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Old 01-04-2018, 09:28 AM
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Replacing brake calipers after pulling axle

Pulled my front axle shafts to replace the u-joints and wheel bearings, but as I was trying to put the caliper back in, it wasn't fitting on the rotor... Came to find out the piston was extended. Tried pumping the brakes to see if it was stuck, now it's charged even further. How do I get the caliper back on the rotor? (Excuse my ignorance.) Does the Jeep need to be on for the piston to retract?

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Old 01-04-2018, 09:31 AM   #2
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Welcome to WF. Open the brake fluid reservoir, then use a C clamp to compress it back in.

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Old 01-04-2018, 09:51 AM   #3
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Welcome to WF. Open the brake fluid reservoir, then use a C clamp to compress it back in.
Yep, just like this....many will use the old pad between the clamp and piston.

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Old 01-04-2018, 10:03 AM   #4
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Tried pumping the brakes to see if it was stuck, now it's charged even further.
You are a very lucky guy. If I had done that, it's a sure bet that the piston would have blown out and sprayed brake fluid all over my paint job.
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Old 01-04-2018, 10:04 AM
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Awesome, thanks! Secondary question: outer oil slingers--necessary, or not so much? My passenger side one cracked off when I was replacing the hub bolts.
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Old 01-04-2018, 10:21 AM   #6
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Or, loosen the brake bleed screw and squeeze it open with your fingers ;-)
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Old 01-04-2018, 10:46 AM   #7
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Hopefully you flushed the brake fluid before you are messing with the caliper and pushing in the piston?
Otherwise you risk getting crud in the seal and the piston locking up.
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Old 01-04-2018, 11:51 AM
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Hopefully you flushed the brake fluid before you are messing with the caliper and pushing in the piston?
Otherwise you risk getting crud in the seal and the piston locking up.
No, I just pulled the caliper off per the guide I found for pulling the axle and found the piston was charged when I went to put the caliper back on the rotor. Haven't really done anything to it aside from try to grease it via the zerk (which it wouldn't take, probably due to the cheap Chinese grease gun I bought) and pump the brakes to see if it was stuck.
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Old 01-04-2018, 11:52 AM   #9
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Shark 13, what?

Sorry lol. I don't get what you are saying... There isn't brake fluid regularly flowing on the outside of the caliper, therefore it doesn't make sense to me what you said.

I think I'd suggest wiping the rubber boot/seal really good before compressing the caliper piston back in. That would keep any grits of dirt/gravel from binding it up. But on a sealed system, there isn't any way for dirt to get into fluid from this.

Unless hypothetically someone extended a piston so far that it actually shot out of the caliper followed by fluid. But, pending the seal didn't break, and fluid didn't spill, wiping the boot before compression should suffice.
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Old 01-04-2018, 11:53 AM   #10
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"No, I just pulled the caliper off per the guide I found for pulling the axle and found the piston was charged when I went to put the caliper back on the rotor. Haven't really done anything to it aside from try to grease it via the zerk (which it wouldn't take, probably due to the cheap Chinese grease gun I bought) and pump the brakes to see if it was stuck."

Thats not a zerk... its a bleed fitting for bleeding air out of your brakes. Good thing it didn't take any, or you'd be injecting grease into your brake fluid
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Old 01-04-2018, 11:59 AM   #11
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OH and yeah... FYI-

Compress the pistons SLOWLY! Otherwise, fluid shoots straight out of the master cylinder and sprays everywhere... note, brake fluid eats paint.
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Old 01-04-2018, 12:11 PM   #12
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Yes VERY important so stressing it again.... there is no grease zerk on a caliper.... that is the bleeder for getting air out....
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Old 01-04-2018, 01:08 PM   #13
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Shark 13, what?

Sorry lol. I don't get what you are saying... There isn't brake fluid regularly flowing on the outside of the caliper, therefore it doesn't make sense to me what you said.

I think I'd suggest wiping the rubber boot/seal really good before compressing the caliper piston back in. That would keep any grits of dirt/gravel from binding it up. But on a sealed system, there isn't any way for dirt to get into fluid from this.

Unless hypothetically someone extended a piston so far that it actually shot out of the caliper followed by fluid. But, pending the seal didn't break, and fluid didn't spill, wiping the boot before compression should suffice.
There are many many instances of folks doing brake work, replacing pads or simply swapping rotors and pushing Pistons back in, and within the next few times they drive, they end up with a stuck piston and overheats the pads/rotors etc.

Since 99% of folks neglect the brake fluid, and it is hygroscopic (absorbs moisture), it is a very good practice to flush the fluid first. Old fluid will allow contaminants to settle in the caliper.
Then the piston is retracted and those contaminants bugger up the piston seal and it sticks.
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Old 01-04-2018, 01:11 PM   #14
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No, I just pulled the caliper off per the guide I found for pulling the axle and found the piston was charged when I went to put the caliper back on the rotor. Haven't really done anything to it aside from try to grease it via the zerk (which it wouldn't take, probably due to the cheap Chinese grease gun I bought) and pump the brakes to see if it was stuck.
There is only a bleeder screw on the caliper, no zerk. I think you might need to do some reading online of proper brake service.
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Old 01-04-2018, 01:25 PM   #15
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... outer oil slingers--necessary, or not so much? My passenger side one cracked off when I was replacing the hub bolts.
Outer oil slinger? Do you mean that round plastic object at the end of the axle tube that the axle shaft passes through? If so, that's not a oil slinger... it's just a barrier to keep pebbles & rocks out of the inside of the axle tubes.
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Old 01-04-2018, 07:36 PM   #16
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What Shark is referring to is, that you pushed your Caliper pistons out farther than normal. Brake fluid will get water in it over time and break down, this is due to condensation. We all know water doesn't compress well. You need to flush your system now which should be done regularly anyway. You can do this a couple ways, Apply compressed air to the master cylinder while bleeding the brakes, and NOT running the master cylinder dry. ( Factory Recommended, at least GM, that is what I work on mostly).It doesn't sound like you are equipt for this, or the later, but just trying to help. You can also get a vacuum pump kit for under $30 that will work ( just takes longer ). YouTube how to do this. From the OP this may be over your head, but needs to be done. Don't mean to offend. JMO
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Old 01-04-2018, 07:49 PM   #17
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We all know water doesn't compress well.
What liquid does? Water compresses just like brake fluid as long as it remains in a liquid state. The problem with water is that is does compress when it turns to vapor.
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Old 01-04-2018, 07:52 PM   #18
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What liquid does?
Supposedly hydraulic fluid ( AKA Brake fluid ) without water mixed in.
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Old 01-04-2018, 07:53 PM
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There is only a bleeder screw on the caliper, no zerk. I think you might need to do some reading online of proper brake service.
I have a zerk on my caliper. If that isn't standard on TJ calipers, it may be aftermarket, but it's a zerk.
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Old 01-04-2018, 08:02 PM   #20
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It is not a zerk! It is a bleed screw or bleed nipple. Correct from Wikipedia.
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Old 01-04-2018, 08:06 PM   #21
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I have a zerk on my caliper. If that isn't standard on TJ calipers, it may be aftermarket, but it's a zerk.
That fitting is not a grease zerk, it's a bleeder valve used for bleeding air out of the brake system. Don't grease it!!!!
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Old 01-04-2018, 08:10 PM
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Supposedly hydraulic fluid ( AKA Brake fluid ) without water mixed in.
Eh, none of this is over my head, I'm mechanically inclined per my job, just never learned how to work on cars--and hydraulic fluid isn't supposed to compress. The point of a hydraulic system is that it transfers power via Pascal's Law in a direct ratio based on the size of the piston on one side to the piston on the other. Having a compressible fluid in the system would reduce the effectiveness of any hydraulic system. AFAIK the main reason for using hydraulic oil as opposed to a less viscous fluid is to reduce leakage past seals.1

The 3-4 guides I read on servicing brakes (I wasn't really servicing them, just needed to replace them after servicing the U-joints and had never pulled the calipers off before) all said to grease the caliper. In my job this means find the zerk and squeeze the handle.
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Old 01-04-2018, 08:12 PM
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That fitting is not a grease zerk, it's a bleeder valve used for bleeding air out of the brake system. Don't grease it!!!!
Roger, I read that later in a more detailed response further up. Man, diagrams of calipers/instructions online are bad.
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Old 01-04-2018, 08:15 PM
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Outer oil slinger? Do you mean that round plastic object at the end of the axle tube that the axle shaft passes through? If so, that's not a oil slinger... it's just a barrier to keep pebbles & rocks out of the inside of the axle tubes.
That's the part, and it's sold as an oil slinger, though I've heard both that it's an oil slinger or more of just a debris barrier. Mostly wondering if it's a necessary component, I ordered another one to be sure, but not having to remove the passenger side axle again would be nice.
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Old 01-04-2018, 08:20 PM   #25
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The point about brake fluid being hygroscopic and absorbing moisture was related to the system corroding/rusting from the inside as well as water in the fluid lowers the boiling point.

Fluid being able to be compressed or not is really not the issue here.

When was the last time your brake fluid was flushed?
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Old 01-04-2018, 08:21 PM   #26
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That's the part, and it's sold as an oil slinger, though I've heard both that it's an oil slinger or more of just a debris barrier. Mostly wondering if it's a necessary component, I ordered another one to be sure, but not having to remove the passenger side axle again would be nice.
There's no oil on the outside of the axle, so it's not an oil slinger.....

This thread is getting a bit weird.
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Old 01-04-2018, 08:21 PM   #27
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Mostly wondering if it's a necessary component,
It's not and anything that describes that plastic piece as an oil slinger is wrong. That plastic piece is definitely not an "oil slinger" which is found inside the large center section of the axle housing where the differential and ring and pinion gears live.

An oil slinger is used to help distribute (sling) oil inside the center section (pumpkin) of the axle housing in areas that need more oil than would be there without the slinger.

The oil slinger inside our axles actually looks like a smooth flat steel disk, like this...

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Old 01-04-2018, 08:33 PM   #28
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There's no oil on the outside of the axle, so it's not an oil slinger.....

This thread is getting a bit weird.
Sometimes I have to remember I'm not in the shop with my guys. My bad.Just change your brake fluid.

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