Any advice on removing parking brake plunger from piston?

dllubin

dllubin

Don
On my first test ride, I noticed the RR brake was dragging a bit. I pulled the boot off the caliper and found that the brake pawl was jammed in the wrong place. I tried to make sure the plunger was screwed into the piston and the alignment mark properly positioned on the bleeder side of the caliper. It would not turn in either direction although it does move in and out. I am guessing that the plunger threads may be a bit seized in the piston.

Any advice on how deal with this situation?
 
If a rear piston moves in and out without being turned, something is wrong inside the caliper. Unless someone else has a better idea, you may have to take the caliper out and open it up.
 
You will need to remove the caliper and reassemble the parking brake mechanism. There is a written procedure for disassembling the parking brake that includes photos:

http://xwebforums.com/wiki/images/2/23/Rear_Caliper_Rebuild_rev4.pdf

I used a C-clamp to relieve the belleville washer preload so I could unscrew the piston without damaging the threads. If you do one side you might as well check the other as a reference. Worse case, a replacement caliper isn't expensive.
 
EricH said:
If a rear piston moves in and out without being turned, something is wrong inside the caliper. Unless someone else has a better idea, you may have to take the caliper out and open it up.
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I've got the caliper apart. I managed to unscrew the piston but it took a fair amount of force. The problem appears to be the parking brake plunger being stuck in it's bore. I've got some penetrating oil on it to see if I can get it to move. I tried pressing it with a C clamp but it was not budging and I did not want to use too much force. The piston, seal, and cylinder bore actually look pretty good, especially considering that it is from 1974. Worst case, I'll need a new caliper but not quite ready to give up on it yet. I also need to check the left rear. It appears to be functional but is dragging a little more than I would like. It was replaced in 1995 shortly before the engine blew so not many miles but lots of age.
 
In the illustration below I think the OP is having trouble extracting the gray shaft (or, plunger) with the o-ring from the back of the caliper.

Dlubbin, you could try heat cycling the plunger with a torch. The expansion contraction might loosen things enough that you can get it to rotate back and forth a bit. You can also warm up the casting a little bit. Once it moves it should loosen up and slip out unless it was bent badly. From your description I think the caliper is too far gone but curious to see what you find. A picture or two would help your thread.

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Cratecruncher said:
In the illustration below I think the OP is having trouble extracting the gray shaft (or, plunger) with the o-ring from the back of the caliper.

Dlubbin, you could try heat cycling the plunger with a torch. The expansion contraction might loosen things enough that you can get it to rotate back and forth a bit. You can also warm up the casting a little bit. Once it moves it should loosen up and slip out unless it was bent badly. From your description I think the caliper is too far gone but curious to see what you find. A picture or two would help your thread.
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My plan, after letting it sit overnight with penetrating oil, is to put some force on the plunger using a clamp and then heating the aluminum body with a heat gun and see if it moves. I don't think the plunger is bent, but 45 years of steel inside an aluminum hole which has not been moved in 24 years probably has something to do with it.
 
Dr.Jeff said:
A pic or two will help, honestly I'm not completely clear what is stuck. But on the surface it does sound like something may be damaged and possibly beyond salvaging.
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If I can get the plunger out, I'll take a picture. Until then, nothing to see. As far as what is stuck, it is the plunger - shown in gray in the drawing above. The hydraulic part of the caliper is fine, so if I get plunger out and cleaned up, it should be OK. It turns out that replacement rear calipers are in short supply right now. I've tried a number of sites, and most have them listed, but when you put them in the shopping cart they say they are out of stock. The only place I found that has them wants over 2x what they normally go for. One of our Fiat suppliers expects some late August or September. I've seen some listed on eBay but need to do a bit more due diligence before going that route.
 
Well, the heat did not work. I might try and cut the plunger off and give up the parking brake function until I find a replacement caliper. At least I'll be able to drive the car without the brake dragging. I was thinking that I might be able to get a Dremel cut off wheel in there.
 
except the park brake plunger also seals hydraulic force... that's the O ring part way up the shaft... if you cut the shaft you won't necessarily be able to seal the hydraulics.

SteveC
 
fiatfactory said:
except the park brake plunger also seals hydraulic force... that's the O ring part way up the shaft... if you cut the shaft you won't necessarily be able to seal the hydraulics.

SteveC
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I just plan to cut the threaded part that contacts the piston. The sealed part of the shaft is frozen in place and is not leaking.
 
I just found out the left rear has the same problem with a frozen plunger. It was frozen further retracted than the right side so it did not drag as much. I have a feeling that the frozen plungers essentially froze the pistons so I was likely not getting much rear braking. This LR caliper was only weeks old when the engine blew in 1995 so the outside, including the boots, look brand new. Unfortunately, it is no more functional than the one on the right side which was put on the car at the factory in 1974. My guess is that the plunger likes to be moved occasionally and is prone to freezing in place when not operated for several decades.
 
dllubin said:
My guess is that the plunger likes to be moved occasionally and is prone to freezing in place when not operated for several decades.
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I agree. As everyone knows brake fluid attracts moisture from the air. And that moisture corrodes internal components, especially when left unused sitting stagnant. Some of the components are particularly susceptible to corrosion (rusting, fusing together, "frozen"), rendering them inoperable. After enough time they will become so damaged they cannot be refurbished without extreme measures. From the sounds of it that is what you might be facing, so replacing both sides may be your best option at this point. I'm not that well versed on the unique features of a '74; can any rear calipers somehow be fitted, or must they be some sort of special ones?
 
Dr.Jeff said:
I agree. As everyone knows brake fluid attracts moisture from the air. And that moisture corrodes internal components, especially when left unused sitting stagnant. Some of the components are particularly susceptible to corrosion (rusting, fusing together, "frozen"), rendering them inoperable. After enough time they will become so damaged they cannot be refurbished without extreme measures. From the sounds of it that is what you might be facing, so replacing both sides may be your best option at this point. I'm not that well versed on the unique features of a '74; can any rear calipers somehow be fitted, or must they be some sort of special ones?
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The replacement part information indicates they were used all years on the X, as well as the 124. From the info I found, on some Fiat models, they were installed behind the axle instead of in front as on the X. This ma kes it a bit ambiguous in some replacement part lists as to what part is passenger side or driver side since it depends on which mounting position they will be in. When I thought I only needed the right side, I almost ordered the wrong part a few times. Now, it does not matter since I need both sides. I also came across some rear calipers for the 125. They have a 38mm bore vs. 34mm for the X/124 so I guess they would be candidates if doing a front brake upgrade.
 
Remove the piston from the caliper and apply force directly against the threaded end of the plunger, while making sure the lever actuated by the cable is moving back to its (at rest position).
I suspect (if anyone ever rebuilt these or took them apart previously) that the plungers were installed with the head 180 degrees out. The head of the plunger is not symmetrical and has to be oriented properly for the wedge key to engage the plunger properly. If placed 180 degrees out it will activate the parking brake when compressed, but could also allow the shaft that's actuated by the lever to rotate past the point of no return. Then the key pops up and out and prevents the plunger from returning to it's normal "retracted" position. Ask me how I know this
 
Tom Ginefra said:
Remove the piston from the caliper and apply force directly against the threaded end of the plunger, while making sure the lever actuated by the cable is moving back to its (at rest position).
I suspect (if anyone ever rebuilt these or took them apart previously) that the plungers were installed with the head 180 degrees out. The head of the plunger is not symmetrical and has to be oriented properly for the wedge key to engage the plunger properly. If placed 180 degrees out it will activate the parking brake when compressed, but could also allow the shaft that's actuated by the lever to rotate past the point of no return. Then the key pops up and out and prevents the plunger from returning to it's normal "retracted" position. Ask me how I know this
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On the right side, I removed the piston, wedge, and lever assembly. I tried soaking it in penetrating oil for a couple of days and tried pressing the plunger out. No luck. I then tried getting the casing real hot. It still would not budge. Any more force would likely destroy the plunger. The left side has the piston frozen on the plunger which is also frozen.
 
WOW! Atsa one stuck brake!

Assuming that (at this point) there's a good chance your'e going to mangle the plunger trying to get it out... did you try grabbing the head with a vice grips and twisting it? Maybe rotary action might work to crack it loose. I've only rebuilt my calipers once. But in all the "brake" threads I've ever read on this forum, I've never heard of the rears being "this" stuck.
 
Tom Ginefra said:
WOW! Atsa one stuck brake!

Assuming that (at this point) there's a good chance your'e going to mangle the plunger trying to get it out... did you try grabbing the head with a vice grips and twisting it? Maybe rotary action might work to crack it loose. I've only rebuilt my calipers once. But in all the "brake" threads I've ever read on this forum, I've never heard of the rears being "this" stuck.
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I have a feeling that not moving those plungers for 24 years may have had something to do with it.
 
The status as of now is that the operating arm/wedge and the belleville washers have been removed on both calipers, the piston has been removed on one caliper. So you have the plunger rod sticking out of the inboard end of both calipers, and they are frozen to the aluminum body of the caliper where the plunger passes thru and the small o-rings makes a seal.

You do need heat and press force, but if the tools you are using are the aforementioned heat gun and c-clamp, I think you are guilty of bringing a knife to a gun fight. The mass of the caliper is too much for a typical heat gun to heat up to any effective level, and the c-clamp can't generate enough force to matter.

You need more heat and more pressure to push it out. As in oxy-acetylene torch and a shop press.

The other consideration is, what kind of damage has already been done to the bore by this level of corrision? Not to mention the damage from forcing the plunger out? Will it be able to seal again upon re-assembly?
 
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