1990 Jeep Cherokee with ABS.

I have been working on the brakes, for quite a while, and can not figure out why I am not able to get any pedal pressure.

The situation:

Replaced calipers, rotors, and pads (before deciding to replace the calipers I was going to replace just the pads and rotors and used a large clamp to compress the caliper, later changed the plan to include replacing the calipers)
after installing the new components, bled brakes, but wasn't able to build any pedal pressure (ran about a quart and a half or fluid through the system and no air was evident);
Made the assumption that the hydraulic unit or master cylinder had been damaged when compressing the caliper;
Sent the hydraulic unit off to be rebuilt;
Received a rebuilt hydraulic unit, reinstalled, bled brakes (a couple of quarts of fluid) and still no pedal pressure;

I am really having a time figuring this out. Has anyone run into any thing similar?

Help!!!!

If you mean the pedal sinks to the floor, you should check the booster.

Can you pumpp the brakes and get some pedal pressure with the engine (and ign) off?

If you mean the pedal sinks to the floor, you should check the booster.

Can you pumpp the brakes and get some pedal pressure with the engine (and ign) off?

The pump has been recently replaced along with the hydraulic unit.

I can get a little pedal more pedal with the ignition off, but it still almost goes to the floor. Thanks for the reply.

First , you were just doing a routine brake job? What was wrong with the brakes before you started?. Once you got the Master cylinder back, how did you bled it? If it isn't bled properly, than your entire system will not bleed correctly. Do you see any fluid leaking out of the base of the M/C were it mates to the booster? If so, your seals in the M/C are bad.

I'm assuming from your post that you did the work. Did you bench bleed the master cylinder (before you installed it)? Do you still have the old booster or did you send it back?

I'm assuming from your post that you did the work. Did you bench bleed the master cylinder (before you installed it)? Do you still have the old booster or did you send it back?

I did the work. I started this because the pads and rotors were in poor condition.

I did not bench bleed the master cylinder and hydraulic unit before reinstalling. As for the process of bleeding the brakes I followed what was called out in the Jeep shop manual.

Install the unit.
Fill with fluid.
Turn on the ignition to presurize the system.
Start the bleeding from the right rear ending with the left front.

Is a bench bleed the missing step? If so, are both the master cylinder and hydraulic unit to be bench bled?

Thanks.

Your master cylinder should have come with instructions to bench bleed it. If you can't find it, contact the manufacturer.

You can also review this.

http://www.misterfixit.com/brakbld1.htm

There is your first problem then. Your master cylinder MUST be bled before you install it to the vehicle. Any parts store will have a bleeder kit for the MC. Simply put you thread the fittings into the ports on the M/C, connect the tubes to those fittings and runinto the fluid in the M/C. Make sure that the tubes stay below the fluid at ALL times. Slowly push the plunger on the M/C. You'll stat to see bubbles. Do this part SLOW. repeat till all evidence of air is gone then install in Jeep( Don't drain the fluid out). Connect your brake lines to the M/C (after you remove the fittings from bleeding), and carry on with the bleeding. Starting with the RR wheel,LR,RF, then LF tire. Hope this helps.

There is your first problem then. Your master cylinder MUST be bled before you install it to the vehicle. Any parts store will have a bleeder kit for the MC. Simply put you thread the fittings into the ports on the M/C, connect the tubes to those fittings and runinto the fluid in the M/C. Make sure that the tubes stay below the fluid at ALL times. Slowly push the plunger on the M/C. You'll stat to see bubbles. Do this part SLOW. repeat till all evidence of air is gone then install in Jeep( Don't drain the fluid out). Connect your brake lines to the M/C (after you remove the fittings from bleeding), and carry on with the bleeding. Starting with the RR wheel,LR,RF, then LF tire. Hope this helps.

Well, I have done the equivalent of a bench bleed, but while in the car. Bled the wheel cylinders again, and still no pedal presssure. I have run out of ideas. I am about to have the jeep towed to the dealer for diagnostics. Are there any other ideas before I resort to the dealer?

Well, I have done the equivalent of a bench bleed, but while in the car. Bled the wheel cylinders again, and still no pedal presssure. I have run out of ideas. I am about to have the jeep towed to the dealer for diagnostics. Are there any other ideas before I resort to the dealer?

Looking under the hood of my Jeep, It looks as if the ABS pump system (which you said you had) could have air in it from the M/C that was not bench bled. I would suggest having the station flush the system and pump any air out all four wheel cylinders one at a time. You may need to pump a quart of fluid for each wheel before air in the ABS makes its way to a wheel oud out.

Sometimes on ABS you have to have a Scan Tool to energize the solenoids on the Accumulator. With ABS systems you should never use a C clamp to compress the caliper without opening the bleeder valve. Other wise you send dirty rusty brake fluid bake into the accumulator.
The ABS system you have is Bendix 9 which has a different bleeding procudure. With the key off pump the brakes 25 to 40 times With key off.
Bleed Right Rear Left front then bleed Right front left rear. This out of my ABS Manual this is different pattern than some vechiles. You still might have to use a scan tool to complete the process.