Lotus Europa Community
Lotus Europa Forums => Garage => Topic started by: surfguitar58 on Tuesday,November 13, 2018, 10:33:21 AM
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Today's feeble minded question:
There has been a lot written on removing brake servos and switching from the stock 0.875 inch dia tandem master cylinder to a Spitfire 0.70 inch dia tandem master cylinder for the Fed TCS. The piston area reduction is 0.64:1. Could one get the same effect by drilling a new hole in the brake pedal and moving the brake clevis location closer to the fulcrum by the same ratio? (See sketch)
Granted the M/C connecting rod would be off axis with the MC, but that could be corrected with a custom off-axis clevis. (The load would still be off-axis, but the rod alignment would be axial.)
What am I missing here?
Tom
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I converted to a hydraulic clutch and did this to get a better pedal. I did on the brakes too but I am running dual masters. There was a brake calculator online that I used to figure out everything when I did my brakes. It is no longer there but it took into account pedal ratio, bore, weight, everything. It gave pedal travel and force required for what ever G stop you wanted. I would search for one online.
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Surfguitar, it looks to me as though the bracket you drew to bring the connecting rod back into alignment will exactly cancel out the extra leverage from using a lower clevis pin hole on the brake pedal. That is assuming that the bracket isn't free to rotate when you press the pedal. If it is free to rotate then I think you will lose leverage overall.
If you can get away with a little connecting rod misalignment, then simply using a lower clevis pin hole might buy you some extra leverage. Is the connecting rod attached with a horizontal pin at both ends? If so then a small change in the angle of the rod away from the "correct" axis will still work. In this case a "small" angle is anything where sin(x) ~= x, over the whole range of movement of the pedal.
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When I removed the brake boosters many years ago, I drilled a new hole as in your first sketch. It was actually Richard Banks who recommended it. That's the only modification I made. The pedal effort is higher than with the boosters but not objectionably so. One thing that has worried me is that I've heard reports of brake levers breaking under excessive pressure but it hasn't happened yet.
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The offset clevis yoke is a cosmetic solution. The load is still applied off axis the piston is loaded off-axis as well. So skip the custom yoke.
Increasing the pedal's mechanical advantage will work. That said, I would fit the smaller M/C myself.
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Thanks for the advice everybody.
Arizona: I worry about breaking the pedal in my current configuration with big bore MC and no boosters. I've mostly gotten used to it but I really have to stand on the pedal in a panic stop. The second hole weakens the pedal, but less force would be required.
JB: Are you concerned about the off-axis loads scrubbing the MC piston against the cylinder wall, potentially causing scoring? Frankly, that is my biggest concern.
Tom
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Two things would worry me about your offset clevis pin.
1) I would triangulate the clevis pin, so as not to put large pressure on a right angle.
2) If you increase the mechanical advantage, you have to increase the pedal travel for the same piston movement. Can the pedal travel far enough to give you sufficient braking?
Personally, I would not mess about with what is essentially equally the most important control for the car along with the steering.
Brake failure = Huge problem. Next thing to stop the car is the umbrella brake (no chance) or whatever is in front.
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Yes, exactly that Mr. S. G. 58. Offsetting the rod on a clutch is one thing, the forces involved are much lower, but a brake m/c sees a far greater applied force. Best to keep it all in line.
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Today's feeble minded question:
There has been a lot written on removing brake servos and switching from the stock 0.875 inch dia tandem master cylinder to a Spitfire 0.70 inch dia tandem master cylinder for the Fed TCS. The piston area reduction is 0.64:1. Could one get the same effect by drilling a new hole in the brake pedal and moving the brake clevis location closer to the fulcrum by the same ratio? (See sketch)
Granted the M/C connecting rod would be off axis with the MC, but that could be corrected with a custom off-axis clevis. (The load would still be off-axis, but the rod alignment would be axial.)
What am I missing here?
Tom
When I removed my boosters, I was advised by Richard Winter at Banks to cut the pedal off and move it up slightly. He gave the measurement at the time but I can't remember. So I cut the pedal off the arm and moved it up. This would be an alternative to drilling a new fulcrum hole.
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Hi,
As the others have already posted, drilling a new hole in the direction shown will increase the pedal ratio and you won't need to move it very much. Assuming your pedals are the same dimensions as my UK TC, the standard leverage ratio is 4.28, moving it only 1/4" downwards increases that to 5 and 1/2" pushes it up to 6. The force will be applied at a slight angle which will mess things up a touch but your principle is right.
So your approach will work and given the length between the pedal & m/cylinder bore I think you'd get away with it. Personally if you're removing the booster/servo then I would fit higher friction pads and see how you feel about it before making any mods. I'd reckon Joe's idea of increasing the pedal length is probably the safest but you could try lowering the pivot point and seeing if there's enough clearance, but if you do go that route I'd weld up the original hole.
Brian
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I have to agree on the change of pads. EBC green pads are good, for street use, and will have a significant impact on how much pedal pressure is needed.
Modifying the alignment, or strength of the pedal is really a bad idea. Welding up the hole even worsens an already compromised arm. In this day of litigation potential, perhaps just changing the pads will give piece of mind too.
I'm running a 7/8 bore Tilton, with 1144 Mintex pads and the pedal is firm, but effective. I used to run the EBC until a track day fried them.....but until the they were great.
Jerry Rude
4005R
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Okay, in my never ending quest to find the laziest solution to any problem, I am revisiting this old thread about increasing boosterless brake pressure by changing pedal geometry. In the thread above I was considering just drilling a new clevis hole in the brake pedal to increase pedal leverage. The consensus was that creating off-axis forces on the MC piston would scrub the piston against the MC cylinder wall and cause premature wear.
Is there any reason I couldn't drill my second hole to increase leverage, then put a block under the whole pedal assembly to raise it up 3/8" or 1/2" to put the forces back on-axis with the MC? I think the clutch cable could accommodate this, and I have big (US size 11) feet, so reaching the higher pedals would not be a problem. What am I missing?
Tom
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That would work just fine.
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Agreed, that will work.
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I got a new servo for about £70. I adapted the Girling fixing bracket to suit, and with a bit of pipe plumbing, all is fine. Clearing the luggage box was forgotten for a short while.
A lot easier than changing all the master cylinder etc.
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Fitting new serves is a great idea. I just get nervous when people “overhaul” their 50 year old servos. Fitting new rubbers seals is not an overhaul! Cylinders and pistons wear and new rubbers is at best a temporary fix, usually not even that.
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The majority of the 14 servos I have removed have badly corroded internal bits which you cannot get out.
If I were paying a decent amount to buy a Europa, I would expect a new working servo.
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Is modifying the pedal assembly really easier than fitting a smaller diameter master cylinder?
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I’m here, I’m listening and reading every word . Undergoing this mod right now but without a moving vehicle it’s a guessing game. I’m in your wheel house now. Thanks for the advise.
Dakazman
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Is modifying the pedal assembly really easier than fitting a smaller diameter master cylinder?
Depends on your willingness to buy a new master cylinder, fabricate new brake lines (the Spitfire MC ports are on the opposite side of the MC) and bleed the system vs simply drilling 1 hole and putting spacers under the pedal assy. I also like the fact that I would be keeping the original equipment MC.
Tom
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reading this thread, have a few random thoughts:
Swapping to a smaller master cylinder is not a permanent irreversible change and no fabrication is required. You can always change back to stock when you want to. The two jumpers can be fabricated in about a half hour.
What brake pads are you using? As others have said, try different pads before modifying the brake pedal.
If you're going to raise up the pedal assembly, make sure that you have sufficient thread engagement on the four bolts securing the assemble to the chassis plate. On my TCS I have about 6-7 threads at the most, ~3/8".
4129R, you mentioned that you are using a single servo? This is for a Federal TCS?
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4129R, you mentioned that you are using a single servo? This is for a Federal TCS?
All 7 of my Europas have been converted to RHD with new single circuit brake master cylinders. I have put in new copper (cunifer) brake pipes and changed from twin servos to single servos.
So I have 14 old servos of various states of disrepair.
So I bought 7 new servos from MGB Spares in the UK at about £62 each, and I am adapting the fixing bracket (flattening one side and cutting off the bit not needed) and connecting them to the single circuit system. I am also renewing the vacuum pipes and all the clips that hold the pipes in place.
Alex in Norfolk.
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Is modifying the pedal assembly really easier than fitting a smaller diameter master cylinder?
Yes.
You can have the pedal assembly out in 10 minutes. No bleeding necessary.
As to the concern of a "weaker" part. Most car will never see more than 100lbs on the pedal.
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Also... the OEM master cylinder has a stepped diameter (~.875” down to .803”) presumably to reduce pressure to the rear drums. I believe the Spitfire MC is a straight .700” diameter and would require a pressure reducing valve for the rears. I got fairly far down the path of planning to sleeve my stock MC down to a stepped .763”/.700” ID before this lazier solution came to me.
D-man, thanks for the vote of confidence, but please keep in mind that I regard this as an experiment and there are far more knowledgeable voices on this thread than I.
G-buns, I share your concern regarding thread length. I haven’t retrieved my car from winter storage yet but pictures of the pedal assembly on rdent.com (autocorrects to “rodent.com”) look like the bolt heads are welded to the pedal assembly and are therefore fixed length. My thought was to use blind nuts, aka sex nuts (do NOT google “sex nuts”) from the bottom to get more thread engagement, but I will cross that bridge when I come to it.
Tom
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In an earlier time, McMaster Carr listed "sex bolts" in their catalog. We thought that was a hoot. You can find them on their online catalog by searching for "sex bolt" or "sex nuts" but they are now called "binding barrels and screws." How long before the terms "male" and "female" will be expunged from our vernacular?
Those are not generally used for applications where strength is important and a quick look at some of the listings did not come up with any fine thread examples. They may be available elsewhere but I think you should be prepared to find a friend with a lathe.
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If you fit a stepped Spitfire cylinder and have issues with the rear brakes, you can adjust the size of the rear cylinders. They are available in three or more different sizes for dirt cheap.
One other consideration regarding raising the pedal assembly. On mine the pedals are very close to the top of the footwell and the steering shaft. Might be tight. Just something else to check.
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In an earlier time, McMaster Carr listed "sex bolts" in their catalog. We thought that was a hoot. You can find them on their online catalog by searching for "sex bolt" or "sex nuts" but they are now called "binding barrels and screws." How long before the terms "male" and "female" will be expunged from our vernacular?
Those are not generally used for applications where strength is important and a quick look at some of the listings did not come up with any fine thread examples. They may be available elsewhere but I think you should be prepared to find a friend with a lathe.
Are the pedal bolts UNF (fine) threads? (Why?) I guess I assumed they were 1/4-20 UNC. As you suggest, something could be fabricated on a lathe. This would even be within the capabilities of my pathetic hobby lathe and my even more pathetic machinist skills.
I agree sexy nuts are not as high strength as conventional grade 8 nuts, but this is not a very high load application. I use these for deck hardware on my sailboat and I’m pretty sure they would rip through the cored fiberglass deck before the nut would strip.
t
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If you want to upgrade, take a look in the old Lotus-Europa website for drawings of the pedal assembly I made for my TCS. I removed the Lotus power brake system and installed tandem Girling master cylinders with a balance bar.
Tom - 74 TCS - 4605R
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I didn't say that very well! You are right, strength doesn't really have much to do with the thread pitch but on cars, most bolted joints, other than with castings, fine threads are generally the rule. For what it's worth, to me, fine threads imply more precision I associated that to strength and that is not necessarily the case. "Binding barrels" would certainly be strong enough for this application.
If you're more comfortable welding, you could always grind the old bolts off your pedal assy. and weld longer 1/4-20 bolts in their place.
All this talk about what threads has given me pause. I could certainly be mistaken about the threads but if I'm wrong, you'll figure that out eventually and adapt.
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Still reading up on removal of the brake servos.
Has anyone reported back on adding a new hole to the brake pedal and then moving the pedal assembly up?
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Thanks for reminding me. There is a thread on that somewhere here and I remember it was successful. Try some searches.
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Surf I'm glad your posting this now.
Are the drawings i the relaxed or applied position? Anything past due north 0 degrees my pedal is almost hitting
the wall. Raising up the entire pedal assembly would throw the entire rearward due to it sitting on a 15 degree angle. \
thanks for posting the angle from a rearward relaxed angle , which I thought was incorrect.
Dakazman
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If not moving the pedal assembly up, how about tilting the MC downward to align the rod to the MC? (It's been a while since I did brake work, so I don't remember if there would be clearance for tilting the MC.)
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It’s on a center fulcrum thru the the frame . The mc is on one side and the pedal assembly on the other. . It’s a direct link as far as I recall. Some mods are direct witch is what they are talking about.
Confused,
Dakazman
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Hey guys, sorry I haven’t checked in in a while. My few remaining brain cells, and the skin on my knuckles, have been devoted to restoring a 60 yo 40 ft sailboat. The car hasn’t been getting as much love as it deserves.
Regarding this brake pedal mod, I honestly have not gotten around to trying it out. It appears to be an easy solution, especially since the studs on my pedal assembly are about 1/2 inch too long. Blocking up the pedals 3/8” and drilling a new clevis hole 3/8” closer to the fulcrum would give about a 30% increase in brake force if I recall, but my recall ain’t so good, so someone should check me on that.
On the other hand, I have pretty much grown accustomed to the boosterless brakes needing to be applied with authority, although it scares the crap out of the poor technician who does my annual Mass RMV safety inspection.
Tom
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Full disclosure, I have a dual tandem master cylinder set up but I used the long factory rod to my pivot and mounting MC mounting holes so that end is the same as stock. I am already running a 5/8 bore on the front so I can't go smaller so I redrilled lower. Slight increase in travel. Big increase in pedal feel. Less effort to do hard stops and modulate. My new hole is forward of the original hole so the rod lengths doesn't need to be charged to keep the same pedal position.