View Full Version : Brake MC Probs.

Newbie Joe
09-13-2003, 10:03 PM
Hey all,
I just replaced both front calipers and rear wheel cylinders in my new used 75 TR6, which had been sitting in a damp garage for 7 yrs. I also detirmined that the MC wasn't working so i got a new one. Now i want to put it in but im not sure how to bleed the master cylinder? How does one go about doing this? Thanks for any help.

09-13-2003, 11:54 PM
Am sure you'll get responses more informative than mine, but my first guess is you'll bleed the system the same way when you replace the MC as you did when you replaced the wheel cylinders.
I will be replacing both rear wheel cylinders on my 7 this weekend. (I'm off Sun. and Mon.) I have access to a vacuum bleeder and will be using that, which is sort of like cheating at peek-a-boo. The last time I tried the traditional buddy pumps the pedal system I ended up doing it over with the vacuum unit to get it right. Good Luck images/icons/smile.gif

Dave Russell
09-14-2003, 12:09 AM
There are a couple of ways to do it.
Fill the MC, connect a temporary hose (Hoses) to the outlet, place other end of hose over MC filler opening, & pump until no air comes out.

Or -- install & fill MC, Leave outlet lines loose & pump MC until no air comes out. Tighten lines & proceed as for regular bleeding. Second way is more messy.

Mark Beiser
09-14-2003, 12:39 AM
Hook it all up, fill the MC and bleed it like you would for any other brake repair. I HIGHLY agree with Dale, get a vaccum bleeder.

Even the cheesy $20 plastic vaccum bleeders sold at discount auto parts stores work great. Brake fluid is cheep keep adding fresh fluid untill you are absolutely sure the system is completely bled. Use only fresh fluid from the bottle, don't be tempted to top up with the stuff you are sucking out with the pump.

09-14-2003, 02:03 AM
And DON'T USE DOT 3 or you will end up doing it all over again 2-4 months from now.
DOT 3 eats British rubber seals.

Jim images/icons/smile.gif

Izual Angel
09-14-2003, 02:11 AM
So, what kind of brake fluid do you use?

Mark Beiser
09-14-2003, 02:27 AM
Hmm, I always used DOT3 when doing repairs on a system, never a problem.
Many peopole have had nightmarish problems with Silicone brake fluid though, DOT5, when trying to convert from DOT3 to silicone in an existing system. They don't mix well, and anything made of rubber is the victom of the conflict.

I saw something once about bleeding some sort of alchohal through the system before putting in the silicone fluid.

I like silicone fluid, but only use it if replacing all of the hydrolic components in the system. Master Cylinder, calipers, wheel cylinders, and proportioning valve, and flushing out the brake piping.

Dave Russell
09-14-2003, 03:13 AM
XK4 & Mark,

A couple of quotes from other sources;
"Why canít I use generic brake fluid in my British car? British brake & clutch systems use natural rubber components which are only compatible with vegetable based brake fluid. American brake & clutch systems use synthetic rubber components which are only compatible with mineral based brake fluid. The only vegetable based brake fluid commonly available in the US is CASTROL GT LMA.Use of improper fluids or mixing of fluids can lead to complete failure of brake and clutch hydraulics. Use of any fluid other than CASTROL GT LMA violates all warranty on brake/hydraulic parts.
Check this out!!! Sent a note to Castrol website last nite! Got this back this am!!
Thank you for your inquiry. Castrol brake fluid, GT LMA is a DOT 3- DOT 4 with a glycol ether ester base which is considered to be synthetic in origin, although it is not advertised as such. Castrol GT LMA, which exhibits low moisture activity and exceeds the most severe performance and safety requirements, is the fluid of choice. For completely reliable brake operation, maintain the required brake system service schedule and use Castrol GT LMA Brake Fluid. The "scoop" is.... Lucas Girling is the brake manufacturer, and Castrol is "Girling Approved"."
DOT 3 Glycol Based: corrosive to paint & rubber, highly water absorbant.

DOT 4 Glycol Based: corrosive to paint, does not absorb water as readily as DOT3, has a higher boiling point than DOT 3, can be mixed with DOT 3.

DOT 4/3 Glycol/Poly-glycol Based: Labeled "Synthetic" and "exceeding DOT 3 and DOT 4 specifications", it is still corrosive to paint, but highly non-absorbent of water, and has a higher boiling point than DOT 4. It can be used in systems having ABS, and can be mixed with standard DOT 4 and/or DOT 3 fluids."

[ 09-14-2003: Message edited by: Dave Russell ]</p>

Mark Beiser
09-14-2003, 10:30 AM
I thought the use of "natural rubber" in the brake systems was something that died out in the '60s?
I had actually forgotten about the old natural rubber problem. Definatly need to watch out for that when dealing with brake systems that have origonal components, or components that are NOS parts. New parts and rebuild kits should all be made from more modern materials though.
I wonder how many cars are running around with 3 or more types of brake fluid in them, not sure I want to think about that to much...

09-14-2003, 12:13 PM
<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by Mark Beiser:

I saw something once about bleeding some sort of alchohal through the system before putting in the silicone fluid.

You are correct sir, if you are going to switch over to Silicone DOT5 after a complete brake overhaul, it is a very good idea to pump some denatured alcohol through the system. However - all rummer parts in the entire system should also be renewed and its a good idea to blow some air through the system through the lines and let it sit for a day before adding new DOT 5, just to be certain that ALL of the alcohol is gone from the system. I did this procedure on my 67 EType when I converted to DOT5 and had years of trouble-free service.


Newbie Joe
09-14-2003, 05:33 PM
When I got the car the MC was entirely dry. However when i tried to get it to work i used Dot 3. Which fluid should i use now? Thanks coolgleam.gif

Mark Jones
09-15-2003, 12:17 PM
I would use DOT 4 to be on the safe side.

09-15-2003, 08:35 PM
I've been using DOT3 on my LBC's since the early 70's with no problems at all (at least none related to the brake fluid). Austins, Jags, Triumphs - all DOT3. I recently replace the brake servo on my GT6 with a Lockheed unit (also British - from the London taxis) as the original Girling is no longer available. The instructions with the Lockheed unit specifically said not to use DOT4 and only to use DOT3.

If people have been having problems with brake systems using DOT3, I'm thinking the source of the problem may lie elsewhere. Lately I've been using Ford spec DOT 3 as it has a 550 degree boiling point (vs about 450 for regular DOT 3), and its much cheaper than DOT 5.

09-16-2003, 09:35 AM
Maybe this will add to the understanding (or the confusion) on DOT3 vs DOT 4. I seem to remember reading somewhere that the old British specification for DOT 3 is equivalent to US DOT 4. I would not use US DOT 3, I stick with Castrol LMA, it makes my LBC's brakes happy. graemlins/england.gif