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Bleeding the Brake Master Cylinder

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KVH

KVH

Obi Wan
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On my TR4A, if I replace the brake master cylinder seal with rebuild kit, will I have to bleed all the wheels again, or is there a way to bleed just the master cylinder?

Also, I'm unclear on the purpose of the boot grease. I assume that's to keep the boot flexible and clean. But is there a reason I can't just put any grease in there? Why the requirement of "boot grease." I'd think any wheel bearing grease or even petroleum jelly would work. (I clearly can't keep my greases straight).

Thx again.
 
The FLAPS sell little sachets of 'brake and caliper grease' -- that is what I use. Nice in that the packets are cheap and you don't have to buy a pound of grease for such a little job.

Yeah, you'll be bleeding all around.
 
I don't think most petroleum-based greases would do the rubber boot (or, if it works its way inside the cylinder, the seals) any good at all. Where did your kit come from, BTW? Most TRW (formerly Lucas/Girling) kits have a little packet of the red brake grease included.
 
Bleed all the wheels -- starting with the one furthest from the master. That's left-rear on a TR3, don't know about a 4A. Keep it up til you see fresh fluid. Then the other rear - then the right front - then the left. The last three will go much more quickly than the first one.

Brake grease, like brake fluid, is specially formulated not to destroy the rubber. No petroleum anything must ever be used near any of your rubber brake parts.
 
tdskip said:
Plan to bleed all the wheels as you don't know where the air got to.
Click to expand...

Should of also indicated that you want any moisture the fluid gathered while the lines were open out.
 
Just about every master cylinder I've rebuilt or replaced has not required bleeding at all four wheels. I bench bleed first, and then finish by bleeding at the line(s) that screw into the master. Just crack the line as if it were a bleeder screw. Tapping on the line itself while the line is cracked open helps dislodge any air in the upper portion of the line. Of course, if you want fresh fluid in the rest of the system, then you have to bleed at the wheels. Also, you have to be careful of the fluid dripping out of the master while bleeding...it's bad for the paint. That's the reason for the bench bleed...less fluid running all over the place.
 
You CAN bleed a master cylinder from the car without bleeding the whole system, but it's really not a good idea to do so. Sure it will be harder but in the long run you will have fresh fluid in the system and wont have to worry about whether or not there is still some air in the system or is the brake fluid still good. I good flushed out system will last you a lot longer than one kinda, sorta cleaned out. Plus you really don't want any crud from the old system in your new master cylinder.
grin.gif
 
Yes, Andrew, I found that little packet and used it when I replaced the seal. I really had a bad leak. My old seal looked like it had been deteriorating. Does that happen just from sitting long periods? I replace it about 6 years ago.

Interesting: the repair kit cost $12. But there isn't anything in there other than a new circlip which isn't critical (since the old one is good for another thirty years), a new seal for the reservoir cap, the grease packet and the primary piston seal. Years ago they would give you a new spring and even that little nylon piece.
 
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