# MK2 & MK4 rear disk brake piston sizes



## Rocco R16V (Oct 7, 2008)

*MK2 & MK4 rear disk brake piston sizes?*

What is the rear disk brake caliper piston size on the MK2 and MK4 ? 
TIA


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## germancarnut51 (Mar 23, 2008)

38mm


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## Rocco R16V (Oct 7, 2008)

Thanks for the answer. Are they the same size? I was told the MK4 is larger, and some who have done it say you will need an adj proportioning valve.


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## germancarnut51 (Mar 23, 2008)

Rocco R16V said:


> Thanks for the answer. Are they the same size? I was told the MK4 is larger, and some who have done it say you will need an adj proportioning valve.


They are the same size, you will have the same rear braking, and they even use the same caliper seal kit.

After thinking about it, it seems I remember seeing some 34mm rear calipers in the salvage yard, but I don't remember what model or year VWs they were on.

The proportioning valve may need resetting when moving from drum brakes to rear disc brakes (for MKIIIs VW sells different proportioning valves), but the setup depending on a number of conditions, including what sort of rear springs you have on the car, and tires make a difference too.


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## Rocco R16V (Oct 7, 2008)

Thank You! :thumbup:


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## jbdubn (Feb 3, 2009)

germancarnut51 said:


> 38mm


I have seen mkiv calipers that are 41mm too...i thought they only came in 38mm



http://forums.vwvortex.com/showthre...-conversion-Are-you-using-38-or-41mm-calipers


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## germancarnut51 (Mar 23, 2008)

jbdubn said:


> I have seen mkiv calipers that are 41mm too...i thought they only came in 38mm
> 
> 
> 
> http://forums.vwvortex.com/showthre...-conversion-Are-you-using-38-or-41mm-calipers




Some Passat rear calipers look the same or similar to the rear calipers like the MKIV Golf/GTI/Jetta, except the hose mounting/connection is different and they will not mount on a MKIII Golf or GTI, or Jetta, or MKII, unless they are mounted upside down because the banjo fitting interferes (it's in the wrong location). Undoubtedly the calipers with the 41 size pistons come from Passats as well.

When swapping to MKIV rear calipers, before buying the calipers, confirm with the Seller that the calipers came from a MKIV Jetta or GTI, not a Passat, and visually check the photos of the calipers (right to right and left to left) to make sure that the parking brake levers and hose ports are in the same position on each caliper as they are on your MKIII rear calipers.

Otherwise, you may be unpleasantly surprised to find you are the new owner of a pair of lightweight doorstops, instead of rear alloy calipers to fit on your MKIII.


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## jbdubn (Feb 3, 2009)

germancarnut51 said:


> Some Passat rear calipers look the same or similar to the rear calipers like the MKIV Golf/GTI/Jetta, except the hose mounting/connection is different and they will not mount on a MKIII Golf or GTI, or Jetta, or MKII, unless they are mounted upside down because the banjo fitting interferes (it's in the wrong location). Undoubtedly the calipers with the 41 size pistons come from Passats as well.
> 
> When swapping to MKIV rear calipers, before buying the calipers, confirm with the Seller that the calipers came from a MKIV Jetta or GTI, not a Passat, and visually check the photos of the calipers (right to right and left to left) to make sure that the parking brake levers and hose ports are in the same position on each caliper as they are on your MKIII rear calipers.
> 
> Otherwise, you may be unpleasantly surprised to find you are the new owner of a pair of lightweight doorstops, instead of rear alloy calipers to fit on your MKIII.


Interesting... I just had someone pull a rear caliper off of a Mkiv Golf that was stamped 41. Maybe a Canadian thing.?


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