highway speed in full time 4X4?

On 06 Jan 2004 12:44 PM, Jerry Bransford posted the following:

The road surface doesn't need to be "extremely" slippery to use part time 4wd. Somewhat slippery will work just fine. There is a lot of apparently bare pavement around here (Anchorage AK) right now but leaving it in 4wd is still the best policy. The surface is just too unpredicable right now to chance shifting into 2wd in most locations.

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"CRWLR" wrote in news: snipped-for-privacy@corp.supernews.com:

Thanks. That was the sort of question I was looking for.

Technically, it's the sort of ANSWER you were looking for :-).

Yes they do. Although not electronic ABS, the proportioning valve acts as a primitive rear antilock brake system. Plain and simple, the rear wheels will NOT lock up, no matter how hard you mash the brake pedal.

Tom

"CRWLR" wrote in news: snipped-for-privacy@corp.supernews.com:

That's what happens when you type while talking to someone about something else.

Hi Barry:

Your selec-trac full time 4x4 setting can be used at literally any speed. You can actually leave it in the full-time setting all year if you want.

Tom

snip

Actually, if it's a Selec-Trac, you can drive in the full-time 4WD drive setting at ANY speed.

Tom

"mabar" wrote in news:EqidnQR1iKm_6maiRVn- snipped-for-privacy@gbronline.com:

Thanks. So how does Jeep full time 4x4 differ from my Ford Explorer's all wheel drive?

BB

On 06 Jan 2004 05:31 PM, L.W.(?ill) Hughes III posted the following:

I've got a manual for my CJ-5. My point is, there is no way to tell from the picture you posted what vehicle manual that is from, whether it is a Jeep, Chevy Nova, Pinto, or whatever. Further, there is no explanation to go along with the picture so it is impossible to tell whether it supports your point or not.

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On 06 Jan 2004 11:09 PM, L.W.(?ill) Hughes III posted the following:

Thanks, I mostly was yanking your chain but the text that went along with that is really interesting. That actually is a rudimentary ABS system complete with the eddy current type speed sensor and modulator, although not computerized. So at least they were trying. Not sure I'd want to drive that system though. I understand if you are biased against ABS after years of working on earlier systems but the new ones actually work pretty well, honest. Mine saved an idiot in a Rav4 from becoming a crumple zone for my TJ the day before yesterday.

I have worked on vehicles of that era but they were british, never had much interest in American cars, other than trucks and 4x4s. About all that I have done with the CJ-5 is pull an axleshaft to find out that I have the late rear axle with 30 spline, one piece shafts. I'm not going to touch it until I can take it down to the frame, and it isn't a high priority project.

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Ok, I think I see what you're trying to get at: the fact that since the front and rear axle are locked together in 4wd pt, if you lock up one set of wheels (front or back), you could effectively lock up all four. I can see that as somewhat of a possible concern. However, it seemed at first like you were implying the number of driving wheels somehow had some relationship to how many wheels could be locked up in a skid; moreover, that you can't lock up all four wheels in a skid when in 2wd mode or in a 2wd vehicle. This, of course, is wrong (if you disagree, please set me straight!); you can skid all four wheels in ANY car (barring antilock braking or traction control system equipped cars, about which I care not). I'm just saying, you can lock up all four wheels and slide sideways into a ditch/do 360s in nothing flat with a 2wd car just as easily as you can in a 4x4 PT vehicle.

And what are you talking about with the "Jeeps especially have rear antilock brakes" statement? Yeah, sure, it's available as an option, but I think a large majority of jeeps, and know a large majority of CARS out there don't necessarily have antilock rear brakes. (I sure as heck don't have antilock rear brakes on my D44!)

Yup, they started using a combination valve in utility vehicles like Jeeps, pickups and station wagons back in the 70's and it 'was' advertised as rear anti lock brakes and said it prevented rear wheel lock to allow straight line panic braking.

They didn't call it 'ABS', that is a new term.

I just had this discussion with someone else here and I quoted the books.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

I can lock them up for the last 2 or 3 feet of a stop if I have all my

200 lb on it, but no way they will lock at speed.

That is what that valve is specifically for.

Locking the rear wheels at speed causes instant 360's. Try mashing the e-brake on while driving 50 mph across an empty parking lot or on a frozen lake.

We actually use this method for getting around corners fast when ice racing, especially in front wheel drive cars.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Will H>

You are correct, I didn't really spit that out right...

And yes, if your Jeep is newer than 1974 you do have rear anti lock brakes or anti skid brakes.

They started putting a combination valve in them for safety reasons to prevent rear wheel lock up at speed so you can panic brake in a straight line and not slide sideways or do 360's.

All newer cars have them. At first it was only utility vehicles, pickups and wagons that came with it.

I remember my Dad getting his first wagon that had rear anti skid system.. He was really pleased with the difference in winter driving being able to brake straight without having to pump the crap out of the pedal.

If you try it, you will find you can lock the front wheels up and the rears won't lock until you are almost at a complete stop. If you can lock your rear wheels at speed, you have a broken combination valve that should be changed ASAP.

Mike

Bob wrote:

They didn't call it ABS, because it isn't an ABS system. It works toward the same goal, but the difference in how it gets there is important. ABS uses wheel speed sensors, a control unit and a modulator. The combination valve is just a valve. You can call it whatever you like but that doesn't make it so.

Which books?

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