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All instructions I have seen regarding the rebuild of IIB Girling boosters show a circlip on the main hydraulic cylinder
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I have just dismantled and found on all 4 units no such circlip or evidence of a groove or witness mark is this a change on units installed on 73 Europa specials and should ones be installed if so How?
 

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All instructions I have seen regarding the rebuild of IIB Girling boosters show a circlip on the main hydraulic cylinder
.
I have just dismantled and found on all 4 units no such circlip or evidence of a groove or witness mark is this a change on units installed on 73 Europa specials and should ones be installed if so How?
Are you referring to the circlip #7 on the control piston? I don't have a Mk IIB servo apart at the moment but a friend is in preparation to rebuild his in a couple of weeks I can ask him when he has his apart.

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Discussion Starter #3
Are you referring to the circlip #7 on the control piston? I don't have a Mk IIB servo apart at the moment but a friend is in preparation to rebuild his in a couple of weeks I can ask him when he has his apart.

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No not on control piston. But according to the instructions I have seen on the main piston somewhere between #11 and #15. This instruction sheet looks much better than one I have and does not show a circlip approx size if 3/4"
 

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Discussion Starter #4
While asking your friend about this circlip. Also find out if he has the "Major Overhaul Kit" if so where did it come from. I have tried and never been able to access a source. All sources ask for the Number on 5/8 hydraulic but all of mine show only the letter "B" and with that they all refuse to supply?
 

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While asking your friend about this circlip. Also find out if he has the "Major Overhaul Kit" if so where did it come from. I have tried and never been able to access a source. All sources ask for the Number on 5/8 hydraulic but all of mine show only the letter "B" and with that they all refuse to supply?
There is a Youtube video of someone disassembling a Mk IIA Girling servo and he shows how to remove the circlip that you may be talking about at the 25 minute mark. That circlip is secured inside the bore of the hydraulic unit. The Mk IIB servo apparently does not have that circlip. We'll know for sure when my friend starts his rebuild. The Europas have the 5-1/2" servo cannisters.


He is ordering his rebuild parts from Paul Matty in the UK.
https://paulmattysportscars.co.uk/product/elan-2-servo-repair-kit-1970/
 

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Watched the video, it has been 30 years but I recall no such clip in my band clamp style servos. Must be a change from the bolted flange style to the band clamp style
 

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Discussion Starter #7
Watched the video, it has been 30 years but I recall no such clip in my band clamp style servos. Must be a change from the bolted flange style to the band clamp style
Watched the video, it has been 30 years but I recall no such clip in my band clamp style servos. Must be a change from the bolted flange style to the band clamp style
Thanks for feedback. The friend; which type of car is he working on. Europa or Elan? All of my Europa have originally manufactured with a band secured with a welded closure plate. When rebuilt find a screw clamp connection. I also from a friend two Elan servos which I understand have a different set of specifications, bore, boost rate, etc.only to be taken apart if really required (welded band).
 

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Discussion Starter #8
Quick check of the Paul Matty site shows only a rebuild kit for S2 no mention of T/C which may or may-not (most likely) be comparable.
 

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Europas had smaller diameter diaphragms

There were different ratios also, but I cannot recall what went where
 

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1972 Europa TC, 2011 Exige S RGB
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My Europa TC has two boosters. The booster for the front discs is 2 times boost and the one for the rear drums is 1.5 times boost based on the area of the two sides of the piston. I don’t know if they are the same as the TC Specials with larger rear drums. The rebuild kit did not have proper seals for both sizes, so I had to reuse one of the old seals. This is based on my memory(?) of forty years ago.
 

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TC/TCS Europa brake boosters all have the same part number which implies that they can be interchanged and have the same boost ratio. I'm not too clear how a unit with the same bore and vacuum canister size can have different boost ratios. Hopefully a hydraulics expert can explain.

My friend has an Elan Plus 2 and is using two 5/8" bore/5.5" vacuum pot servos from a Europa.I may be wrong on this but looking at the Plus 2 parts manual, the Plus 2 apparently uses either one or two 5/8" bore, 7" vacuum canisters (this is looking at the canister cover which has three separate indentations). My Plus 2 S130 came with one 7" servo. I'm not sure if the rebuild kit that Paul Matty sells is for the 7" unit or the 5.5" unit. Next time my friend calls Paul Matty, I'll have him confirm. It's also strange that they don't have a servo rebuild kit for the TCs but only the S2s.

Picture 1 is the parts page for the TCS brake system
Picture 2 is the parts page for the Plus 2
Picture 3 shows the difference in size between the 7" Plus 2 servo and the 5.5" Europa servo

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Plus two servos are different from each other but not in the way you might think

THe front one has its band rotated so the clamp is not at the top to avoid cracking the the bonnet. Ask me how I know....
 

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TC/TCS Europa brake boosters all have the same part number which implies that they can be interchanged and have the same boost ratio. I'm not too clear how a unit with the same bore and vacuum canister size can have different boost ratios. Hopefully a hydraulics expert can explain.
Don't rely too much on part numbers for accuracy.
The "Hydraulic Body" (part 42 from your post above) has an identification number cast into it. One of mine says "5/8 Girling" and the other one just says "Girling". I did not notice the difference when I removed them in 1980 and found that the rebuild kit fit one and not the other one, so I had to figure out which one was which.
I'm no hydraulics expert, but I will try to explain:
The boost is controlled my the relative diameters of the two sides of the "Control Piston" (part 2 from your post above). I don't remember the exact sizes, just the ratios. If Control Piston is centered, then the system is in equilibrium. That is: the hydraulic pressure times the piston area on one side of the Control Piston equals the hydraulic pressure times the area on the other side of the Control Piston. So the hydraulic pressure on either side is in the same ration as the piston area. In our application, the hydraulic pressure from the brake peddle is pushing on a larger piston area than the hydraulic pressure going out to the brakes. Therefore, we have boost.
If the Control Piston is offset on one side or the other, it allows either outside air or engine vacuum into the far end of the "Diaphragm" (part 31) via the "Vacuum Pipe" (part 36), moving the Output Piston to apply more or less hydraulic pressure to the brakes.
My Europa is a TC Federal and that is the way that it came from the factory. Your application may be different.
Good luck. When the stock brakes are working properly, they are wonderful.
 

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Discussion Starter #14
Plus two servos are different from each other but not in the way you might think

THe front one has its band rotated so the clamp is not at the top to avoid cracking the the bonnet. Ask me how I know....
Don't need to ask I am sure you discovered why.
 

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Discussion Starter #15
Don't rely too much on part numbers for accuracy.
The "Hydraulic Body" (part 42 from your post above) has an identification number cast into it. One of mine says "5/8 Girling" and the other one just says "Girling". I did not notice the difference when I removed them in 1980 and found that the rebuild kit fit one and not the other one, so I had to figure out which one was which.
I'm no hydraulics expert, but I will try to explain:
The boost is controlled my the relative diameters of the two sides of the "Control Piston" (part 2 from your post above). I don't remember the exact sizes, just the ratios. If Control Piston is centered, then the system is in equilibrium. That is: the hydraulic pressure times the piston area on one side of the Control Piston equals the hydraulic pressure times the area on the other side of the Control Piston. So the hydraulic pressure on either side is in the same ration as the piston area. In our application, the hydraulic pressure from the brake peddle is pushing on a larger piston area than the hydraulic pressure going out to the brakes. Therefore, we have boost.
If the Control Piston is offset on one side or the other, it allows either outside air or engine vacuum into the far end of the "Diaphragm" (part 31) via the "Vacuum Pipe" (part 36), moving the Output Piston to apply more or less hydraulic pressure to the brakes.
My Europa is a TC Federal and that is the way that it came from the factory. Your application may be different
Good luck. When the stock brakes are working properly, they are wonderful.
All 4 units I have two each from JPS Specials. All have same identifiers cast in "5/8 Girling" with the end stamped "B" I also have two which are from Elan and they are 0.70 diameter. So difference is 0.70 to 0.625 or 0.075" (75 thou.) in bore more volume versus more pressure. Typically speaking a larger diameter diaphram would equate to greater pressure applied on boost ratio of square inches of surface and would also be effected by the engine amount of vacuum, Way too many variables to contemplate and establish a Boost Ratio.
 

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Discussion Starter #16
All 4 units I have two each from JPS Specials. All have same identifiers cast in "5/8 Girling" with the end stamped "B" I also have two which are from Elan and they are 0.70 diameter. So difference is 0.70 to 0.625 or 0.075" (75 thou.) in bore more volume versus more pressure. Typically speaking a larger diameter diaphram would equate to greater pressure applied on boost ratio of square inches of surface and would also be effected by the engine amount of vacuum, Way too many variables to contemplate and establish a Boost Ratio.
Also not certain when the change in size of brake shoes on rear would affect the fact of same or different size in boost ratio for purpose of balance therefore different part number.
 

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All 4 units I have two each from JPS Specials. All have same identifiers cast in "5/8 Girling" with the end stamped "B"
My "5/8 Girling" also has a "B" stamped into the end. The "Girling" has a "21" stamped into the end.
We are talking about a very small sample of three cars. I wonder how other TC and Special were equipped. Are there any other Europa owners out there that know how their car was originally equipped? Perhaps this conversation would be more useful on the LotusEuropa group? OOPS! I see that you just posted that question.
 

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Rick, I don't doubt your experience with your booster rebuild. Are you sure that your boosters came from the factory with two different servo units. If you're not the original owner,perhaps a PO swapped out the units substituting one of the "correct" servo units for the one that you currently have. For a system as critical as braking, I can't see the factory installing different sized boosters that can be swapped around with potentially serious consequence and still have the same part number.

All of the Europa servos that I have (6 or 7) all have 5/8" and Girling stamped on the flange area and have the letter "B" on the end. Your servo that has "21" does not sound like a stock Europa TC/TCS unit. If the "21" equates to bore size in mm, just speculating, that would equal to 0.828", much larger than 0.625" for the 5/8" bore

Eurobill, did you determine if the MkIIB servos have the circlip ?

I also found a couple of original Girling service kits for the MkIIB in the original boxes.

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Rick, I don't doubt your experience with your booster rebuild. Are you sure that your boosters came from the factory with two different servo units. If you're not the original owner,perhaps a PO swapped out the units substituting one of the "correct" servo units for the one that you currently have. For a system as critical as braking, I can't see the factory installing different sized boosters that can be swapped around with potentially serious consequence and still have the same part number.
I am not the original owner. I bought the car when it was a year old (1974). It was always local during that time and I know the repair shops that worked on it. None of those shops did any brake work. It has not been in any repair shop since I bought it. The original owner was incapable of any mechanical work. There was no physical evidence that one of the boosters had been changed. That does not eliminate the possibility that Lotus used whatever they had in stock to build the car, the importer changed/repaired something, or the original dealer did something strange.
Sorry about taking this thread so far off topic. I do not remember the anything about the circlip one way or the other.
 

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Puzzling indeed. Not enough data to make any definitive conclusion yet. During my long slow restoration effort on 3923R, I was initially was going to delete the boosters and install a 0.75" tandem master cylinder, which I did. This discussion has got me intrigued enough to tackle my own servo rebuild since I already have the rebuild kits.
 
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