Spitfire master cylinder braking impressions

[Grumblebuns]

I just posted an article in the Technical section on installing a Spitfire MC to the Europa. If anyone sees any errors in the article please post it.

Also I'm looking for impressions from owners with real world experience with the conversion, especially the TC(S) guys. I'm several months away from getting my TCS with the Spitfire MC on the road. My only experience with alternate MCs on the Europa has been the Ford Courier MC on the S2 and a F10 conversion on a TCS. The Courier conversion had minimal overall difference in the balance as can be expected with a straight 0.75" bore. The pedal was slightly harder in feel, but not unreasonably so. I have a S2 with a completely stock brake system and used that for back to back comparison with Spitfire S2.

The TCS with the 0.75" F10 MC was sold after only a few miles on the road so I didn't get to really test the brakes hard. With the several hundred street miles, I really liked the feel of F10 master cylinder. For some reason, it didn't feel as hard as the S2 with Courier even though both bores are a straight 0.75" and I didn't really notice the longer pedal travel for the TCS.

Joji Tokumoto
Fallbrook, Ca   

[EuropaTC]

As you know I've tried a few options to the braking system on my car, some I liked, some I didn't. Brake pedal travel is one of those areas where for me a small change makes a big impression in my mind.  You can change pads to give better initial bite for example, but I found that if the pedal moved more than I was expecting that preyed on my mind more that the car's stopping distance. An extra 1/2" is enough to get me thinking I'm not going to stop, silly I know, but that's me.

So, being happy if I have maths and numbers to hand, I started recording pedal travel. Nothing fancy, just a length of Al pressed against the end of the footwell and a marker pen to run alongside the pedal rubber. Then depress the pedal as hard as you can by hand and mark again. Yes, we would get a bit more travel with leg pressure so the numbers aren't 100%, but I've found it useful.

Firstly you know if you are miles away from the calculated volume/travel or if further bleeding is likely to shift some recalcitrant air bubbles.  I find it reassuring to know I've not reached the full stroke of the m/cylinder piston travel and there's reserve in hand. And finally I've found it's handy as a reference during future work;  you know where you should be and won't fall for that "I'm sure it used to be better than this" feeling.

Brian

Edit to add: when I had the 0.7" spitfire on and standard brakes front and rear, my record shows I had 1.5" travel.  YMMV - rear brake adjustment, etc.

[Certified Lotus]

Joji & Brian, thanks for this information. I am in the midst of changing my brake master cylinder during my restoration as I removed the boosters. Joji your writeup made me feel much more confident I'm heading in the right direction as well as explain what to do regarding the threading of the pushrod.

[2483R]

I had a Spit master on my TC for 30 years so I can comment on the conversion.

Pedal effort: In theory, the Spit master should reduce pedal effort by a about third over the stock master without servos. With the servos and stock master pedal effort is reduced by 50% (if my info about the stock servos is correct). A further reduction in pedal effort, although slight, can be had by using softer pads and shoes. So the Spit master requires more pedal effort than the stock setup, but not much more.

I really can’t tell the difference in pedal effort between my Europa with a Spit master and my daily driver Toyota with power brakes.

Pedal travel: You don’t get something for nothing. Pedal effort is reduced by a third but pedal travel is increased by the roughly same amount. I have seen comments from other Europa owners on the Yahoo group, who regard the travel as too much. But I suppose it is a matter of personal preference. Your foot gets used to it, and you do not notice the increase after a few miles. Brian’s letter above only shows a slight difference in travel between a 0.75 and 0.70 bore, so I am not sure how much you gain by going to 0.75 bore.

I went with a Spitfire master for several reasons;

1. Spit masters/rebuild kits are cheap and easy to get
2. Spit masters are a bolt-on conversion
3. 0.70 bore is the factory non-servo Europa master diameter. I assumed Lotus engineers tend to know what they are doing.
4. At the time of my conversion, American brake fluid was not compatible with British brake rubber. I still have an old Sports Car World catalog which warns of using American brake fluid in a Lotus. Thus, I was wary about mixing brake types and wanted all the brake rubber/seals to match. I had Girling calipers/wheel cylinders, so I wanted a Girling master. Today, I believe all brake parts are so highly regulated that it does not matter.

An additional concern should be the Spit tandem reservoir. The tandem reservoir, designed to be mounted at an angle in a Spitfire, will separate the front and rear systems. If one system leaks all of its fluid, the other system will still have fluid. Call this a reserve capacity, for lack of a better term. My own measurements (mind you these are not exact as I do not own a test laboratory) show the Spit reserve capacity, as installed in a Triumph, of 1.5 oz front and 2.5 oz rear.

But when a Spit master is installed in a Lotus the reservoir is now horizontal and the reserve capacity changes to 3 oz front, 1.25 oz rear.

Does this make any difference? How much reserve capacity is needed? I do not know the answer and will invite others to comment.

[jbcollier]

Not much is needed at the rear as you adjust the brakes to match wear -- except of course for the special which "sort of" automatically adjusts itself.  Fronts do "use" quite a bit of fluid as the pads wear so the extra capacity is a good thing.  As long as you check your brake fluid and adjust your rear brakes at every oil change, you'll be fine.

[EuropaTC]

(part Quote)
An additional concern should be the Spit tandem reservoir. The tandem reservoir, designed to be mounted at an angle in a Spitfire, will separate the front and rear systems. If one system leaks all of its fluid, the other system will still have fluid. Call this a reserve capacity, for lack of a better term. My own measurements (mind you these are not exact as I do not own a test laboratory) show the Spit reserve capacity, as installed in a Triumph, of 1.5 oz front and 2.5 oz rear.

But when a Spit master is installed in a Lotus the reservoir is now horizontal and the reserve capacity changes to 3 oz front, 1.25 oz rear.

Does this make any difference? How much reserve capacity is needed? I do not know the answer and will invite others to comment.

I did some very rough calcs using my brake spreadsheet by altering the pad/shoe movement to assume you'd worn away all of the linings.  I took figures of 9mm for each front pad and 3mm for each rear shoe lining, pure guesswork because I've not seen a brake shoe in a while.    Anyway, it came out at roughly 130cc/4.5 fl oz for the front, and an insignificant amount for the rear (<0.5 fl oz).   

So if you're in the habit of getting through a set of front pads between oil changes then you might want to check fluid levels 'coz the rear brakes alone ain't up to much.... 

On the pedal travel aspect those measurements are on a 4x disc setup so not directly comparable to disc/drum but even so going from 0.7" to 0.75" bore came out at around 1/4"  IIRC and as you say, not a lot.  It's a personal thing and like the guys on the Yahoo group we all have our own comfort zones.  Strangely enough I use the 0.7" on the Elan which has larger front calipers and thus more fluid displacement. Pedal leverage ratio is lower but foot travel is still longer than the Europa and yet...   I think it's perfect !  Comfort zones again.....

Brian