Powerstroke123

My tranny gave up the ghost on my 91 3.0 4wd runner with ADD, found a good used one out of a 93pickup 3.0 4wd with manual hub....long story short is my ADD relay in the dash is not clicking on like it did before the new tranny was installed. It worked fine before, is there something on the original tranny I can swap to the new tranny? I had them side by side before install to check for differences and all I found was the 91 had a cable speedo and the 93 was electronic. I switched those before install. My dummy light on the cluster does come on. Any help would be appreciated. Picking up a cabless and bedless 91 3.0 4wd manual this wknd to swap frontend, rearend and 5speed into my runner but it will be a few months to get everything together, really need my 4wd to work in the meantime!

skypilot

iTrader: (1)

I think you missed a wire on the trans. Anyway all you have to do is take the ADD cover off, lock the lock and put a screw clap over it the keep it in place. Put cover back on.

scope103

Is the Transfer Position Switch a) connected and b) aligned correctly?
http://personal.utulsa.edu/~nathan-b...32prelimin.pdf
That's what triggers the ADD relay.

Powerstroke123

Does the transfer position switch control the 4wd dummy light? Everything is hooked up, I've triple checked that. I've seen some Info on a transfer pressure switch but can't locate it...I'll check to see if it's lined up when I get home this afternoon. Thanks for the response!

Powerstroke123

Is the transfer pressure switch in the engine bay?

dropzone

iTrader: (6)

gonna sound stupid but did you put the front d/s in?

Powerstroke123

Yes sir, the ADD system is not receiving communication from my tranny to lock the front end. That would be funny as hell if the d/s was left off!

dropzone

iTrader: (6)

You would be surprised, one guy said he could not get his truck to work in 4wd, he was new and wasn't aware of locking hubs.

I wish i knew more about ADD. Good luck!

vasinvictor

iTrader: (3)

The 4x4 dash light doesn't come on until the front ADD collar locks.

vasinvictor

iTrader: (3)

If you have the manual hubs now, you could just do this. Permalock the ADD and lock the hubs in and out instead.

The transmission doesn't know if it's an ADD trans or not. The ADD is contained in the front axle. there are 2 vacuum lines that supply vacuum to the front diff that unlock and lock the ADD. The collar locks if the transfer case is in 4wd position, the vacuum solenoid on the passenger side engine bay is engergized and vacuum is applied to the locking side of the ADD. There's another VSV that "devacuumizes" the ADD to unlock it. For a test, you can find the "locking" side of the vacuum hose and hook it up the manifold vacuum. That was any time the truck is started, the ADD collar is locked. I ran my truck for a while like this during my 3.4 swap.

Powerstroke123

My hub are not manual, my 4wd light does come on but my relay in the dash does not click like previously. I was under the impression the light was engaged by the transfer position switch. What does the transfer pressure switch do in my pic above.

scope103

The light is turned on by the ADD actuator; it confirms the end of a sequence of events that finishes with the ADD engaging.

The schematics I have for the 1994 and the A340H do NOT show a "transfer pressure switch." Instead, there is a "Detection Switch" in the transfer case, which grounds a Purple-Green wire, which closes the ADD control relay. (There is also an L4 detection switch, which grounds a red wire to the ECU.)

The wire FROM the ADD control relay is Green-red, and switches to Purple-Green in the ID1 connector.

I would check the Green-Red wire to the ADD relay, and see if it goes to ground when you switch to H4. If it does, the relay is bad. If it doesn't, find the wire coming from the transfer case that DOES go to ground in H4. That's the one you want.

Powerstroke123

Just got home, gona look now and I will let you know what I find. Thanks for the input!

wyoming9

iTrader: (1)

Do all the Transmissions have the switches for ADD even if installed in a non ADD vehicle.

I am not a Auto person so have no clue.

RJR

Are you sure the 4WD isn't working? As scope says, the 4WD light is controlled by the switch in the ADD mechanism, in series with the transfer position switch, and indicates that the ADD is locked and the transfer case is in 4WD. The light won't be on unless both of those conditions are true.

It's possible the reason the relay isn't clicking is that it is always "ON". If the control line to the ADD relay is permanently grounded, the light would still go on and off with the transfer case position, but the ADD would remain locked even in 2WD.

Have someone watch the front drive shaft while you drive it slowly in 2WD, to see if it turns. If it does, you've got the ADD relay permanently grounded and ADD always locked.

You could get the behavior I'm describing if your transfer pressure switch is always ON.

Powerstroke123

Sorry I haven't replied, phone gave up the ghost. The 4wd is working but is not disengaging the sleeve. I've been switching the vaccum to the vsv's manually so it's not locked all the time. Just picked up a donor 91 pickup 3.0 4wd 5speed. Now to figure out what I need to install the 5speed, front and rear end into my runner! I appreciate all the feedback and help!!

skypilot

iTrader: (1)

I'll go out on a limb and suggest you fix the donor truck. swapping to a stick is a lot of work. Hanging pedals, no thank you. Did it once on my back with a 14mm 1/4 drive flex head socket to get the linkage's in. While an automatic may not be your cup of tea, it does work.