Need a switch to tell computer when in 4-low - any ideas?

[Daveo91Burb]

https://www.digikey.com/en/products/detail/omron-electronics-inc-emc-div/SS-5GL2/137204

I would think this would work.

Yeah, I think so too. I actually ordered the one that @yevgenievich posted since I found it on Amazon, but it's the same idea - lever switch. Thanks.

yeh you could either drill into the metal there, or fabricate a bracket and use the rear bolt to mount it. I'd make sure there was no flex, I don't know what would happen if the switch disengaged while driving.

The one I ordered has two mounting holes through the body of the switch, so I think I'll try and mount it right to that plate. Agreed on no flex - PCM would definitely become confused if it started jiggling in and out of 4-low.

 

[yevgenievich]

The arm on a switch allows for some overtravel without damage to the switch. Other switches posted that have a plunger should have some overtravel as well, just have to check the specs. There are plenty of sealed versions as well, just more expensive.

I should have put a warning on the one I posted. It was not very carefully selected, just first one that popped up from a known manufacturer and met the requirements with the design that I was thinking of.

 

[Daveo91Burb]

The arm on a switch allows for some overtravel without damage to the switch. Other switches posted that have a plunger should have some overtravel as well, just have to check the specs. There are plenty of sealed versions as well, just more expensive.

I should have put a warning on the one I posted. It was not very carefully selected, just first one that popped up from a known manufacturer and met the requirements with the design that I was thinking of.

It's all good - I'm pretty sure it's going to work out pretty well. I like the one you posted since I could order it on Amazon. (i.e. no signing up for yet another online account)

I got it mounted today. Looks like it's going to work just fine, with hopefully good longevity. The arm is flexing a bit when it's in 4-low, but not enough to worry about, just ensures positive engagement. Tested with multimeter - switch goes to ground when in 4-low, just as it should. No interference when the boot/indicator assembly is installed either. (I was a little worried about that)

Thanks to all for the suggestions.

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[Camar068]

It's all good - I'm pretty sure it's going to work out pretty well. I like the one you posted since I could order it on Amazon. (i.e. no signing up for yet another online account)

I got it mounted today. Looks like it's going to work just fine, with hopefully good longevity. The arm is flexing a bit when it's in 4-low, but not enough to worry about, just ensures positive engagement. Tested with multimeter - switch goes to ground when in 4-low, just as it should. No interference when the boot/indicator assembly is installed either. (I was a little worried about that)

Thanks to all for the suggestions.

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What pin was it? I looked it up and was a little confusing to me. I'll look again in the mean time.

[edit] the part thats confusing me is my vss is on the output shaft of the trans. It states:

4WD Low Signal (KEEP IF USING STOCK TRANSFER CASE IN A 4WD APPLACTION, WITH VSS ON OUTPUT OF TRANSFER CASE.

 

[Bextreme04]

What pin was it? I looked it up and was a little confusing to me. I'll look again in the mean time.

[edit] the part thats confusing me is my vss is on the output shaft of the trans. It states:

4WD Low Signal (KEEP IF USING STOCK TRANSFER CASE IN A 4WD APPLACTION, WITH VSS ON OUTPUT OF TRANSFER CASE.

You'll just have to modify your 4WD shift tables to match what the trans output sees rather than what the actual vehicle speed is in 4lo. If you have an electric speedo, you should really have the VSS on the transfer case output.

 

[R Carnella]

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i did the same but i mounted mine underneath the gate plate.i used a micro switch, you can see the little wheel of the switch poking out. I couldn't drill through that plate for **** so used two part epoxy to mount the switch....

 

[Daveo91Burb]

What pin was it? I looked it up and was a little confusing to me. I'll look again in the mean time.

[edit] the part thats confusing me is my vss is on the output shaft of the trans. It states:

4WD Low Signal (KEEP IF USING STOCK TRANSFER CASE IN A 4WD APPLACTION, WITH VSS ON OUTPUT OF TRANSFER CASE.

It's pin F8 on a 7427 PCM. This is a diagram from '94 2500, 4L80e trans. This pin has a reference voltage on it and when it's grounded, the PCM knows it's in 4-low.

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You'll just have to modify your 4WD shift tables to match what the trans output sees rather than what the actual vehicle speed is in 4lo. If you have an electric speedo, you should really have the VSS on the transfer case output.

'91-'93 4wd with 4L80e (like my '91) are a weird beast. There are three speed sensors: input on trans, output on trans, and output on rear of t-case. If the PCM saw a differential between trans output and t-case output, it knew it was in 4-low. In '94 they changed this. They eliminated the trans output VSS and put a plug in there (I've read some account that there actually was a sensor installed, but it wasn't hooked up). Then they added a switch on the t-case shifter, like I'm adding here, that gave the PCM a signal that it was in 4-low, so fuel and shift tables would change accordingly. (Sorry if I'm stating the obvious here - I know you know this stuff pretty well!)

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i did the same but i mounted mine underneath the gate plate.i used a micro switch, you can see the little wheel of the switch poking out. I couldn't drill through that plate for **** so used two part epoxy to mount the switch....

LOL - thank you for posting this! I thought I was going crazy trying to drill into that plate. Tried a bunch of different bits, drill press, hand drill, different speeds, cutting fluids etc. One thing finally did work, though: diamond tipped blade for making a hole in porcelain tile!! Cut through it like butter. What the hell is that plate made of anyway??