The car itself was just the good side of 1400 quid. Not really a bargain in the grand scheme of it, that’s about what these go for. People who know will know what that’s gonna cost me to have on the road here, people that don’t will think I have a bargain.
Now, a bit of bollocks about the car for you all to read. Apologies if it makes no sense, it’s almost midnight. That said, welcome to my TED talk.
This was the last generation of the Sprinter Carib, the Corolla 4wd carried on with more basic AWD systems after this. The Carib started with what most places knew as the Tercel 4x4 and then Corolla 4x4/Corolla 4wd. The systems used in each changed over the years, I’ll do a quick list below:
Tercel 4x4: Part time selectable four wheel drive, old school style, no centre diff.
Corolla 4x4: Full time AWD with manual locking centre diff on manuals, or a hydraulic multi plate clutch locking centre diff on autos.
Sprinter Carib 1.8: Same as above, with a viscous coupling used to lock the centre diff on models with ABS.
Later Corollas did away with the centre diff, instead just using a fixed spinning shaft to the rear with a viscous coupling. That meant the cars were predominantly FWD, the slip in the front wheels would then heat the coupler up to send power to the back. Works well and is cheap, but has it’s own issues. Will cover later for those of you still reading.
For this here we will focus on the automatic 1.8 Carib, the last version of the auto system mentioned above. It was proper full-time AWD with a centre diff, with the power distribution varied/controlled by a hydraulically controlled multi plate clutch, up to a complete 50:50 lock depending on certain conditions. This launched in 1988, on an ecobox! I’ve nicked some diagrams to help the wall of text.
There were two versions of it, this one for the sub 2.0 cars, and one for the bigger stuff. Mostly similar but with a little bit more electronic control to make it smoother, that came out in the same year on the Camry and would go on to be fitted to things like the Mk1 RAV4.
For the last Carib here in it’s top spec with 1.8, the system fitted got a little bit more of these electronics to help it work with ABS. That’s the biggest reason I went for the auto, ABS. I like ABS, I feel like it’s the best electronic driver aid and it’s always there for when you don’t know you’ll need it.
The manual gearbox version with the fully manual locking centre diff was unavailable with ABS, and instead had a viscous coupling to lock the centre diff similar to the Celica GT4. While that’s a better system than just having a viscous coupler, I didn’t want to risk the coupling having aged and gone weak, meaning the centre diff would always be open.
The auto had some modifications so the ABS system could fire signals to the clutch solenoids, preventing it locking if the ABS needed to do it’s thing. Also from what I can tell some other modifcations were made to allow it to work with the then new electronic gearbox control, Toyota’s ECT-S. S is for Sport, which makes me laugh - means this thing has switchable Economy, manual and Power modes. You’re also able to disable the clutch entirely, for things like brake testing on rollers at MOT, towing etc.
The clutch pressure depends on a few measurements - current speed, gear, throttle opening, pressure generated from a difference in speed between axles etc. and has a few situations where it changes. For example, putting the shifter in L or R lock it up to get you out of the bad stuff, and over 100kph it unlocks completely.
It’s quite a compact nicely designed unit as you’d expect from Toyota, with the centre diffs and locking clutches all being built into the same unit up at the front.
So yeah, that’s a vaguely abridged version of what must have taken Toyota thousands of hours of development time, and why I went for what might seem like an old fashioned 4 speed auto. I’ve had bad experiences with older viscous coupling systems without the centre diff in the past (looking at you, Land Rover Freelander) and this seemed like something that’d still be pretty capable now, and if I was going AWD anyway I figured I might as well pick the fanciest one.
It’s main weakness is it would still fail a diagonal test, with one wheel at each end up and spinning, as it’s got no VSC or LSDs to help it out there. A popular mod in Russia to help with that though is to fit the rear LSD from a Celica GT4 - that might be on the list at some point but as I won’t be doing any serious offroad work, that likely won’t be needed.
The fact this thing was so ahead of it’s time in the late 80s probably explains why it went on to 2002, until costs took over and viscous coupling only systems with VSC started to take over, or the electrical clutch based stuff seen more recently. They all have advantages and the system in this Carib won’t win any awards for cost or efficiency, but it’s nice knowing it’s always there and ready. People still brag now about being able to vary the torque between the front and rear, albeit this is much simpler than modern systems.
Anyway, it’s now 1am here and if you’ve read with me this far about an obsolete Corolla AWD system - thanks, but what’s wrong with you?