SOTF (Shift-On-The-Fly) Troubleshooting

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SOTF (Shift-On-The-Fly) Troubleshooting

Postby Tad » Sun Dec 07, 2008 9:37 pm

As a follow-up to my article on hub types I thought I'd post a few troubleshooting tips for SOTF trucks.

The original article:
http://www.planetisuzoo.com/articles.ht ... _Explained

SOTF trucks operate on the following:

1) Both CV shafts are always spinning. This means that your CV joints and boots are also always spinning which provides a nice segway to yet another article.

2) The left-side CV shaft has a vacuum or motor operated disconnect. The purpose of this is so that you aren't spinning the front differential to the point of noticeable drag to the driver. (drag as in a stiff steering wheel).

3) The transfer case also has an automatic shift mechanism for shifting between 2-high (2H) and 4-high (4H).

4) There's a computer that controls the system.

5) When you push the button the following happens:
A) The transfer case engages. For TOD trucks this just means that TOD starts doing its thing. For non-TOD SOTF trucks where's a motor on the back of the transfer case that shifts the shift-rail into 4H.
B) The computer watches for the 4WD system to become engaged (via a sensor in the t-case).
C) The computer switches two vacuum solenoids. It disables the disengage solenoid and enables the engage solenoid. If your Rodeo has the electric system it just sends power to it to engage the axle.
D) The computer watches for the front axle to become engaged (via a sensor in the SOTF actuator).
E) If anything in the chain fails, it blinks the light)

6) The Solenoid system consists of two solenoids. One colored green/blue and one colored grey. Chances are if you are having a problem with the system the solenoids are the problem. It's a good idea to exercise them periodically. (I try to do so at least once a month.) You can bypass the solenoid by moving the vacuum source directly to the engage part of the solenoid.

If you are looking for used solenoids (which you will once you price new ones), look for 2nd gen Rodeos. They have the solenoids right next to the brake-booster under the hood so you don't have to lay down in the mud at the junkyard to remove them. They will swap to a Trooper.

I've only heard of one shift-motor failure on the transfer case. That was mine. That t-case had gear lube in it at some point so that might have been the source of the problem. I could get it to engage (sometimes) by tapping the motor with a hammer. Same thing with disengaging.

If you have an electric motor on the front axle then this article might help:
http://www.planetisuzoo.com/articles.ht ... _Mechanism

It also lists the solenoids as having 42-ohms. It's interesting sure but the solenoids come as a pair from the dealer so that info might not be very useful.

For interest I removed the SOTF system on my 99 Rodeo after I got tired of futzing with the shift-motor on the t-case. To do so I
1) Replaced the transfer case with one from a 94 Trooper (automatic). This was a bolt in swap but it did require a large socket to swap the output flange from the Rodeo t-case to the Trooper t-case. I used the Rodeo shift lever because it was the right length.
2) I made the front axle permanently engaged by connecting the vacuum source from the engine directly to the lock position on the front axle solenoid. I forget which color is lock (green or grey) but I can easily check for those who care.
3) I will connect the 4wd indicator light on the dash to the 4wd switch in the t-case.
4) I will install manual-hubs. I'd have done this with the SOTF system in-tact in order to prolong the life of my CV boots, increase gas mileage (sometimes by as much as 1mph) and make the steering feel lighter.

That was a mouthful. Any Questions?

-Tad
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Postby SurferJoe » Sun Dec 07, 2008 10:18 pm

Thanks for that Tad - it's out of my realm of experience to work on this part of the drivetrain and I appreciate the extra things you presented here.

I did a C/P of the article you wrote..is that OK with you?
Joe Vreeland - In The Bitterroot Valley, Montana
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Postby Gizmo42 » Mon Dec 08, 2008 1:44 am

Here are some diagrams and a pic I have on my photobucket page for SOTF system incase anybody wants them..

2nd gen rodeo front axle actuator..
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'96-97 SOTF diagram...
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'98+ SOTF diagram..
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Postby Tad » Mon Dec 08, 2008 8:38 am

So those diagrams tell me that the gray hose is for the LOCK side of the actuator. Now all of you with bad solenoids can go connect the vacuum source (from before the solenoids) to the gray hose thus making the system locked all the time. On my Trooper (can't speak for all Isuzus) this would provide 4wd just fine and 2wd with the light blinking (because the computer couldn't get the actuator to disengage).

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Postby Guarino97rodeo » Sat Oct 17, 2009 5:24 pm

so does connecting the gray hose mean it is always in 4 wheel drive or can u still switch between H L and 2 wheel drive? i have a 97 rodeo by the way with a shift on the fly problem
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Postby Gizmo42 » Sat Oct 17, 2009 6:03 pm

Connecting the gray hose will keep the front axle locked in. But if you have manual hubs you can unlock those and it will be the same as the actuator unlocking once you shift the t-case to 2wd. The light will always blink in 2wd though because it will see the front axle always locked in.
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Postby Guarino97rodeo » Sat Oct 17, 2009 7:44 pm

I fixed the problem thanks to ur guys help, just need to find the selonid so it will be normal, for now the bypass works great.
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Postby Guarino97rodeo » Sat Oct 17, 2009 7:45 pm

i have autolocking hubs, so will it affect my front axel if i keep it hooked up the gray hose way?
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Postby Gizmo42 » Sat Oct 17, 2009 8:58 pm

'97 should have drive flanges instead of manual or auto hubs from the factory. Drive flanges act like hubs that are always locked so the front cv shafts will turn all the time. With the front axle always locked in, not only will the cv's be turning but the front diff and front driveshaft will always be turning. Shouldnt really hurt anything other then maybe some power and unnessecary wear on the front drive componants. Now that you know where the problem is I would make it go back to 2wd until you get it fixed. Or get some manual hubs to replace the drive flanges. I keep my stock drive flanges in my rodeo as trail spares in case I break a hub on the trail.
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Postby Guarino97rodeo » Sun Oct 18, 2009 2:19 pm

I can shift out of 4 H and 4L back into 2h but the light stays on, and i can tel its in 2h but u think its better to set it up so it has to go through the solenoids so 4h doesnt work? what do the flanges do? is it easy to install manual hubs? do you have to by those new or can u get them from an older rodeo or something?
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Postby Guarino97rodeo » Sun Oct 18, 2009 2:29 pm

i have autolocking hubs, so will it affect my front axel if i keep it hooked up the gray hose way?


i have flanges my mistake, is putting manual hubs on easy? Costly?
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Postby Gizmo42 » Sun Oct 18, 2009 3:45 pm

Manual hubs are easy to install.

http://planetisuzoo.com/articles.htm?id ... Conversion

They can be pricey depending on what you get. Superwinch are the cheapest and weakest, they are what I have and havent broken one yet. They run about $100 (part # 400533). Warn is kinda in the middle and run $170-200. Aisins are the strongest and what isuzu used on older vehicles from the factory. Can find some used ones for around $100, sometimes cheaper at a salvage yard. They can be found on 87+ first gen troopers, first gen rodeos, and first gen amigos. Not all of them had manual hubs, alot had auto hubs. Also, 83-86 troopers and all pickups that had them had a different spline count so wont work on yours.

I would recommend either getting manual hubs, or replacing the front solenoids, or both. You really dont want the whole front drive line turning all the time.
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Postby Guarino97rodeo » Sun Oct 25, 2009 3:46 pm

off of what model isuzus can i find the solenoids? will 2nd gen rodeo ones fit on a 1997 rodeo? is there any other model that fits in stock location?
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3in lift, Shackle and Torsion.
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Postby Gizmo42 » Sun Oct 25, 2009 5:01 pm

VALVE UNIT; AXLE
8-97101-858-1

RODEO 12-1995 and LATER (it says later but 98+ mounts on the firewall instead of axle and have a different part number)
TROOPER 09-1995 to 05-1996
TROOPER 06-1996 and later
TROOPER 08-1997 and later
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Postby Guarino97rodeo » Sun Oct 25, 2009 5:15 pm

what are the numbers in front of the year for? so all those years are a exact swap from the original ones?
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Postby Guarino97rodeo » Sun Oct 25, 2009 5:46 pm

is the part number you gave me the whole vaccum switch or just the solenoids? i looked up the part online, and it was $197
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Postby Gizmo42 » Sun Oct 25, 2009 8:28 pm

The numbers in front of the year are the months. Sometimes they make changes in the middle of a model year.

That part number is for the solenoids and bracket all together. They dont sell them separately. Much cheaper to find some in a salvage yard if you can.
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Postby Guarino97rodeo » Sun Nov 01, 2009 8:30 pm

Help PLEase i cant find a part that works, went to junk yard and part doesnt work, can i buy a new one online or from dealer? send me info if any, thank u. Could the seloniod be the only problem?
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Bigger Tires and New Head unit
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Postby Guarino97rodeo » Tue Nov 03, 2009 11:18 pm

is there any chance that the solenoids are ok, and the vaccum switch itself is bad or not functioning right?
i have vaccum in 4wd and 2wd, could there just be a gunked up part in the switch that causes it not to shift?
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Re: SOTF (Shift-On-The-Fly) Troubleshooting

Postby DWBeards » Mon Aug 31, 2015 1:51 pm

I have an 02 Rodeo and I accidently took apart the SOTF system and I have no idea how to put it back together. Any suggestions? Also I have attached a picture of what I am looking at now.
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