A-518 Lockup and OD question

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jos51700

jos51700

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I'm prepping an A-518 for use in a non-factory equipped older car, and I'm adding the switches to automate the lockup and overdrive functions.
What vacuum switch do I use, and where is a good place to get them?
Thanks all
JOS
 
mopowers said:
I think PATC sells an adjustable vacuum switch for that purpose. They also sell the hydraulic pressure switches to actuate the OD and lockup solenoids, but it sounds like you've got that covered.

Performance Automotive Transmission Center
Click to expand...
I think this is what you are talking about...

transmissioncenter.net

* PATC 518/46RH Lock Up and Overdrive Switch Kit. (Not made for "RE" transmissions) - PATC - TransmissionCenter.net

# 727518. With these four parts you can convert your 727 transmission to a 518 overdrive transmission. What this kit does is makes a 518 transmission shift without a computer.
transmissioncenter.net transmissioncenter.net
 
Yeah I saw that but don't feel like blowing out $100+ for two ten dollar switches and some fittings. Maybe it's worth it after all.

I just figured someone had posted the vendor info off that kit somewhere.
 
I'd maybe give them a call to see if they sell just the vacuum switch. Seems like that would be a pretty universal part. Maybe google "adjustable vacuum switch" and try to find one similar.
 
I have spent hours looking for other vacuum switches and not come up with anything cheaper or better. I found a couple of other places selling the switches for about the same cost.

I think there are two different models that adjust over different ranges so it may be worth calling PATC to make sure you get the right one.
 
You don't HAVE to use vacuum switches. You can just use a pair of toggles and manually control it
 
for my thinking, toggle switches are too much hassle. if you want to pass someone or forget to toggle them off when coming to a stop. we have 2 units with the patc kit and love it.
 
Last edited:
jos51700 said:
I'm prepping an A-518 for use in a non-factory equipped older car, and I'm adding the switches to automate the lockup and overdrive functions.
What vacuum switch do I use, and where is a good place to get them?
Thanks all
JOS
Click to expand...

mopowers said:
I think PATC sells an adjustable vacuum switch for that purpose. They also sell the hydraulic pressure switches to actuate the OD and lockup solenoids, but it sounds like you've got that covered.

Performance Automotive Transmission Center
Click to expand...

jos51700 said:
Yeah I saw that but don't feel like blowing out $100+ for two ten dollar switches and some fittings. Maybe it's worth it after all.

I just figured someone had posted the vendor info off that kit somewhere.
Click to expand...

mopowers said:
I'd maybe give them a call to see if they sell just the vacuum switch. Seems like that would be a pretty universal part. Maybe google "adjustable vacuum switch" and try to find one similar.
Click to expand...

Headintheclouds said:
I have spent hours looking for other vacuum switches and not come up with anything cheaper or better. I found a couple of other places selling the switches for about the same cost.

I think there are two different models that adjust over different ranges so it may be worth calling PATC to make sure you get the right one.
Click to expand...

NOS sells the adjustable switches as nitrous fuel cut off switches.
In this scenario they stop the nitrous if there isn’t sufficient fuel pressure to support it.
They work the other way as well.
When the trans governor produces the pressure to activate the switch at whatever pressure you set it for it engages the shift.
When you slow down the switch opens dropping that gear.
I have mine to automatically engage OD at 50mph and lockup at 65mph.
Then I have manual switches on my shifter so I can disable either or both.

ShifterArt.jpeg
 
excellent posts from TrailBeast and 1WildRT. explains a lot for those that are thinking about this setup. as i said, we love our patc setup.
 
FWIW I've looked at the PATC setup and a few others... I wish I could remember who did the design of the one I posted... He's designed what I consider the best way of controlling the RH series O/D's...

Using timers solves the shortcomings of most designs...

I did my first 518 install back in 2000 which used more parts sensors, switches, vacuum bleeds than it needs but twenty three years later it still works pretty well.. It has a few quirks that are going to cause me to swap out the current controls to the timer relay design...
 
rbkt65 said:
excellent posts from TrailBeast and 1WildRT. explains a lot for those that are thinking about this setup. as i said, we love our patc setup.
Click to expand...
I used the same parts as the patc kit, but with a couple differences.
My adjustable pressure switches are plumbed off the governor and routed up to the back of the intake manifold so I can change adjustments under the hood.
Didn’t like the idea of that stuff vulnerable to road hazards either.

I found that I don’t need the vacuum kickdown switch either.
I just reach down and turn off lockup, and no problem using OD for passing.
This car is my daily driver, and has been running this setup for 5-6 years without a single problem with it.

Worth every penny, and the labor to do it.
Did the entire 42RH installation and controls over one weekend.
 
I have done a bit more research on the vacuum switches

PATC supplies Superior Products switch KO58 6 to 22 ins vacuum
Superior Transmission Parts offer KO52, 1 to 6 inches of vacuum for GM and KO58 for Chrysler, so it looks as though 6 to 22 is the required range.

By my calculations this equates to 3 to 10PSI or 20 to 75KPa so I guess if you are going for the Ebay switch the -70KPa is probably the one to go for.

I'm not an expert and haven't tried one of these switches yet so please don't rush to buy on my suggestion. I'm going to risk $22 on one for myself and will report back. I plan to measure the hysteresis - difference between on and off vacuum on both types of switch to see if one is likely to be better than the other regarding cycling on and off.
 
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