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MG MGA - Thoughts re: Sleeving a master cylinder

Hi Folks. I finally got the pistons out of my old master cylinder, and honed the bores. There is much deep pitting, which renders the Master cylinder unusable as it sits. I found a place that sells 1" OD diameter stainless steel tubing, with a 7/8" ID diameter bore. This would be ideally sized to fit the MGA master cylinder pistons. Essentially, all I would need to do is bore the cylinders out to accept the stainless steel sleeves. Once the sleeves were inserted, and drilled for the reservoir feed holes, and honed, the master cyinder should be useable. Has anyone ever attempted a home sleeving job? If so, any input would be appreciated. Anyone with machine shop skills have any idea what would be involved in machining the cylinders oversize to accept the SS sleeves? Does the bore need to be an interference fit, or could the bore be the same size as the SS OD? I may know someone with Machine shop facilities that might be persuaded to do this little job, if it isnt too complicated or time consuming. Thanks! Glenn
Glenn

They should be a light interference fit. Class FN1 force interference fit is a precision machining job (0.0003" to 0.0012" interference for 1" bore). You can not risk leaking fluid around the outside of the sleeve. A touch of Loctite may be in order as well. If the sleeve is loose, and you glue it in with adhesive, you had better be sure the adhesive will not disolve in brake fluid.
Barney Gaylord

Only 2 cents to offer...let a pro redo the mc sleeve...for me a new $450.00 mc is worth every penny.....nothing worse than coming down a steep hill and finding out that u have no brakes, call me old fashioned if u want...
Mike

Hi Mike. The problem with new master cylinders, is that the bores are cast iron, and they inevitably rust and pit, often rendering the expensive master cylinder unusable! Rather than buying another master cylinder that will also end up with rusty bores, it makes more sense (to me anyway) to install stainless steel sleeves that wont rust. This job, while requiring some (admittedly) precision machining, doesnt strike me as being prohibitively difficult, if proper machining tools are available. It would seem that the only real "trick" is in precisely aligning and then machining the master cylinder bores to an oversize dimension that will allow the Stainless steel sleeves to be a snug press fit. Once the cylinders are bored, installation of the sleeves should be relativly easy using a turned, close fitting mandrel, and a hydraulic press. OR, I am perhaps erroneously oversimplifying, and this is a terribly complex, NASA aerospace grade machining job! I look forward to other comments, and appreciate the input thus far. Cheers! Glenn
Glenn

Cool the 1" diameter stainless steel sleeve from 65dF to -250dF and it will shrink 0.002" and slip right into a bore with FN1 or FN2 force interference fit.

Boiling temperture (dF) of cryogenic liquids at one atmosphere pressure (14.7 psi):

Natural gas - 240 (widely available if you cool your own)
Nitric oxide -240 (nasty stuff, not Nitrous oxide)
Oxygen -297
Argon -302
Carbon Monoxide -313
Air -318
Nitrogen -320

Easy if you do it every day. Otherwise leave it to the pros.
Barney Gaylord

Glenn-
Expanding on Barney's comments, and making it a bit more useful for DIY, you can get -108F approx., by using dry ice in alcohol. Must be 95%+ alcohol (ie not rubbing alcohol), or it will freeze up. You can easily heat the casting to 300-400F or better in your wife's oven, to obtain a large temp differential. Calculations for expansion of metals can be touchy, as the coefficients vary a lot with temperature - you can't just take typical "room temperature" coefficients and use them for these calcs. The coefficient for steel is about half the room temp number at -300F.
Using "7/8 ID" stainless could be a problem, as the ID is likely to be off from the true "7/8". Machining very light cuts from stainless is frequently very difficult, as the material work hardens, causing large errors. If the SS tube is not seamless, more trouble will come from the welded seam. I would suggest brass tube for DIY jobs of this sort. All brass tube is usually seamless due to the production process, it is much easier to machine, and the expansion coefficient is larger, giving greater differential expansion/contraction. I would suggest a brass installation mandrel, so that you can cool the sleeve and mandrel together, thus giving a lot of thermal mass, and preventing the sleeve from heating up when halfway in.
FRM
FR Millmore

Glenn:

It's your life...Take what chances you want with it.

There are two points that you make that I would like to comment on. First, it is not inevitable that the bores of the M/C pit to the point of unusable. This is true of all cars. I have the original still on my car and I have another that I removed from a car years ago. Neither need re-sleeving... The extent of corrosion depends on how much moisture has entered into the brake system. If the fluid is changed every couple of years or so, and the car (or stored M/C)is in a dry location, the amount of water in the system is greatly reduced.

Second, like the bushings in the trunions or the king pins bushings in MGB the swivel axles, when done properly the sleeves will require reaming to size. This is because the i.d.'s will shrink when pressed into the body of the M/C. Because the M/C pistons float on concentric rubber seals, the reaming is not as critical as the brass bushings with steel inserts. Therefore, if one had the experience, it might be possible knowing the wall thickness of the sleeves, the o.d. of the sleeves, and the i.d. of the bored M/C to make sleeves that would wind up very close to the required bore. However, this requires experience and machining skills. Get it wrong and fluid will leak past the sleeves and/or the pistons will seize in the bores. Either failure is potentially life-threatening since it involves the braking and/or clutch systems.

Just having an experienced shop doing the work does not guarantee that either will happen, but it significantly improves the odds that the job will be done correctly. You are not paying for the amount of actual work so much as the machinist's knowledge of how to do the job right. Call it automobile mrchanical R&D expense...

Brass would not be a choice of materials that I would make for the sleeves. Easy-to-machine translates to fast wear...

Again, it is your life...You ultimately make the choice - not the members of the BBS.

Steve
Steve Brandt

Hi Steve. Your points about safety are well taken. I in fact do very much value my life, and know very well the consequences of a complete brake system hydraulic failure, and particularly in a single master cylinder brake system setup. If this sleeving endeavor cannot be done with with absolute certainty about sucess, with complete hydraulic system integrity and safety, then I will not proceed, period. I do agree with you that water in the hydraulic system is the primary cause of pitted master cylinder bores, and also agree with you that regular brake fluid changes would help alleviate or eliminate the problem. Having said that, I have at least 5 old master cylinder units (purchased inexpensively at flea markets) that are pitted beyond redemption, unless they are fitted with sleeves! Regarding brake fluid changes: I know full well that many people simply would not be willing to change their brake fluid, because it is a p.i.t.a. job! I also agree with you that brass is not the ideal material to sleeve the cylinders with. FR, and Barney, thanks for your technical wisdom and specific insight into stainless steel sleeves, and the potential pitfalls involved. FR's comment about seamed vs seamless tubing in particular is a possibility that had entirely escaped me! I certainly appreciate people's safety concerns, comments and ideas regarding the sleeving of master cylinders, and look forward to more input. As always, it seems that there is more to any endeavour than meets the eye at first glance! Perhaps my DIY ideas will need to be modified to HID (have it done!) Court is still out! Cheers, Glenn
Glenn

Glenn
maybe you can find some useful advice at that link:
http://www.whitepost.com/brake.html

toni
toni

Glen, The point has been well made that the sleeve has to be an interference fit in the machined casting and I think you can achieve this by shrinking the sleeve and heating the casting and provided you can do this there will be no problem. Loctite in this situation would frighten me as well, I like a solid mechanical interference. The problem lies in that the sleeve in itself is a piston and hydraulic pressure will act on the annulus between the 1" outside and 7/8" inside diameters. giving an area of about .165 ins. Every time the brake is depressed if a hydraulic pressure of 500psi is generated an 82lb end load will be generated trying to force the sleeve back out again and if this happens the pedal will go to the floor. I'd rather do this work myself than entrust it to others but you must be sure that the fit is solid. I addition I believe that the inside of the tube will need final finishing after assembly. You will have to measure the original bore before opening out and then hone finish.
Iain MacKintosh

Hi Iain. I dont understand how the sleeve could become a piston, since the sleeve would be pressed in flush with, and tight to the bottom of the bore. Perhaps I am wrong, but I would think that the press fit of the sleeve, and the tight circumferential fit of the sleeve with the bottom of the casting would prevent hydraulic fluid from acting on the annulus area. Even if there was hydraulic pressure there, the piston retaining piece bolted to the casting would prevent the sleeve being forced out of the bore, would it not? Perhaps I am missing something here. Could you please elabourate? Thanks! Glenn
Glenn

I thought you might come back on this one !! You are not correct in assuming that hydraulic pressuse won't act on the end of the sleeve... it will find its way in and act on its annulus to make it a piston travelling the opposite direction to the main piston. Now 80 odd pounds is not a lot if my guess at 500 psi is at all near the mark but it does emphasise the need for a good shrink fit. Now, I don't know the construction of the other end but if the sleeve is full length, and it will be, and the piston retainer is bolted to the cylinder casting and contacts the end of the sleeve then there is no fear. If it were me I'd go for it.
Iain MacKintosh

Hi Iain. Thanks for the clarification, I see your point! You are correct about the pistion retainer being bolted to the casting. My MGA and this forum are a continuous and amazing learning experience! One cannot help but pick up a broad spectrum of information, technical knowledge, working physics, and assorted trivia. By the time I am old, feeble, and on my death bed, I will perhaps truly be a cesspool of knowledge! lol. Thanks again! Glenn
Glenn

All this talk makes me glad im using DOT 5 fluid.....but I do agree that a fluid change every other year will keep moisture in the brake system a non problem.
Mitch Smith

I'm not sure what the use of DOT 5 fluid has to do with this didcussion. If it were me and on any 50 year old car I'd certainly be using DOT 5.1.
Iain MacKintosh

Gleen,
Have a look at Apple Hydraulics. They sleeve your cylinder in brass for $75 per hole. Mine has been fine for four years.
Jim
James Wiebe

Glen,

Why not ask Bob Grunau to do it for you. I'll bet its much more cost effective than trying to jury-rig some setup yourself - and probably safer too.

Bob is a professional engineer in Mississauga and makes his living of making prescision after-market MG parts, like high-tensile half-shafts, spin-on oil filter adapters and the famous Alfin brake drums, to mention just a few, all of which are re-sold by Moss, Abingdon, and other MG stockists.

Bob can be reached at [905] 274-4136, www.grunau.garage@sympatico.ca.

Gord Clark
Rockburn, Qué.

Gordon A. Clark

Casual comment here, just for information. Dot 5.1 fluid is not silicone fluid. It is closer to DOT 4 in chemical make up, and it will eat paint.
Barney Gaylord

The original topic of this discussion was corrosion in the master cylinder. Using DOT5 fluid ( which is not hydroscopic) would have prevented the corrosion in the first place. Seems pretty relevant to me.
PS: dot 5.1 is borate ester based.....higher boiling point, absorbs less water but still a good paint stripper. Im going to stick with DOT 5 on my 46 year old car.
Mitch Smith

This thread was discussed between 04/02/2006 and 09/02/2006

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