MGC Forum

The PO had 1x 16P caliper on the right shoe and 1x 16PB caliper on the left shoe of my GT. I replaced the right one several months ago with a rebuilt PB unit because it was seized and I set the old one aside, never noticing that it was a P. Now I'm tearing into it to rebuild it and I noticed on the back it says 16P. I thought the P units had different size pistons? This P unit has the pistons with the large groove just like my PB calipers do. Was there a model change to the P units during their manufacture lifetime? Or did this guy just put PB pistons in a P caliper... and is there any problem doing this?

This website: http://www.buckeyetriumphs.org/technical/Brakes/Front/Front.htm says that they caliper casting is identical other than the "PB" on the back and the only difference to the pistons is the groove for the boot, other than that, dimensions of the piston are the same.

Can someone please clarify?

I have 2x PB calipers installed now, but I've got this P unit in my spare parts bin...

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Cheers,
Joel

MGC "how-to's" available on YouTube:
https://www.youtube.com/playlist?list=PLSuil-nCBffJwKeCv5ZKF02CgPkp1sVvj



Edited 1 time(s). Last edit at 2017-04-11 05:44 AM by jsrivard.

The difference is indeed in the piston's groove width which is driven by the style of dust seal. The 16P has the dust seal lower edge secured by the piston in a very thin groove in the bore of the caliper, very near the outside. The 16PB, with the wider piston groove, has the dust boot retained by a split steel ring that clamps the boot into a groove in the casting that is proud of the bore. the pistons are the same size, and the inner fluid seal is the same. It's all about the dust boot and its retaining method. The wrong piston or the wrong dust boot wont seal well.

Very easy to see, once you look at them both together.

(Then there's the "metric 16PB" as found on Triumphs from mid 1972. It has 10mm line threads, and uses a 10mm mounting bolt. A 10mm bolt can not be inserted into a non-metric 16PB caliper. That's how you ID those 2)

Oh, and this might help buying correct parts.
16P with narrow groove piston uses Girling piston 64325561 and kit SP2501

16PB with wide groove piston uses Girling piston 64321880 and kit SP2589 or SP2959 (interchangable)


Peter C

Thanks Peter, great info. Now, if one were to use the PB pistons and PB boots/split ring on a P caliper, is one asking for trouble? It appears that the PB caliper and PB boot/split ring had sealed OK with the P caliper for the PO.

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Cheers,
Joel

MGC "how-to's" available on YouTube:
https://www.youtube.com/playlist?list=PLSuil-nCBffJwKeCv5ZKF02CgPkp1sVvj

There's nothing to retain the outer edge of the PB dust boot on a P casting. It is flat where you'd want a raised boss. It would just flop around. So.... no.

The O-ring sealing the two halves of the caliper are also a different size when comparing the 16P and 16PB so if doing a rebuild and buying parts, make sure you tell them the type. Ask me how I know...

jay

Jason thanks for that info I didnt know about the o rings!!
And some kits dont include.

Good information guys! I'm about to rebuild my calipers and this clears up a lot. Does anyone have a picture of where the 16P/PB mark is?

Jay, are you sure about those pictures of the o-ring? Here is mine, first the two together, the shiny one was removed from the P caliper and the other one is a PB o-ring I ordered from Mr. Kirk. They are both the same size except the new PB unit has squared off edges. You can see that they both fit in the recess between the caliper halves in the 2nd and 3rd photos attached. In your photo it appears that the two are clearly not interchangeable and one would not fit in the recess made for the other.

Peter, In the 4th picture you can see that there is a lip for the split ring to fit around on this P caliper. I've installed a split ring around it in the photo for reference.

Noble, In the 5th picture you can see that the type marking "TYPE 16 P" in this case is visible on the inner half of the caliper (dirty half in the picture as I haven't cleaned it up yet), right above the mounting bolt hole. If this were a PB unit, it would be marked in the same location.

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Cheers,
Joel

MGC "how-to's" available on YouTube:
https://www.youtube.com/playlist?list=PLSuil-nCBffJwKeCv5ZKF02CgPkp1sVvj

In my photo the small O-ring was the one I physically removed from my 16PB calipers during the rebuild. I ordered new parts for my caliper rebuild but did not know there were different calipers used for the MGC (16P and 16PB).

The bigger O-ring was what arrived and on checking the order they said they had sent me pistons, seals & O-rings for the 16P caliper. I sent them back and they sent the correct pistons, seals and O-rings for the 16PB.

So it could be that they sent me the wrong O-ring and it was not for a 16P or 16PB. Hopefully others will chime in.

Jay

the flat o-ring is correct. Girling # 67320782 as further info on my earlier post.

Peter

The casting marks are conspicuous in bas relief as evidenced in post #8 via Joel.

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Regards,
Robert Kirk

kirkbrit@yahoo.com
E-mail PLEASE for quote/questions/orders

Business phone 563 323 1017

http://kirks-auto.com/
Moss distributor/UK importer
Beat or match most retail/delivered quote



Edited 1 time(s). Last edit at 2017-04-12 01:46 PM by kirks-auto.

How about this thought... are aftermarket manufacturers making these things (P & PB) both with the necessary casting to accept the new boot and split ring. It's obviously the better design. The only difference on my PB and P units is the "P" or "PB" on the back. They both have a lip around the piston that will hold the split ring.

I'm going to rebuild this P unit with the newer pistons and the associated boot and split ring, it is obvious from looking at it that it will fit.

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Cheers,
Joel

MGC "how-to's" available on YouTube:
https://www.youtube.com/playlist?list=PLSuil-nCBffJwKeCv5ZKF02CgPkp1sVvj

the original 16Ps, of which we have rebuilt 100s, have always had the 2 grooves inside the bore. the lower thick one for the piston seal, and the thin upper that retains the dust boot.

To be honest, though, we are just accustomed to looking for the dustboot style, and call it a day.

Peter C

One of the reasons for confusion about the seal needed when splitting the halves is Lockheed use a different seal and a lot of POs believe the local hardware store O ring is "good 'nuff".

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Regards,
Robert Kirk

kirkbrit@yahoo.com
E-mail PLEASE for quote/questions/orders

Business phone 563 323 1017

http://kirks-auto.com/
Moss distributor/UK importer
Beat or match most retail/delivered quote

Folks
If one is replacing calipers as assemblies, is there any reason a PB can't be used in place of the P?
Cheers
Roger