Collin

The story:

So a few weeks ago I picked up a '91 Cherokee Laredo for free, and it's been pretty reliable so far. It has no ABS, single diaphragm early type booster.

When I first started driving it the brakes weren't the greatest. Totally soft pedal, with absolutely no change in the pressure I have to put down; but it still stopped great even if it had no pedal feel. It did pull to the left a bit when I really slammed the brakes, but not under light braking.

Today I was driving across town on a very short trip and about halfway there the pedal just started sinking straight to the floor and it would barely stop. I had to use the ebrake just to get home.

I park and look over the booster and the master cylinder and it's clearly leaking out of the the reservoir cap (old style metal dual-blister cap) at the back of the cylinder. It looks like it may also be coming from where the master cylinder joins the booster, but it could all be from the reservoir cap.

No leaks anywhere else in the system, I checked at all the wheels and all the lines. All fine with no rust/corrosion.


On to the questions:

1) Is this being caused by the leaky reservoir cap?
2) Is it an internal leak in the master cylinder?
3) Is the booster diaphragm busted and is air leaking through that way (wouldn't this make it harder to push)?

BuckB91XJ

You have definitely got a bad Master Cylinder. You have fluid leaking past the piston which is causing your spongey pedal with no signs of leaking at the wheels.

fantic238

2x

Collin

Thank you sir, I'll have the new one in soon and post with results.