Different Size Spare?

[Doc]

Just to clarify, part time 4wd trucks have no center differential.

Well, that helps me out then.

91-92 FJ80's had a 'center differential lock' button from the factory. So the FJ80's are full time 4wd, but do not use a VC like the latter 80's do. That kind of sucks.

 

[Land Speeder]

Land Speeder, your truck (if it is indeed minus a VC) is like my FJ60 example, a traditional 4wd. Running a smaller size spare will hurt nothing, even on a powered axle.

I thought though, that 91-92's were still full time 4wd? If this is the case, do they not use a VC? Do they use some other method?

Doc, I don't know, I was told earlier in this thread that I didn't have a VC. I have full-time 4wd, but my drive shafts do not try to spin equally unless the center dif is locked, 91-92's came factory with this button. If unlocked and both my front tires are off the ground, then they will spin and the rears will not (found this out while installing my lift). This seems contrary to the VC idea mentioned. I don't know, but I will educate myself on this since it seems that what I can do and have done is not possible without breaking something. So my question is, if all three diffs are open, why is there any question? Nothing will bind.

edit: this thread is too fast for me, by the time I posted this, most questions were answered... thanks

 

[dieseldog]

Doc, I stand by my advice--even with a vehicle with open diffs. Look to the last portion of my reply and you'll notice a comment regarding handling and braking, etc. Smaller diameter spares are a dumb idea--all the time--regardless of what you drive. Just say NO to donut spares.

You don't get to choose the time/place of a tire going flat. Could be when you are loaded down, or offroad, or bad weather, etc. A full-size spare is the only way to go.

 

[Doc]

Agreed, but it CAN be done.

Your rear (powered) axle will just think your driving in circles if you install a smaller spare on the powered axle. It'll see more rotation on the smaller wheel, just like you do in a corner. You can drive in circles all day long right? It'll effectively be the same thing. But braking forces, handling etc will be different on the same axle, and that's never a good thing.

 

[landtank]

First, only 80s with ABS have a VC. Since the original poster has a 97 and all 97s have ABS, he has a VC.

My understanding is that if the VC is in constant use it tends to burn out. They are expensive, in the order of 800.00 just for the part.

The original poster was asking about using a smaller spare for use up to a 75 mile drive. I'd imagine that this would fall into the area where the VC would start to bum out. That would be like an hour and a half of constantly being engaged if most of the drive was at highway speeds.

In a vehicle without a VC, I don't think there is a problem with any mechanical issues unless you lock the center diff, but it will provide a truck that will behave differently.

 

[Aussie_Locker]

The Aussie Locker operating guide calls out tires that are no greater than 3/8" difference in the circumference. The reason for this is that the locker will see a different size tire (smaller for example than the usual tire set up) as the "spinning wheel" and will disconnect this wheel from the cam gear. When driving a distance this results in constant lock/unlock or just constant unlock on one side with all driving done on one wheel. Can you do this in an emergency, sure, but be aware of the issues in handling and wear and stress on the diff. Hope this clarifies why this requirement is called out in our manual and is a warranty consideration. We dont care if you run 37" tires, but do need them to meet the size specifications for proper Aussie Locker operation.