Hot Rod Forum banner

1 - 6 of 6 Posts

·
Registered
Joined
·
5 Posts
Discussion Starter #1
I know there are a number of kits available to rewire/reprogram for different lock-up points for the converter in a 350C, but isn't there a low buck/no buck way to wire up a toggle switch to enable or disable the lock-up function in a '86 half ton? The 305 is a good engine(at least as good as it can be)but it is a pain to pull a trailer with my truck with the converter locking up and the only alternative being to drive around in 2nd. Any suggestions?
 

·
Registered
Joined
·
994 Posts
Why wouldn't you want the converter to lock? It seems to me that reducing the slip to zero would decrease the tranny temperature and increase the life of the tranny, especially with a heavy load. If you had a manual tranny what would you do - slip the clutch in third or drive in second?
 

·
Registered
Joined
·
86 Posts
there should be a switch on your brake pedal the disengages the lockup when the pedal is pressed, you could probably tap into one of the wires from that switch to a toggle switch on the dash to disable the lockup function.
 

·
Registered
Joined
·
505 Posts
Lockup converters are supposed to be wired through the brake switch so that they disengage (unlock) when the brake pedal is pushed.

There will be a hot lead into the brake pedal switch -- it will probably be jumpered to provide a hot lead to a second part of the switch also. The switch provides two functions using the two hot input leads.

Brake light function - the output to the brake lights is disengaged (Normally Open) until the brake pedal is pushed in a little bit, then the output becomes hot and power goes to the brake lights.

Converter lockup function - a second output (Normally Closed) sends power to the lockup switch inside the transmission until the brake pedal is pushed in a little bit. When the brake pedal is pushed this lead goes cold interrupting power to the lockup switch so the converter will unlock when the brakes are applied.

Use a voltmeter to determine which are the two hot input leads. Test the other leads to see which one is hot or cold when the brake pedal is pushed in.

You can put a toggle switch in series in the lead that goes to the lockup converter (hot when the brake pedal is not pushed in).

What I did was:
- get a ON/OFF toggle or rocker switch from Radio Shack
- find the Normally Closed output lead that comes off of the brake switch and goes to the converter lockup switch and disconnect it from the brake switch
- connect this lead to one of the rocker switch leads
- then use the right connectors to run a wire from the other rocker switch lead to the converter lockup output connection on the brake switch.

Now, for power to get to the lockup switch in the converter, the brake pedal must be out and the rocker switch must be in the ON position. To keep the converter from locking up, put the rocker switch in the OFF position and power cannot reach the converter lockup switch.

John
 

·
Member - AMC/Rambler "guru"
Joined
·
1,774 Posts
Make SURE you have a good trans cooler! If you don't have an external one (not just the one in the radiator) get a good aftermarket cooler BEFORE disabling the lock-up converter.

When the converter isn't locked, more heat will build up in the trans. On the good side (for trailer towing), the slipping converter will also create more torque. Older US trans converters multiply torque from the engine at around a 3:1 ratio (a 300 lb/ft torque engine can produce as much as 900 lb/ft through the tranny). That's why they generally use a higher (lower number) rear end and first gear than a stick shift. At speed, even with a non-lock-up converter, there is less torque multiplication as the drive and driven parts ofthe converter run at closer to the same speed. The lock-up will prodcue better mileage by keeping the two at the same speed, and less heat because of no slipping. That's why on the older lock-up trannys they only lock at cruising speed too. Newer models with high efficiency (less slip) converters lock in every gear (like the Jeep AW-4, which only produces a 1.4:1 torque multiplication, and needs a lower rear end gear and first gear, and locks in all but first gear immediately after a shift).

So you can get a bit more pulling power by disabling the lock-up, but heat generation will be a problem. I bet the "problem" now is the lock-up goes in and out a lot when towing a load, especially in hilly country. I think disabling the lock-up for towing will be a good idea, but you MUST get that cooler if you want the trans to last! I wouldn't recommend that on a newer trans like the 4L60E, or any of the electronic shift and/or OD trannys. Just drop them into 3rd and not OD. An extra cooler is still a good idea for towing though!!
 

·
Registered
Joined
·
5 Posts
Discussion Starter #6
Thanks to everyone for the replies....of course my overall problem is I'm dealing with a virtually stock(only a Performer intake and a 600 Edelbrock carb for goodies)305 that is one sweet little engine that nets me 19 mpg under just about any conditions but pulling a trailer and that in a full size half-ton. I have a much greater understanding of what I'm dealing with here and thanks especially for the tranny cooler tip!
 
1 - 6 of 6 Posts
Top