highway speed in full time 4X4?

Del, do you know why they put a combination valve in Jeeps?

Hint: It isn't just there to make bleeding the brakes a pain in the butt.

Mike

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

That's probably more a function of the particular valve than an inherent characteristic of the system. Most of my observations on the antilock brakes actually comes from pickups where load sensing adjusters are common as well, so that will make a difference. The day I forgot to reconnect the load sensor lever and tried to stop when the MJ was empty with the load sensor saying I was on the bump stops was highly enlightening, to say the least . Those proportioners are really a very simple regulator that keep the pressure differential front-to-rear at some pretty much fixed ratio so in theory you can lock everything solid but as you point out it's not easy.

That little trick with the emergency brake is useful in a lot of places but the foot operated ebrake makes it a real PITA to use. I've looked at replacing mine with the hand-operated type several times but haven't actually tried to change it over. For me, I almost have to open the door to have enough room to clear the steering wheel when applying the ebrake. Plus, it's hard to feather how much braking you get with it. Combined with a manual tranny it makes for 4 pedals and only 2 feet. Now add in the release lever and you have 4 pedals, 2 levers, and 1 steering wheel - all spread out in exactly the wrong relative positions for only 2 feet and 2 hands. ARRGGH!

All of my kids have been run thru the exercise of that rear ebrake on a long, wide runway. It is a real eye opener for them when you tell them to stop from 60mph or so using ONLY the ebrake.

Del, there is one reason and one reason only for the proportioning valve part of the combination valve they put in Jeeps, pickups, SUV's, etc.

That is, to quote the Haynes manual, "The proportioner section provides balanced front-to-rear pressure during hard braking, reducing the rear line pressure so the wheels don't lock up."

Simple eh?

And they even managed to do it before computers.

Well crap Del, I just went and looked and it was you that didn't believe what a proportioning valve was for in the post I am referring to.

I am sorry if you can't grasp the basics of this valve, but there is absolutely no other use for it 'Except' to prevent rear wheel lock under hard braking.

I am not going to argue this further with you. I provided book quotes to you before and have tried to explain it.

If you don't believe it, take the sucker out and try your brakes or even easier start using your e-brake to stop and see what happens.

Or try to come up with something in writing that refutes what I have posted both here and in the last thread on this.

I am not mistaken on this.

Mike

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

That is exactly the function of the valve Will. That is why they put them in.

Mike

Will H>

That's right Del, brakes that fail to lock are not necessarily ABS. It is certainly not an ABS system by intent. It might turn out to be a primitive form of ABS, but there was no design theory that made this happen.

That was three jobs ago Bill. Sheesh, can't you keep up at all? ;-)

Regardless of the kind of writer one happens to be, the OP already had the question, he was LOOKING for an answer.

Wow, I am amazed.

There is one and only one reason for a proportioning valve.

That is to prevent the rear wheels from locking up when hard braking.

That 'is' the design principle of the thing.

What doe the acronym ABS mean?

I always thought it meant 'anti lock brake system'. Was I mistaken?

The proportioning valve is there to 'prevent' the brakes from locking the rear wheels.

What does 'anti lock' mean? Could it mean to go against locking up or to 'prevent' the brakes from locking the rear wheels or am I wrong?

Mike

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

Pretty much whatever the automobile engineers and marketing flakes say it means.

Yes.

Which has nothing to do with ABS, which I am reasonably sure you already knew but are merely giving someone a deserved rough time.

You're wrong. That is a proportioning valve. Or if you insist on an acronym, a PV. Or even perhaps RWALPV.

Dunno what the fraud laws are up there, but you wouldn't want to try your argument as a sales pitch or even lawsuit defense for calling the proportioning valve an anti skid brake system or anti lock brake system and sell or advertise it as such down in BSE land.

LOL!

Good points.

Mike

"L0nD0t.$t0we11" wrote:

I always thought the job of the portioning valve was to balance the braking "power" equally, or proportionally, between the front and rear brakes. Without the portioning valve, the rear brakes, especially on a front disc brake system would not have the proper braking pressure appled even if the brakes were properly adjusted.

No, you are not mistaken, ABS does indeed mean Anti-lock Braking System. But, the portioning valve by itself does not constitute an ABS system.

Well, that very well may be a byproduct of the portioning valve, but an ABS system is much more than that. If there was no portining valve, then when you mashed the brake pedal, all four wheels would get the same amount of braking force applied, but the front brakes need to do more work, or they are simply capable of doing more work, so the portioning valve equalizes the braking force applied to the front and rear brakes. The portioning valve is there to properly proportion the braking power from the master cylinder to the front and rear brakes. If the rear brakes fail to lock, then that means the traction they get is too great for the brakes, or the braking pressure the brakes get is too small.

Either way, this is an indicator of a braking system that isn't workng well, it is not an intent of the valve.

On 07 Jan 2004 09:39 AM, Mike Romain posted the following:

Yes, I know what the damned valve does. Just because it serves to keep the rear wheels from locking up first in most conditions doesn't make it ABS. The term ABS, as accepted by the entire automotive industry, refers to an active system which includes wheel speed sensors, a control unit, and a modulating unit.

Let me put it this way. After paying hundreds of dollars for ABS in my TJ, if all they had given me was the proportioning valve, I would have been pissed.

---------------------------------------------------- Del Rawlins- del@_kills_spammers_rawlinsbrothers.org Remove _kills_spammers_ to reply via email. Unofficial Bearhawk FAQ website:

On 07 Jan 2004 10:03 AM, Mike Romain posted the following:

You had the terminology wrong then, and you have it wrong now. ABS is an industry term referring to a specific type of system and a proportioning valve ain't it, even if they work to the same overall purpose.

I understand how the valve works. That is not at issue.

I understand your position, there is no need to explain it further. I reject your expanded definition of the industry term "antilock braking system" because it is incorrect. You should expect an argument as long as you continue to post your alternate use of the term ABS in this newsgroup, which is also read by people who do not understand the difference between the proportioning valve and an active, electronically controlled ABS system. This may seem like a stupid argument (and it is), but if your personal definition of ABS goes unchallenged it could cause less knowledgable readers to think they have, or are getting, something very different than what they are expecting.

If that is what it is going to take, fine. Notice there is no mention of the proportioning valve, which all current production vehicles have whether or not they are equipped with ABS:

[begin quoted material] ABS Acronym for "Anti-lock Brake System." Vehicles equipped with ABS use wheel speed sensors and a computer-controlled brake pressure regulator to prevent wheel lock-up during sudden stops. When the computer senses one wheel is slowing faster than the others (indicating it is about to lock-up and skid), the computer reduces brake pressure to that wheel by momentarily isolating brake pressure, releasing pressure then reapplying pressure in rapid sequence. This allows the wheel to regain traction so the vehicle doesn?t skid. ABS also allows the driver to maintain steering control while braking hard on wet or slick surfaces. ABS improves braking safety on wet or slick surfaces. [end quoted material]

This definition was found at:

---------------------------------------------------- Del Rawlins- del@_kills_spammers_rawlinsbrothers.org Remove _kills_spammers_ to reply via email. Unofficial Bearhawk FAQ website:

Hi Will:

My 200 lbs WILL NOT lock the rear wheels of my '02 TJ on dry pavement. They will lock on snow/ice, but only after mashing my brake pedal as hard as I can. My rear brakes are adjusted and working properly.

Tom

What causes this? Please excuse my ignorance, but I've done this on slick roads at speed on my motorcycle several times and never been spun around. (My bike doesn't have ABS or linked f/r brakes.) The rear does get 'sloppy' and move all over the place, but it doesn't cause a bike to immediatly swap ends. Why is a Jeep so different?

And as a second question (not necessarily to you Mike)- if you are in part-time 4wd how is it even possible to lock the rear without locking the front and ever get into a situation like that in the first place? Don't the front and back have to turn at the same speed?

Probably the same reason big rigs jack-knife when the trailer wheels lock-up... sliding wheels, having lost their traction, travel faster than the wheels that are braking with traction. And around she goes!

-- JimG

80' CJ-7 258 CID 35" BFG MT on 15x10 Centerlines D44 Rear, Dana 30 Front. SOA 4.56 Gears, LockRight F&R Dana 300 w/4:1 & Currie tw>

A bike will still do this, but I suspect that there's a couple of reasons why it may be less common with bike:

1) The gyroscopic effect of the rotating mass of the wheels is more significant. 2) The rider, being up to half as massive as the bike, can compensate more effectively by leaning to either side and essentially manipulating the entire chassis.

/Peter

Ok, what 'should' I call it?

As I mentioned the term ABS didn't exist back when the valve came out....

I sure wish I could find the old vehicle advertisements where this was advertised as rear anti skid or rear anti lock brakes.

That is sure what my Dad figured he bought....

Mike

Del Rawl>