Before

After

If you have a problem with the rear brakes locking up before the fronts on your SE5A then this mod could be for you.

Converting

Buy a mini rear brake pressure-limiting valve (also called a brake proportioning valve). The best one to have, apparently is the early cast. You can either get one from a scrap mini or you can buy a new one for about £20.

If the valve is from a scrap mini dismantle by unscrewing the large end cover. Then carefully remove all the internal parts and clean them thoroughly. Make sure you remove the plunger and spring.

If the rubbers look suspect, get another valve. Drill the bottom closed end as shown in the diagram using the drain hole as a guide, then tap a thread to take an M12 bolt. Screw in a suitable bolt and nut to help lock the position. Reassemble the valve using brake fluid as a lubricant.

Fitting

The limiting valve needs to be fitted to the rear brake circuit. It should be firmly mounted somewhere near the master cylinder so adjustments to be made easily. The main feed pipe from the master cylinder to the rear brakes needs to be cut and connected to the feed into the valve as shown in the diagram. The other part of the pipe that goes to the rear brakes should be fitted to either of the outlet connections. The other outlet should be blanked off with a UNF bleed nipple. Note that the ends to be flared on the brake pipes are different, one is a single convex flare and connects to the inlet that has a concave facing, the other is a double concave flare and connects to the outlet that has a convex facing. Make sure that you get this the right way round.

Adjusting

To adjust the front/rear balance you need to find an open space with little or no traffic and unscrew the adjustment bolt. Drive gently at around 20-30mph and while turning declutch and then brake gently. You should feel the front of the car run wide (understeer). Turn in the adjusting bolt around half a turn and repeat, not forgetting to declutch. Repeat this process until you feel the back of the car stepping out (oversteer). When this happens, lock up the adjusting bolt. Now drive in a straight line and make an emergency stop. The front wheels should lock up just before the rears.