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TR4/4A TR4A Brake Master Cylinder Internal Spring and

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K

karls59tr

Obi Wan
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Piston assembly. How do you remove thepiston and spring to change out the rubber seal? Do you pull back the spring far enough to pry back the flap in the metal sleeve(or push the flap in?) to release the rod and piston?
 
Use a small screwdriver to reach through the spring and pry the flap up, just enough to slide the sleeve off the main piston.

Then slide the rod to the side of the sleeve, where it will slip through the large part of the keyhole-shaped hole.
 
Thanks Randall. I see you have a totalled TR3A. What are your plans for it...eventual resto?....parting it out?...saving spares for daily driver? How bad was it hit?
 
The damage was pretty severe. The front wasn't all that bad, but the body buckled at the B-posts and the trunk was collapsed. I later discovered that the front suspension was ripped off the frame, too. Unfortunately I didn't take any photos at the time, but here's one I took later:

DSCF0080.jpg


It's already mostly stripped for parts, and a few things got installed on the 56. I've still got the carcass, just a few more things to pull off before it goes for scrap. I'm going to have to cut it open to get the gas tank out, and I guess I'm reluctant to start cutting on the old girl. The panel above the tank is one of the few straight areas left, but no one seems to want it.
 
Hi Randall I got the brake master innards apart. The repair kit contains a seal for the front and a larger one for the piston and also a very small ring shaped rubber seal. Do you know where the latter seal would go? There was no old seal like it to replace unless it is to replace the small wavy metal ring that is near the front castellated type piston? Too bad about your 3A...glad to see you have another 3 to put on the road. Karl
 
Not TR, but the Dunlop cylinder on my Jag has a small groove on the piston at the pushrod end.....kind of like a wiper.
My manual calls it an o-ring.
Some pistons don't have that.
 
Beats me, unless you are talking about the "valve seal" in this diagram. Early Girling cylinders had the O-ring that TOC is talking about, which the diagram calls an "end seal", but it was officially deleted around 1960 (even for pistons that have the groove) and I've never seen it included in a rebuild kit.
 

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Randall,

Any idea why they deleted the end seal (any TSB's on it)? Sure seems like a good idea having one to keep fluid from immediately draining to your feet when the main seal fails. Having only worked with TR4As and early Spitfires, I've only seen brake and clutch master cylinders without the groove and second seal.

Scott
 
It's a mystery but it's good to know that Its not needed for the rebuild. The little O ring that I found in the kit was not big enough to be an end seal that was mentioned....it's actually about the size of the spring washer in the picture???
 
Well, although that diagram makes it look bigger, the end seal is about the same diameter as the wavy washer though of course it is much longer. And it is important, should be included in your kit. If not, I'd say you've got the wrong kit (or it's defective), which could also explain the mystery O-ring.

I've seen a note about deleting the end seal, but can't seem to find it at the moment. But as I recall, it didn't say anything about why, just to leave the groove empty (if present). Gazing into my crystal ball though, I would guess that preventing a leak when the main seal failed was exactly the reason they removed it. The main seal is shaped such that the pressure of the fluid against it helps force the seal against the cylinder, while the O-ring shape would do just the opposite (fluid pressure would tend to force it away from the cylinder). That could potentially cause it to seal when the pressure was low (ie brakes lightly applied for a normal stop) and then not work when the pressure was high (panic stop). A very undesirable attribute, especially with single-circuit brakes. But that's just a WAG.
 
Karl - if no one has mentioned this make sure to be ready for the spring to, well, spring once released and try not to bend the spring while moving it around. It isn't hard to do - ask me how I learned that.
 
I just found out what you mean.Lol. bit of a trick to get everything assembled but it worked out. I was surprised at how little corrosion there was in the MC bore for a car that sat since the 80's.
 
TR3driver said:
I've seen a note about deleting the end seal, but can't seem to find it at the moment. But as I recall, it didn't say anything about why, just to leave the groove empty (if present). Gazing into my crystal ball though, I would guess that preventing a leak when the main seal failed was exactly the reason they removed it. The main seal is shaped such that the pressure of the fluid against it helps force the seal against the cylinder, while the O-ring shape would do just the opposite (fluid pressure would tend to force it away from the cylinder). That could potentially cause it to seal when the pressure was low (ie brakes lightly applied for a normal stop) and then not work when the pressure was high (panic stop). A very undesirable attribute, especially with single-circuit brakes. But that's just a WAG.
Click to expand...

Randall,

Probably as good a guess as any other (other than some accountant at Girling wanting to save a penny (pence?) on each one they made).

After seeing it on the repro in Frank's thread and on the Miata clutch master cylinder that I just rebuilt, I thought this was some modern idea. :smile:

Scott
 
HerronScott said:
After seeing it on the repro in Frank's thread and on the Miata clutch master cylinder that I just rebuilt, I thought this was some modern idea. :smile:
Click to expand...
Good eyes, Scott; I missed seeing that first time around on Frank's thread! I remember seeing that seal way back about 1972-3 on a TR3A master cylinder and also on an early Herald master cylinder. But I think Randall's right about the circa 1960 deletion of said seal, and it's been probably a good 40 years now since a Girling rebuild kit included that extra o-ring seal?
 
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