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XJ/TJ/ZJ Front Knuckle Repair - Brake Pad Grooves

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#1 · (Edited)
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! :rofl:

You should ultimately get something that looks like this:





and thanks to mrblaine for confirming this was a good idea :thumbsup:
 
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#3 ·
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.
 
#4 ·
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?
 
#9 ·
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.
 
#10 ·
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.
 
#12 ·
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.
 
#18 ·
Just out of curiosity, why wouldn't one be able to simply file the divots flat to match the rest of the ear surface? Of course, the divots would form again, but it would be better than doing nothing. I understand the welding adds hardness, is that the reason?
 
#19 ·
no the reason you weld/fill the divot instead of grinding it flat is to retain the same clearancing between the caliper and the rotor. if you file the divots down flat you'll screw up the distance between the rotor, pad, caliper & hub....without changing the caliper mounting points, the pads will get less support and still slide uneven.
 
#22 ·
Anybody try this with a stick welder? I of course have these grooves, not as bad as in the pics, but still there. I'm trying to fix a squeak problem coming from my right front wheel and I'm slowly overhauling the front brakes trying to fix the problem. I'm probably going to have to put this on the list.
 
#23 ·
Another answer might be to fill the divot and then use a replaceable slider cap as Ford does on the 8.8 axles. In that case, one might be able to fill the divot using an alternate filler such as JB Weld or epoxy.
 
#25 ·
I'll second the desire for a slider cap - When I did the brakes on my Dad's '96 Explorer last summer I was jealous of how well those caps held up and of course the undamaged cast iron underneath. This seems like a logical need that the aftermarket should step in to fill the gap.
 
#28 ·
It's a great aftermarket idea. So great that I had about 20 sets built, but they are expensive in small lots, or about 2 bucks each. And lest we forget, we have to machine the slots in the ends of the brake pads larger so they will slide and that adds to the overall cost.

When I finished up with the costs and added it all up, it was something near 15 bucks cost added to a set of pads with slider caps.
 
#26 ·
Would a 115V mig welder work for this? I have a Lincoln WeldPak 3200HD, and I have .035" flux core wire in it. It can do up to 1/4" steel, output of 90A @ 19V @ 20% duty cycle.

I have a 96 ZJ with the same issues on BOTH knuckles. My friend has a 94 with the same problem, and his wife has a 95 with the same problem. This would make ALL of our lives better!!!

Thing that sucks is I can't weld! I would have to get my friend to lay the welds for me, and then do the dress work myself....

Yeah yeah... I own a welder and can't use it... LOL
 
#30 ·
what about steering pull?

Could dragging pads be the result of these divots and would it be noticeable right after new pads, calipers, and rotors in the front? i would imagine they'd have to wear down a bit before the travel distance would be affected by the divot, or is it the other way around?
 
#31 ·
Yes, it could cause enough drag to have a pull.

I've done this on a few sets of knuckles.
The last set i did had grooves worn almost entirely across the slide.
I use arc with hard facing electrodes. Now the slides are harder than the pads.
 
#34 ·
Ratmonkey, how hard was it to smooth out the hardface weld? Did you use a file, grinder, other? I've hardfaced engineer equipment before, but nothing that had to be shaped after. I know there is a hardfaced TIG rod available but have never used it, this might the best application.
 
#35 ·
You are welcome to use the special rod, but a normal mig weld will pull the carbon out of the knuckle as it freezes and it accomplishes the exact same thing. The new surface when finished with hard grinding disc is now much harder than the surrounding iron knuckle that it will never wear down again.

Try it on a junk knuckle and you'll be pretty impressed at how hard the weld winds up being.
 
#37 ·
Thanks for the write up. Just did my brakes today and was surprised to see these divots - didn't know it was a common problem and wasn't sure how to fix. I wasn't sure it was a good idea to weld on the cast knuckle, so I just decided to figure it out later and put the brakes together without fixing them. I couldn't believe NAPA was asking $750 for a pair of knuckles... Yikes. Now that I see you guys have welded them up, I'll have to go try that later. Much better solution for me!
 
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