4L80E lockup overide

[DaveBr]

Is it possible to install a switch that allows one to overide lockup? When towing up hill sometimes I can make the tranny come out of lockup and stay in overdrive if I tap the brake pedal lightly and have the accelerator in the right position.(not an exact science) Many times this is all the help I need to get the old girl over the top of the hill. It's annoying when it kicks into 3rd and you know you could have made it without listening to the engine rev @ 3000 rpm.

If I could flip a switch and overide lockup I could let the tranny stay in O.D. longer before kicking down. Is this possible or should I throw away my Fantasy Island re-run collection?

I did a search in past threads but did'nt find an answer.

[DmaxMaverick]

You can interrupt the TCC circuit, unlocking or preventing a TCC lock. However, IMO, it is a very bad idea. An unlocked converter generates a lot of heat, and heat kills (trannies). It is much better, effective, and healthier in 3rd gear (direct) and locked. Your tranny is dropping into 3rd for a reason....survival. Running in OD when it shouldn't will shorten the life of your tranny. When an auto is in direct, there's a lot less moving parts, moving, thus a lot less stress and heat generation. Your are much better letting it drop a gear. Or, manually drop into 3rd before the "big load", and give it a chance to lock up. You'll have more power transfer, and a lot less heat generation. Incidentally, the heat generated is either dumped into the cooling system, or the tranny dies young. Also, switching to synthetic ATF can help it live longer (fluid stays healthy longer, under the same harsh conditions).

[Robyn]

I agree 100% with Maverick on this issue.
I have seen 4L80 trannies scorched really good by trying to defeat the Lockup and run OD alone under high load conditions.

The OD can run fine at lower speeds as it normally does between about 35 and 45 but these are low load conditions and dont generate much heat.

Let the system work as it was designed. Dropping the tranny to 3rd and letting the lockup hold is fine. Running the engine in the 2500 to 3000 rpm range wont hurt it one bit.
Even running the thing on the governor wont hurt it.

I have run my 6.5's right up hard on the governor for many miles while pulling a hill.

The only issue is that if you have a chip and an aftermarket control on the boost you need to be watching the EGT's and make sure it stays out of the "CRISPY ZONE"


Best

Robyn

[DaveBr]

Thanks for the input. I would rather listen to my engine rev than shell out the bucks for a rebuild. On the subject of generating heat I bought the biggest tranny cooler I could find. I had to notch out the center support to get the thing to fit. I hooked it up so the fluid goes through the rad cooler before it hits the air cooler. around town temp is 125*F and pulling uphill the highest I've seen it go is 175*F. I also put TOW COOL in the fluid. Is it possible to over cool a transmission? Now that it's getting cold and white I notice that lockup occures a lot further from home than it used to. Is Synthetic fluid worth buying. Amzoil is around $7.50 a quart in the great white north.

[Kick Ass Matt]

Thanks for the input. I would rather listen to my engine rev than shell out the bucks for a rebuild. On the subject of generating heat I bought the biggest tranny cooler I could find. I had to notch out the center support to get the thing to fit. I hooked it up so the fluid goes through the rad cooler before it hits the air cooler. around town temp is 125*F and pulling uphill the highest I've seen it go is 175*F. I also put TOW COOL in the fluid. Is it possible to over cool a transmission? Now that it's getting cold and white I notice that lockup occures a lot further from home than it used to. Is Synthetic fluid worth buying. Amzoil is around $7.50 a quart in the great white north.

Its normal for the tranny to not lock up yet when it gets colder. When it's not locked it generates heat quicker, warms up the tranny sooner.

[Robyn]

A temp sensor is used on some trannies to keep the lockup off untill the tranny is warmed up.

Yes you can get it too cold but 125F is fine.

The high $$$$$ oil is not worth it IMHO. I have seen trannies run 200K plus on good old red juice.

Just change it once in a while along with the filter.

Best

Robyn

[DaveBr]

I change fluid in the pan every year and the filter every 2nd yr. Keeps it the right shade of red. What I meant about lockup occuring farther from home was comparative to the same temp range as this time last year. I was thinking TOW COOL is thick(like STP) when poured out of the bottle. Is it possible that it changed the viscosity of the fluid? Is using a cooling additive in fluid OK or is it bunk?

[DmaxMaverick]

ANY fluid additive is bunk. Perhaps something you'd use on a tired tranny before selling it (dishonest, IMO), or trying to get by before shelling out the bucks for an overhaul. The viscosity of standard ATF is 10 weight. Thickening it, for no particular reason, would likely cause more damage than good. Your increased cooling ability is due to your large cooler, not the additive. Synthetic ATF is expensive, in the short haul. With it, you can double (or longer) your service intervals. It puts up with abuse better than dino ATF. Your choice. For only a daily driver that gets regular service, dino fluid is fine. I've never treated any of my vehicles "normal", and my 1985 is on its nearly original (no overhaul, only some upgrades when new) TH700R4, with synthetic ATF since about 50K (500K+ now). I have never had to overhaul an auto tranny when synthetic fluid was used exclusively.

[DaveBr]

Thanks for the replies. One last question on this subject before we put it to bed. Synth. ATF & reg ATF should be compatible? I was thinking of draining the pan and refilling with synth. and doing so again come spring. I think synth is the way to go for me because I pull a 5th wheel and a boat behind the 5th wheel. This adds a whole new dimension of wear and tear to the old girls parts. It runs great and I would like to keep it like that.

[DmaxMaverick]

The fluids are compatible, within the same grades (Dex-III, etc.).

You could do the drain/fill exchange. A full flush is easy to do yourself, or have a shop do it. With a full flush, you'll be exchanging 95% of the fluid (you never get all of it), versus less than 1/2 at a time during a drain/fill. It is also a good time to install a drain plug into the pan. If you are exchanging fluid often, it is unnecessary to change the filter every time, and it's much easier than pulling the pan. If you are towing heavy and/or often (sounds like it), I highly recommend the full flush with synthetic ATF. Also do the same with your transfer case (if you have one, and it isn't an Autotrac TC). You should also be using synthetic lube at least in the rear end, and the front as well if you have and use 4x4 a lot.

[DaveBr]

The do it yourself full flush sounds like the ticket. Could you explain how it's done or is there a thread somewhere that explains how it's done? I installed a drain plug this spring. Always wondered why auto manufacturers never put one in.

[DmaxMaverick]

Try a quick search in the late model 2500HD/3500 Drivetrain forum. I've described it several times. If you don't find it, I'll post it here. The DIY procedure is the same for any auto.

I think the reason mfg's didn't install a drain plug in the pan is to encourage filter replacement at service (more likely, they cut a corner....used to have drain plugs in torque converters $$). The Allison has one, but the internal filter is an "overhaul only replacement", and it has an external spin-on filter.

[DaveBr]

Found what I needed. Thanks everyone for all the help.