Classic cars forum & vehicle restoration.

[pigtin]

I now have to drag myself away from the computer and do a final check on the A7 special before the MOT this afternoon.
Have spent over a week working on the brakes and now see what was meant when I was told: 'The brakes should not be too good on a seven.'
Bags of power from the Morris Minor hydraulc system on the front and it pulls up straight at lower speed, but above 30mph things start to flex and it waves about a bit.
Still, fingers crossed for this afternoon. I shall probably have to beef up the radius arms at some time.

[Uncle Joe]

I'm assuming that on your special, you have drums on all four wheels. Is that correct? And is the Master Cylinder on the bulkhead, or under the floor?

[pigtin]

Morris Minor drums on the front, a hydro/mechanical A30 system operates standard A7 rear rear drums. a Land Rover clutch master cylinder is mounted on the bulkhead on a Reliant Robin pedal cluster.
Confused? I am... As you may gather I used what I had lying around and could pick up at Autojumbles when I built the beast.

[Uncle Joe]

The reason I asked was that I was wondering if it wouldnt be a good idea to add an adjustable proportioning valve to your system?

[pigtin]

Sounds a great idea UJ, but you'l have to tell this old dinasaur (stuck in the 30s) what one of those is?

[Uncle Joe]

Simply put, a proportioning valve is something that allows pressure to front and rear change in a linear fashion.

Up to certain pressures, a proportioning valve allows equal pressure to both the front and rear brakes. However, when a preset pressure is reached, the rear brake pressure continues to build, but at a slower rate than the front brake pressure, thus decreasing the amount of rear braking proportional to the fronts.

There are other ways to do this, but this is the easiest.

[ukdave2002]

Mini's have them , without them because the back end is so light, the rear would just lock up under heavy braking.

[pigtin]

Great! sounds like the answer, where can I get em? I'll try ebay first.

[Uncle Joe]

The one I usually use is the one from you friendly neighbourhood Chrysler dealer, under part number P5249088. Added to that you need two nipples for the brake pipes you use. If I remember correctly they are 7/16" thread.

Do Google brake proportioning valves first though, and get a little more information on them, to make sure that they are exactly suitable for you. I would like to be responsible for anything bad happening to you! Unless of course you have decided to leave me the special in your will.....

[pigtin]

Many thanks for info UJ. About the will... I, like many of my age
have taken up SKIing: (Spending the Kids, Inheritance)... If the memsahib and I get it right there shouldn't be anything left.

[pigtin]

Good News! Pigtin passed the MOT now the bad news: took the documents to the post office gripped in my hot sweaty little hand to be told there was a problem and to come back in 15 mins, thirty minutes later they told me the Swansea computer was off line and they couldn't de-sorn and tax it.

[Uncle Joe]

That is good news.

UK might have suggested a cheaper way to do things, though on the Mini they arent adjustable....

[Penman]

Hi
re the proportioning valve, don't forget that on FWD the rear wheels only stop the boot dragging on the ground, so if the rear brakes are too efficient they lock up too easily.
With your seven, the wheels still have some drive to them until you dip the clutch.
You also have to avoid having too sharp a braking action because the contact area between the tyres and the road is so much smaller, half the tyre width would give half the contact area but because the tyres are likely to also be a larger diameter but with less flattening at the bottom xplys compared with radials, the actual contact area may be less than half that of a modern car.

[pigtin]

The fronts are 400/17 crossplys which give sod all adhesion in the wet
When the're a little more worn I'll swap them for 450s, the same as on the back. The back brakes are very feeble compared with the front.

[47p2]

Well done on the MOT pigtin. DVLA were most likely out sunbathing today
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