Center Differential Lock Not Working in Low

80t0ylc

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The FJ80 had the CDL switch to enable the driver to lock the center in high range. Remember, it came with 3 open diffs. The FZJ80 had a viscous coupler in the center diff, so apparently the engineers felt that it was sufficient for 99% of situations. After daily driving both for many years I tend to agree.

On the FJ80 all that's needed is to remove the low range sensor plug off of the transfer case. This gives you manual control of the CDL in L and H.
Alternatively, you can ground pin 7 of the CDL relay and this will give you manual control as well. However removing the plug on the transfer case is completely non-invasive.

The difference between a pin 7 mod on an FZJ vs. an FJ is the transmission shift points. The FZJ has an electronically controlled transmission. In low range the shift points change. The A440F in the FJ80 is hydraulic, so it doesn't care what you do.
Thanks for the info, Jon! I never owned a FJ80, but I remember you had a '91. I guess the OP has a '93 that kinda fell in between the FJ80 and the FZJ80 with all the "upgrades". Some were an improvement, and some were at best, questionable. The VC and no CDL switch for example.
 
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Thanks for the info, Jon! I never owned a FJ80, but I remember you had a '91. I guess the OP has a '93 that kinda fell in between the FJ80 and the FZJ80 with all the "upgrades". Some were an improvement, and some were at best, questionable. The VC and no CDL switch for example.
Like I said, with the VC in the center, it's pretty rare that I need to lock it up in high range. I live on a pretty steep hill with a stop sign half way up. In the snow with my 91 I needed to lock the center to get her past the intersection from a dead stop. With my 97 I never had to do that. I like to leave the CDL unlocked in low range because of all the tight trees we have in the northeast. Much less understeer and less strain on the drive line.
 
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Just to back up what the OP said, I have a 93 and they do have a factory installed CDL button, and when everything is working the center locks when shifted to low without having to use the button.
Good to know. I was questioning my sanity.
Just to back up what the OP said, I have a 93 and they do have a factory installed CDL button, and when everything is working the center locks when shifted to low without having to use the button.
And you have ABS as well, correct?
 

80t0ylc

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It’s a 93, locking differentials. It came with the dash switch for the CDL.
Curious question, do you have the full floating rear axle & disk brakes in the rear as well as the front? Locking axles implies the FF rear axle, but just trying to make sense of why yours came with the CDL switch. '91 & 92 yrs had the semi floating rear end with drum brakes, but there were some '93s that fell in between the FJ80 & fully equipped FZJ80 with the FF axle, VC in the center diff, 4 wheel disk brakes and 16" wheels.

The FF has the hub in the center that protrudes through the wheel.
Example to identify FF rear axle hub:
IMG_1134 (2).JPG
 
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This makes absolutely no sense. If this is true, I have even less respect for Toyota 80 series electrical engineers. If the manufacturer provides a CDL switch to control T/C lockup, why do they want to force you to lock the T/C in lo range? So you're saying that '91 & '92 owners need to do the pin 7 mod to gain full control? Never heard that before, not even sure those years have a pin 7.

Curious question, do you have the full floating rear axle & disk brakes in the rear as well as the front? Locking axles implies the FF rear axle, but just trying to make sense of why yours came with the CDL switch. '91 & 92 yrs had the semi floating rear end with drum brakes, but there were some '93s that fell in between the FJ80 & fully equipped FZJ80 with the FF axle, VC in the center diff, 4 wheel disk brakes and 16" wheels.

The FF has the hub in the center that protrudes through the wheel.
Example to identify FF rear axle hub:
View attachment 2890657

I caution you on generalization. People reading this will take it as gospel.

Us spec models match your description. Imports do not.
 

80t0ylc

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I caution you on generalization. People reading this will take it as gospel.

Us spec models match your description. Imports do not.
I understand that. This is still the USA, I think, and imports are still relatively rare here.
 
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I understand that. This is still the USA, I think, and imports are still relatively rare here.

There's a good number of members not from the us.

Imports are far less rare than you think especially as these age and it becomes easier to import them. I can look locally on cl and see a handful of imports.


And it's new owners that will see this info. New owners are more likely to have an import than someone who's already got an LC on the forum.
 
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93 didn't have a CDL dash switch from the factory since it turns off ABS, it must have been added by the PO.

i can promise you that switch was added.

A few 93 & 94 80s were sold in the US market with no ABS, rear drum brakes, rear semi-floating axle, and factory CDL switches.

I was corrected by @cruiserdan himself on this subject:

 
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Curious question, do you have the full floating rear axle & disk brakes in the rear as well as the front? Locking axles implies the FF rear axle, but just trying to make sense of why yours came with the CDL switch. '91 & 92 yrs had the semi floating rear end with drum brakes, but there were some '93s that fell in between the FJ80 & fully equipped FZJ80 with the FF axle, VC in the center diff, 4 wheel disk brakes and 16" wheels.

The FF has the hub in the center that protrudes through the wheel.
Example to identify FF rear axle hub:
View attachment 2890657
Hi- Thank you for the pic of your truck.
My LC, has three locking differentials. Front and rear disk brakes and FF axel (please see the pic below), as well as ABS. The previous owners, a lovely family, had the car for over 24 years and, I'm guessing they weren't the mechanically inclined type (as evidenced by over 100 pages of service records, everything from putting new wipers on to topping off oil, replacing seatbelts, etc) -- so I really don't see them having the CDL installed.
I prefer to have the CDL switch, as its useful in snow and in sand at speeds higher than I feel comfortable in low. I searched the forums trying to find an answer but never reached a clear answer. I only recently put it in L, to assist a vehicle stuck in the snow.

Rear Hub.jpg
 
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cruiserdan

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If the center will lock using the dash switch but will not lock when shifted into low range the low 4 position indicator is unplugged or there is a problem with the indicator switch or the circuit feeding it.

When you shift into low do the transmission shift points go up? They should if the circuit is working properly.
 
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If the center will lock using the dash switch but will not lock when shifted into low range the low 4 position indicator is unplugged or there is a problem with the indicator switch or the circuit feeding it.

When you shift into low do the transmission shift points go up? They should if the circuit is working properly.
Thank you for your message. Yes, it definitely goes into low and shifts up. Matter of fact, I made the mistake of shifting into low with the engine cold and high idle -- I had to stand on the brakes to keep the truck from creeping forward. -- but no CDL. I tend to agree with your assessment, it doesn't know that TC is in low.
 
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To clarify, when in low range the the shift points move up to a higher RPM. Very much like when you switch to the power mode. If the transmission shifts rapidly through the gears in low range the low 4 position circuit is not working.
I apologize for not being more clear. Yes, the gears wind out, just like when the ECT button is pressed. The transmission takes longer to shift and at a higher rpm.
 

cruiserdan

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I apologize for not being more clear. Yes, the gears wind out, just like when the ECT button is pressed. The transmission takes longer to shift and at a higher rpm.
That means the low 4 position switch is sending a signal to the transmission ECU. This means the system is behaving as though pin 7 has been disconnected.
 
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That means the low 4 position switch is sending a signal to the transmission ECU. This means the system is behaving as though pin 7 has been disconnected.
Thank you (and everyone) for the help. To close this thread, I’m Not really sure what I did. I jumped the circuit the lights came. Put it back together and it’s locking now. Thank you again.
 

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