Rear brake caliper replacement...38mm vs 41mm

ALH TDI Rear brake caliper replacement...38mm vs 41mm

Hi all.
So Ive had a stuck caliper for a while now on my 02 Wagon, and am finally getting around to repairing (replacing) it. Trouble is, the factory caliper has a 41mm bore, and the TRW replacements have a 38mm bore.
Is this going to be an issue?
And yes, its a caliper issue, not a parking brake cable issue. I believe the parking brake mechanism is the issue, but wont know for sure until I get it out and apart.

I had planned to rebuild the originals, but time constraints on the vehicle being down have made it necessary to just replace. I will still rebuild them, and depending on the thoughts on the difference in piston size, put them back on.
I dont know that it matters a lot, but the difference in piston size to a smaller bore means less force on the pad/rotor correct?
Replacing both would negate any effects side to side, but not overall, if there is a difference.
I did search, and all I really found was that someone replaced one and not both, and they were different sized afterwards which created issues.
Honestly, I thought being a direct replacement, they would be the 41mm bore, but they arent.

Is there anything to be concerned with?

Thoughts on leaving the 38s in vs rebuilding and replacing with originals later?

So, near as I can tell, from searching different variations of caliper piston size vs brake force, its seems that there will be a difference in braking performance in the rear from the difference in piston size.
What isnt clear is which way it goes. Ive read some that say smaller piston vs original equals more brake power, others say less.

I guess what Ive decided is that Ill rebuild my originals as time permits, and put them back on when they are done.

I am surprised that no one has mentioned anything, but then again, that may be because this is not really an issue to be concerned about.

The same PSI of brake fuild will be applied to each piston, the larger the surface area the larger the force. So in theory you may have some pull to the side that has the 41mm bore as it will be clamping slightly more than the 38mm bore. Seeing that its the rear, I'd be surprised if you'd notice it normal braking or even in emergency braking.

The 38 mm caliper is for a Golf. Jetta should have 41 mm.

740GLE said:

The same PSI of brake fuild will be applied to each piston, the larger the surface area the larger the force. So in theory you may have some pull to the side that has the 41mm bore as it will be clamping slightly more than the 38mm bore. Seeing that its the rear, I'd be surprised if you'd notice it normal braking or even in emergency braking.

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Both rears are the same bore diameter, 38mm, so even if it would create a pull to one side, which it seems it does from another post I found, it wont in my case, because there is no difference side to side.

Alchemist said:

The 38 mm caliper is for a Golf. Jetta should have 41 mm.

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Correct for factory new cars, but TRW doesnt make a 41mm caliper that is sold in the US. They do make one, but its not sold here.

To get the 41mm, Ill have to rebuild mine, which I will do, but in the mean time, the 38s will have to do.
Seems since I cant find anything one way or the other, and I know lots have used the TRWs, it must not be an issue.
I guess Ill find out tomorrow.
Id have known by now, but ordered the wrong front pads, and they will be here tomorrow.

Seems like I found Centric makes a 41mm caliper, but reman, not new.
Not sure it matters, but Ill look at mine, and if they cant be rebuilt, I may get the Centric if they are good quality. I never have much luck with reman calipers though. Seems lots of companies like to cut every corner they possibly can in the process.

Alchemist said:

The 38 mm caliper is for a Golf. Jetta should have 41 mm.

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Interesting - wonder why that is?

Where do the NBs fall? 38 or 41?

Looking at a parts listing here in Canada (roselandtech.ca), Golf and New Beetle share same replacement (TRW) caliper part number (38mm piston); Jetta is different (41mm).