Lotus Europa Forums > Technical Articles and DIY tools and tips
Thoughts on TCS Brakes
Bryan Boyle:
Hope I'm not starting a religious war here...but probably talking heresy regarding the braking system in US JPS 142.
IMHO, a 1500 lb car with 120(?) HP in this day and age...it's over-engineered a bit to put double boosters in the circuit, aside from the piping complexity. Like...I'm not going to autocross, not doing hot laps at Jersey Motorsport...I'm going down to Dunkies for my morning caffeine fix, driving the SO to Second Beach in Newport, or carving some corners in the backroads of Bristol County MA. So...the unworking boosters, assorted vacuum lines, and other items are coming out. That's a given; while waiting for the various bits and pieces of interior stuff to come back...figure it's time to sort the brake system out (along with overhauling/cleaning up the pedal assembly, replacing the original clutch and accelerator cables, etc.) before assuming the Lotus Position and cleaning up the 'back of the dash' from 50 years of unconcerned mucking about back there. And, to be honest...the S2 got away just fine with an unboosted system, and it's within a couple hundred pounds of its later sibling.
So...what to do?
As a starting point (the rear cylinders were replaced recently, along with pads, so, assuming the job was done correctly, going to leave sleeping dogs lie after inspecting)
After this?
1. Open the taps and drain the system, disposing of the existing fluid.
2. Disconnect and remove the vacuum units, patching the holes in the fiberglass, and repainting the side wall on that side (truck bed liner paint, minus the grit which I filter out is my preferred finish for the engine room and wheel arches).
3. Remove the flex hoses from the front and rear. They are original...and will be replaced with armored hose replacements.
4. Rebuild front calipers with stainless pistons (have a set left over from my own stock), paint calipers, reload with fresh pads.
5. I have new disks I was going to put on 693R but never got a round tuit...so, might as well use them here.
6. Remove the MC. It's a girling unit, looks like the original...but who knows? Mucking through the extensive records I have, don't see any indication that it was replaced along the line, but, pretty sure not every bit was recorded in the POs OCD record keeping.
Now...it's all in bits...where to go from here?
There are a lot of thoughts about which direction to travel; let's face it, some of the parts, while made by Girling, were made to Lotus' specs and are not current production. There are docs on the manuals site (either Dan's or my mirror) that go into gory detail about decisions: Nissan/Tilton/Spitfire/you name it. Some bits are still available, some not. It seems at this point it will be pretty much narrowed down to either a Tilton or the Spit master...(in my mind...).
Removing the boosters means that the bore size of the master and travel will need to be somewhat different. In the S2, for instance, the .70 bore took care of the fronts, and the stepped-down bore (don't recall offhand the size) at the rear of the cylinder took care of the rears. Fair enough. The replacements today have a constant bore in various sizes...Tilton, being a universal fittment, is available in multiple bores: 5/8, .70, .75, etc. Generally, the larger the bore, the less travel to fully engage...the smaller the bore, the more travel. Basic fluid dynamics, right? Coming up with a compromise between feel, travel of the pedal, and force applied becomes a question to answer.
Aside from the physics of fluid travel, pipe bending and terminating, etc., and accounting for the removal of the boosters (which modulated the feel of the brakes and balanced the force needed), I'm in the range of thinking that moving from an assisted to a non-assisted system is pointing towards ensuring that the front-rear balance is maintained properly...which means that
1. the fluid force applied to the rear will have to be moderated by a proportioning valve to make up for the larger MC bore feeding them and
2. using the same bore size as the unboosted cars used for the fronts will provide both the right travel as well as fluid force for the calipers (which are the same on the TC as were on the S2).
Am I off here? For the record, I'm basing this on reading Aaron Hines' work done in the early aughts, as well as Dave Maugham's document on his changes...and some of the Lotus West material (thank goodness for the archive, right?).
Where I'm leaning towards (yeah, using a heavy iron speed shop...) is:
1. Tilton 74-700U master cylinder (https://www.jegs.com/i/Tilton/454/74-700U/10002/-1) with reservoir remote mounted up on front trunk bulkhead and front line direct connected to fluid T on front of frame, removing the back-and-forth piping to the removed booster. That means the PDWV goes away. Simplifying the piping means fewer points of failure, which the valve was meant to monitor. (I realize this may result in some comments, so be it...I'm open to reasoned arguments to keep or not)
2. Jegs Proportioning Valve model 63020 (https://www.jegs.com/i/JEGS/555/63020/10002/-1) in place of the rear booster (in essence)
The details still to be worked out...;) But throwing this out there, with my thoughts, for discussion...flames to /dev/null, ok?
Grumblebuns:
The Tilton MC appears to be a single circuit design. Nothing more scary than lose all braking with a single system coming into an intersection and blowing through it with no brakes as happened with my Elan with a single circuit MC. Not condemning single circuit MCs but why when there are several tandem MCs out there that will work for our application.
Clifton:
--- Quote from: Bryan Boyle on Monday,March 07, 2022, 09:00:03 AM ---Generally, the larger the bore, the less travel to fully engage...the smaller the bore, the more travel. Basic fluid dynamics, right? Coming up with a compromise between feel, travel of the pedal, and force applied becomes a question to answer.
--- End quote ---
I agree on the single circuit being not the best way to go.
The pedal ratio is shorter than most cars. The pedal feel, lbs to stop 1G is higher on Europa's than most cars. I don't have stock calipers or MC but I used a program to come up with and compared it with the Europa and other cars. I still softened it up more by moving the pivot on the clevis for a little more travel. I know you aren't making a track car but getting it to were you can brake hard and close to lockup without locking up too easily is the safest and has the best feel. Hard pedals feel dead. If you drill new holes and the radius off the MC, you can quickly change the pin and not change the pedal height too, just feel/travel.
Bryan Boyle:
so....what is the current thinking of replacement MCs? I know the issue with single circuit systems (lack of residual braking in case one circuit goes tango uniform)...The one that's in the car right now seems to be ok; the issue with the boosters (they've been disabled, but the brakes are still plumbed through them...) being just dead weight at this point. Just seems to me that the system is more complex than it needs to be for what the car is (all protestations about it being a sports car and so forth notwithstanding; its predecessors did just fine without them), and simplifying the plumbing will add reliability without necessarily increasing the risk of driving it.
I'm approaching this as wanting to have a KISS system.
EuropaTC:
Hi Bryan,
If you're after a very simple system, then despite the safety aspects a single circuit is the way to go. Yes, I know that's controversial and it's coming from someone who converted his single circuit UK car to dual circuit, but if your aim is for simplicity then single circuit with no servo assistance is the one.
From hazy memories servo assistance was accompanied by harder front brake pads, or at least it was on the Elans so I can't see why the Europa would be different. I can remember the servo failing on the Elan in the early years and finding it very unnerving with the high pressure required to stop. The point here being that the servo/boosters were there for a reason & not just a marketing tag line, it was a deliberate design/spec change.
These days we're spoilt for choice on pad materials so removing the servo/boosters isn't such a big deal, you can easily find a pad that will restore the cold braking bite for road driving. The other point has already been made by Clifton, the pedal leverage ratio is high on the Europa compared with other cars (4.3 ?) hence the assistance reduces the need for gym work on the legs.....
I ran my TC with a single 0.75" m/c (0.7" OEM) standard brakes & servo until 2014 when I replaced it with the Spitfire 0.7" dual circuit m/c, no servo/booster. It worked and I've no doubt that you'd find the same although you'd have fractionally more travel than I had. The other snag is that it was designed to be mounted at an angle so either you accept a lower reservoir volume, change the reservoir or plumb in a remote one. A remote makes filling much easier and you can easily get one with a low fluid warning cap.
In terms of feel, it was ok, no drama but then again I was running Greenstuff pads, designed for similar applications.
So while I'd personally junk servo assistance I think you'll need to address more than just the m/c selection. If you have the genuine Lotus pads designed for boosters then that's the first change. If you still don't like the pedal weight then you can make minor changes to increase the pedal ratio - more travel, less effort.
I'd suggest you step back and ask what you really want, is this a one-off mod or will you be bitten by the bug and it's just the start ? Many on here have custom brake systems, usually discs all round with both servo/non-servo options so there's a well trodden path to follow either from a bolt on kit or making your own. And if a rear disc conversion is in your future then you might end up wanting to change the m/c again for optimal braking depending on where you go to. For example my 0.7" spitfire m/c ended up as a 19mm (approx 0.75") m/c when I changed calipers & discs.
Brian
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