G'day. In the process of restoring a 1963 MK1 850 and replacing all the brake components. I've ordered new drums, wheel cylinders (old ones where rusted solid) and shoes and have a question about the brake bias (part number 21A1774 on Minisport) which is also referred to as a Pressure regulator valve.

This is the valve that is mounted on the rear subframe and where the line from the front is then split to the back wheels.

Are there parts that wear out in this valve and do I need to replace this, or can i get parts to service it or is it OK to use after I flush the old fluid out? All I can find parts wise is a spring.

Cheers, Rocky

Rocky,

As you've discovered the repair kit that includes the two rubber seals is virtually unobtainable. When I stripped mine I found the rubbers were in good condition, as was the bore so I cleaned everything and reassembled. I had purchased a new spring but didn't use it.

I'll post the Lockheed maintenance manual later today in case that helps.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

I just posted the Lockheed brake and clutch service manual here - viewtopic.php?f=25&t=98788

The pressure regulating valve is on pages 16 and 17.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

Thanks Winabbey - terrific info. I'll pull it apart and see what it's like. Also good info on the master cyls - they're next on the list.

They are available new again: for example

http://www.minispares.com/product/Class ... o%20search

Not very cheap but will last a long time if anything like the originals.

Thanks for the info Bill - I'm getting some other bits from them and will add a new one to the list if mine is buggered when I pull it apart. Seeing as though I'm renewing everything else brake wise, it is most likely the beat option to get a new one.

Cheers, Rocky

Just noticed Minisport have a kit.

https://minisport.com.au/mini-rear-brak ... -valve-kit

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

I stand to be corrected about this, but the mini pressure limiting valves I've taken apart have the 2 rubber cups swaged onto the piston becoming a single unit and the main reason original overhaul kits are the only option. They didn't use separate cups like other brake parts.

Mine has two removable rubber seals and a metal band that goes around the outside of the larger seal.

I'm guessing the Minisport kit comprises the closest seal fit from readily available parts. The taper on the large seal shouldn't be an issue as the band will flatten it. This one seals on its face, not the edge.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

That's very interesting winabbey.
I will have another look at these bits.
This could be a practical solution.

Just had a look at one.
Winabbey, does the metal band look like it could be refitted to a new seal?
And, does the larger seal look like a normal brake seal ie with flared lip at one end? or is it a special profile? A bit dark in your photo.

On my one, the larger seal ends in a taper that, like you said, closes with its face against a ledge inside the housing. The Minisport seal looks more like a normal seal with a skirt that is meant to flare out against a bore.

Other sites have members claiming to have used 'ordinary' brake seals to suit but if it was so easy I wonder why few know about it.

Yes, I'm sure the metal band can be reused. It doesn't touch anything other than the seal so not liable to wear or break. I suppose corrosion could weaken it but mine was fine.

I don't know about the large seal profile but I think it has straight sides, not flared, or only slightly flared (see enlarged images below). In any case, as you've noted, it's the lip of the cup on that seal that controls the flow of brake fluid so having a slight flare under the metal band should not impact its operation.

Mine is all back together again. If you are keen to follow this through why not remove it from the one you have? I used a very small screwdriver to gently ease it off the piston.





I inspected the original seals closely and couldn't find any sign of wear or fracture so I lubed them up and reinstalled.

_________________
ex-NSW Police 1970 MK II Cooper S
VMCI #43

Thanks, winabbey.
Worth keeping the old bits if they are useable.

Keep an eye out, they do turn up from time to time.

I checked various Lockheed publications and thought the following might help to answer some questions, as well as providing data that should help in the search for replacement rubber seals for the Pressure Regulating Valve.

First, we need to be aware that the only difference between the valve assembly fitted to drum brake model Minis and the disk braked Cooper S is the strength of the spring. On the Cooper S the spring is 'stronger' at 35-42 lbs compared to the standard at 28-32 lbs. All other components of the assembly, the body, plunger and seals are exactly the same.

The Lockheed part number for the Cooper S spring is 4313-743 (BMC Part 27H6620) and for the drum braked Mini is 4313-673 (BMC Part 37H2009). These springs are still available from Mini parts suppliers, meaning a regulating valve assembly can be moved between vehicles provided the correct spring is fitted.

The repair kit for the Pressure Regulating Valve is Lockheed part SSB802

The page below shows the two seal part numbers in SSB802 as 100341 (smaller seal) and 101546 (larger seal).

Click on a page image to enlarge it.



Following page confirms that these two seals are only used for this application, whereas some other seals have multiple application.



The shape and dimensions of each seal may help in tracking down a source of supply, maybe by identifying an alternative of similar shape and size to use as a substitute.





Note the larger seal does not have a flared lip although, as mentioned earlier, this may not be an issue if an alternative can be found where all other dimensions are the same.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43