Our 1986 Toyota Land Cruiser (HJ60 with H55F transmission) came with vacuum operated 4-wheel drive. When I first tried it I loved the freedom of being able to press a button on the dash, and have the truck automatically engage into 4x4 (assuming the hubs are locked). However, after taking a closer look at the system, what were the engineers at Toyota thinking???
Here's the thing: in a traditional lever actuated system there is one thing that can break - the lever and linkage. And even if the linkage breaks, you can always crawl under the truck with a hammer and push the shifter into place to engage 4-wheel drive. In a vacuum operated system there are six - yes, six major components that can fail. Further, the system defaults into 2-wheel drive, so if any of the components fail, the truck slips out of 4-wheel drive. So, without further ado, here are the six reasons:
- A broken fan belt. Yes, that's right, if the belt that drives your alternator is broken, or even slips (as it might well do during a deep water crossing), the alternator will stop turning. This will cause the vacuum pump, run off the back of the alternator shaft, to stop pumping. This will stop the vacuum, and the truck can slip out of 4 wheel drive. Imagine this occurring in a fast flowing river.
- A broken vacuum pump. On a diesel, the engine produces very little vacuum. Instead, vacuum is produced via an auxiliary pump. Should any part of the pump break, vacuum will stop, and again, the truck can slip out of 4 wheel drive.
- The solenoids that open/close the vacuum lines could fail. Should these solenoids fail, or any of the electronics that operate them (fuse, dash switch, wiring in-between), the truck will not go-into or out-of 4 wheel drive.
- The steel lines could rust. Toyota runs most of the vacuum lines with steel to prevent them from collapsing. Because there is only air running inside of them, they are prone to moisture on the inside as well as the outside (as opposed to steel brake lines that have brake fluid inside of them). Therefore, corrosion occurs from the inside-out, which is non-detectable until there is a failure.
- The rubber lines could crack. Short sections of the system use rubber lines to allow for vibration and alignment. Old rubber can crack, and even a tiny pinhole will break the vacuum.
- And last, but not least, there's the whole diaphragm assembly. This is the unit placed in front of the transfer case that actually engages 4x4. It has a bonnet lined with a rubber diaphragm, a vertical shaft connected to the rubber, and a cam that translates the vertical shaft into a horizontal shaft. It is encased in a 2-piece cast body, with a gasket sealing it together. Any part of this piece can fail, and again will render 4-wheel drive useless.
OK, so what if you've got this system? Get rid of it. We are looking for a conversion - if you've done it or know of a way, leave us a comment below. Otherwise, we'll post the fix when we know!
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I am an ex-Land Rover Series II and Landcruiser BJ60 owner. Both had strictly mechanical four wheel drive engagement systems. I now have a 1992 Dodge Dakota 4×4 with the vacuum actuated front axle dog clutch. Strangely it works really well. But I have seen a DIY conversion on the net using a push-pull cable. Simple
enough. I would recommend a quality PTO cable.
Bob
Brnadon, Mnaitoba, Canada
You can convert it with the parts from a Toyota. The case is the same the hole for the detent ball is not drilled and tapped so yoy have to do that, the post installed in the transmission is short unscrew it and replace with the longer one, install the two shift arms and support replace the shift shaft and you are about done. The parts are available from many sources.
Jim
All of the points mentioned have some (though very limited) validity. The vacuum operated 4WD shift that is found in Land Cruisers is very reliable and has an extremely low failure rate.
1. Once in 4WD the mechanism cams over and will not come out of 4WD. These belts have been known to go for 100s of 1000s of Kms. Later model Land Cruisers have gear driven vacuum pumps (1HZ, 1HDxx) or electrical shift of the transfer case.
2. Diesel engines do not produce any vacuum.
Some models that have a venturi/diaphragm for metering fuel can can be considered to generate vacuum, but it’s not really usable for operating the brakes, clutch, 4WD shift etc.
The older alternators do have a reputation for wearing the splines on the vacuum pump, rendering the pump as dead. See #3 below.
3. Yes, the solenoids can and do fail – though it is very, very uncommon, even on vehicles with several hundred 1000 kms. If you have any mechanical experience at all, and have even a modicum of understanding of how the system works, you can simply switch the location of the vacuum tubes to engage or disengage the system in a matter of seconds.
4 & 5. More false arguments… In 20 years I have replaced only a handful of lines and I work on these things full time nowadays. It has always been the steel tubes that have rusted through, and by the time they are done, so is the rest of the frame/vehicle.
6. I have yet to see one of these diaphragms fail. They are not exposed to much in the way of elements that will lead to their rapid decay. Systems that have been in place for over 25 years and >500,000 kms are working just fine.
The vacuum shift can be replaced by the mechanical system that was used prior to the vacuum system and that was also found in less high spec vehicles. I have done several of these conversions with parts from earlier models that had the manual shift. Anyone of reasonable mechanical skill can retro-fit the old system or convert their vacuum operated system.
In summary, this article is a waste of words. If you’re going to embark on any kind of prolonged camping trip (popularly called an “expedition” these days), you should have a reasonably high level of skill in operating and repairing your 4WD vehicle of choice. Simple mechanical problems should not be any sort of a handicap to the prepared driver.
John, easy! We appreciate your comments.