ABS pump works but no abs? Also engine swap Q.

Just bought my jeep (1991 Laredo I6 NP232 AX4) and the brakes feel like the ABS is not working. Stiff brakes and when you hit them hard, you feel like you cant stop in enough time. I have no idea where to even start. The pump turns on and everything. Point me in the right direction please?

Also, my engine is a 4.0 HO, meaning it was swapped. How can I figure out what year it came out of?

Thanks in Advance.

How do you know the ABS pump is turning on? How do you know you have ABS?

Also, you cannot have an NP232. Is it a 231 or a 242? (not that it matter for this issue)
What lift, tires, gearing, etc do you have? It makes a difference in braking performance.

ahh thanks. I keep saying 232 but mean 231. The ABS pump I know turns on due to hearing it pump continuously. Stock Gearing and looks like stock suspension also, but looks higher than normal. Tires are 225/75/15. I also forgot to mention that the BRAKE light is always on even with the brake off, and the CHECK ANTI LOCK is on also.

No, your engine was not swapped, 1991 was the first year of the 4.0 HO.

It sounds like you have the Bendix ABS system, aka the Bendix death trap ABS system. It uses an electric pump to accumulate gas pressure that is used to force the brake fluid through the lines to apply the brakes when the pedal is pushed. This is NOT just the ABS pump, its the pump needed to make the brakes work. This is why you have no feel in the pedal, and there could be a leak which is why it doesn't really want to stop (perhaps the pump isn't putting out enough pressure).

These units fail fairly often, and no one bothers to fix them due to their unreliability and knack for leaking/failing. Your best option is to replace the brake system with a dual diaphragm booster out of a '95-'96 Jeep cherokee, or use a WJ booster.

Bendix Master on the left, with pump visible. Dual Diaphragm booster that I swapped into my '91 to replace it on the right.

You have the Bendix 9 ABS Brake system. There is no help for it. Ditch it for a standard master cylinder and booster.

thanks guys really appreciate it. Yes that is the brake booster I have on the left. Do you recommend getting a booster from a 95-96 XJ from the Junkyard? Also the pump noise I hear is on the opposite side of the booster, right underneath where the the water bottle is supposed to be under my car. When I take the old booster out should I take the relay out of that pump as well?

Sure, getting one from the junkyard can be the cheapest option, but there is a small chance every once and a while that you can get a bad booster/master. I would do it though.

Remove the pump, and remove the relays. You can actually see my pump sitting on the left side of the Bendix booster in the picture above, lower left hand corner.


You just remove this bracket, and you can see the pump is attached to it. (ignore the relays and wires at the top of the picture, those are for my headlight harness)

Thanks Begster you saved my butt. The booster from the 95-96 XJ is plug and play too correct? Or will I have to fabricate anything? Sorry for all the questions, its just that when it comes to brakes, I want to be 100% sure I got everything right.

The booster from a '95-96 is essentially plug and play, you will have to redo hardlines though. I forgot to mention before but you will need the brake pedal from the donor vehicle since you have ABS.

You can see that the pin for the rod to attach to the pedal is higher on the '91 (right in picture below) compared to a set up with a dual diaphragm system (pedal from a '99 I had laying around). With a '95 booster installed, the pin will now be too high, and the rod would be at too steep of an angle for the booster and could cause premature wear on the booster. I couldn't even get the rod onto the pin when I put mine in. It looked like I could have just pressed the pin out, redrilled the hole in the correct position, then drilled and pressed the pin in the new whole, but I happened to have a pedal from a '99 I parted out sitting around that worked perfectly. No need to reuse the torsion spring from the original pedal.

Ok thanks. I think I might have to go another route then.. I have no way of redoing the hardlines. I have basic tools thats it. I will grab the parts and keep em for later on when I am able to keep this rig under the knife for more than a weekend.

TheLaredo said:

(1991 Laredo I6 NP232 AX4) a

Also, my engine is a 4.0 HO, meaning it was swapped. How can I figure out what year it came out of?

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I don't know if anyone answered this yet. The engine wasn't swapped. 1991 was the first year for the HO.

the 95/96 booster swap is actually quite simple. and if you dont have means of making hard lines, you can get adapters to use your stock lines and connect them to the short lines that are on the new proportioning valve. you get the booster/master, proportioning valve with the hard lines that attach the master to the valve, and the pedal assembly from a 95/96 and remove all the bendix stuff. it all bolts right up. i had no problems doing this with my 89 and the breaks work awsome. i have a double flaring tool so i made my own lines by cutting the stock ones and swapping fittings. but like i said, you can get adapters that will work also.

oh, and do this soon. those bendix antilocks go out at any givin moment. and when they do, you dont just lose the antilock system, you lose the ability to make pressure to the brakes, so you wont have any breaks at all. just hope you have a long straight highway to coast to a stop.

Yeah Talyn thanks, Begster addressed it..

Jesus really? Well then good thing its staying parked in the driveway for now!!! (No plates, bought from Nevada). With the flaring tool, did you just take the fittings off the 95 jeep and put em on yours? I thought Begster meant I had to replace the whole line, thats why I was like oh crap.

Once again guys, Thanks. This is really helping me not destroy the car.

update!

It is registered and now waiting for the booster and flare kit.

because of the weird configuration of the lines going back and forth to the pump and master, you will end up useing less lines. i cant remember if i used any of the lines from the donor 95 vehicle, or just re-flared some of my existing lines. i am pretty sure you have all the lines you need except for the short ones for the master and booster hook-up. but if you are getting them from the junk yard, you take them all ready together anyhow. now all you need to do is attach your original lines from each wheel cylinder, to the proportioning valve. its quite simple, and if you look it up on here and other sites, you will find step by step with pictures. while at the junk yard, do cut off a few of the key tubing ends and leave them connected when you remove the master/booster. that way you have the correct ends and know were they go. just cut and remove the old ones, and replace them with the ones from the junk yard, and re-flare the tubing. look up the swap and you will see it is simple. remeber to also get the pedal assembly from inside the cab too. yours is differant and wont work. oh and also get the brake light switch from the 95, you will want to use that instead of the one thats in there now.

I decided against it. I have read too many write ups that contradict eachother so I would rather not do the swap and end up having a useless vehicle. Unless I can get someone to help me who has done it before It looks like the brake will be untouched.

2stix said:

oh and also get the brake light switch from the 95, you will want to use that instead of the one thats in there now.

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Untrue, there is no modification needed for the brake light switch on a '91.

TheLaredo said:

I decided against it. I have read too many write ups that contradict eachother so I would rather not do the swap and end up having a useless vehicle. Unless I can get someone to help me who has done it before It looks like the brake will be untouched.

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Umm...what? What contradicting information have you read? It certainly isn't "don't swap out the bendix brakes, because they work fine." Everyone agrees, that brake system is dangerous and will fail, and it sounds like your system is already at that point. I'm sorry, but just because you've read one person do a swap differently than another, is no excuse to leave a dangerous system in there.

What part of the swap don't you understand?

whether or not I need the brake pedal assembly, I need to switch the lines over to SAE or Metric, If I need to do anything to the part re drill into part of the thing that comes out the other side of the booster. Not to mention all the extra lines out of my truck since its ABS. I cant find any singular decent write up in the search box, and when I try google its telling me WJ/ZJ swap which is not what I need.

All in all when it comes to this particular mod, I need step by step instruction.

Begster is probably right, the brake light switch you have is probably ok to use. mine was totally differant but i have an 89 wagoneer.

as for the swap being scrapped, id say you are making the wrong decision. and the booster rod re-drill thing was for the folks that didnt want to take the pedal assemblies and swap them. the pedal assembly on the newer XJs with ABS but not the bendix system is very close to the regular ones. so they opted to just reposition the booster rod ends. why i have no idea when the correct pedal assembly is so easy to unbolt and swap. no need for shims or anything. were in so cal are you? i would be willing to help, but you would need to bring it to me. trust me, you do not want that bendix system. even jeep had a nation wide recall on it. unfortunately they only replace certain parts, and they will fail again. it is a dangerous system. get rid of it.

Im in Riverside. About 40 mintues from you.