Brake Servo Question

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Re: Brake Servo Question

Postby thomas » Fri Jan 15, 2021 8:53 pm

SP2482 would be for a 0.812 (13/16) inch bore size, which I thought you mentioned it was, SP2485 is for the same design master cylinder but 0.875 (7/8) inch bore.

Did you manage to get the other catalogues and the illustrations catalogue that diagram came from? :wink:

Caribougone's leaflet is excellent too, showing separating the bottle, otherwise absolutely forbidden, what I don't have is part number data for the circlip or bottle seal, which seal I imagine might be like a used piece of black chewing gum by now. Similar tandem master-cylinders abound, often with remote twin outlet or paired reservoirs, you need to watch though for correct orientation of the mounting flange, horizontal in this case, I think, not vertical. Modern bolt on replacements from the likes of Wilwood might be suitable.

I had looked into this back in 2016-2017, with a view to changing my servo-ed 0.812 single circuit system to tandem, split front-rear, but chronic more pressing bodywork issues, still ongoing, intervened. Not helped by having a spare brand new 0.812 master-cylinder and a few SP 2381 service kits for that master cylinder laid in.

Had thought a Ford AV0 rs2000 mk1 Escort type suitable, as it bolts to the same Girling Servo in that application. Also possibly some post-77 MGB/MGBGT cars might be similar but do not know the bore sizes of these BL or the Ford ones, to know if they're truly compatible. I really needed someone else to do this first, as an unwitting guinea-pig/test-pilot, rather than obtain parts on a trial and error basis, but I'm sure suppliers could provide further data on their wares to aid in a decision.
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Re: Brake Servo Question

Postby jpsmit » Sat Jan 16, 2021 2:43 am

Thanks for this information Thomas, I very much appreciate it! Yes I did get the files, thanks so very much they are very helpful.

Just did a quick measure and it is a 7/8 bore - so SP2485 it is then.

I do have a good (I believe good - looks rebuilt) MC it is just that it is for a RHD car with the lines exiting towards the engine (for my LHD car) I also have this (original?) MC which I will see if I can rebuild mostly for accuracy.

FWIW it is also a vertical mounting flange.

So, off to ebay (or suppliers to see what I can find.

thanks again and all input genuinely welcomed!
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Re: Brake Servo Question

Postby jpsmit » Sat Jan 16, 2021 3:15 am

One more brake question. According to the manuals 'some' cars had a trap valve for the rear brakes. I haven't seen a part anywhere in the bin that corresponds to what the pictures look like. Any thoughts, should I have one? and, if so, is there a picture or are they available?

thanks all!
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Re: Brake Servo Question

Postby thomas » Sat Jan 16, 2021 10:00 pm

As it's brakes I recommend you consult as widely and as thoroughly as you can. Weight the advice of anonymous bloviators on the internet appropriately. Having said that ...

I presume it's a residual-pressure RP valve. One is specified (Girling Catalogues) for the .812 TVCV single T28 (6 1/2 inch) Supervac equipped cars, but not for the .875 TVCV MKIIB twin servo equipped cars, which is what you have.

They're fitted as well as to some single-circuit drum only or drum/disk cars. And to some tandem ones, front and rear circuits. And to some tandem ones rear only. Quite confusingly almost arbitrarily.

It is just an inline connector with a internal sprung valve (essential it's connected the right way round), of varying 'hold' pressures. If a Pressure Differential Warning Indicator is fitted, both PDWA pipe inputs I'd assume must come from upstream of any RP/Trap valve(s).

You might not be able with a tandem system to detect excess pedal travel needed before any brake activation takes place of one or another circuit, i.e. the fronts can be fully-on but the backs still not coming into play due to one or another or both rear wheel-cylinder pistons, shoes and so on still moving out unresisted.

Single circuit disk equipped cars could maybe do with one in the pipe from the 4-way connector going to the rear, as the front disks won't begin to bite until all the travel in the rear brakes is taken up.

Neither the master-cylinders nor the mk11B remote servos in this application provide any residual pressure AFAIK.

If the back brakes are properly adjusted, shoes and/or drums not too worn, thus wheel cylinder pistons not having excess travel, I'd say a trap-valve shouldn't be necessary.

They can cause unwanted binding and heat, more so if a disk or drum is a bit warped. In theory disk circuits shouldn't need one. Drum brakes once in use tend usefully to have some reluctance to retract all the way due to friction, hold-down pins/springs etc. and as rear brake backplates shoes etc. develop surface corrosion.

It's something you could easily add later to the rear circuit if a garage brake-tester finds the rear service brake inefficient and the rear brake shoes and drums, wheel-bearing(s) maybe too, are all within specification.

I'd say they're (trap-valves) not necessary, a fudge and only rarely useful to mitigate other issues, wear, maladjustment... A solution looking for a problem.

Keep us all posted, it's an interesting (to me at least) discussion.

:goodluck:
Last edited by thomas on Tue Jan 19, 2021 9:05 pm, edited 1 time in total.
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Re: Brake Servo Question

Postby jpsmit » Sun Jan 17, 2021 2:26 am

This is unbelievably helpful and quite certain you aren't a anonymous bloviators (even if I knew what that was :lol: )

I very much appreciate the knowledge on this forum.

keep the info coming!
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Re: Brake Servo Question

Postby jpsmit » Fri Jan 22, 2021 4:21 am

thanks all for your advice and help. Yesterday I went out and puttered with the brake splitter. I must have turned that thing 8 different ways before I finally got it right. Tonight I was trying to make sense of the brake lines only to discover I had the servos backwards (front had to move to back and vice versa) This because the one (rear) servo has a anti flow valve from the factory for the rear brakes. In the manual this valve is described as code 186 and 190.

Looked them up to find that it is the same thing one for Vauxhall one for Envoy. I hadn't realized until now that they had Envoy/Vauxhall specific codes for the same part.

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Re: Brake Servo Question

Postby jpsmit » Wed Apr 14, 2021 2:02 am

Greetings friends and thanks for your ongoing help! I managed to trace down and order a rebuild kit on this side of the pond for reasonable-ish dollars. I found a Lotus part supplier. I have repainted the MC and cleaned the reservoir and tonight started to rebuild the gubbins.

In the attached pic you will see the rear plunger. The instruction sheet tell me how to take it apart, but, the instructions make no sense at all do I can't figure out how. More to the point, as I look at it is there any reason it need to come apart at all or do I just give it a good clean replace the rubber bits and reassemble?

thoughts and opinions gratefully received.

JP

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Re: Brake Servo Question

Postby jpsmit » Thu Apr 15, 2021 2:01 am

well, pingfukit - guess I get to clean the garage. :evil:
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Re: Brake Servo Question

Postby jpsmit » Thu Apr 15, 2021 11:49 pm

jpsmit wrote:well, pingfukit - guess I get to clean the garage. :evil:


found it, on top of a bookcase after I had cleaned out all the stuff on the floor. OTOH the garage is cleaner and I got to install an LED fixture that I had been putting off so, all is not lost. :lol: - and of course the part is found!
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Re: Brake Servo Question

Postby droopsnoot » Fri Apr 16, 2021 9:13 am

jpsmit wrote:found it, on top of a bookcase after I had cleaned out all the stuff on the floor. OTOH the garage is cleaner and I got to install an LED fixture that I had been putting off so, all is not lost. :lol: - and of course the part is found!


I was given a fuel pressure regulator the other week, it had been sitting around on a shelf for some decades so it needed cleaning up. I've got a brass wire wheel in my bench grinder, so I had a quick go and got some nice results. Then I strayed a little too close to the centre and my wire wheel, in one operation, undid the dome nut and chucked it around the garage, then undid the lock nut below it and sent that off somewhere too.

I was very lucky indeed - the lock nut landed right next to the grinder, and the dome nut on the floor just behind. If it had gone off towards the back where all the old furniture and racking is, I wouldn't have found them until I'd forgotten what they were. I'd also have had to make excuses to my mate, who gave me the regulator, as to why I hadn't done anything with it.
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