• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

XJ - towing and brakes

B

blistovmhz

NAXJA Forum User
Location
Vancouver, BC
Hey all. 98 XJ, 6.5" lift, 33", 4.10, ax15.
I've got a d44 rear with a set of liberty disc brakes and front d30 with WJ knuckles/brakes.
I thought I should be easily able to tow a few thousand pound trailer, but took it out today for a quick test drive around the block, and braking was horrible. Took easily 10x longer to stop than unloaded.
Trailer is probably under 2000lbs and had maybe 1000lbs of junk in it. Tongue weight is probably around 600lbs.

I hear heaps of guys talk about towing up to 5000lbs with a stock XJ with drums and the tiny d30 brakes. What gives? Are they all nuts or are my brakes just not working as well as they should?

Unloaded, I can JUST about lock up all 4 on dry pavement.
 
That said, I suspect there must be something wrong with my setup.
Everyone who's done either the WJ front or KJ rear swap has said either provided a massive upgrade to braking, but I've never found anyone who's done both, and it's possible I've messed something up and just can't find it.

The WJ calipers/rotors are brand new, and the KJ pads have been replaced after cleaning the hell out of the KJ rotors (and hitting them with 400 grit sanding to make sure any glaze is removed).
When I brake, the Jeep usually pulls either left or right on the first application of the brake, but all subsequent braking is straight. Perhaps I've got a pinched line, but that shouldn't affect overall braking force as much as I'm seeing.

When I did the swap, I unfortunately did front and back at the same time so I've no way to know which might be the problem. I did also run the MC dry, but did a bench bleed after (though maybe messed it up?).
All I can think is I missed something simple, several times in a row (because I've checked everything 20 times) or perhaps the caliper volumes between front and rear are just too far off.
The latter doesn't seem valid though, as there are tonnes of guys with just the WJ fronts, and the stock drum rears who say it works amazing, and a growing number of guys with the KJ rears and stock fronts who say the same. I'm always a little suspicious that Jeep guys doing the KJ swap might all just have a bit of ego, and don't want to admit the swap didn't work as well as they claim, but perhaps someone can chime in with an honest answer?

Can anyone think of a reliable way to measure braking force to compare against a stock XJ? My buddies stock XJ on my old 31's seems to stop about the same rate as I do on my 33's. that doesn't seem right.
 
did you change the master cylinder to match the fluid volume needed for larger front calipers and rear calipers?

I'd guess that you will want something that moves more fluid to get the benefits of the brakes you have.
 
Shorty said:
did you change the master cylinder to match the fluid volume needed for larger front calipers and rear calipers?

I'd guess that you will want something that moves more fluid to get the benefits of the brakes you have.
Click to expand...

I haven't yet, because tonnes of guys say they run the stock MC/Booster without a problem. Perhaps BOTH my front and rear together though, require more volume that the puny stock MC can dole out?

This is the thing with the XJ community :) There are always 10 different definitive answers to every question. Half the guys who do the WJ swap say the bigger MC is needed, while the other half say it's not, and both claim they have a huge braking upgrade. Same goes with the rear.
Personally, I'd prefer to have a 50/50 split between front and rear anyway as I'd rather my ass end lets loose before my front end dives.

Was just talking to a buddy at work (engineer and fellow truck guy) who, after a 15 minute conversation said his first order of business would be to try a bigger MC. What's a good upgrade?
 
I didn't see in your explaination above whether or not you either;

A-changed the internals of the proportioning valve or

B-changed the whole proportioning valve with one from a vehicle that has front and rear disks or

C-removed the proportioning valve and replaced it with an adjustable proportioning valve.

When you do the rear drum to disk upgrade you must allow more flow and pressure to the new rear calipers.
 
Warlock1 said:
I didn't see in your explaination above whether or not you either;

A-changed the internals of the proportioning valve or

B-changed the whole proportioning valve with one from a vehicle that has front and rear disks or

C-removed the proportioning valve and replaced it with an adjustable proportioning valve.

When you do the rear drum to disk upgrade you must allow more flow and pressure to the new rear calipers.
Click to expand...

I've had this discussion heaps of times, and the answer I keep getting is that the prop valve does exactly what I think it does. Restrict flow to the rear on extremely hard braking. My problem is with all braking, light or hard.
Also, yes, because everyone always brings this up, I did try a prop valve from a WJ, as well as from a KJ. No difference at all in either case because all the prop valve would do is prevent my rear from locking up under hard braking. Even without the prop valve, I can't lock up the rear, so no prop valve is going to make things better as far as I'm aware.
Hell, If I put the rear up on stands and let the truck idle in 1st gear, I can hammer on the brakes all day and never stall the engine. It grabs, but not hard enough to overpower the engine at idle.

That said, if I lift up the whole truck and throw it in 4x4, I can stall the engine with about 1/4" of brake pedal travel.
 
Trailer brakes.

That doesn't help you resolve your Jeep's braking issue (if there is one) but I wouldn't attempt to tow that much weight behind an XJ without trailer brakes.

I tow my 1,600 pound camper behind my XJ on 31's without trailer brakes but I wouldn't consider towing any more than 2k pounds. Especially on larger tires.
 
first off, i think you're asking alot of your brakes with that trailer. i'm inclined to think the MC volume is in question. upgrading the brakes on one end of the rig the increase in volume can usually be compensated by the stock MC, but when you change both ends you may be needing more volume than is available.
though i never looked into it for an XJ, i'm pretty sure a late 80s E350 MC is a direct swap for YJs with similar issues, and i think a friend once told me he used a 76 El Dorado on his ZJ with D60s and 4 wheel discs.
this is all assuming you have properly bled the system. maybe do it one more time with a pressure bleeder.
 
sidriptide said:
first off, i think you're asking alot of your brakes with that trailer. i'm inclined to think the MC volume is in question. upgrading the brakes on one end of the rig the increase in volume can usually be compensated by the stock MC, but when you change both ends you may be needing more volume than is available.
though i never looked into it for an XJ, i'm pretty sure a late 80s E350 MC is a direct swap for YJs with similar issues, and i think a friend once told me he used a 76 El Dorado on his ZJ with D60s and 4 wheel discs.
this is all assuming you have properly bled the system. maybe do it one more time with a pressure bleeder.
Click to expand...

I really should have mentioned this in the OP, but my pedal is firm under all braking conditions. If the MC was too small, wouldn't my foot go to the floor?
I can't push it more than 3/4 to the floor with my 200lbs behind it.
I'm definitely into upgrading the MC if it's goona help, but the pedal travel (seems to ?) indicate the MC has more than enough volume. Am I missing something?
 
blistovmhz said:
Hell, If I put the rear up on stands and let the truck idle in 1st gear, I can hammer on the brakes all day and never stall the engine. It grabs, but not hard enough to overpower the engine at idle.
Click to expand...

This might be a problem. Is this with the new rear calipers and is it with or without the proportioning valve?
 
Just talked to my buddy, he has the same gears and a manual trans and drum brakes and he can stall his motor with the back end jacked up. I think you have a problem between the MC and the rear calipers.
 
Quick rule of thumb, a trailer half the towing vehicles GVW without trailer brakes and equal to the GVW with trailer brakes is the vehicles normal capability. Funny about this rule. I just worked it backwards out of curiosity. I often haul firewood in my trailer. I'm comfortable with 750 KG. gross trailer weight (loaded) without trailer brakes, just what I'm comfortable with. That works out to almost exactly half the GVW of my XJ. My experience and the general rule work out to be almost identical, go figure.

I think trailer towing maximum specs are inflated as a selling point. And anybody who has towed a 5000 lb. trailer without brakes and gotten away with it, was lucky.

You likely offset the added ability of the your new discs by having 33 inch tires. Leverage is working against you.

Heating up the pads and discs is also a factor.

I've been wondering when someone was going to install a Chev 3/4 ton P.U. hydraulic boost master cylinder. Instead of using vacuum, it uses the power steering pump for boost.

I've seen at least half a dozen car/trailer wrecks over the years. Some have been really spectacular. Most were caused by sway and/or insufficient braking. I learned from example (the less painful way is watching somebody else screw it up), if it starts to sway, gas not brakes is the answer. And having too much trailer weight is one of those things you get away with until you don't, it only takes one failed panic stop to really mess up your day.

I watched one guy have his really overloaded trailer push him right past/through an intersection, he panicked and turned the steering wheel, rolled his car and trailer three times. Watched a guy come down a small hill in the rain that curved left at the bottom, no matter what he tried, him and the trailer just went straight, across the beach and into the ocean. His trailer actually floated really well, his car, not so much. Nobody got (seriously) hurt, but it sure ruined his vacation.
 
Warlock1 said:
Just talked to my buddy, he has the same gears and a manual trans and drum brakes and he can stall his motor with the back end jacked up. I think you have a problem between the MC and the rear calipers.
Click to expand...

Yup. I've tested this on my buddies Jeep as well, with his stock 3.55 gears, and it easily stalls out.
I'm beginning to wonder if everyone who's done the KJ rear swap is just retarded and never bothered to do a real comparison between a working set of drums, against their new KJ rear discs. I'm almost willing to bet the comparison is between a completely destroyed and entirely non-working set of drums, against the KJ rears.
If this is the case, the problem is almost certainly going to be the MC's rear piston being much larger on the KJ than it is on the XJ. I suppose I can go pick up a KJ MC (and hope it bolts on) and give it a try.
 
8Mud said:
Quick rule of thumb, a trailer half the towing vehicles GVW without trailer brakes and equal to the GVW with trailer brakes is the vehicles normal capability. Funny about this rule. I just worked it backwards out of curiosity. I often haul firewood in my trailer. I'm comfortable with 750 KG. gross trailer weight (loaded) without trailer brakes, just what I'm comfortable with. That works out to almost exactly half the GVW of my XJ. My experience and the general rule work out to be almost identical, go figure.

I think trailer towing maximum specs are inflated as a selling point. And anybody who has towed a 5000 lb. trailer without brakes and gotten away with it, was lucky.

You likely offset the added ability of the your new discs by having 33 inch tires. Leverage is working against you.

Heating up the pads and discs is also a factor.

I've been wondering when someone was going to install a Chev 3/4 ton P.U. hydraulic boost master cylinder. Instead of using vacuum, it uses the power steering pump for boost.

I've seen at least half a dozen car/trailer wrecks over the years. Some have been really spectacular. Most were caused by sway and/or insufficient braking. I learned from example (the less painful way is watching somebody else screw it up), if it starts to sway, gas not brakes is the answer. And having too much trailer weight is one of those things you get away with until you don't, it only takes one failed panic stop to really mess up your day.

I watched one guy have his really overloaded trailer push him right past/through an intersection, he panicked and turned the steering wheel, rolled his car and trailer three times. Watched a guy come down a small hill in the rain that curved left at the bottom, no matter what he tried, him and the trailer just went straight, across the beach and into the ocean. His trailer actually floated really well, his car, not so much. Nobody got (seriously) hurt, but it sure ruined his vacation.
Click to expand...

Yea, I really hate doing stuff like this, but I don't have a bigger (working) truck available right now, and the city has started to complain about the construction garbage all over the front. We've got all the non-wood stuff loaded into the trailer, so they'll be less pissed at us now, but I'd still like to get it done. The dump is a pretty smooth drive about 15 minutes away, but it's right through town.
I'm debating renting a truck to haul the trailer, which is depressing as I just build myself a new, beefy ass drop hitch and finally wired up my trailer lights :)
 
Most of your braking is one the front.

This is an interesting read. Some bits and pieces in there that may be interesting for you. http://www.custompowerbrake.com/faq.html

Locking up the rears is to e avoided, your vehicle tends to want to swap ends. No matter what your instincts say, you want most of your braking in the front.
 
What I would check is;

1-Double check for air in rear lines coming from MC on back and

2-check for kinked line from MC to proportioning valve and

3-check hard line from PV to rear flex line for dents or kink and

4-check flex lines. when they get old, sometimes the inner lining can degrade and prevent full flow. and

5-check that the bleeder screws are at the top of the calipers and that all air is gone from system.
 
8Mud said:
Most of your braking is one the front.

This is an interesting read. Some bits and pieces in there that may be interesting for you. http://www.custompowerbrake.com/faq.html

Locking up the rears is to e avoided, your vehicle tends to want to swap ends. No matter what your instincts say, you want most of your braking in the front.
Click to expand...

Yea, I understand you want more braking force in the front, but not being able to stall your idling engine with the rears, something's wrong.

Thing is, I've checked that the rear calipers are retracting the correct distance from the rotor, and they're moving at the same rate as the front. All I can think is that the front, despite being much larger, require less fluid volume than the rears, and the piston in the MC is preventing the rears piston from moving far enough to properly engage the rear.

I suppose I could take the front rotors out, and stick something half the rotors width, inbetween the front rotors, then jack up the rear end and see if the rears can clamp down hard enough to stall the motor.
It may just be a volume distribution issue, in which case I have to figure out what MC has the correct distribution for my setup.

Either way at the end of the day, I don't think this is an issue of not enough pressure from the MC overall, but just not enough pressure to the rear piston, in which case the problem is very likely the piston volume.
I don't think adding a bigger booster will help anything because if it's a distribution issue, i'd have to blow up the front brake lines before the rear piston can move far enough to engage the rears.

This make sense?
 
blistovmhz said:
Yea, I really hate doing stuff like this, but I don't have a bigger (working) truck available right now, and the city has started to complain about the construction garbage all over the front. We've got all the non-wood stuff loaded into the trailer, so they'll be less pissed at us now, but I'd still like to get it done. The dump is a pretty smooth drive about 15 minutes away, but it's right through town.
I'm debating renting a truck to haul the trailer, which is depressing as I just build myself a new, beefy ass drop hitch and finally wired up my trailer lights :)
Click to expand...

The story I told about the trailer pushing the guy through an intersection, that was right in front of the dump (no kidding). Five guys in the car, rolled three times, the trailer unloaded itself and the car and trailer landed on the tires. All the windows blew out of the car, most everybody had glass in their eyes.

If I had to drive yours that way, I'd leave way early (deserted roads) and drive like it was my first time on ice skates.
 
blistovmhz said:
Yea, I understand you want more braking force in the front, but not being able to stall your idling engine with the rears, something's wrong.

Thing is, I've checked that the rear calipers are retracting the correct distance from the rotor, and they're moving at the same rate as the front. All I can think is that the front, despite being much larger, require less fluid volume than the rears, and the piston in the MC is preventing the rears piston from moving far enough to properly engage the rear.

I suppose I could take the front rotors out, and stick something half the rotors width, inbetween the front rotors, then jack up the rear end and see if the rears can clamp down hard enough to stall the motor.
It may just be a volume distribution issue, in which case I have to figure out what MC has the correct distribution for my setup.
Click to expand...

Trying an adjustable proportioning valve would be my first guess. I'm lucky I have access to a brake machine (for free). It will tell you quick if they pull or how they are proportioned. Most every mid size truck shop around here has a brake testing machine. I have no idea what a test costs, it isn't likely to be that much.

What kind of pads are you using? A lot of hype about brake pads, I tend to stick with what I know works instead of believing the hype. Good old Raybestos semi metallic, Bendix a close second. I drive the autobahns here (no speed limits) and have to slow down (radically) daily from around a hundred MPH, Bendix semi metallic work just fine. Though they are a little hard on the discs, it is most always a trade off between stopping power, disc and pad life anyway.

I've put copper shims behind the pads before to help with brake squeak. You can find copper sheet, in many thicknesses, in most any hobby shop. A good pair of scissors cuts it just fine.

I read a calculator for MC size and wheel cylinder size awhile back. I really should have book marked it. If I remember were I saw it, I'll get back to you.
 
Warlock1 said:
What I would check is;

1-Double check for air in rear lines coming from MC on back and

2-check for kinked line from MC to proportioning valve and

3-check hard line from PV to rear flex line for dents or kink and

4-check flex lines. when they get old, sometimes the inner lining can degrade and prevent full flow. and

5-check that the bleeder screws are at the top of the calipers and that all air is gone from system.
Click to expand...


1. Checked lines for air tonnes of times. I DOUBT I'm missing anything here.
2. No kinked lines as far as I can tell upon visual inspection.
3. Same deal.
4. Flex line to the rear is pretty old and could be a problem. But assuming it is, wouldn't it just slow the fluid to the rear, so the longer I hold on the brake, the better the braking would get? I can hold it down with all my weight while pushing my seat till I break a mounting bolt (ask me how I know), and the rears still won't stop the engine.
5. bleeders are all at the top :). I've even pulled them while bleeding to make sure the bleeder was deadly at the top.
 
You must log in or register to reply here.

Similar threads

X
My brakes are crap
Replies
12
Views
3K
xjklmnop69
X
M
Poor pedal feel and weak brakes.
Replies
17
Views
2K
Bent
Bent
B
Dash brake light on after replacing rear brakes
Replies
1
Views
1K
RCP Phx
R
N
Rear Differential Oil Towing once
Replies
3
Views
1K
Nomad Nate
N
S
Putting ABS Brakes On A Non-ABS XJ?
Replies
2
Views
2K
IslanderOffRoad
IslanderOffRoad
Back
Top