27 replies to this topic

[driftz]

I have a 76 Canadian Market Mini and am having some brake issues. I recently did a full rebuild of the brakes and have new single line master cyl, many new hard lines, all new flex lines, new rear wheel cyl and an MK1 Fiesta front brake conversion.

 

When I step on the brakes the rears are locking before the front. Brakes are all bled and all function when wheels are in the air so I know its down to the brake bias.

 

I have a single line running from the master to this on the bulkhead

 

notice the top right line goes to master, bottom right goes to rear brakes and left goes to front.

 

I believe this is a Pressure Differential Warning Activator however the front brakes are located where a block off piece should be (see attached)

 

http://www.calverst.... pic1 on le.jpg

 

This shouldn't regulate brake pressure, however since its apparently setup wrong i'm not sure.

 

The rear line goes to this on the rear sub frame http://www.7ent.com/...80-13h7757.html

 

This should be a pressure regulator however i'm not sure its working.  

 

 

 

Does anyone have any insight into the setup that I have and possibly any solutions to my problem. I'm looking on getting an adjustable bias valve however if I can get my stock setup to work that would be much more convenient

 

(sorry for the long post)

 

 

 

 

 

 

 

 

[Spider]

A you say your Master Cylnder is a Single Circuit type and given how you say the set up has been plumbed at the Differential Valve, Yeap, I'd say you have no front brakes, however as you say you have them when the wheels are in the air, the the Differential Valve sounds like someone has fiddled with it and some bits are missing from inside it!

 

Normally, these would ONLY be fitted to a Tandem System and is is basically so a switch can be fitted to the system to bring on a lamp if there is a failure in either of the Hydraulic Circuits. It should not allow fluid to pass from one circuit to the other through the valve. I'm guessing someone has taken the guts out of it and it's now being used as a simple Tee Piece. If indeed some of it has been left inside, it will restrict the flow of fluid to your front brakes.

 

I'm not at all familiar with your local Registration Laws, but I think your car being a 1976 model in Canada, should be Tandem Circuit to meet local regulations, I only mention this in passing and is for you to follow up on (or not).

 

The Valve on the Side Rail of the Rear Subframe is a proportioning valve and is fitted in place of the Pressure Shut off valve that the earlier cars had and also in place of the (crap) Bias Valve the later UK Minis had. They are actually quite good in their operation and also that they rarely give trouble, even when poorly maintained but like anything, they can play up.

 

Also, I'd check what size rear wheel cylinders you have and if they would normally give balance with your set up (having the Fiesta Brakes on the Front), I think, but am not familiar enough with these to say for sure, that you'd normally run 5/8" Rear Wheel Cylinders. Bigger ones will make them more easier to lock.

 

So, to get this system working, I'd check what's inside the Differential Valve or replace it with a normal Tee eg;-

 

https://www.minispar...px|Back to shop

 

And check what size rear cylinders are fitted (and if they are correct for this set up).

[driftz]

I had a feeling that might be the case.

 

is there a visual way to check what size the rear wheel cylinders are? I was told when I bought the car that they had just been changed, and they look new, but im not sure on the size. I also still have the new front cylinders that I removed to do the fiesta swap. If they are a different size could I replace them with those?

[minidaves]

I would say switch front and rear pipes around and see what happends as it sounds like you are restricting the front presure

[Spider]

 I also still have the new front cylinders that I removed to do the fiesta swap.

 

Sorry, I should have asked, but sounds like you did have Drums up front originally?

 

If that's the case, then the Rear Wheel Cylinders will likely be 3/4".   For Disc Brakes that were fitted to Minis, these will cause the Rears to lock before the fronts and at a guess, with the Fiesta Brakes, it's probably the same. Fairly easy to measure them with reasonable accuracy. If you take a rear drum off, clean the wheel cylinder and peal back a boot, measure the Piston dia, it will be about 0.020" (roughly) smaller than the cylinder size.

 

I'm sure someone who has done the conversion can confirm the appropriate Rear Wheel Cylinder Size.

 

The Front Cylinders are a different design and not interchangeable with the Rears (and are 15/16" or 1" in any case).

Edited by Moke Spider, 25 October 2015 - 07:25 AM.

[dklawson]

I am not convinced that what is shown in the picture is a PDWA.  PDWA's do not have a pipe connection off the horizontal branch of the "H" configuration as shown in the picture above.  WIth that black cable in the picture running over the fitting... I cannot see if there is a PDWA switch on the component.  To me, that just looks like a splitter.  Any chance of another picture without the black cable in the way?

 

Regardless, I agree with those who suggested the rear brake cylinders may be the wrong size for a disk conversion.  It has been a while since the Fiesta brake conversion was discussed here but the search feature may reveal a few old threads (also use Goggle with keywords "theminiforum" and "Fiesta" which may reveal more threads).  I believe this topic also comes up periodically on Mini Mania so you may wish to search there as well.

[Spider]

Doug, it looks similar this PDWA to me

 

Edited by Moke Spider, 25 October 2015 - 09:09 PM.

[Ethel]

The rear valve is an inertia valve, it needs to be mounted the right way round and at the right angle. It could also be gummed up internally.

[dklawson]

Thanks Chris.  I am not familiar with that PDWA configuration.  I appreciate the picture.

 

EDIT:  So... if the car has a single line master, what is the reason for having a PDWA?  I would think a simple T fitting would suffice.

Edited by dklawson, 25 October 2015 - 10:43 PM.

[Ethel]

Non original cylinder? The pedal foot pads will tell us what should be fitted. I can see how the shuttle valve might stop fluid loss, if the failure occurred while the pedal was pressed and you kept your foot down, but not reliable enough to make the valve worth fitting.

[Spider]

Thanks Chris.  I am not familiar with that PDWA configuration.  I appreciate the picture.

 

EDIT:  So... if the car has a single line master, what is the reason for having a PDWA?  I would think a simple T fitting would suffice.

 

 

Non original cylinder? The pedal foot pads will tell us what should be fitted. I can see how the shuttle valve might stop fluid loss, if the failure occurred while the pedal was pressed and you kept your foot down, but not reliable enough to make the valve worth fitting.

 

That's what I was getting at / wondering in my first post. If the PDWA is all there, then that could well be the issue here, however, I suspect the shuttle has been removed from inside it and it's now an over-grown Tee or is that Tree!

[dklawson]

If the shuttle has been taken out, then the switch would have to be removed and replaced with a bolt/plug since the switch isn't sealed.  I see your point that if the shuttle is still there, then half the braking system probably isn't working at all. 

[Ethel]

I can't see any switch (could be hidden by that cable). Got me wondering if there's a cut off valve only version in some parallel universe.

[Spitz]

You should have a tandem master cylinder on a 76 model destined for CA

It would be the large round plastic lid type

If you have a single line system....someones put the wrong master cylinder in.

 

As said above, that proportioning valve needs to be the right way up...there's a large steel ball inside

[driftz]

thanks for all the help!

 

Yes the car came with drums all around, I did the Fiesta conversion.

 

Sorry about the picture. It does not have a elecrical connection on the bulkhead, after seeing the picture posted above, I am certain it is a PDWA with the electrical conection blocked off and the front brakes coming off the horisontal connection.

 

here is an old picture from when the engine was removed, you can see the bolt in place of the sensor

 

 

It must have been gutted by the previous owner or i would have no front brakes.

 

I replaced the master cylinder with a new one (http://www.minisport...nfo_GMC171.html)

that I thought was the original configuration (when i got the car it had a single line master, and was plumbed like so)

 

The brake pedal has a square pedal like #1 in this diagram http://www.minispare...ers.aspx?1~9~77

 

 

As for the proportioning valve, does anyone have a picture or diagram of one mounted correctly so I can be sure mine is.

Edited by driftz, 26 October 2015 - 06:58 PM.