80 series auto diff lock ALWAYS on.. WTF?

[semlin]

I personally don't believe that the VC engages around corners. The reason I don't believe this is because you can remove a DS (just one) and when you hit the gas, the vehicle won't move for a few seconds. It will the slowly start to move until it builds up some speed, then will drive like normal. (Until you let off the gas, that is.)

Since all the power is going to the disconnected side, that's a lot of rotational difference that is required to engage the VC. You're talking about basically a 100% rotational difference (one side spinning, the other side not at all).

the vc is not an aussie locker and is not supposed to be able to transfer enough power to one axle to start the vehicle from a standing stop or allow it to drive normally on only one axle. the only way it might be able to do that is if the vc oil was red hot. i would think that your experiment would burn out a vc pronto.

as i understand it, the vc is designed to "limit the slip" not "stop the slip" (e.g. lock the diff). and it is a gradual engagement. in normal operation it will quickly get you 10 or 20% more power and torque to the non slipping axle but no more. enough to hopefully temporarily maintain traction where you otherwise might lose it, but without creating the stresses caused by locked axles.

Now the rotational difference required to start engaging the VC is likely far south of 100%, otherwise folks wouldn't see the VC locked up from "normal" driving.

exactly. it's nowhere near 100%. the question is how much more slippage is allowed for before the vc engages over and above plus the normal slip from turning. it makes sense that it is not very much given toyota's warning not to use mismatched tires.

Additionally, Toyota would not want the VC to lock while turning.

but it does not lock: it just limits the slip. and there is no way to prevent it activating more often when turning than on the straights, because the turn itself will cause some baseline wheel slippage that will count towards whatever the vc threshold engagement is. the vc has no way of distinguishing normal cornering slip from traction slip.

Toyota introduced ABS at the same time as the VC, but they aren't tied together. It's believed that the VC was introduced primarily to help reduce the clunk and slop in the drive train, the better handling on slick surfaces was a bonus that made it worth while.

But the two systems aren't connected in any way, shape, or form.

i agree they are not physically connected but the abs system works based on monitoring the rotational speed of the wheels. there may be an abs related design reason that toyota used a vc when it introduced the abs. if the abs is calibrated to expect a vc to be helping limit wheel spin differential then it may apply more brake force than the engineers thought would be safe for that level of difference with no vc in place. remember that the abs system was introduced in 1993 which is early days for abs.

and, as i said, i do not know if it impacts on abs, i just suspect it.

 

[Ebag333]

the vc is not an aussie locker and is not supposed to be able to transfer enough power to one axle to start the vehicle from a standing stop or allow it to drive normally on only one axle. the only way it might be able to do that is if the vc oil was red hot. i would think that your experiment would burn out a vc pronto.

It doesn't burn out the VC pronto, as it's been done more than once. Some people have driven around this way not realizing it and the VC was fine.

Once the VC locks up it's not going to be producing much heat. It's the engaging and disengaging repeatedly that will generate lots of heat, and cause the VC to fail.

as i understand it, the vc is designed to "limit the slip" not "stop the slip" (e.g. lock the diff). and it is a gradual engagement. in normal operation it will quickly get you 10 or 20% more power and torque to the non slipping axle but no more. enough to hopefully temporarily maintain traction where you otherwise might lose it, but without creating the stresses caused by locked axles.

but it does not lock: it just limits the slip. and there is no way to prevent it activating more often when turning than on the straights, because the turn itself will cause some baseline wheel slippage that will count towards whatever the vc threshold engagement is. the vc has no way of distinguishing normal cornering slip from traction slip.

It does lock, that's why you can remove a DS and drive around mostly normal (except for a feeling of slipping when taking off).

It's also why the VC will weld itself together and be locked (and act like the CDL is engaged).

Remember that the torque converter is also a fluid coupling (different design, but same basic principle), and the TC even when unlocked will still transfer the majority of the power. Just because it's a fluid coupling does not mean that it transfers a limited amount of power.

it makes sense that it is not very much given toyota's warning not to use mismatched tires.

This is a recommendation from every manufacturer, vehicle and tire alike, this has nothing to do with the VC. Running mismatched tires introduces all sorts of problems, handling issues, wear, etc, the VC is actually pretty far down the list.

i agree they are not physically connected but the abs system works based on monitoring the rotational speed of the wheels. there may be an abs related design reason that toyota used a vc when it introduced the abs. if the abs is calibrated to expect a vc to be helping limit wheel spin differential then it may apply more brake force than the engineers thought would be safe for that level of difference with no vc in place. remember that the abs system was introduced in 1993 which is early days for abs.

and, as i said, i do not know if it impacts on abs, i just suspect it.

The VC has nothing to do with the ABS system, not just physically but at all. They have no interaction what so ever. The only way that they would have a connection (very indirectly) is if the vehicle had traction control, which the 80 series doesn't.

The only thing ABS does is prevent the tire from not spinning at all. The VC doesn't have care about that, if a tire is going to stop spinning that means all the power is going to the other tire on the opposite side of the axle, which means the center diff (and axle diff) isn't sending any power to the tire that ABS is going to kick in on anyway.

If there is power to the tire, ABS can't kick in on it, because if there is power it's going to spin. Does that make sense?


Just because Toyota released them at the same time doesn't mean it's a connection. Correlation, not causation. That's like saying that 16" wheels causes the VC to run better, because Toyota ran 16" wheels in 93" instead of 15" wheels. Or that R134 has an effect on the full floating axle (as opposed to R12 on the semi-float).

 

[semlin]

ok, ebag we just disagree pretty fundamentally. i will state my last word on this recognizing you will not agree but just to cut to the chase. i certainly respect your right to an opinion and hope you respect mine

1. regardless of whether it can eventually heat up enough to lock the central diff, the vc is not designed to lock the diff in normal operation. it is designed to quickly limit the slippage that would otherwise occur at the axle that has not lost traction and then release. for this reason it is designed to engage fairly quickly once the level of slippage of an axle exceeds what normally occurs in a turn. i do not know exactly what the threshold is to engage the vc but i know that a relatively small tire diameter differential can cause it to engage.

2. if you run tires of different dimensions this will create a constant slip at the centre diff because of the different rotational speeds of different wheels. if the slip difference is enough to pass the threshold engagement of the vc, this will burn out the vc over time because the viscous fluid will get hotter and hotter and cause the diff to slowly lock up until it all fuses together, at which point your truck will behave exactly as if the cdl is locked all the time.

3. constant engagement and disengagement of the vc does not by itself allow the vc to get hot enough to harm the vc. the vc is designed to do this. this is why you can drive a landcruiser on a windy loose gravel road or through a sandy desert without fear of burning out your vc.

4. possibly, a combination of mismatched tires and gravel road/sand/snow operation could cause a vc to burnout more quickly than it could happen on pavement. i do not know.

5. assuming the same driving conditions, the vc engages more often on corners than in a straight line by design because it cannot distinguish between normal corner wheel slip and abnormal straight line wheel slip and so it has a "head start" on engagement on corners. it is therefore intended to engage improve traction in corners. it does not fully lock the diff on corners, it just passes a small amount of power and limits any slip beyond the normal threshold.

6. the vc improves traction and limits skidding which in turn makes the job of the abs system easier, especially when braking in corners. i do not know whether the traction performance improvement assumed for a vc system was considered an essential part of the abs design for the truck. i do know i am very skeptical that the vc was introduced at the time abs was introduced to compensate for driveshaft slop.

7. i have not heard of an 80 series with abs but with the non-vc tcase. i do know there are 93-94 north american 80s that had semi floater rears and no abs, and it would not surprise me if they also had the non-vc tcase. if there are confirmed cases of an 80 series from the factory with abs but no vc then i would agree that the vc is not necessary to abs function.

i may well be wrong about some or all of the above. i am simply setting out my understanding of the matter.

 

[crooozer]

You reckon I can drive it over the next couple a days? Or is the diff likely to break?

 

[CJF]

You can drive it without causing any (more) damage.

Oh, and if you're really worried, just remove the front driveshaft and drive it that way.

 

[Ebag333]

Oh, and if you're really worried, just remove the front driveshaft and drive it that way.

This.

Driving with a locked center diff (whether it's the VC seized or CDL engaged) on pavement is hard on the front end. Not likely to actually break something, but will cause additional wear and stress on it.

 

[semlin]

You reckon I can drive it over the next couple a days? Or is the diff likely to break?

if you have a centre diff switch on the dash i think i'd formally lock the diff to take any stress off the vc, but i expect you have already done the damage. i agree with dropping the front drive shaft.

sorry for hijacking your thread by the way.

 

[landtank]

You reckon I can drive it over the next couple a days? Or is the diff likely to break?

take a few minutes and do a few simple tests to narrow down where the issue is.

Place the tranny and Center diff in neutral.

Now jack 1 tire off the ground at a time and see if you can turn them.

If you can't turn any of them then the Center diff has a problem.

If you can turn some but not others then that means something else.

Take the time to work through this and we can help.

FWIW, the fact that your mechanic stated that the VC was immersed in oil is a red flag for me, It's not!

 

[rove_mcanus]

This is a recommendation from every manufacturer, vehicle and tire alike, this has nothing to do with the VC. Running mismatched tires introduces all sorts of problems, handling issues, wear, etc, the VC is actually pretty far down the list.

Everybody, except Mazda

http://i00.i.aliimg.com/photo/v0/101565844/Used_Japanese_Mazda_Truck.jpg

 

[Ebag333]

Everybody, except Mazda

http://i00.i.aliimg.com/photo/v0/101565844/Used_Japanese_Mazda_Truck.jpg

Running different sized tires on different axles is no big deal. The comment more refers to running different sized tires on the same axle. Even Mazda says not to do that.

You can even do that on an 80, as long as you drop one of the DS's and have the CDL locked (or a part time kit).

 

[crooozer]

Thanks guys, how do i disconnect the front driveshaft?
Is it just those 4x bolts?

I have to drive 300km this weekend, most of it over straight highway though which is good.

Ok thanks guys, I'll jack it up and work through it here. Awesome!! Thanks for helping out so much

 

[semlin]

Thanks guys, how do i disconnect the front driveshaft?
Is it just those 4x bolts?

I have to drive 300km this weekend, most of it over straight highway though which is good.

Ok thanks guys, I'll jack it up and work through it here. Awesome!! Thanks for helping out so much

yup. 4 bolts at each end.

 

[Ebag333]

yup. 4 bolts at each end.

Yeah, don't forget the other end. That'd be bad.

 

[crooozer]

Sweet guys! I take it off now and hopefully she'll be sweet for the long drive down.

Ok I've just jacked each tyre. Started at the back. When I jack the first tyre, the wheel slips as it is juuuust getting off the ground from all the pent up pressure it has. it turns like all the rest with Park, and only turns about half a centimeter with the transmission in neutral. Its very hard to turn. Same goes with the other rear wheel, then the front tyres have the same amount of free-spin in Park, or neutral, which is different to the rear.

 

[Ebag333]

Ok I've just jacked each tyre. Started at the back. When I jack the first tyre, the wheel slips as it is juuuust getting off the ground from all the pent up pressure it has.

That'd be an indication of drive train windup.

it turns like all the rest with Park, and only turns about half a centimeter with the transmission in neutral. Its very hard to turn. Same goes with the other rear wheel, then the front tyres have the same amount of free-spin in Park, or neutral, which is different to the rear.

I'm not sure what exactly you're saying here. So the back tires are hard to turn, but the front tires spin freely? This is with only one tire up at a time, yes?

 

[crooozer]

Man, just tried to get those bolts of the driveshaft but they're a PAIN!
I'm leavin' it on for what it's worth.

 

[semlin]

croozer, the minimal movement is just the play or slop in the axles and diffs. the wheels should all turn freely. the problem is that your central diff is locked up.

if the yellow abs and yellow diff light comes on on your dash if you go into 4high, and goes out in 4lo, this suggests the cdl is working normally. those lights are triggered by a sensor in the tcase that only activates when the cdl is in place.

so it seems to be your vc is frozen.

you have not mentioned whether you have a cdl switch. i assume you do not, so i suggest you do the following

1. put the truck in 4 lo until the yellow lights come on. turn the ignition off leaving it in 4lo.
2. pull the "diff" fuse in the dash fusebox under your knee
3. put the truck back into 4 hi
4. remove the front drive shaft

pulling the fuse freezes your central diff locker "on" in 4hi instead of relying on the frozen viscous coupler. this will prevent any further damage to the vc while driving in 4hi, although is suspect it is already toast.

you can now go about your business in 2wd until you can get to a mechanic.

your mechanic has been wrong on everything you have told us he said so far so i would suggest you find another one. you can also search in this forum for instructions on how to remove your viscous coupler.

 

[semlin]

Man, just tried to get those bolts of the driveshaft but they're a PAIN!
I'm leavin' it on for what it's worth.

they can be. if you don't have a breaker bar use two wrenches and break the nuts loose by tapping that wrench with a mallet.

i would not drive any distance on a paved road with a locked centre diff and both drive shafts. you are stressing your axles and diffs and birfs every time you turn.

 

[landtank]

Sweet guys! I take it off now and hopefully she'll be sweet for the long drive down.

Ok I've just jacked each tyre. Started at the back. When I jack the first tyre, the wheel slips as it is juuuust getting off the ground from all the pent up pressure it has. it turns like all the rest with Park, and only turns about half a centimeter with the transmission in neutral. Its very hard to turn. Same goes with the other rear wheel, then the front tyres have the same amount of free-spin in Park, or neutral, which is different to the rear.

Just to be sure, BOTH the transmission and transfer case is in neutral during this test?

 

[crooozer]

Yes, you got it right.
One wheel up at a time

That'd be an indication of drive train windup.



I'm not sure what exactly you're saying here. So the back tires are hard to turn, but the front tires spin freely? This is with only one tire up at a time, yes?