Abs Bleeding??

[Kkilmer87]

does an abs system have to be bleed differently than a regular braking system?  thanks guys struggling to find anything in the search bar

[Eagle]

Dunno.

 

Did the Comanche ever come with ABS as an option?

[Kkilmer87]

I am asking for a cherokee this is why I don't like anything but Comanches I'm having problems with my girlfriends new cherokee after I replaced all the lines I'm having trouble bleeding it but today I bleed from master down to the abs block and seems better I'm gonna pull abs fuse so it don't work but brakes are still spongy............sorry for the cherokee question but I know u guys know about a lot.....

[Eagle]

What year Cherokee? I think Jeep changed the maker of the ABS system somewhere in there.

[Oyaji]

:hijack:

 

As an aside, I've been toying with the idea of adapting an ABS system to a Comanche. I was thinking that a custom chip with one-off programming would be required. But it occurs to me that a Cherokee system might be a good place to start...

 

Thoughts, anybody?

[Kkilmer87]

It's a 97 and abs is awful I wouldn't put it in personally you have no control over the vehicle

[Kkilmer87]

But I'll sell u my setup if I decide to pull it out....

[Eagle]

:hijack:

 

As an aside, I've been toying with the idea of adapting an ABS system to a Comanche. I was thinking that a custom chip with one-off programming would be required. But it occurs to me that a Cherokee system might be a good place to start...

 

Thoughts, anybody?

 

Why would you need to reprogram anything? You would need to use the XJ axles, in order to get the tone rings, but the system works by sensing when the wheels stop turning. Why would it matter if the wheels are under an XJ or MJ chassis?

[reece146]

The easiest way to bleed the ABS is to take it out into a clear parking lot or quiet back road and do a couple of hard stops that trigger the ABS. You don't need a lot of speed - you just have to trigger the pumping action. Be careful, I dunno about down there but up here there is snow and ice on most pavement now. Don't go spinning off into a ditch.

 

You may have to re-bleed the lines to the wheels again afterwards but I've never encountered that personally. I've never had to reopen the system other than to check the level at the reservoir. This was on my old S2000. Car was tracked and had normal pedal feel after every fluid flush and "panic" re-bleed.

 

Good luck!

[reece146]

As an aside, I've been toying with the idea of adapting an ABS system to a Comanche. I was thinking that a custom chip with one-off programming would be required. But it occurs to me that a Cherokee system might be a good place to start...

 

IIRC the XJ ABS computer is a completely stand alone unit from the PCM and TCU. As stated above, it only needs data from the axle tone rings to make calculations.

 

An hour of research on NAXJA would take all the guess work out though...

 

HTH

[Oyaji]

 

 

:hijack:

 

As an aside, I've been toying with the idea of adapting an ABS system to a Comanche. I was thinking that a custom chip with one-off programming would be required. But it occurs to me that a Cherokee system might be a good place to start...

 

Thoughts, anybody?

Why would you need to reprogram anything? You would need to use the XJ axles, in order to get the tone rings, but the system works by sensing when the wheels stop turning. Why would it matter if the wheels are under an XJ or MJ chassis?

Different wheelbase and load conditions, and possibly lift (if so equipped) would all combine to make a different baseline than the donor vehicle had. ABS calibration is quite a task in the design phase for every vehicle so equipped, and tweaking goes on for months for each vehicle before production starts (and sometimes for months afterwards, too!).

 

All depends on the programming; it might compensate adequately for the differences between vehicles, but then again it might not. I am a pessimist by nature, and so before I dived in I would want to be sure I could cover all the bases before I start.

 

I am also unfamiliar with the ABS as equipped on Cherokees. Early-generation ABS (and their early yaw control derivatives) on other vehicles was not that great; though some were better than others, I used to be able to out-brake (and out-handle) all of them on all the vehicles I tested in the 1990s. The main reason was the duration and frequency of the brake pulses (and possibly the modulation routine too), but a custom chip and reprogramming just might offer significant improvements for someone knowledgeable and patient enough to do such modifications. I have to ask myself if I am up to the task now, though.

[reece146]

With respect, I think you are overthinking this.

 

We are talking about a POS Chrysler system, not BMW, Porsche, etc. I really doubt the ECU sampling rate and testing done by ChryCo is anything to write home about, particularly in a truck application. This is a not a performance application. All the system cares about is not locking the wheel.

 

That said, I think an unloaded MJ would be a perfect candidate for this system if for no other reason than to keep the truck from swapping ends under hard braking and/or to maximize effect (i.e. actually get the rear brakes to do something). Hmm...

 

2¢

[Eagle]

With respect, I think you are overthinking this.

 

We are talking about a POS Chrysler system, not BMW, Porsche, etc. I really doubt the ECU sampling rate and testing done by ChryCo is anything to write home about, particularly in a truck application. This is a not a performance application. All the system cares about is not locking the wheel.

 

That said, I think an unloaded MJ would be a perfect candidate for this system if for no other reason than to keep the truck from swapping ends under hard braking and/or to maximize effect (i.e. actually get the rear brakes to do something). Hmm...

 

2¢

 

I agree -- this is just an ABS system, not a traction management system. And, as much as I generally dislike ABS, I think it makes moire sense for a pick-up truck than the failure-prone height-sensing rear proportioning valve used in the MJs. And IMHO the XJ's proportioning valve is even worse -- what you want is something that prevents rear wheel lockup in a panic stop. What the XJ "proportioning valve" does is exactly the opposite -- it prevents the rear brakes from working UNTIL you're in a panic situation and really stomp on the brakes.

 

My wife's 2000 XJ has 105,000 miles on it. We're well into the second set of front brake pads. I just changed the rear brakes a couple of weeks ago, but the problem was a rusted line and loss of pressure. I changed out the wheel cylinders and shoes while I was working on the brakes, but after 104,000 miles the rear shoes were less than 50 percent worn. There's only one way that can happen -- they aren't doing anything. Why? That stupid proportioning valve.

[Oyaji]

I'll take your comments under advisement - thank you for offering.

 

Regarding proportioning valves: the idea is to reduce pressure to the rear wheels to avoid lockup, of course. Load in the rear allows more braking from the rear axle, but the Cherokee valve doesn't have a clue as to load. I don't know what is dialed in on them as a preset relief pressure, but at best and of necessity it is a compromise.  Seems like an adjustable prop valve would be desirable for someone interested in maximizing brake performance there. That is a fine advantage of the Comanche load-sensing valve... provided it is properly adjusted. If brake performance is not what it should be on either vehicle, I reckon a hard look at the prop valving on them could yield some gains.

 

Incidentally, it's pretty typical for rear shoes to last 3 times longer than front pads, even when the brake system is functioning optimally. It's just how it is, since so much of braking depends on the front axle. Braking performance is probably somewhere around 75% front/25% rear on Cherokees, with front bias even more pronounced on the (unloaded) Comanche. Lifts on either would raise the CG and potentially increase nosedive as well (depending on spring rate), further reducing the braking contribution from the rear axle. Since braking depends on load on the axle, you just cannot expect much rear braking from either vehicle. If the proportioning system is functioning properly, ABS cannot be expected to net any better results except under lockup conditions, and even then depending on whether the ABS modulating routine can actually outperform the driver (and with early-generation ABS, this is by no means certain). Reece146's and Eagle's comments about Chrysler's sampling rate and and hard braking are particularly apt here. (By the way - does anyone know what supplier provided the ABS system on Cherokees?)

 

What I would be seeking in particular is to improve braking under panic-stopping conditions under a variety of load conditions, especially when pulling a loaded trailer. Traffic has gotten ten (or more) times heavier around here over the years, and unfortunately idiots on the road are not in short supply. It has become so bad these days that I have to pick and choose my times to tow a load to minimize risk. Anything I could do to improve safety is a plus; perhaps getting a better truck is the best option.

 

All things considered, I am not averse to the idea of considering a later-generation better-performing ABS system from an entirely different truck as an option. It's just that I really do like the Comanche (for many reasons), and it seems that adopting the Cherokee ABS might be an easy way to go to achieve my goals. It's a shame I never tested any Cherokees equipped with ABS - I think some driving experience with some old ones would be worthwhile, provided I can get or make the opportunity. I do plan to do some reading about the specifics of that system, provided I can get my hands on the material. I'd also like to talk to some of the engineers who designed that system, if I can track any of them down and we can find the time and desire to talk shop...

[Kkilmer87]

i got a jeep factory cassette still in the wrapper that explains the abs system came with the jeep i didnt open it but that may help the situation I'm gonna post pics in the for sale section tomm maybe see if anyone is interested its a cool piece of history I'm glad my stupid question sparked so much conversation so much easier to learn the pros and cons from the back and forth talk,,,,,,,thanks guys and I'm gonna bleed my brakes some more prolly or eliminate it completely