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MG MGA - Master Cylinder Rebuild

I know we've probably been over this many times but I'm unable to find an answer in the archives.

I converted to Dot 5 over ten years ago when I did a total body off restoration.

I just received back my master cylinder from Apple Hydraulics with the brass sleeves installed. I know all of the talk about how they won't guarantee it when Dot 5 is used. When pinned down they say it is because the rubber seals don't hold up because some manufactures use inferior rubber.

Which is it? Do the brass sleeves have an adverse reaction to Dot 5 or is there a problem with the rubber?

I want to stay with Dot 5 and may decide to buy a new cylinder instead.

Any advise?

Joe W.
Joe Wiley

Couple of things. The master cyl/wheel cyl reconditioners moved from brass to stainless steel here in Oz many years ago. The latter (and the brass too) effectively rules out the need to use silicone brake fluid. I used to use it in my various MG's about 30 years ago but had a lot of trouble with rubber seals swelling and hoses delaminating.
Barry Bahnisch

If there were a problem with the rubber it probably wouldn't matter if you had brass or stainless sleeves or if you had a new unsleeved cylinder. I think the main problem is that DOT5 is thinner and will leak out easier.

I had mine sleeved in brass by Apple about 6 years ago, and have used DOT5 since then. I have had a problem with weeping where the bottom of the cylinder stays slick with fluid, but it has not been a big enough problem to get me to remove and replace it. I just wipe off the bottom of the master every month or so. None has dripped onto the paint, and I have only added fluid once in those 6 years and then just a few drops.

I think there was a problem in some of the early formulations of silicone fluid having to do with excessive swelling of rubber parts but I believe they have that under control now. Normal glycol based fluids will cause rubber to swell, and as I understand it, swelling agents have to be added to silicone fluid to match the characteristics of glycol. The DOT tests actually specify both a minimum and a maximum amount of swelling. http://www.nhtsa.dot.gov/staticfiles/DOT/NHTSA/Vehicle%20Safety/Test%20Procedures/Associated%20Files/TP-116-04.pdf

Jeff Schultz

The original rubber compound used in the brake systems was called "SBR" it is not compatable with Dot 5 and swells greatly.You would most likely have trouble if you managed to find any NOS rebuild kits. I rebuilt our "A" in 1996 and have had no problems with the DOT 5.
J Heisenfeldt

Jeff, The NTSB is doing work on their site and the link you provided is down. Could you add some further information to help those less computer literate to get to the supporting article re: standards for rubber swelling?
Jacqueline Peabody

Google has it cached in html form here. http://209.85.165.104/search?q=cache:xf80rup3B-EJ:www.nhtsa.dot.gov/staticfiles/DOT/NHTSA/Vehicle%2520Safety/Test%2520Procedures/Associated%2520Files/TP-116-04.pdf+%22dot+5%22+ethanol+isopropanol&hl=en&ct=clnk&cd=6&gl=us

Don't know if that link will work as this forum has a problem with some links with punctuation mark in them. If it doesn't, then just google for "TP-116-04" and click on view as html.
Jeff Schultz

The comment by J Heisenfeldt is correct. The original pieces were not compatible with any "American" brake fluid. The fluid from the 60s was Girling only. Any of the normal fluid from the period ate up the English seals. I use only DOT 5 in my cars. It is a bit more difficult to deal with but considering the location of our master cylinders I won't use the regular "paint thinner". The DOT 5 won't eat the paint off the heater shelf.
R J Brown

Since going back to "traditional" brake fluid I stuff some "rag" under the master cylinder in my MGA's (where it can't be seen) so the start of any future weeping will be absorbed (instead of removing the paint as so often used to be seen on MGA's!).
Barry Bahnisch

Going back to one of my original questions, does the brass have an adverse reaction to the DOT 5? So far I've only heard about the swelling of the seals. I have been using DOT 5 for years before the rebuild with no problems either. My concern now is stories I've heard from individuals (other than this board) who are probably only passing on what they've heard somewhere.
Joe Wiley

There should be no reaction between the silicone and the brass. The only negative I have heard is that some have experianced silicone fluid seeping in between the sleeve and the bore. This results in a small amount of fluid weeping out between the sleeve and the bore at the pedal end of the cylinder. this could likely be eliminated by coating the sleeve with something like Loctite shaft and bearing sealer before pressing it in. When I did ours I did not sleeve it, just honed out te small pits in the bore and put it together. 12 years, no problems.
J Heisenfeldt

I had my master cylinder sleeved in brass a couple of years ago. At that time I installed all new hoses and wheel cylinders and converted to DOT 5 fluid. I've had no problems with fluid leakage anywhere, just had to put up with the extra effort required to bleed all the air after refilling the system. My seals for the master cylinder were sourced from the local Moss distributor and are holding up fine. I believe there is supposed to be a benefit of DOT 5 in reducing the tendency of the fluid to trap water from the air and thus accelerate corrosion inside the wheel cylinders. Certainly most of mine were "frozen" having used DOT 3 for many years previously. Hope this helps with your decision.
Tom Heath

Thanks everyone. I have also been using DOT 5 since my total restoration several years ago. I used all new lines etc. during the resto. but didn't have the master sleeved at that time. I just honed it as best I could and it worked for many years with only a small weeping of fluid. I thought I would do the sleeves this winter while I wasn't driving it.

Now I will put it all together with new seals etc. from Moss and fill 'er up once again with DOT 5. I'll never go back to the "paint stripper" DOT 3.

Joe
Joe Wiley

This thread was discussed between 09/03/2008 and 11/03/2008

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This thread is from the archive. The Live MG MGA BBS is active now.