The parking brake doesn't rely on the hydraulic system at all. Here's a picture of a rear caliper from a car with an electronic parking brake:The idea of a manual emergency brake is when your brake lines rust through (see 1997 F-150) you have the ability to STOP in an emergency. If your hydraulic brakes fail, you have a manually activated way to stop. What happens when you hit the electronic brake if you are moving? Does it stop the car?
See that splined shaft? That's where the parking brake actuator engages and directly drives the piston. So you could have a busted line or no brake fluid or anything, and the actuator would still be able to apply rear brake pressure.
4H: The front and rear axles are locked together by the transfer case. Depending on whether or not the front and rear diffs are also locked, all four wheels could be 100% mechanically locked together. Great for crawling up rock walls or powering through mud or sand. It is NOT intended to be used on a paved surface with high traction. It causes chattering and wheel hop when turning as the tires actually need to rotate at different speeds when making turns, but they can't because they're all locked together.Also, while I'm here typing, can someone tell me why we have 4A "awd" when we have 4H for "awd" just curious. Had a Raptor in the shop today and the owner told me the 4A was for "automatic" 4WD, it is in rwd until it senses slip and engages the front diff. Just seems odd to me, I am old school and I am used to the N(neutral)as the other option. good for flat tow like behind an RV.
Thanks for the info and I think the interior looks bitchin'.
4A: The transfer case modulates lockup between the front and rear diff, transferring power to where it detects traction.
If you're driving on the road in bad weather with intermittent slick patches, 4A is 100% preferable. You don't want all four wheels locked together when you have good traction. You want the system to send power to wherever it can find traction.
And if you pull away from a slick stop in 4H with everything locked together, all four wheels will spin, allowing the vehicle to drift side to side. 4A would take power away from the spinning wheels and give it to the ones with traction, improving acceleration and maintaining control.
People get all sorts of bent out of shape about the above. "I've been driving with 4x4 in the snow for years! Just turn it off if you don't need it! If you can't get around in the snow in 2wd you're just a dummy and a bad driver!"
I'm not saying it's impossible to get around in 4x4 or 2wd, I'm saying the optimal configuration for maximum control and acceleration in slick conditions is one that can actively choose where to send power. The Wrangler finally got 4A with the JL, before that I couldn't understand why people bought a Wrangler as a winter vehicle. Without 4A, you're just running around in 2H all winter except the few mornings when you beat the plows to the roads.
But 4H and locking diffs is 100% optimal for mud, sand, or rocks.
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