8 replies to this topic

[minicooper1.3i]

Afternoon all.

 

Have any of you ever swapped the pedals on an MPi (or late type mini with same servo and clutch) to the very early smaller pedal types that sit lower? If so, how much of a pain was it to do?
Years back, my brother did it for me to my first Mini ( '83 City) but that didn't have a servo and also had a different clutch. I know I'd need to modify the throttle pedal to accept a return spring but other than that would it be straightforward?

Cheers :)

 

[tiger99]

DO NOT even attempt that. There are serious safety considerations such as reliably getting sufficient pedal travel to ensure that if one hydraulic circuit fails, the other will always achieve full braking before the pedal hits the floor, with the worst case tolerance buildup and simultaneously slightly slack adjustment of the rear brakes. All of these things get checked as part of vehicle Type Approval and there is no good reason to mess about with them.

You would need to inform your insurers as it is a safety related modification.

[minicooper1.3i]

I'm fully aware that pedal travel would be less. I drove my first car safely and successfully for 6 years with early type pedals fitted. The extra leg room and lesser angle on the ankles was highly beneficial owing to my height.

I was asking the question because less pedal travel would obviously require greater pressure as presumably the piston travel on the master cylinder would still be the same. Or would it with a servo assisted brake? I'm not sure how much movement or leverage there is in an early pedal box. That's the question I was asking. If the pressure required was greater but the brakes operated the same then so be it. I'd get used to it.

For the record I found driving my 83 city with early type pedals extremely comfortable and saf, and it passed it's mot every year before I sold it.

[Ethel]

The small pad brake pedal does have less travel, that's partly because the pedal box geometry is slightly different - just like different ratio rocker assemblies, relocating the pivot while the pushrod remains perpendicular is the way. So swapping just the pedals won't have the desired effect. It is possible to swap the complete pedal boxes, but you'd have to make some modifications to how it attaches to the parcel shelf. That's still leaves you with the pedal travel/ mechanical advantage to resolve. The brakes should work, but lose a hydraulic circuit and things could get interesting.

 

The reason the later brake pedal sits higher than the clutch is because it's cranked to give more reserve travel. The horizontal master cylinder is the largest bore of the lot, but I couldn't say if the bell crank leverage is 1:1 or some ratio that cancels out the difference the cylinder bore would have on overall mechanical advantage.

[minicooper1.3i]

Thanks Ethel

Going by previous experience as described, the swap over was quite direct. No mods necessary. But as stated that was on a non-servo assisted car.

I'd appreciate it if you could expand upon your mention of mods and hydraulic loss.

[Sprocket]

Early early pedal box is easily identified, the pedals them selves usually have a strengthening rib welded on the side of the main shaft of the pedal. The box its self is a different shape at the point where it fixes to the dash rail and steering column.

 

The box its self is irrelevant as the pedals can all be swapped into which ever box you wish to use, so in reality, all you really need are the pedals. There are three!! each with a different cranked angle on the main pedal shaft. Word of warning though, the early strengthened pedal and some of later ones were never designed to work with the mechanical brake light switch, as they used a hydraulic switch instead. Not the end of the world though and a work around is usually an easy task. Choose wisely!

 

All valid points about reserve pedal travel, but it also depends on which master cylinder is going to be used.............

Edited by Sprocket, 30 May 2017 - 11:33 PM.

[Ethel]

The later boxes are longer to be clamped by the steering column bracket. The pre '75 single circuit ones are shorter with a couple of bolts securing them.

 

Like I said, dual circuit pedals are also cranked higher to stop the pedal hitting the floor if you have to push the piston of a failed circuit all the way before you can generate any pressure with the remaining one. The only way to get the same reserve travel with the pedal closer to the floor would be to have less mechanical advantage.

 

Swapping the pedals is possible, but it's the pedal box that controls how far the pedal shaft is away from the axis of the master cylinder and hence the effective length of the lever on the cylinder side.

 

single circuit master 17.8mm bore

original dual circuit 17.5mm

stepped dual circuit 19.0/17.8mm (yellow band)

horizontal 20.6mm

 

 

.... and note that a bigger master bore won't help reduce travel in a failed circuit as it won't be pushing fluid. You'd have to look at the distance between back and front pistons and from the front one to the closed end of the cylinder .

[minicooper1.3i]

Thanks all for the detailed and informative responses. I can't remember which system my old city had, all I recall were the horrible drums all round lol. Interestingly, my brother also swapped the pedals on his first car (as he went for a retro look inside and out) and his was an '85 Mayfair with front discs.

 

I think I'll leave it as is for now and review the whole set up during the planned rebuild :)

[Sprocket]

Pedal pivot point has not changed over the years. The three different pedals will all fit on one pivot shaft with the Clevis pin holes also lining up