I and several others are adapting T56 transmissions (and LT1 and LS1 engines) to RX-7s, and a debate about how best to handle the actuation of the reverse lockout solenoid has come up.

The GM PCM controls the solenoid, "disabling" it when vehicle speed is below 5 mph, I believe. Can any confirm this, or add to the criteria under which the solenoid is "opened", allowing the reverse gear to be selected?

The main problem is that I am using a FAST SEFI-8LO stand-alone engine management system to control my 396 LT1. I don't have the manual (it went to California with the system to Mark Montalvo) so I don't know if there are any speed-related (or other) outputs from that system that could be used, and haven't found that information anywhere else.

Since I obviously don't have a GM PCM to control the lockout solenoid, there are several options...

Option #1 - Remove the solenoid or wire it so that it is open all the time. Pretty dangerous, since a hard shift to 5th could find reverse instead. This would be the absolutely last possible option, and in fact, shouldn't even be considered except that it is, indeed, one valid option.

Option #2 - Add a switch/button/etc. to open the solenoid. The main problem with this solution is that the car is no longer "standard" and handing it over to anyone else to drive now requires that they be in on the secret of how to get the car into reverse. This is not a highly desireable situation either.

Option #3 - Add an MSD RPM-activated switch (assuming one could get a 1k rpm module from MSD) and a relay which on its normally closed posts, gives an uninterupted ground contact to the reverse lockout solenoid. With this ground lead and power from a 12V+ ignition switched source in the "run" position, the solenoid would normally be open, allowing selection of reverse. If engine rpm exceeds 1k rpm (faster than approximately 5 mph, depending on gearing and tire size) then the ground output of the MSD switch trips the relay, opening the contacts, and breaking the circuit to the reverse lockout solenoid.

The potential problems with this solution are 1) the assumption that MSD can provide a custom 1k (or whatever) module for their switch, and 2) the assumption that while the car is in reverse and engine rpm climbs above 1k rpm, that the closing of the solenoid will not inhibit the function of the reverse gear or kick the transmission out of reverse. Anyone know the answer to this?

This would be a fairly simple, relatively inexpensive option that would work well, assuming the potential problems turn out not to be. One way around the second problem would be to use the reverse light wire to keep the solenoid open, possibly. So far, I like this option the best.

Option #4 - Use a more complicated device like the A'pexi Rev/Speed meter which has a lot more functionality than we really need, but does apparently have a speed-related output that could be used to either enable or disable the reverse lockout solenoid, depending on how that functionality works.

http://www.apexi-usa.com/meters_revspeedmeter.asp

From the product documentation, the device has an "RPM Induction Output Setting" which is apparently a fancy way of saying it has a built in rpm switch. This switch is adjustable from 100 rpm up to 9,900 rpm, so it would probably handle the job of the MSD switch outlined in Option #3. The device also has a "Vehicle Speed Induction Output Setting" which is adjustable from 0 km/h up to 350 km/h. I'm assuming both control an output that goes to ground when activated, since that isn't specified.

This presents another problem. Where does this silly thing get its speed signal from? If there's no ECU/PCM for it to read a speed signal from, then what? From the documentation, it reads from the ECU's speed signal output. The problem is that I don't have a "conditioned" VSS output without the GM PCM, and I'll have to use something that Dakota Digital claims they used to make (the SGI-1, not the SGI-5) to condition the VSS signal. Then this thing can probably deal with that, perhaps.

Option #5 - Create some custom circuitry to read the raw output of the T56 VSS to detect vehicle speed, and enable (or disable) the reverse lockout solenoid based on that reading.

The main problem with this is that it could be potentially expensive and labor intensive, and I don't even know where I'd start. I'd have to find someone who knew enough about electronic circuit design to process the VSS signal properly, and so on.

Any input or ideas would be greatly appreciated. I haven't found an engine swap site on the net yet where they didn't use the GM PCM as part of the conversion, so I'm not sure what people do when they don't have the PCM available.

At this point, since I have to condition the VSS signal anyway with a device that would probably cost $80+, and figure out some way of actuating the reverse lockout solenoid with another device, it might just be easier and cheaper to buy a PCM, and see if I can wire it up just to handle those two chores. The bad part is that I'd have to add an ALDL connector and buy LT1 Edit to configure the PCM for the different tire size and gear ratios, and I'd need custom programming to match the 8,000 ppm (at 60 mph) that my electronic speedometer is expecting. Guess what... I had a '95 PCM that matched that description, had the ALDL/RS-232 connector, and LT1 Edit and sold them because I didn't think I'd need them. After a little thought, this option would be far more expensive than it's worth, and the PCM isn't small.

Help??!?

Thanks!

 

1. The nice thing is that the MSD pills are just fancy wire-wound resistors. These are actual measured resistance of some MSD pills, posted by someone on the 4th-gen list a while back:
3000 - 1.89k
6000 - 4.56k
7000 - 5.66k
8000 - 6.87k
You can extrapolate these numbers to determine that a 1000 RPM pill would be a little over 600 ohms.

2. Closing the solenoid just puts pressure on the shifter to the left, it won't be able to kick it out of gear since you have already pushed it forward into reverse. BTW I don't know whether you know this, but you can still push it into reverse with the solenoid activated... it is just much harder.

 

Interesting. I found this how-to page while I was looking around for more information...

http://www.corral.net/tech/powerplant/arm/

No, I didn't know that. With a shifter arm mounted on the transmission and the transmission in a car, I'm sure it'd be quite a bit easier, but trying to push just the shifter "stub" into reverse by hand with the transmission out of the car resisted all efforts.

Thanks for the advice, I appreciate it!

 

i put a program from an auto in my car once and it basically reversed the operation of the solenoid. it was very hard to put into reverse while stoppes, but after i was moving it wanted to slide right over to reverse! i looked through everything and the only thing i can think of would be something to do with how the Automatic function tables are programmed in a manual car. you may want to get a stock .bin from a manual and insert the tranny tables into your program and see what happens.

 

when i converted to the T-56 from A4 i didnt do anything about. it is very hard to get into reverse the way i left it. i almost need two hands to push it side ways so there is no way i'd ever get it into reverse while shifting hard.

 

I'm using an SEFI-8LO in stand-alone configuration, so there's no control of the transmission from the ECU.

What I do believe, however, is that the SEFI-8LO has additional outputs (it will control up to three stages of nitrous, I believe) that could be used and programmed to activate at a specific rpm, saving me the cost of an MSD unit. I could use one output to close the reverse lockout over a set rpm, and a second lead from the reverse lamp output to disable that circuit when the transmission is shifted into reverse, elminating any pressure on the shifter or internals while in reverse, even over the rpm limit I've selected.

 

Another alternative would be to use a stock PCM... a few parallel inputs from key sensors, and it is totally functional. I run the stock PCM in parallel with my MoTeC for VSS, IAC, a few other things, and for the reverse lockout (when the car was an M6). Totally stock lockout function.

I think you are over complicating it.... just put a switch in. Hard to believe you would be "handing it over" to someone at all to drive - I know I don't - and that the person you entrusted this monster too wouldn't be smart enough to handle the reverse lockout switch....