93GreenGrand

I have a 93 Grand that has been sitting for 13 years with out being touched! I recently got it out to start the project / or DD one of my favorite cars ever! Replaced the coil and engine runs great but the issue i am having is stopping! As in i can't! So I bleed the brakes and with the car not running it pumps up and everything is great feeling. then i start the car and the pedal goes to the floor with ease and doesn't seem to have any affect on the wheels what so ever. So i am looking for suggestions i have been over it and no leaks and everything looks good. So i am wondering do i flush and replace the fluid or should i go ahead and swap out the MC? Any and all suggesting are greatly appreciated! Also if I do replace the MC is there an upgrade i should move to or just keep the stock one?

Cleman Simpson

If it has anti lock brakes there is probably air in that part of the system. edit to add: if it has been sitting up for that long you probably need to clean and lube the sliders on the front calipers as well.

tony270

If I did the work that you say I would immediately think that it was possibly in the vacuum boost brake assist system.
I would check and replace the vacuum booster check valve before anything else.
I would step on the break pedal and listen for air leaking from the vacuum booster, and inspect the vacuum boost brake assist line circuit looking for vacuum leaks. Then I would look for a leak under the steering column, the hydraulic cylinder and rod (piston) that actuates the vacuum booster diaphragm.

tony270

If you didn't purge the air from the brake system using the correct sequence you most likely have air still in the brake lines. That is the same symptom that a leaking booster can have. What caliper (wheel) did you start bleeding 1st, then 2nd, then 3rd, and then 4th?

tony270

And what Cleman Simpson wrote.

tony270

There's a lot of technical stuff involved with the brake system so get a manual. The manual says that if air has gotten into the hydraulic control unit the entire system must be bled first manually, and then with a DRB scan tool, and then bled manually second time. The DRB scan tool is something that most home mechanics don't have. If the pedal feels spongy or the ABS light doesn't go off take it to a licenced shop.
Also if you opened any lines other than at the calipers there is a special procedure to bleed the master cylinder. If so the master cylinder needs to be bled before the calipers are, you should go get a manual. And if you need to bleed the master cylinder on a 1998 and early model you'll need to bleed the lines at the combination valve and where the lines enter the ABS HUC. AGAIN GET A MANUAL PLEASE

If the lines have only been open at the calipers it says that the bleeding sequence starts by depressing the brake pedal to remove any vacuum in the brake booster. It says to start bleeding at the right rear caliper (rear passenger side), then the left rear, then right front then left front.

dave1123

My question is does a 93 even have ABS? I'd be more suspicious of the vacuum booster, especially if you have a hard pedal with the engine off.

93GreenGrand

It does have ABS! So i started at the drivers front and then pass front then pass rear then driver rear so i was completely out of order there. Also i jacked up the front and with the car off i can spin the wheel and get the wheel to stop by hitting the pedal but with it running it does not seem to have any effect on it. I finally found my haynes manual on it so i figured i would see what it says about it as well! Thanks for the great input i cant wait to take a look at it tonight.

dave1123

Okay, when I first got my WJ, it seemed like it lacked stopping power. My mechanic and I discovered the front brakes weren't working at all! He started to bleed the brakes, but got no pressure in the front calipers. We had to open all 4 bleeders and pump the brakes to get it flowing again. It's been fine ever since and that was 100K miles ago.

93GreenGrand

So looks like i am going to hit pull a part in the morning and grab a booster and MC combo as the price is much better that way. Am i correct in thinking i can use any 93-98 zj 95-96 xj or 99-04 wj setup? I know it might take a bit of modification but from what i have found all those will bolt up? any thing else i should look for?

tony270

Start with an assistant pumping up the brake pedal. And when the pedal gets high and hard (check yourself) have the assistant keep depressing down on the brake pedal while you loosened the bleeding nipple at the caliper.

You have to keep communicating with the assistant saying hold it (depress on the pedal), as you open the bleeding nipple the fulid and air will start coming out , and at the same time the brake pedal that the assistant is depressing is going to the floor. Ask the assistant is it at the floor, tell him to hold it when it reaches the floor, then tightened the nipple back up.
You have to do that 4 times on each caliber, until you see no more bubbles in the fulid, make sure that the master cylinder doesn't drain dry while bleeding the system. It is necessary to perform that at least 4 times at each caliber, that should be enough. It takes me 3 times per caliber, but you do 4 because your new. That is a total of 16 times.

tony270

Did you bleed the system like above? The manual says use a vinal tube or rubber hose and attach it to the nipple. Then run the other end into a container and capture the fulid in the container, look for air bubbles, when you get the bubbles to stop the caliper is purged of air. That's why I wrote 4 times per caliber.
Don't get a junkyard power booster or master cylinder, they will soon fail. Get the power booster check valve from the parts store, it is a common part, or check it.

93GreenGrand

yes i got the whole no air bubbles thing and yes it all is clear of air. That is why i am going to change out the booster and possibly MC. My only hesitation is i want to keep my ABS in place.

tony270

Do you hear the booster leaking air or vacuum when you depress the pedal, or escaping form this valve? You should be able to isolate the issue, we just don't change parts, lol.

dave1123

You may need to pressure bleed the ABS unit itself. A good brake shop can do that.