I have been searching all over and have read the tech articles concerning defeating ADD. My 4-wheel drive has failed to engage for what is now the 4th or 5th time and this has become a major reliability issue. I want to do things right and cost is not the utmost consideration.

ErikB previously posted:
"If you permanently engage the ADD mechanism(and if the hubs are locked if you have manual hubs), or if you do the same by swapping in an axle that doesn't have ADD, the front and rear driveshafts will always be spinning the same speeds so you can easily shift in or out of 4wd at any speed. Its actually easier since you don't have to put pressure on the shifter to engage the synchro (clutch/brake)."

I was under the impression that all T-100 came with ADD so how does one swap in an axle without it?
Assuming this would be everything but the third-member, can anyone recommend the best components to use for such an upgrade? I already have Aisins.

I don't drive my truck much annually (~4K) but when I do it has to be rock-solid. I also intend to keep it many, many years and don't want to have to continually source vacuum lines, solenoids, etc. another 10-15 years from now. Thanks in advance. Thanks in advance. Brew <img src="/forums/images/graemlins/cheers.gif" alt="" />

I found my 4WD shifting to be intermittent. About the only time I ever shifted into it was a few times during the winter. Now I make it a practice to shift it into 4 once a month and I have had no problems with it since. I don't know if it was the electrical part or the manual but something must get some corrosion on it or get mucky if you don't shift it in for a long time. My 2 cents.

The axle swap I was referring to would be a straight axle swap. <img src="/forums/images/graemlins/wink.gif" alt="" />

However, you can do it keeping your IFS and using factory parts: you can swap the non-ADD axle stub/housing from a non-ADD truck onto your ADD diff. Its a bolt-on affair.

You basically get a non-ADD IFS diff, unbolt and remove everything from the driver's side of your ADD diff, and bolt in the non-ADD stuff. The only little tricky part is removing the little ADD stub axle from the diff, but I've always managed to pry it out with a couple of screwdrivers. A proper puller would be a little easier, but not mandatory.
You also need to install a new seal in the cast center section that matches the one on the passenger's side because the oil seal is in the ADD housing that you just removed on the ADD diff. Its fairly self-explanatory once you take everything apart.

You can also do the same thing in reverse if you want to make a non-ADD diff ADD, which I have done as well.

The one tool you will need is an external Torx socket (E-12?), which Napa carries on the shelf, at least here locally. I've gotten by pounding a 7/16" socket on the bolt, but it doesn't always work very well. Those bolts are TIGHT.


The cheap/easy way to defeat the ADD is this though:
http://www.4x4wire.com/toyota/tech/add/

Thanks for all the replies. I now have an A.D.D.-defeated T-100. My friend, who owns an import vehicle shop, devised an alternate method of locking the shift fork without using the clamp method described in the 4x4wire article.
He explained that there was an inspection port on the axle tube with a bolt in the center of the cover. He said the shift fork had a hole or detent that this bolt aligned with when the fork was slid-over into the locked position. He fabricated a longer bolt with an extended conical tip that now holds the fork in the proper position. He marked the axle tube "Locked" and removed the now unnecessary vacuum lines. He thought it was a more robust method of insuring nothing every moved or became loose.
On a side note, the failure this time was actually an electrical relay that controlled the vacuum portion of the A.D.D. system but I was tired of this overall issue and am now happy to have everything simplified. It rained here this AM so I decided to try out the 4WD operation. The trasfercase engages with zero effort and the occasional grind I got when engaging 4H from 2L is now absent.
Thanks again for your assistance. Brew <img src="/forums/images/graemlins/cheers.gif" alt="" />

Brew, do you have a picture of where this bolt is located? Looks like a clean solution. Thanks.

Hey Marion,
I've been a bit busy but when time permits I'll post a pic. Not sure of all the intimate details as this was done while I was busy at work. My skidplates are all back in place so I'll have to get under and root around to detail the location. Brew <img src="/forums/images/graemlins/cheers.gif" alt="" />

I took a couple shots that should properly reference the cover. You can see that he has wired the bolt in place. He wanted to be sure nobody inadvertently screwed this up. The first image is a close-up and the second should give you all the reference you need. Brew <img src="/forums/images/graemlins/cheers.gif" alt="" />

Thanks Brew, a picture helps!

So...

If you can still shift on the fly, and there is less that can go wrong, why have ADD in the first place? What is the purpose/function of ADD that has now been eliminated?

I guess I'm just confused on why disabling ADD is not different than not having it.

Joel

Honger,
If I had the standard OEM hub flanges(Live Hubs) then ADD allows for the front axle to be disconnected...or at least half of it. <img src="/forums/images/graemlins/zombie.gif" alt="" /> However, I have installed Aisin manual hubs that allow the axles to be disconnected at the hub making ADD unnecessary.

With the shift-fork locked(ADD-defeated), both front half axles are connected and would always be spinning when the truck is moving. The Aisin hubs simply replace the ADD fuctionality although completely versus halfway.

Running with the manual hubs locked and ADD-defeated wouldn't be as bad as running 4WD on dry pavement but it would be additional wear and tear on the front drivetrain as well as a draw on mpg.

When someone says shift-on-the-fly with reference to my truck they are assuming my Aisins are set to the "locked" position. Otherwise I have to get out and lock them.

If our trucks came from the factory with Aisin hubs then we wouldn't have needed ADD. Hopefully this makes sense. Brew <img src="/forums/images/graemlins/cheers.gif" alt="" />

p.s. - Here's a link to an ADD system document on another site.