110 Drum to Disc Conversion - Pedal Box/Servo/MC Query

The vehicle: 1989 110 with Salisbury rear axle (being rebuilt). I have converted the drums to discs.

I have two new servos (the original was ditched years ago). One servo is the smaller type 50 (STC2878/NRC4775); this fits onto my original pedal box (NRC6058). The other servo is larger (LR013488/STC441) and does not fit onto the pedal box, the holes for the servo studs are way off.

I have two new master cylinders. One is the larger pre-rear disc variety (NRC8690), which fits onto the smaller STC2878 servo. The other MC is LR013018/STC441, which fits onto the larger servo, LR013488/STC442; it does not fit the smaller servo.

I'm aware there is a pedal box that was fitted to later 110s, which is NRC7933/LR010403. I'm wondering if I need this, or if I can simply drill new holes into my pedal box, or indeed if I should just retain the servo that fits my pedal box, and the accompanying MC.

My 1989 90 has disks on the rear. The MC is NRC8690, and the servo is STC2878. It also has a G valve on the bulkhead support bracket, which by all accounts seems to be a 90 thing rather than a 110 requirement.

Google reveals that some people stick with the larger servo, and either remove or retain the PDWA. Those who remove it also put the 300tdi MC cap on the earlier MC and adjust the wiring accordingly.

I see that there are a few options:

1. Fit the smaller servo (STC2878) and larger MC (NRC8690). Fit to 300tdi MC cap and adjust the wiring. Ditch the PDWA. Fit a T piece for the front calipers. Hope for the best.
2. As above but retain the PDWA and don't fit a T piece or MC cap with low fluid level thingy.
3. Drill the pedal box and fit STC441 and STC442; possibly fit ANR1415 too.
4. Get a new/second hand pedal box and fit STC441 and STC442; possibly fit ANR1415 too.

Any words of wisdom will be appreciated!

My old originals work the all round discs now fitted on the 86 90.

Gmacz said:

My old originals work the all round discs now fitted on the 86 90.

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Thanks - I'm assuming you kept the G Valve, being a 90?

Sounds like you are wondering if you can leave it out.
I dont know if you can do that, rear of 90 is light and valve cuts power to rear brakes when you slam them on, this stops rear wheels locking up long before front. With discs I would think it would be even worse as more power.
Not sure if this is correct but it is my take on the brake system.
110 has more weight at back and I dont think it needs one but early ones had one I think.
Mine is fitted as it was there and working.
I would have experimented with the brakes if it wasn't and tried without first and see what happened with the brakes.

Gmacz said:

Sounds like you are wondering if you can leave it out.
I dont know if you can do that, rear of 90 is light and valve cuts power to rear brakes when you slam them on, this stops rear wheels locking up long before front. With discs I would think it would be even worse as more power.
Not sure if this is correct but it is my take on the brake system.
110 has more weight at back and I dont think it needs one but early ones had one I think.
Mine is fitted as it was there and working.
I would have experimented with the brakes if it wasn't and tried without first and see what happened with the brakes.

Click to expand...

Thanks - the differences between the 90 and 110 perhaps warrant different consideration. I'm not seeing any examples of 110s with the earlier MC and servo setup, so I guess my question is probably more directed at converted 110s. We know that drums require more fluid volume than calipers, whereas the latter require more pressure. I wonder if these differences are understood in the Defender community or not - that would provide some helpful data to analyse.