# Mk4 rear calipers: pistons won't retract



## eedneco (May 10, 2010)

Hi everyone, 

(First post here, I do the maintenance on my wife's 2000 Mk4 (euro version). 
I have plenty of mechanical experience but on non-VAG cars.) 

Question: I am trying to change out the rear pads. I already know from the german aftermarket manual that I have, that you need to turn the pistons clockwise to retract them. I made up a T-shaped tool out of steel bar stock, and ground the end to fit the teeth in the piston, and have duly turned and turned the piston clockwise, while pushing as hard as possible (in the direction of retraction). 

But, the piston refuses to retract at all. It simply stays at 26mm gap to the outside "teeth". 

I've also tried doing the same with my finger holding down the e-brake lever in case that would help the piston engage thread or similar inside the caliper. No difference in behaviour. 

I also tried it while having the bleed screw cracked open (with hose), in case the blockage was hydraulic. No difference in behaviour, and no fluid exiting the bleed screw. 

The piston turns relatively easily, and I can see it move in and out a small amount while actuating the e-brake lever at the caliper. It shows no signs at all of seizure. 

Does anyone have any diagrams/pictures/experience with the inside of this caliper ? 
Any suggestions on how to get these to retract ? 

I have not gone out to try to buy/borrow the special tool, but neither can I see that it would be putting all that much more force into the direction of retraction, so for now I'm focussing on why a piston might get somehow internally disconnected from the e-brake mechanism. 

Thanks 
Neil


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## Anony00GT (Mar 6, 2002)

It can be tough, if not impossible, to push hard enough while turning by hand alone. Get the proper tool for the job, it does apply a lot more pushing force than your bare forearm can deliver, especially while turning it. 

If you can't make it retract with the special tool, replace the caliper.


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## csapp (Mar 22, 2005)

harbor freight under $20! 

http://www.harborfreight.com/caliper-tool-set-for-disc-brakes-40732.html 

Use it once, throw it away.


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## eedneco (May 10, 2010)

Thanks for the replies, and the harbor freight link. Fair enough, then, I'll see how much the tool is on this side of the pond. 
I guess my expectations were "coloured" by the only other caliper I've worked with that had handbrake actuation via the pistons, and in that case, retracting the pistons was very easy. 
Regards 
Neil


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## Anony00GT (Mar 6, 2002)

Yeah some of them go back real easy. In the US market, for example, Honda calipers go back with virtually no pressure, while Ford and VW require a ton of force...some Ford calipers even have to spin counter-clockwise with pressure to make them retract...requiring a ton of patience or another tool altogether. Good luck dude.


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## germancarnut51 (Mar 23, 2008)

26mm is pretty far extended for the rear caliper pistons. Your brake pads must have been extremely worn, OR you must have stepped on the brake pedal with the calipers off the car to get the pistons out that far. 

I've found when you extend the pistons extremely far out, IF the parking brake mechanism is not damaged, it can be extremely difficult to get the pistons turned back in. Without a piston retraction tool you are going to find it impossible. Even with a piston retraction tool, you are probably going to need the assistance of a vice of some sort to hold the caliper, AND an extension to the handle of the brake piston retraction tool to get the piston to start turning. 

Recently I broke the roll pin that holds the pressure screw to the nut on my brake retraction tool when trying to retract the pistons on a pair of VW rear brake calipers that were fully extended on the rear brake calipers of a 97 Jetta GT that I just got. I replaced the roll pin, and added a 12" extension to the handle of the tool to get the pistons to retract. 

You may be able to order a brake retraction tool set (they now offer two models, with the more expensive model including two tools (tools turn in opposite directions), and you get a lifetime warranty) directly from Harbor Freight, or possibly from a company that offers their tools (ECSTuning sells some tools made by Harbor Freight) that would be willing to ship to a foreign country.


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## Anony00GT (Mar 6, 2002)

This is FAR and AWAY the BEST rear brake caliper tool for turning the pistons in. It's a little pricey, but it's worth every penny. It does require an air compressor though. 

http://www.amazon.com/Sir-Tools-SIRST9020-KIT-Pneumatic-Compressor/dp/B000WNN6I8


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## redman43 (May 7, 2010)

Similar issues last night on my mk5 jetta. Drivers side rear pads are EXTREMELY worn down, causing the piston to be fully extended to the point that I can't even get the Harbor Freight tool between the piston face and the inboard edge of the outer "teeth" of the caliper. Adding to the frustration was not being able to handle the caliper and the tool on my own. It's almost like I needed three or four hands to even stand a chance. 

Suggestions?


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## herb2k (Jul 29, 2007)

Anony00GT said:


> This is FAR and AWAY the BEST rear brake caliper tool for turning the pistons in. It's a little pricey, but it's worth every penny. It does require an air compressor though.
> 
> http://www.amazon.com/Sir-Tools-SIRST9020-KIT-Pneumatic-Compressor/dp/B000WNN6I8


 There is a manual (no air compressor) version of this tool available, I was able to rent it from my local auto parts store. It works nicely and you don't need to have 4 hands to operate it (there's a plate that fits into the caliper similar to a brake pad which stabilizes the tool during use).


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## Anony00GT (Mar 6, 2002)

Herb2k - Yes, I've used the tool you're talking about. It's nice and works well when you analyze it in a vacuum, but once you've used the air-powered one, you realize how much it sucks. Then again, I do this on a professional level and use the tool several times a week, if not every day. For a DIY-er, the manual one will work fine. Granted, if you're renting the tool from AutoZone it is what it is, but if you're a DIY-er with even a small air compressor and want to buy the tool, I'd recommend getting the pneumatic one, it doesn't cost all that much more than a good manual one. 

RedMan - I don't trust these kinds of specialty tools from Harbor Freight. Their stuff is cheap, and when it comes to tools, especially automotive specialty tools, you get what you pay for. Most of the more expensive tools for turning back caliper pistons (both manual and pneumatic) have very thin pieces made from high-quality hardened steel that can fit even the smallest spaces for the most extended pistons. Some of the cheaper tools (like the stuff from Harbor Freight) are made of lower quality metal, meaning they have to be much thicker to be strong enough...the result is that when a caliper piston is extended to near its limit, the tool won't fit. If you can get the tool to fit, you'll probably have to try to brace the caliper against something like the mounting bracket while you try to turn the piston back in. Then again, if your driver side pads were worn and the passenger side pads weren't, you might have a problem with that caliper anyway, so do a proper diagnosis first and figure out why the driver side wore so much faster than the passenger side.


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## redman43 (May 7, 2010)

Thanks Anony00GT. I didn't even get to the passenger side yet. I got stuck on the driver side and by 11pm last night, I was tired. 

I know Harbor Freight is good for cheap stuff that doesn't always require precision, but thought I'd give this one a try. The backing plate is really thick (looks to be about a 1/4") and the plate that meets with the piston is actually a 2-piece set up, one part permanently attached to the tool and another seperate plate that can be swapped for different plates for use on different applications. In all, the tool is about 1/4" too long for the space available. I'll be returning it in a few days and will try to get one from AutoZone or Schucks/O'Reillys when the triple square driver gets here in a day or two. Then I'll be able to deal with the rotors and the pads at the same time.


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## germancarnut51 (Mar 23, 2008)

I've had the Harbor Freight tool set for getting close to ten years, and it works fine on MKIV alloy calipers.

You must be putting it together wrong somehow.

The only time the Harbor Freight tool is too long is when you're running the pistons out to replace the caliper seal and dust boot. In this case, the tool is too thick to allow you to completely extend the piston outward. I end up using a bicycle bottom bracket wrench to complete the last few turns extending the piston so it can be removed.

When the brake pads are extremely worn-out, it can be difficult starting the piston to retract. If you remove the brake pads and step on the brake pedal the caliper can be damaged, and if that happens it may be impossible to get the piston to retract and buying a replacement caliper may be your only option. A couple of months ago, I broke the roll-pin that holds the nut on the pressure screw when trying to get the piston to start retracting on a set of calipers I bought that had extremely worn brake pads. I replaced the broken roll-pin, and used 1/2 of a handle from a compact floorjack on the tool handle to get it the piston to start retracting.


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## Anony00GT (Mar 6, 2002)

germancarnut51 said:


> I've had the Harbor Freight tool set for getting close to tem years, and it works fine on MKIV alloy calipers.
> 
> You must be putting it together wrong somehow.


I don't know about the Harbor Freight tool in particular, but I have seen cheaper tools that don't fit nor work as well as the more expensive ones. Also, if your Harbor Freight tool is 10 years old and his is new, it may not be exactly the same thing.


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## germancarnut51 (Mar 23, 2008)

The tool set is still exactly the same. Even comes in the same cheap plastic case. The only thing different is that Harbor Freight now offers a 2nd same tool set in a blue colored case with a lifetime warranty, and a 2nd pressure screw assembly that is threaded in the opposite direction for calipers that are threaded going the other way. The new set also has some additional adapters and costs an extra $15 (list price is $45).

When I saw it, I wanted it (I'm partial to blue), so I offered my old red case set in the For Sale Section for $10. Nobody wanted for $10, so I'm still using it, and it still works fine.


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