B&M Lockup W/ Vacuum and Brake Switch? - Third Generation F-Body Message Boards

cal30_sniper · 10-31-2009, 03:41 AM

Hello All,

Still trying to finish off my transmission swap right on my now non-computer controlled Formula. I'm going to need a lockup torque converter, and from what I'm seeing, I really like the B&M kit due to it's ability to be selected at multiple speeds (personally I liked the feature of the trans being able to lock up in 3rd gear sometimes, not an option with the other kits).

So, my question. Can a vacuum switch like used in the homemade lock up wiring be used to break the 12V signal from the B&M kit to the transmission in order to disengage lockup under load such as acceleration? Is there a factory vacuum switch already there that could be used? (I have an '87 LG4 car). Is there a way to unlock the converter under light load such as coasting as well? (I.E., same switch, or one in parallel)

Thirdly, and separately, can the factory brake switch be used to disengage the lockup when the brake is applied?

From what I'm reading, the B&M Converter Kit supplies a 12V power to LOCK the converter, while everything else here would supply 12V power to UNLOCK the converter. So, couldn't I just build a relay for the B&M kit that reversed the signal being sent?

This all seems too simple really. Is it really, or is the simplicity just a fact of watchstanding at 0330 fogging my brain? I'm mainly interested in having a vacuum disengage, with the brake disengage and coasting disengage being secondary considerations.

Thanks fellas,

-Levi

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cal30_sniper · 10-31-2009, 04:33 AM

I think I might be on to something here...

In this setup, 12V is supplied to the Torque Converter Lock up plug on the trans when the kit determines it should be (above set speed), unless:

-Either the vacuum switch or brake switch closes due to load or brakes being applied, respectively.

When these switches close, it should cause the 12V power not to reach the lock up switch, because it will be grounded out through the closed switch.

Seems like it should work, right?

-Levi

skinny z · 10-31-2009, 11:21 AM

If you wire it as shown, you will have a dead short when either switch is closed.
Put the switches in series with the 12v source and use normally closed contacts. If the brake is applied the switch opens or if the vacuum drops ( as in under acceleration) the switch opens. Either case will cut the power to the trans.
Somewhere at thirdgen.org is an article with diagrams. I couldn't find it with a quick search. You may have better luck.

camaronewbie · 10-31-2009, 07:10 PM

The TCI kit works opposite from what you have shown - I assumed they all worked the way the TCI kit works - are you sure you're understanding the B&M wiring coerrectly?

With the TCI kit, you have the 12v+ that runs to the tranny ALWAYS (conected to a hot-in-run). Then the vacuum switch gets enough vacuum to engage, and that vacuum switch provides the ground, completing the circuit and locking up the TC.

There is an option with the TCI kit to have a GM brake switch installed on the brake pedal, that cuts the 12v+ when the brake is applied. The instructions with the part number for the GM brake switch are available online at www.tciauto.com

There is also an option with the TCI kit to have a manual lockup switch - you simply wire a toggle switch to provide the ground - when toggle on, ground is applied, circuit complete, TC locks - when switch is off, no ground, no TC lockup UNLESS the vacuum switch gets the the necessary vacuum to complete it's ground circuit.

I'm running the TCI kit, but I'm not using the vacuum switch as it broke when I was installing it (it's a very tiny POS vacuum switch and the nipple for the vacuum line to connect to broke off the first time I touched it). I'm simply using the toggle switch, and manually locking when I'm on the highway. Been running like this 3 years now with no issues.

I used a lighted toggle switch for my lockup - so I had to use a relay in there, since the goal is to provide ground and a lighted toggle gets 12v+ to operate the light in the switch - when I turn on the switch, the 12v+ runs to a relay that engages, with the other two connections on the relay making a ground contact (one wire gounded under the console, the other going to the lockup wiring under the hood) - the engagement of the relay makes the ground connection complete.

Anyway - don't know if any of that helped you (I have no knowledge of the B&M kit), but good luck with it.

cal30_sniper · 10-31-2009, 08:57 PM

Doesn't the TCI kit require you to drop the pan and install wiring inside the transmission as well?

My problem is, I just put the transmission in, changed the fluid and filter, and realized that I needed the lock up switch after I got it all in because the carb is non-CC.

Is there another solution other than the B&M kit which does not require removal of the transmission pan?

Thanks,

-Levi

camaronewbie · 10-31-2009, 09:11 PM

Yes - the TCI kit has you drop the pan and install a new solenoid.

camaronewbie · 10-31-2009, 09:14 PM

Which B&M kit are you looking at?

cal30_sniper · 11-01-2009, 12:01 AM

This one:

http://www.summitracing.com/parts/BMM-70248/

B&M 70248

camaronewbie · 11-01-2009, 12:28 AM

I looked at that one after I asked - seems alot easier than dropping the pan and only costs $60 more than I spent on the TCI kit. Plus, no screwing with vacuum lines and the crappy TCI vacuum switch. Wish I'd seen that before I did the TCI kit! I think you can easily accomplish what you want with this kit - just draw out the circuits and think about each one at a time.

cal30_sniper · 11-01-2009, 12:36 AM

So which of the following does this kit work by:

1. Sending power to the trans (normally nothing, but sending a 12V power signal when it wants the converter to lock up)

2. Cutting power to the trans (normally sending a 12V signal to the trans, but cutting the signal when it wants the converter to lock up)

3. Completing the ground (finishing the ground to a 12V signal when it wants the converter to lock up)

4. Something I haven't even thought of?

I guess which way it works will have a large impact on how I build the switch circuit.

Thanks for all the help, I'm only working with a background in bare bones Mopars and a semester of Electrical Engineering to get me through this show, haha.

-Levi

camaronewbie · 11-01-2009, 12:53 AM

Might want to double check with their tech support, but looked to me like:

1) Small black and red wires running to the VSS tell the "box" what speed you are
2) Adjustment knob sets speed at which the "box" sends signal to the transmission
3) Red connects to 12v+ hot-in-run, black to ground.

Looks like "box" senses speed off the VSS, at the right speed (that you adjusted for with the knob), the 12v+ is switched through the "box" from the red wire to the yellow wire, sending 12v+ to the tranny and activating the lock up. If speed reduces below the adjusted setting, then the 12v+ supply is cut off by the "box". Looks also like there is a provision for the brake light switch - when the brakes are applied, then the 12v+ is again cut, so the TC unlocks.

So the simple answer looks like it sends 12v+ through the yellow wire to lock up the TC.

I don't see any provision for a vacuum switch, nor do I see a need with this setup - it's all based on the speed read from the VSS, and what speed you adjust to engage the lockup.

cal30_sniper · 11-01-2009, 01:47 AM

Thanks for the info, really great stuff, and just what I needed to know.

I've only got one question though. Why would you not need a vacuum switch? Doesn't the OEM have a provision where the converter is unlocked under load which would cause a vacuum? I would assume this is there for some reason, perhaps to prevent damage to the transmission. Why would you want to cut this feature out?

Thanks,

-Levi

camaronewbie · 11-01-2009, 08:22 AM

Vacuum under load theories beyond my feeble brain LOL.

But I can tell you, I tried replacing the vacuum switch that broke in my TCI kit with a standard GM transmission vacuum switch, and I wasn't happy with the results. It seemed that my TC would lock in 2nd and 3rd, and unless I really floored it (opening up my secondaries and sucking down fuel on my 4 barrel) it wouldn't let go.

Like getting on the highway - running the cloverleaf at a slower speed like 30, then merging on the straight the TC would stay locked until I really hit it hard. I yanked it all back out and decided to just use my manual switch.

But I should mention that I have no idea what the vacuum requirements are to activate the GM switch I used, so it may have been too sensitive or not sensitive enough - the TCI vacuum switch is preset for 8-10 in/Hg - and so my issues may have been with the GM switch.

So, only using my manual lockup toggle switch, I just have to remember to lock on the highway, and unlock when coming to a stop - and trust me - the car lets me know when I forget to unlock, as it starts chugging as I'm slowing down.

Given that this B&M kit doesn't require dropping the pan to install - I'd definitely give it a shot!

skinny z · 11-01-2009, 09:41 AM

Regardless of how the kit operates, if there is only a single wire going to the trans then that is 12v+ by default.
If you want to have additional control either with the brakes ( recommended ), vacuum or a manual on/off function then it's a simple matter of splicing into that single wire. Just remember that you're not switching to ground ( as in your diagram ) but opening or closing the circuit to the trans.
The ratty drawing shows my installation however rather than the kit, I only have a 12v ignition source for the power. There could be any number of switches in the trans itself however they may or may not affect the operation of the TCC.

cal30_sniper · 11-01-2009, 02:03 PM

So, with the factory brake and vacuum switches being normally open, where do I find switches that are normally closed?

Gracias,

-Levi

skinny z · 11-01-2009, 05:18 PM

The brake switches generally have to sets of contacts. One normally open for the lights and the other normally closed for this function or cruise control.
The vacuum switch ( and I should correct myself ) is actually a normally open switch (shelf state) and is closed under vacuum. Sorry for the confusion.
All the parts should be available at the scrap yard from just about any GM vehicle of the same era. Or you can go a GM dealer and ask for the parts specifically. Try an early third gen ( with no computer ).
There was an excellent post (that I can't find) that had part numbers for this mod. Maybe someone can recall.