AP Brakes balance - how to fit adjustable valve.

The standard brakes on the MGF/TF are adequate, but only if maintained at top efficiency.

MGR's answer was to replace the standard 240mm disc (with single piston sliding caliper) with a 304mm disc (with an AP 4 piston caliper). However, they failed to re-balance the brakes so that with the APs fitted most of the braking is done by the front brakes.
This often leads to the rear calipers seizing through lack of use.

I wanted to improve the brakes of my Freestyle but was unhappy about this imbalance. I was fortunate to pick up a pair of APs with an already made up section of brake pipe with an adjustable valve that had been used on a racing MGF.

This is the valve, (or one very like it!)



you need to remove the original bias valve. It is a fixed reducer to allow only a reduced hydraulic flow to the rear calipers.



Here is the section of pipe and the removed valve.



The preformed replacement section allowed me to simply remove the old setup and replace it with the adjustable valve.





Now as I've replaced the hoses with braided, the front discs and calipers with 304mm with APs and fitted the adjustable valve I cannot judge how much of the startling improvement to the braking is down to the valve but I intend to visit a friendly MOT station to get some figures for the brakes. I will be able to try the various settings of the valve at the same time and get braking force figures for each

I've tried the various settings on the local road and note that the more fluid I allow to the rears does reduce the tendency for the fronts to lock.



Yes I've decided I want silver calipers! Incidentally, I needed 6mm spacers with these wheels.

Sorry about the crappy quality of some of the photos. Useless camera on my phone. :nonod:


Quote from the seller.

The reason for the valve is this; The AP Callipers are so powerful that you don’t get much of an advantage in stopping distance when fitted with standard valve. But with the adjustable one you can send more power to the rear wheels and on the MGF that will bring down stopping distances by up to 30% We have had this on a track day MGF all this year and could out brake almost anything.

A good job there David. Don't be pushing that lever willy nilly when your adjusting something or you might start doing donuts at the next roundabout. When Graham swapped my brakes I had a OMG moment when the new brakes kicked in.

Where do we buy these valves then? I've got new pipes and SS hoses to fit in the very near future, so I may as well add one of these while I'm at it

Cracking job David..

I've made a mount for mine on my brake servo brace



Mounting the damn thing is probably the hardest bit.. Don't want it moving about

How are you finding the brakes now? :drive:

The one I bought already had a bracket to fit on where the original was so really easy to swap. :yesnod:

The brakes now are terrific, but as I said above i can't judge how much the bias valve is adding as I also changed to 304s on the front.

I would say that they are even better than my Nissan brakes and I think they are great. The only difference is the Nissan has ABS so you can really whack the brake pedal without locking up. :spank:
I will update this thread with comparison brake force figures when I get them measured. I already have brake figures for the standard set up so it will be very interesting to compare.

So the results are in. :yesnod:


The standard set up

Front 240mm disc single piston calliper 220kg. F
Rear 240mm disc single piston calliper 170kg. F
(front rear balance = 56/44) Total force = 780kg. F


The AP front set up

Front 304mm disc four piston AP calliper 310-320kg. F
Rear 240mm disc single piston calliper 160-170kg. F
(front rear balance = 65/35) Total force = 980kg. F


The 280mm Disc with blocked out standard calliper option
(Various options are available.)

Front 280mm disc with blocked out standard calliper 240-250 kg.F
Rear 280mm disc with blocked out standard calliper 210-220kg.F
(front rear balance = 53/47) Total force = 980kg. F


My set up with adjustable bias valve

I tried the various settings on the bias valve for brake balance/feel by road test and then took the car to be checked at the MOT station. Interesting that the best feel was with the valve at maximum opening allowing most fluid to the rear. (This valve only affects the amount of fluid going to the rear. The front is on a separate line and is unaffected.)

Front 304mm disc four piston AP calliper 310-320kg. F
Rear 240mm disc single piston calliper 200- 210kg.F
Total force = 1060kg. F


Conclusion

I have found the brakes to be much improved over standard. The stopping power is a lot better while being balanced. i.e. braking hard gives amazing braking, and the fronts only lock under provocation.

Looking at the figures it appears that I now have a an almost exact 60 / 40 front / rear split. :woo2:

That's a cracking read David well done

I make that a 36% improvement over standard.

Stunning!

Robin

Thanks for putting this together. Very interesting data from simple modifications. :yesnod:

Is there a guide anywhere that explains exactly what is needed and how to go about upgrading to AP calipers with the bigger discs (and now the bias valve)?

Having seen this categoric proof of the improvement achievable I'm quite tempted to have a go.

Robin