Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Thoughts please Brake Proportion Valve

Occasionally when we have had to brake hard we always find the rear end drifting away, a thought is under hard braking the weight of the car travels more onto the front wheels and therefore more braking can be had on the front but only under hard breaking.

Our Morgans have the same pressure applied to all 4 wheels at all times, some have aded greater braking pads and discs to their front ends but under hard braking which proportion of braking is applied to each wheel?

We do need some tech gurus to perhaps explain more but it is possible to fit proprtion valves so under harder braking they come into play (under normal braking they are ineffective)

Some racers fit and tune these so that they perform say on left or right hand circuits ie they tune the left and right wheels to perform to track and car conditions.

see photos of part and web link. Web link here for valve brakes

i by Robert & Ali Davies, on Flickr

i (1) by Robert & Ali Davies, on Flickr

Interesting video explains all!

Love the accent too....

Rob

In which of you 4 Morgans is this a problem?

The Morgan racers normally fit tandem master cylinders, with one feeding the fronts , the other the rears . They have a balance bar inside the car which can be operated during a (longer) race to allow adjustment. This is by far the best solution.

Personally I would not really want to fit a load proportioning valve , as I don't feel the need , but I think many tin-tops have/had them as standard before the days of ABS etc.

If the back steps out under braking , just catch it , and remember to adjust the rear brakes when back at the workshop. (later cars have the auto adjusters on the rears of course)

No experience of these on Morgans, but I have used them on 90's VWs when upgrading the rear brakes to discs and needing to ensure that clamping force stayed at about 40% of the fronts under hard braking. We used to call them 'in line pressure restrictors' and would set a car up by putting it on 4 space-saver tyres and driving round a yard (at a moderate speed rather than track speeds) and braking hard with some front steering angle to find the adjustment point at which you can brake the hardest but keep the back end true.


Some guys did use a true 'proportioning valve' for front/rear brake pressure adjustment, but as I always understood that you'd have to swap your diagonally split circuit for a F/R set up, I thought this was risky on a road car.

Ps - love the guy in the video. He's found his calling in Life....

You can vary brake pressure to the rear by using different dia slave cylinders, I do not think bias/balance bars are allowed for the MOT they have to have the locking nut on the balance bar welded.
But if you balance correctly then it does not matter once it is welded to stop further adjustment.

David Byrne

Rob,
all my Mogs would lock up on the rear on really hard braking. But it had to be really hard. Do you brake that hard often to need to compromise the rear braking?

Incorrect, David

A balance bar/bias pedal box is not an MoT fail irrespective of whether the locking nut is welded or not.

My stage and road rally cars used to sail through the MoT test's with bias pedal boxes fitted.

Used a brake proportioning valve on a Group N 205 GTI and that was because the hydraulic handbrake was a bit fierce on the gravel. Never needed it on tarmac.

Getting back to the matter in hand, I dont think they are needed on a Morgan.

Arwyn

Brake problems are often counterintuitive as you focus on what's happening as opposed to what's not. As in the statement "all my Mogs would lock up on the rear on really hard braking".
The problem could in reality be "I can't get the front brakes on hard enough" - in which case the solutions go down a completely different route.

Ok all looks like it sounds better left alone, its just that on the only 2 emergency stops I have ever performed on both occasions the back slipped first and great pool of smoke.

I would hesitate to say that its prefferable for the back to slip first as one has some control unlike if the fronts slipped! When it would be a different story.

Rob, either your fit a Citroën CX brake/suspension system.. or you could actually 'take off' an extra half inch of the brake lining on the shoe that 'meets' the rotation of the drum. It takes away some of the 'self-energizing' effect on that shoe. Originally that lining is already shorter. It will reduce brake efficiency slightly but it will probably only be noticeable during hard braking.
'Try this at your own discretion'