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Unread 12-13-2009, 01:07 PM   #1
Unlimited04
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XJ/TJ/ZJ Front Knuckle Repair - Brake Pad Divots

I'm building an XJ HP D30 which I got from the junkyard, and the knuckles were grooved pretty bad from the brake pads riding on them. This is a write-up on how to fix the grooved area, which applies to ZJ's, XJ's and TJ's.

Tools you will needs:
4.5" angle grinder
4.5" THIN cutting disc (must be new)
MIG/Flux-Core welder with welding wire
hardened steel machinist's file
hardened steel welder's file
wire brush
heat gun
digital non-contact thermometer

Here's the two files I used:

A "Pipeliner" file from the local welding supply shop, with several shark teeth cut into it (works GREAT for removing slag and sharp welding edges)
A machinists fine file - something I inherited, its probably older than my dad.
The reason you want to use a NEW cutting wheel is because the edges are much finer, you haven't rounded or damaged the edges yet!

So the reason you're reading this is because the front brakes are sticking, making noise and the pads are wearing uneven. This is caused by grooves that are ground into the knuckle over time as the pads slide across the ears.

Step 1 - Remove the calipers and discs.

Step 2 - Use a wire brush to vigorously clean all the rust and junk off the ears

Step 3 - You should have something that looks like this:



Step 4 - Use the heat gun to warm one knuckle ear at a time, then use the non-contact thermometer to measure the temperature. I was able to get mine to ~250*F in about a minute. When you weld any metal, the welder must heat up the surrounding metal before the welding process can actually begin. By pre-heating the knuckle ear, the weld will flow better and the welder will not skip/spark near as much when you initially begin welding.

Step 5 - Burn plenty of extra material into the groove. I used a pretty hot setting with a slower wire speed on my Hobart 140. IT IS IMPORTANT THAT YOU PERFECT YOUR WIRE/HEAT SETTINGS ON A PIECE OF SCRAP STEEL. I used some junk I had laying around and welded two passes about 2" long to make sure the settings were good. You DO NOT want to be adjusting settings while trying to fix your knuckles.

Step 6 - You should end up with something that looks like this:
One Pass

Two Passes:


Step 7 - Use the machinist's file to remove any excess slag from welding, trying not to damage the knuckle surface

Step 8 - Use the THIN cutting disc to cut off the top excess off the weld.


Step 9 - CAREFULLY and SLOWLY use the THIN cutting disc to grind the weld down. Take VERY small bits, and keep the disc parallel to the knuckle surface. Move it back and forth over the entire weld area, don't stay in one place too long. When you start grinding into the knuckle surface, you need to stop. You should be able to make this quite flat by feeling with your fingers.

Step 10 - Run your fingers along the knuckle, noting the chamfer and flats that are present. Use the welder's file to remove large burrs of weld, and use the machinist's file to bring the weld flat to the rest of the knuckle. Use the files sparingly, only as final touches after grinding. You do not want to rely on file to remove lots of material because the welding process pulls carbon out of the cast knuckles, making the weld extremely hard. The file will remove little material, and is LOTS of work - but it will allow you to shape the chamfer and flats nicely...but it takes work.

Step 11 - Test fit the calipers with pads, pushing the calipers back and forth to make sure the pads slide nicely. You don't want any sharp edges or uneven metal for the pads to catch on.

Repeat 9-11 many times until it you're satisfied. Don't try to do it all at once...go slow and methodical. You need to be surgical with this grinder!

You should ultimately get something that looks like this:





and thanks to mrblaine for confirming this was a good idea


Last edited by Unlimited04; 05-04-2010 at 02:58 PM..
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Unread 12-13-2009, 02:20 PM   #2
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Thanx for you're input...
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Unread 12-13-2009, 03:56 PM   #3
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Done this half-a-dozen times now as I have been through a fair few front axles (but thats a different story!). It works great and is far, far, far cheaper and easier than replacing knuckles. To be honest, even if you don't get a perfect finish it is still going to be better than the hole you are starting off with. If you do grind too much off you can always hit it with a welder a second time but ideally it should be done in one pass as you have done.
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Unread 12-13-2009, 05:15 PM   #4
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Can I ask what the advantage is to having the knuckles smoothed out like that? Is so the brakes can slide back and forth easier?
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Unread 12-13-2009, 05:36 PM   #5
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Originally Posted by NH44XJ View Post
Can I ask what the advantage is to having the knuckles smoothed out like that? Is so the brakes can slide back and forth easier?
The pads create the notches and get caught in them. They are supposed to slide along those rails.
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Unread 01-03-2010, 01:59 PM   #6
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Amazing. Good stuff here U04
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Unread 01-03-2010, 02:19 PM   #7
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Great write-up. Thanks!
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Your shaft isn't long enough to handle that kind of droop...
My build thread: http://www.jeepforum.com/forum/f9/ru...thread-792423/
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Unread 01-03-2010, 02:58 PM   #8
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Yeah, thanks for the write up !! great pics ~!
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Unread 01-13-2010, 03:54 PM   #9
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Hey U04, this is gonna be a newb question. (as I'm new to brakes and such) but what if I order centrim plenum rotars w/ my yellow pads. Would I still run into this knuckle problem? I assume yes but not sure if new rotars comes new knuckles with em.
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Unread 01-13-2010, 05:00 PM   #10
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Quote:
Originally Posted by CCJ View Post
Hey U04, this is gonna be a newb question. (as I'm new to brakes and such) but what if I order centrim plenum rotars w/ my yellow pads. Would I still run into this knuckle problem? I assume yes but not sure if new rotars comes new knuckles with em.
no matter what pads or rotors you use the pad wear will end up being uneven, and you'll end up grinding a groove in the knuckle. its a design flaw in the knuckle & brake design itself. this is something the Vanco brake system or WJ knuckle/brake swap addresses because both use a different caliper design that doesn't rely on the brake pad sliding across the knuckle.
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Unread 01-13-2010, 09:11 PM   #11
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Originally Posted by Unlimited04 View Post
no matter what pads or rotors you use the pad wear will end up being uneven, and you'll end up grinding a groove in the knuckle. its a design flaw in the knuckle & brake design itself. this is something the Vanco brake system or WJ knuckle/brake swap addresses because both use a different caliper design that doesn't rely on the brake pad sliding across the knuckle.
And yet another reason I should pull trigger on Vanco. Thanks for explanation and for having these links in your sig.
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Unread 02-26-2010, 10:13 PM   #12
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Can this be done with an epoxy or a JB type of weld product? As I don't know how to weld nor own a welder.I need to do this on my wifes 95 GC. I see that the caliper bracket is not removable on this era D30 as it is a seperate peice on my 89 xj. Anyway, thanks for any info.
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Unread 02-27-2010, 01:36 PM   #13
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Quote:
Originally Posted by my2monkeys View Post
Can this be done with an epoxy or a JB type of weld product? As I don't know how to weld nor own a welder.I need to do this on my wifes 95 GC. I see that the caliper bracket is not removable on this era D30 as it is a seperate peice on my 89 xj. Anyway, thanks for any info.
heck no. if the pads wore into cast iron, can't imagine any epoxy will last.
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Unread 03-22-2010, 09:06 PM   #14
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awesome write up
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Unread 03-23-2010, 04:33 PM   #15
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Wish I could weld...yet another reason to buy a welder.
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