48RE Manual Torque Convertor Lockup (cheap?)

[GECCO]

Hello all,



Does anyone have an inexpensive solution for manually locking the TC on my 48RE? I know doing so has the potential for being hard on the transmission, but I know enough not to lock it up on a stock transmission under hard acceleration. I am mainly looking to lockup sooner under normal driving, light acceleration situations for the mileage benefit. I find myself in traffic, cruising at 35 mph or so thinking "there is no reason for the TC to be slipping and having the engine turning higher RPM's".



Thoughts? Ideas?



Thanks!

 

[ECappleman]

Do a search on Diesel Truck Resource.

There is a guy on there that has the wiring to just throw a switch and it locks up in every gear.

 

[jcroman]

Hello all,



Does anyone have an inexpensive solution for manually locking the TC on my 48RE? I know doing so has the potential for being hard on the transmission, but I know enough not to lock it up on a stock transmission under hard acceleration. I am mainly looking to lockup sooner under normal driving, light acceleration situations for the mileage benefit. I find myself in traffic, cruising at 35 mph or so thinking "there is no reason for the TC to be slipping and having the engine turning higher RPM's".



Thoughts? Ideas?



Thanks!

You can make a lockup switch for under 5 bucks. I have one and I dont really like it much. the kicker is you have to manually turn it off before you come to a stop and the transmission doesnt like to shift while locked. my recomendation is to get a low stall coverter and you will not need to worry about locking the converter because its almost like being locked all the time at low throttle.



If you still want to try the switch just locate pin 7 on the 8 pin transmission harness and tap into that wire. then run a ground wire to your switch with a 33ohm resistor inline and thats it!!!!

 

[Dieselnerd]

Gecco, since you have an '05 just put it in Tow/Haul and it will lock up in 3rd gear at lower speeds. As long as you don't go fast enough to engage OD it will stay locked in 3rd. I do this and it works great.

 

[GECCO]

Thanks, guys, this gives me some options to play with.



As far as having to turn the switch off at every stop, I had a TH400 wired for manual lock up on an old van I had... basically you hit a momentary switch that activated an electrically held relay, then if you hit the brakes it opened the relay (unlockingthe TC) until you hit the button again. Worked pretty slick, I think I'm gonna try that route and see how I like it on this truck.

 

[jcroman]

Thanks, guys, this gives me some options to play with.



As far as having to turn the switch off at every stop, I had a TH400 wired for manual lock up on an old van I had... basically you hit a momentary switch that activated an electrically held relay, then if you hit the brakes it opened the relay (unlockingthe TC) until you hit the button again. Worked pretty slick, I think I'm gonna try that route and see how I like it on this truck.

Ya that would be one way to make it disengage. but you will still have issues just slowing down without brakes if its locked. for instance lets say you are locked up in overdrive cruising at 50mph for whatever reason you end up slowing down to 35mph without braking. well the truck will not shift down while locked up so it will stay in 4th gear locked and drag the engine down and stall, chatter and buck. other than that your idea will work fine... ... ...

 

[GECCO]

Ya that would be one way to make it disengage. but you will still have issues just slowing down without brakes if its locked. for instance lets say you are locked up in overdrive cruising at 50mph for whatever reason you end up slowing down to 35mph without braking. well the truck will not shift down while locked up so it will stay in 4th gear locked and drag the engine down and stall, chatter and buck. other than that your idea will work fine... ... ...

aaahhhhh, yes, very good point!

 

[KSHall]

I, like you wind up in the no-mans land of 20-35 mph alit and put mine in tow-haul to get rid of the loosey-goosey feel of that pitiful tq converter. Does anyone make some kind of a do dad to make it lock up at lower speed than 30mph? If you slow down to 25 it will unlock again and you have to speed up to get to lock again. Problems, problems, problems!

 

[jcroman]

I, like you wind up in the no-mans land of 20-35 mph alit and put mine in tow-haul to get rid of the loosey-goosey feel of that pitiful tq converter. Does anyone make some kind of a do dad to make it lock up at lower speed than 30mph? If you slow down to 25 it will unlock again and you have to speed up to get to lock again. Problems, problems, problems!

It would be nice if tow/haul would also lock the coverter in 2nd. im not sure why they didnt do it. if you put it in manual 2nd it locks so wjy not in tow/haul? sometimes its hard to understand their logic!!!! especially removing the 4th lockout feature!!!! that was soooooooooo... ..... stupid!!!!!!

 

[GaryCarter]

Gecco, do you have the overhead mileage display? It may not be 100% accurate, but it is a good tool for knowing what gear gives best MPG. It is sensitive enough to show if you have the wind behind you or ahead of you.

FWIW I've made some observations and noted that in stock trim my truck gets it's very best mileage at slow speeds where the trans is in OD but TC is unlocked. This seems counter intuitive, but every time I've switched it over to tow/haul and locked it up in third, the mileage goes down.

Over the course of a lot of observations, I've concluded two things:

Mileage goes down after you get past 35-40 mph.

Low RPM's give the best mileage. Dropping the RPM by going from third locked to fourth unlocked gives better mileage (in stock condition).



Hope this helps. And BTW, I've also noticed that with 35's things have changed- the slippage is greater unlocked.



Gary