WJ/KJ brakes in my XJ, poor rear braking.

[techno1154]

Did any of you guys get any acceptable results with the braking system? My XJ brakes seem to be opposite to what you are experiencing. The brakes are very hard,...as if the pedal is hitting a stop and not a lot of stopping power. After running several stops I think it may be the proportioning valve. I need to make changes to improve the braking power, but what should I change? I do not just want to through money at it until I achieve the desired results. I want to do it right the first time.

 

[blistovmhz]

Did any of you guys get any acceptable results with the braking system? My XJ brakes seem to be opposite to what you are experiencing. The brakes are very hard,...as if the pedal is hitting a stop and not a lot of stopping power. After running several stops I think it may be the proportioning valve. I need to make changes to improve the braking power, but what should I change? I do not just want to through money at it until I achieve the desired results. I want to do it right the first time.

Yes. Also, my pedal felt fine. The problem was that while the pedal was firm, the rears were barely engaging. The fronts would lock up on dry pavement easily while the rears couldn't barely prevent the engine from idling away in 1st.

I removed the guts of the prop-valve and now braking is awesome. I suspect one of two possibilities:
1. Prop-valve was defective. - It was working and doing proportioning, but maybe way too early. This may be normal though which brings us to:
2. The rear calipers just require way more fluid than the stock combo valve will supply.

Either way, I'd recommend pulling the o-ring off the prop-valve and stick it back together and see what happens. If it solves your problem, do as has been suggested by several people, and invest in a good adjustable combo/prop valve, or at least plumb your front and rear directly to the MC, so you're not losing your front/rear isolation.

 

[yossarian19]

Did any of you guys get any acceptable results with the braking system? My XJ brakes seem to be opposite to what you are experiencing. The brakes are very hard,...as if the pedal is hitting a stop and not a lot of stopping power. After running several stops I think it may be the proportioning valve. I need to make changes to improve the braking power, but what should I change? I do not just want to through money at it until I achieve the desired results. I want to do it right the first time.

Hard pedal + poor brakes = bad booster most of the time

 

[techno1154]

Yes. Also, my pedal felt fine. The problem was that while the pedal was firm, the rears were barely engaging. The fronts would lock up on dry pavement easily while the rears couldn't barely prevent the engine from idling away in 1st.

I removed the guts of the prop-valve and now braking is awesome. I suspect one of two possibilities:
1. Prop-valve was defective. - It was working and doing proportioning, but maybe way too early. This may be normal though which brings us to:
2. The rear calipers just require way more fluid than the stock combo valve will supply.

Either way, I'd recommend pulling the o-ring off the prop-valve and stick it back together and see what happens. If it solves your problem, do as has been suggested by several people, and invest in a good adjustable combo/prop valve, or at least plumb your front and rear directly to the MC, so you're not losing your front/rear isolation.

M plan is to remove the proportioning valve, Tee the front together and use an adjustable valve for the back wheels. I also have the ZJ disc in the back. With the O ring in the prop valve removed, the rear lock way too early on wet pavement. Normal progressive breaking is good with plenty of pedal feel. For panic stops one have to tighten their butt, bite their lips and pray the XJ stop before it hit the vehicle in front of it.
After the initial pedal travel with the expected progressive slow down the pedal become rock hard, no further movement and no additional slowing/stopping power.


QUOTE=yossarian19;246280505]Hard pedal + poor brakes = bad booster most of the time[/QUOTE]

The booster is/was new from Napa about 8 months ago. It did improve pedal feel and the initial/normal slow down. Beyond that i.e. panic stop remains exactly the same.

If I isolate the front or rear by loosening a line or bleed valve the pedal travel is exactly what I would expect with only one half of the system working. When both front and rear are combined (the way it should be) is when it feel like someone put a limiting block of wood between the pedal and the floor. At present, I cannot find that proverbial block of wood.

Over the last say 3,000 miles the entire brake system was replaced with the exception of the master cylinder and the combo valve. This includes all the soft lines and part of the hard line going to the back. No, the pedal do not go down no matter how long I hold it or how much pressure I put on it.

 

[Talyn]

Hard pedal + poor brakes = bad booster most of the time

This is what I would say.

 

[TheBlueXJ]

I have this same problem on my xj with drums though I have zero rear brakes at this point can anyone help? Ebrake with will active brakes but other than that there is no rear brakes even if front is super locked up