How does the 4x4 system on a '81 blazer work?

[derherr65]

New to 4wd, still waiting on my service manual to arrive, but can't wait on the answer. How, exactly, does the 4x4 system work? I know that the engine puts out power to torque convert, torque converter hits stall speed and turns gears in transmission, and consequently the output shaft... then what? In both 2wd and 4wd. Does it have limited slip differentials? Are the front and rear drive shaft locked together in 4x4, or do they slip, or can one overrun the other? Same for the hubs, how do they work, do they lock and squeal tires in turn or overrun or what?

 

[dyeager535]

Assuming the '81 is the right transfer case, the 4WD in the case works with a chain. Shift the lever, and the input from the transmission is split to the front and rear outputs on the transfercase. Always putting power to the rear output (except when the t-case is in neutral) of course.

Since the stock front axle is an open differential, you don't have any real binding problems when turning.

There is no "differential" in the system. That's actually AWD (arguments ensue). 4WD means the front and rear driveshafts turn no matter what, they are "locked" together through the transfercase. There are of course front and rear differentials in the axles, however those don't slip if all the wheels have traction, which is why you don't run 4WD on good traction surfaces.

In the axles themselves, unless modified, you will have an open differential in the front axle, and either open, or gov-loc in the rear axle, which is a hybrid type locker that acts open until a rear wheel spins, then it locks.

 

[derherr65]

Great info, thanks. ANd the auto locking hubs? I keep hearing "replace them!" Seems like a hand feature if you could overcome their weakness. How do those work and what fails?

 

[apache]

Stepping back to the 70ies when the 203 full time was released there is actually a differential of sorts in the transfer case. Recall if you will the High ,High lock,low,low lock,neutral and 2wd Hi positions. The unlock position allowed power to be put the end supposedly in need,lock position did exactly that and locked the transfer case outputs. I remember yanking the spend front drive shaft from a room mates Chevy 4x4 with a 203, as the U joint fell poped out of the yoke the truck damn near killed me as it rolled out the driveway which was on a slope.

 

[Metrodps]

Assuming the '81 is the right transfer case, the 4WD in the case works with a chain. Shift the lever, and the input from the transmission is split to the front and rear outputs on the transfercase. Always putting power to the rear output (except when the t-case is in neutral) of course.

Since the stock front axle is an open differential, you don't have any real binding problems when turning.

There is no "differential" in the system. That's actually AWD (arguments ensue). 4WD means the front and rear driveshafts turn no matter what, they are "locked" together through the transfercase. There are of course front and rear differentials in the axles, however those don't slip if all the wheels have traction, which is why you don't run 4WD on good traction surfaces.

In the axles themselves, unless modified, you will have an open differential in the front axle, and either open, or gov-loc in the rear axle, which is a hybrid type locker that acts open until a rear wheel spins, then it locks.

Since the front differential is open, stock, there is no real binding with the hubs locked in.

That is one of the best descriptions I have ever read. Where did you steal it from.......

The Auto hubs have a tendency to go bad when you need them the most. Way out in the boonies and you need the front hubs locked. IMHO (in my humble opinion) I like the manual you get a little better mileage and if you frack your rear drive shaft you can cheat and use the front wheel drive to get back to civilization.

 

[dyeager535]

I wrote that. It's lacking detail, but a general overview to keep it simple.

x2 on auto hubs. They do tend to fail at the worst time. After shifting to 4WD, if working correctly, as the vehicle starts to roll (or continues, if shifted on the fly) they "lock in". To unlock, you need to put it in 2wd, then back up approx. 10ft. Can't go wrong by backing up further, just in case.

Manual hubs are ok, if you know you are going to need 4WD, you can always turn them in and leave it in 2wd. They also help when towing. You can put the t-case in 4 low, with the hubs turned out, and in the case of a 208, is a pretty good ratio. It helps slow the vehicle down for backing with a trailer. At least for me, since I've got a stick. I can put it in reverse and not have to worry about the clutch as much.

 

[Metrodps]

Opps sorry i forgot to add these no offense was meant Dorian.
I apologize was just kidding. But yea it was the best and to the point explanation I have ever seen.

 

[Chevy305]

Great info, thanks. ANd the auto locking hubs? I keep hearing "replace them!" Seems like a hand feature if you could overcome their weakness. How do those work and what fails?

Everyone says they suck, yet after the near 4 years of having my truck they have never failed on me and I have put them through some rough suff too. My only problem I have had with them is that I took them apart to service the wheel bearings and couldn't figure out how to put them back together... I was then forced to go with manual hubs in order to get wheeling again.

BTW the milage comment isn't true, I haven't noticed a single difference between auto and manual hubs.

 

[dyeager535]

Should be no difference in mileage. Any turning components in 2WD will turn solely based on parasitic drag.

Based on the failures noted on this board, the auto hubs are *MUCH* more prone to failure than even stock manual hubs that are as old or older than the autos. It is important to remember that maintenance and usage on vehicles this old are completely past the manufacturers intention, therefore calling components weak at the age they are is a little bit misleading. Saying auto hubs don't age as well as manuals would be a true statement.

The real problem with the auto hubs is that when they DO fail, it's when you need them, therefore they can, and will, leave you stranded. I've had my manual hubs fail (my fault) too, but I was able to get them apart with an allan wrench, and fix them with a flat blade screwdriver in 10 minutes. Auto's won't be that easy to fix.

But I digress. There are other threads where this has been covered in-depth.

 

[derherr65]

cams?

It looks like automatic hubs are cam activated. You have to make a few rotations before the cam fully locks, hence the 'weakness'. Throttle and partially engaged anything is a recipe for disaster. Similarly, you have to back up at least 10' to disengage.