. Think of driving a stick shift car in the first two gears...if you come on and off the throttle in even a slightly abrupt manner, it gets awful “trailer hitchy” doesn’t it? With all the slack in a typical full size truck drivetrain, this trailer hitching effect would be a bit more dramatic and just bad for all the parts involved.

 

[Mike95060]

Exactly that. This is why the big boy drag racers have high stall speed converters. This is why converters go into lockup at light throttle/cruise conditions, but immediately disengage as soon as you feed in even moderate throttle.

Also they stay disengaged at slower speeds to maintain driveline smoothness and of course not stall the engine when you come to a stop. Think of driving a stick shift car in the first two gears...if you come on and off the throttle in even a slightly abrupt manner, it gets awful “trailer hitchy” doesn’t it? With all the slack in a typical full size truck drivetrain, this trailer hitching effect would be a bit more dramatic and just bad for all the parts involved.

Holy shit I got one right!!! :laughing

Thanks Rob.

 

[msethhunter]

Exactly that. This is why the big boy drag racers have high stall speed converters. This is why converters go into lockup at light throttle/cruise conditions, but immediately disengage as soon as you feed in even moderate throttle.

Also they stay disengaged at slower speeds to maintain driveline smoothness and of course not stall the engine when you come to a stop. Think of driving a stick shift car in the first two gears...if you come on and off the throttle in even a slightly abrupt manner, it gets awful “trailer hitchy” doesn’t it? With all the slack in a typical full size truck drivetrain, this trailer hitching effect would be a bit more dramatic and just bad for all the parts involved.

The "big boy drag racers" have high stall convertors to get into/closer to the power band at launch. Too high of a stall speed will actually make the car slower at the top end of the track because a converter that doesn't lock with a clutch never stops slipping.

Think of it more as a clutch. Yes, there is some torque multiplication happening but it's not much different than slipping the clutch in a manual. But it allows the clutches in the transmission to lock and the converter to "slip" in place if a manual clutch.

 

[TheRobSJ]

Think of it more as a clutch. Yes, there is some torque multiplication happening but it's not much different than slipping the clutch in a manual. But it allows the clutches in the transmission to lock and the converter to "slip" in place if a manual clutch.

Absolutely like slipping a clutch in a manual. And it’s what makes automatics so easy to handle doing parking lot maneuvers. This is why torque converters are used in many of the modern DCT setups. Slow speed smoothness. I’ve driven some DCTs that use computer controlled clutches, and they are nowhere near as smooth driving at speeds below 10mph as torque converter equipped DCTs.

Interesting fact though, the torque converters in DCTs go into lockup at very slow speeds compared to a conventional automatic.