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Brakes...when in 4-low

J

jk_surgeonfish

NAXJA Forum User
Location
AZ
This past week I put new Napa Premium rotors, new calipers, and safety stop pads. Bled the system and all is great....or so I thought. Driving around the Jeep stops great. I can almost lock up the tires when I do a quick stop for 45mph. It stops way better then it did before.

Here are the specs:

99xj
31" MTRs
armor and heavier bumpers.

Here is the problem:

Was running Broken Arrow in Sedona,AZ this past weekend and when I got to the steps (steep part of the trail) I had my foot to the floor and pushing the brake pedal as hard as I could and it still would creep foward in 4 low. The trail is easy but when you come to that and have no way to stop it does make it interesting.:shocked: I had to pull e-brake to give me more stopping power and then it barely helped.

I did adjust the rear shoes after I did the front brakes as well.

So what is the problem? Master Cylinder? Or is this the norm? I have already checked the brake booster check valve and it appears to not be leaking. If you pump the brakes up and then start the Jeep the pedal goes down so that indicates the brake booster is working.

Thanks!
 
The wonders of having an auto in 4 wheeling. The engine and tranny are still trying to power thru just like if you were going over some rocks. Next time out go down hill and if the brakes dont stop you completly throw it into neutral and you should have all braking power that you will ever want. This is just one of the cons with running an automatic
 
I can stall my motor in 4 low with my brakes.

I would say master cylinder.

I had one do the same thing on a long hill descent. It works fine when you're driving and when you slam on the brakes, but the master would bleed the pressure off internally if you had to hold the pedal down for a while.

Replaced the master, all was well and I could stand on the brakes as long as I'd like.

unless you're geared stupid low with doublers and such your brakes should have plenty of stopping power. You should be able to step on them and rev the engine in 4 low without it moving.
 
87manche said:
I can stall my motor in 4 low with my brakes.

I would say master cylinder.

I had one do the same thing on a long hill descent. It works fine when you're driving and when you slam on the brakes, but the master would bleed the pressure off internally if you had to hold the pedal down for a while.

Replaced the master, all was well and I could stand on the brakes as long as I'd like.

unless you're geared stupid low with doublers and such your brakes should have plenty of stopping power. You should be able to step on them and rev the engine in 4 low without it moving.
Click to expand...

Thanks...I'm thinking MC as well. I'll just replace it and see what happens.... assuming it can't make it any worse.... I hope..LOL. Oh... and no doublers... just stardard 231 TCase.....
 
98XJLongBuild said:
The wonders of having an auto in 4 wheeling. The engine and tranny are still trying to power thru just like if you were going over some rocks. Next time out go down hill and if the brakes dont stop you completly throw it into neutral and you should have all braking power that you will ever want. This is just one of the cons with running an automatic
Click to expand...
I can stop in 4 low with an auto.
 
jk_surgeonfish said:
Was running Broken Arrow in Sedona,AZ this past weekend and when I got to the steps (steep part of the trail) I had my foot to the floor and pushing the brake pedal as hard as I could and it still would creep foward in 4 low. The trail is easy but when you come to that and have no way to stop it does make it interesting.:shocked: I had to pull e-brake to give me more stopping power and then it barely helped.


Thanks!
Click to expand...

I did that one not that long ago as well. Are you sure you weren't just sliding down the staircase?
 
jk_surgeonfish said:
Thanks...I'm thinking MC as well. I'll just replace it and see what happens.... assuming it can't make it any worse.... I hope..LOL. Oh... and no doublers... just stardard 231 TCase.....
Click to expand...

read up on bench bleeding.

it's important.
 
Reclipse said:
I did that one not that long ago as well. Are you sure you weren't just sliding down the staircase?
Click to expand...

No sliding... was at the top part before it drops off the first real step. It is still steep at that point and it was all I could do to keep it from going over the first step. Definetly not sliding... you could hear the brake creaking as they were slowing rolling forward.
 
I bled the brakes out today with at least 1/2 of the large bottle of fluid. Had assistant pump pedal 3 times hold and I crack it open and close. Did that at least 5 times at each wheel. Started at Pass rear, then driver rear, Pass front and finally driver front. I made sure to refill often so it never went empty.

Did not help. In fact, the brakes seem to be worse now which makes no sense. I think I will just get the new MC from Napa and bench bleed it, install and then rebleed the wholed system. If still not any better I am not sure what I'll do next.
 
Did the mc ever go dry while you were changing the calipers? If so, a bench bleed may be in order.

Next thing I would check would be adjustment of rear brakes, which you said has been done.

If the engine is off, do you have a firm pedal?
Does it help to pump the brakes?
What is the condition of your front wheel bearings?

I know, some off the wall stuff, but I'm not a real mechanic, so orderly testing sometimes is out of my league...
 
What gear ratio in the axles?

I had no problems with 33s, 3.55s, and an auto with a properly functioning (at best) stock brake system on my 96.

Also no problems with 33s, 3.55s, and an AX15 right now, but that's because I have 3 pedals.

The deeper your gears get, the tougher it is going to be to stop with an auto without putting it in neutral. Fixing the brake system and possibly upgrading it may be in order - or find a way to set the transmission up to default to the highest gear possible (2nd in 1-2, 3rd in 3, OD in D) when 4WD is activated, speed is low, and the brake pedal is depressed. At least the transmission won't be working quite as hard against the brakes then. Shouldn't be too difficult with an arduino and some basic interface hardware but may trigger a CEL if you are not careful.
 
kastein said:
What gear ratio in the axles?

I had no problems with 33s, 3.55s, and an auto with a properly functioning (at best) stock brake system on my 96.

Also no problems with 33s, 3.55s, and an AX15 right now, but that's because I have 3 pedals.

The deeper your gears get, the tougher it is going to be to stop with an auto without putting it in neutral. Fixing the brake system and possibly upgrading it may be in order - or find a way to set the transmission up to default to the highest gear possible (2nd in 1-2, 3rd in 3, OD in D) when 4WD is activated, speed is low, and the brake pedal is depressed. At least the transmission won't be working quite as hard against the brakes then. Shouldn't be too difficult with an arduino and some basic interface hardware but may trigger a CEL if you are not careful.
Click to expand...

31s and 4.56s.....
 
98stocker said:
Did the mc ever go dry while you were changing the calipers? If so, a bench bleed may be in order.

Next thing I would check would be adjustment of rear brakes, which you said has been done.

If the engine is off, do you have a firm pedal?
Does it help to pump the brakes?
What is the condition of your front wheel bearings?

I know, some off the wall stuff, but I'm not a real mechanic, so orderly testing sometimes is out of my league...
Click to expand...

Pedal is firm when engine is off. When engine is running it does seem to help when I pump them. Not sure what the front wheel bearings have to do with the brakes though???
 
You sure you bled them properly? Not meaning to be judgmental I've just never seen this. In 4low with my aw4 I can stop on a dime and I have stock brakes.
 
trust96xj said:
You sure you bled them properly? Not meaning to be judgmental I've just never seen this. In 4low with my aw4 I can stop on a dime and I have stock brakes.
Click to expand...

It is an XJ...I'm sure of nothing...LOL.

I was reading another forum and came across this method to bleed the brakes and plan to try this today:

From mrblaine the brake wizard:

In this order-
Open bleed screw, say down
Helper pushes pedal down fast with enthusiasm and when the pedal is down, says down.
You close bleeder and say up
When the pedal is up, helper says up.

You open bleed screw and say down. Rinse and repeat 4 -6 times per caliper.

If it takes more than two rounds of that, stop and find the problem because all you're doing after that is wasting time and fluid.

If your master ever went dry, remove it and bench bleed it. Get the plastic plugs that fits the ports and install them. Clamp the master in a vise with the ports plugged and the master level. Fill half to three quarters full of brake fluid and start stroking the plunger. Start with short strokes and increase to repeated full strokes until you can only depress the plunger 1/8" to slightly less or so.

Install master back into the rig, remove the plugs one at a time to hook up the lines to the combo valve. No muss, no fuss.

Then do your bleeding again.
 
If you want to use the master and bleeders to bleed them ten go buy speed bleeders. They will be in the dorman Help section. I forget the correct sizes. They're about 10 bucks a pair and worth every penny. This will also allow you to bleed them by yourself.

They are the best thing ever when it comes to bleeding the brakes with the pedal. They will even allow you to get air out of the master if you work the pedal fast enough.

otherwise, vacuum bleed them. I love my mityvac, but before I made the investment I did a DIY vacuum bleeder with a vacuum pump I had laying around and a mason jar.
It's the only way to properly bleed a clutch.
 
When everything is working properly, it will stop you in 4lo. My 01 with 4.88s and 4:1 would stay on a hill. I was holding the brake with all I had, but it held. I usually popped it into Neutral to make it easier though.

Edit: I had rear discs, which helped tremendously.
 
Fronts are 3/8-24, rears I don't know for an XJ. With a ZJ disc conversion, you buff the caliper metal down about 1mm where the bleeder screws in, then use a 3/8-24 there too.
 
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