12 replies to this topic

[dasupersprint]

Let's play a game!

I want to renew the braking system, and digging in my parts and old pictures, I can't put the finger on the right parts I need.

 

Case: 1978 Left Hand Drive Canadian Mini.

 

Theoretically, should I have a Front Rear split system, with a PDWA valve on the front bulkhead and an inertia valve in the rear subframe?

 

I do have the inertia valve (don't know what it is or what it does, educate me if you will). But looking at these old pictures, the pipes seemed to go directly to the front wheels and to the rear without any sign of PDWA valve (don't know either what this do).

 

I seem to have the correct Canada-special master cylinder.

 

To help me, I'm looking at the awesome Somerford Mini pages

 

Front Rear Split LHD 1969-80: we see both PDWA and inertia valves

http://www.somerford...page=page&id=63

 

Do I need the PDWA valve? Can I convert all of this to different system? I don't even know if the inertia valve works, so could I start from scratch?

 

For info: I converted the front brakes to 7.5'' discs.

 

Old pics:

 

 

 

 

 

Thanks...

 

[Bat]

Hi,

You'll have to wait for a lhd person to come along as I've never seen that valve on the subframe on a UK car.

As far as i know we either have the pwda or the inertia valve at the back but it doesn't look like yours...

Cheers 

[Spider]

That's the same spec as we got here in our Mokes from 1979. I think they did use a similar set up in some of the UK cars around 1976 but only for a short period.

 

The Master is a GMC167 and it would have had 5/8" Rear Wheel Cylinders with the Inertia Valve. You can do away with the Valve, but they seldom give any trouble. IMO, they also give a more 'intelligent' front / rear balance than any other factory set up.

 

If you do want to remove the Valve, you'll have to go to 1/2" Rear Wheel Cylinders, but the rear brakes, for what ever it's worth, will be less effective. I'm not sre if you have annual checks for registration, however, if you do, they may knock the car back if the rear brakes are found less effective than they should be.

[dasupersprint]

That's the same spec as we got here in our Mokes from 1979. I think they did use a similar set up in some of the UK cars around 1976 but only for a short period.
 
The Master is a GMC167 and it would have had 5/8" Rear Wheel Cylinders with the Inertia Valve. You can do away with the Valve, but they seldom give any trouble. IMO, they also give a more 'intelligent' front / rear balance than any other factory set up.
 
If you do want to remove the Valve, you'll have to go to 1/2" Rear Wheel Cylinders, but the rear brakes, for what ever it's worth, will be less effective. I'm not sre if you have annual checks for registration, however, if you do, they may knock the car back if the rear brakes are found less effective than they should be.

When you say I could remove the valve, you are talking about the rear inertia one? Because I could easily keep this one. It's the PDWA one I'm wondering if it's necessary or not.

[Spider]

When you say I could remove the valve, you are talking about the rear inertia one? Because I could easily keep this one. It's the PDWA one I'm wondering if it's necessary or not.

 

 

Has it actually got a separate one?  There is a PDWA built in to the Master on these, as shown on the inset drawing (though referred to as 'Pressure Failure Switch');-

 

[Gilles1000]

Hi,

I have an LHD european Mini 998 from 1979.

I have the PDWA valve at the front fixed to the bulkhead, but on the rear frame I only have a T-piece. Ther's a pipe come from the front and then 2 going to each wheel.

 

My master cylinder also looks the same as yours from the pictures. Should look for pictures to be sure.

 

Regards

Gilles

[Itsaminithing]

So much confusion is caused by parts suppliers giving wrong information!

 

I don't know much about braking systems but as i understand it a PDWA (pressure Differential Warning Activator) is a type of shuttle valve, if one side of the braking system loses pressure (due to fluid loss) the internal piston is pushed across & closes off that half so that you still have two working brake cylinders-they often incorporated a failure switch to let you know -they have no effect on rear brake pressure.

Rear brakes can lock up under certain conditions so a lot of Minis are fitted with a pressure reduction system for the rear brakes. Either a rear subframe mounted fixed rate pressure reduction unit for the earlier cars or a bulkhead mounted variable pressure rate regulator for later cars (front/rear brake bias varies according to conditions, fitted from 1978 to Canadian spec cars but 1980 on for UK cars). http://www.minispare...ck to catalogue

This is the part that can cause problems (& often incorrectly called a PDWA!) & is sometimes replaced by fitting an earlier brake pressure regulator.

https://www.calverst...ias-adjustment/

 

I'm guessing your master cylinder is a GMC168 (Canadian front/rear split master cylinder) http://www.somerford...page=page&id=57

If you're going to replace parts (some things like that master cylinder are no longer available) you will need the advice of someone who really knows about brakes to tell you which parts you need to fit for the most effective set-up.

[dasupersprint]

 

When you say I could remove the valve, you are talking about the rear inertia one? Because I could easily keep this one. It's the PDWA one I'm wondering if it's necessary or not.

 

 

Has it actually got a separate one?  There is a PDWA built in to the Master on these, as shown on the inset drawing (though referred to as 'Pressure Failure Switch');-

 

 

 

 

So, would it be okay if I redid all as it was with my car? (with new pipes, and maybe new master cylinder)

 

Master cylinder going directly to front discs, and master cylinder going to inertia valve and rear drums?

 

I don't know if it worked well that way, i never drove the car before the restoration

Edited by dasupersprint, 31 July 2018 - 05:16 PM.

[Spider]

 

 

When you say I could remove the valve, you are talking about the rear inertia one? Because I could easily keep this one. It's the PDWA one I'm wondering if it's necessary or not.

 

 

Has it actually got a separate one?  There is a PDWA built in to the Master on these, as shown on the inset drawing (though referred to as 'Pressure Failure Switch');-

 

 

 

 

So, would it be okay if I redid all as it was with my car? (with new pipes, and maybe new master cylinder)

 

Master cylinder going directly to front discs, and master cylinder going to inertia valve and rear drums?

 

I don't know if it worked well that way, i never drove the car before the restoration

 

 

Yeap, that's how they are plumbed.

 

The lower Port on the Master going to the Fronts and the Upper Port to the Rears via the Inertia Valve.

 

The Masters are getting a little hard to come by and you may have a GMC168, which are NLA, though the GMC167's were remade a few years back, the only difference being the latter has M10 x 1.0 threads instead of 3/8" UNF, so, although the 3/8" fitting feel like they fit, there's next to no engagement.

[dasupersprint]

 

 

 

When you say I could remove the valve, you are talking about the rear inertia one? Because I could easily keep this one. It's the PDWA one I'm wondering if it's necessary or not.

 

 

Has it actually got a separate one?  There is a PDWA built in to the Master on these, as shown on the inset drawing (though referred to as 'Pressure Failure Switch');-

 

 

 

 

So, would it be okay if I redid all as it was with my car? (with new pipes, and maybe new master cylinder)

 

Master cylinder going directly to front discs, and master cylinder going to inertia valve and rear drums?

 

I don't know if it worked well that way, i never drove the car before the restoration

 

 

Yeap, that's how they are plumbed.

 

The lower Port on the Master going to the Fronts and the Upper Port to the Rears via the Inertia Valve.

 

The Masters are getting a little hard to come by and you may have a GMC168, which are NLA, though the GMC167's were remade a few years back, the only difference being the latter has M10 x 1.0 threads instead of 3/8" UNF, so, although the 3/8" fitting feel like they fit, there's next to no engagement.

 

 

Okay thanks, it's getting clearer now in my head. I'll install everything as I think and anyways it will be double checked by a pro before I put it on the road.

[Itsaminithing]

 

The Masters are getting a little hard to come by and you may have a GMC168, which are NLA, though the GMC167's were remade a few years back, the only difference being the latter has M10 x 1.0 threads instead of 3/8" UNF, so, although the 3/8" fitting feel like they fit, there's next to no engagement.

 

 

Info i've got is that GMC167 are diagonal split.... & GMC168 are front to rear split.

http://www.somerford...page=page&id=57

 

 

[dasupersprint]

 

 

The Masters are getting a little hard to come by and you may have a GMC168, which are NLA, though the GMC167's were remade a few years back, the only difference being the latter has M10 x 1.0 threads instead of 3/8" UNF, so, although the 3/8" fitting feel like they fit, there's next to no engagement.

 

 

Info i've got is that GMC167 are diagonal split.... & GMC168 are front to rear split.

http://www.somerford...page=page&id=57

 

 

 

Yep, I don't have it with me now but I'm sure I got a GMC168

[Spider]

 

 

The Masters are getting a little hard to come by and you may have a GMC168, which are NLA, though the GMC167's were remade a few years back, the only difference being the latter has M10 x 1.0 threads instead of 3/8" UNF, so, although the 3/8" fitting feel like they fit, there's next to no engagement.

 

 

Info i've got is that GMC167 are diagonal split.... & GMC168 are front to rear split.

http://www.somerford...page=page&id=57

 

 

Apart from the threads (as mentioned ^ ^ ), they are the same cylinder. We only ever had the GMC167's here and we never had diagonal split systems.