Westfield Miata Pedal Box mods

[DanM]

So I'm posting this tech question separate from my build thread and its directed to those of you with experience building the Westfield Miata.

 

I have read a bunch of build threads that say there are adjustments to be made to the pedal box to accommodate for clutch pedal issues (Bore size or something like that).

 

Could someone please let me know if it is still an issue to be addressed and explain exactly what you had to do to correct it (With pictures etc.) because I haven't got a clue! 

 

Dan

[MPG]

I had to make that modification to mine. Well, actually the folks at Flyin Miata did that.

 

I don't know whether the factory has changed that since. I can go measure mine tomorrow, assuming I can get the garage warmed up enough.

[DanM]

Thanks @MPG, any help will be welcome.  Like I said, I haven't got a clue what I need to do!  It's almost like this mythical thing that only exists deep in the FM vaults! lol

Edited January 16, 2022 by DanM

[MPG]

LHD Westfields use top hung pedals which are mounted to this box on top of the scuttle:

 

 

There's a cover I've removed in that picture. A RHD Westfield uses floor mounted pedals, so nobody in the UK knows what you're talking about when you ask questions about this.

 

For a Mazda based one, they use the brake & clutch master cylinders from the Miata.

 

If you look down into the box, you can see that the clutch pedal has 2 holes.

 

 

When the factory made my box, the mounting point for the clutch master cylinder was lined up with the lower hole. My understanding is that with a stock Miata master cylinder, that's going to give you a very short stroke. So Bill at FM modified the box to move the MC up to line up with the other hole.

 

 

He did that by welding a filler into the old hole in the front of the box, cutting off the 2 studs, then cutting a new hole and welding new studs in. It's not terribly clear in that picture, but you also need to cut this cross piece that goes from one side of the box to the other because the top of the MC would now interfere with it.

 

The result is that the clutch has quite a long stroke. Some folks who are shorter than me find it too long.

 

So I think you could try mounting the clutch MC on the box and see which hole it lines up with. If it's lined up with the top hole, then the factory probably changed things since they made mine. 

 

If it is lined up with the bottom hole, then you can either:

 

1) modify the box to move the MC up

2) change to a MC with a different diameter

3) live with the short stroke

 

 

 

 

 

 

[MPG]

There are 2 other things I modified in this area.

 

The Miata had 2 switches on the clutch pedal. One is wired to the ECU and tells it when the clutch is out for something to do with the idle. I mounted that switch in the box. The other is wired into the ignition so that you can't start the car w/o depressing the clutch. I just removed that from the wiring harness completely to simplify things.

 

I also replaced the stock flywheel with a 10 lb one. That makes the engine feel a lot zippier and makes shifting really quick.

[DanM]

Thanks for the info @MPG that's really helped me to get a better sense of things.

 

I took out my pedal box from storage and took some photos. It looks like a vey nice unit!....... seems such a shame to cut it up!!

 

On inspection I noticed that there isn't a second hole on the clutch pedal.

 

I also noticed that the clutch master cylinder had 0.700 on the side, which I think may be different to yours (0.625)

 

With this in mind I think it will be worth me reaching out to Westfield to see if something has changed in the last few years to take away the need to adjust the box.  

 

In the mean time do you have any measurements from the pivot to the 2nd hole? I can then do some comparisons.

[MPG]

Quote

In the mean time do you have any measurements from the pivot to the 2nd hole? I can then do some comparisons.

Hard to get an accurate measurement because things are pretty crowded in there once it's assembled, but it looks like the top hole is about 30mm from the pivot and the lower is more like 60mm.

[DanM]

Thanks @MPG.

 

So I spent a little time researching and learning a bit more about cylinder bore, and clutch pedal ratios, and found a couple of useful article that have helped me to get my head around it. 

 

How to Set up a Hydraulic Clutch

How to adjust your clutch pedal ratio

 

I thought I'd share my findings to help some other newbie's like me who are looking for information on this.  I also reached out to Manik Sports cars (Westfields North American distributor) to see if they had some useful insights as well.

 

From these articles I've learned that the optimal pedal ratio for a clutch MC bore of about 0.825in or below is 6:1.  (My bore is 0.700.)  Using this ratio and the length of the pedal arm you can calculate where the connection to the clutch pushrod should be. 

 

 

Taking some crude measurements from my pedal box, I estimate that the pedal ratio is close to 3.5:1 and to get an optimum ratio I would have to move the push rod connection up by approx. 25 - 30mm.  To achieve this, the LHD builders have been moving their MC hole and bolts at the front of the pedal box up by that amount.

 

 

Tom at Manik was kind enough to share what FM had done to their vehicle and it looks like they moved it up about 30mm as MPG estimated.  While the Flyin Miata guys decided to make the modification to bring it in line with the optimal ratio, Westfield felt that the standard pedal box would still work fine and so did not make any changes. I guess the decision for us as builders is to decide if we want to make the FM mod during the build phase or wait and see for ourselves how the pedal performs.

  

 

 

Edited January 20, 2022 by DanM

[Dave W]

If you decide to modify the pedal box, you might want to consider adding a pedal stop to the clutch lever. You will already will have half work for a 2nd clevis pin that can slide thru a hole, or into a tube or block.  Much easier now the later, after you are on the road.

[lg2k]

I used the dimensions shown in this build which originally came from Flyin Miata. 

 

https://www.flickr.com/photos/23287408@N02/sets/72157603818053364/

 

Here is a picture of mine I took while working on it way back when. I don't remember if I put a pedal stop. I would have to pop the top and look. 

 

 

 

[DanM]

This is amazing! Thank you for sharing the thread.
 

That is the same drawing that Manik shared with me! 

[DanM]

For those interested in seeing what I actually ended up doing, here is a link to some pictures on my build thread.