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Brake Master Cylinder-TRW -NEW Bench bleeding

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RobBB Rob H
Burbank, California, USA   USA
Hello Forum,
I have just finished bench bleeding a new TRW Master Cylinder . When I finished, I removed the tubes and to my surprise, both brake lines proceeded to leak out all the brake fluid that was in the reservoir !
I have bench bleed many MC over the years, and have never seen that.

My first thought is I have a faulty MC. Either dried up seals or a missing seal, etc. The bench bleeding procedure was normal, with no signs of anything wrong.

Or is this SOP for a MC of this design? Has anyone experienced anything like this from a NEW TRW Master Cylinder?
The car is a 72 Spitfire Mk. IV.
Rob

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Lizzard d id
san jose, ca, USA   USA
And this is why I don't bench bleed . For a master to work there has to be an inlet and an outlet . With the master in your hand the inlet and the outlet are open , the fluid should go into the inlet and right out the outlet .

RobBB Rob H
Burbank, California, USA   USA
HI Lizzard,
so your saying,

A), not to bother with bench bleeding,
and
cool smiley, this is normal .

If so, I'll move ahead and install the MC and continue with assembling /finishing the brake job.

I've just never seen that before.

rob

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clshore Carter Shore
Beverly Hills, Florida, USA   USA
Yeah, coming up on 50 years with Spitfires/GT6
Have NEVER bench bled them.

Ever wonder why the MC are mounted at an angle, instead of horizontally like many 'regular' cars?
It's to make the MC self bleeding, the air bubbles all collect at the high end where the MC reservoir is located.

Brake lines and slave cylinders do of course require regular bleeding.

dplass Avatar
dplass Silver Member David P
Merrick, New York, USA   USA
1972 Triumph GT6 MkIII "The Beast"
2011 Ford Fusion
Out of curiosity, does this apply to clutch master cylinders too?

In reply to # 1501159 by clshore Yeah, coming up on 50 years with Spitfires/GT6
Have NEVER bench bled them.

Ever wonder why the MC are mounted at an angle, instead of horizontally like many 'regular' cars?
It's to make the MC self bleeding, the air bubbles all collect at the high end where the MC reservoir is located.

Brake lines and slave cylinders do of course require regular bleeding.



-D

1972 GT6 MK3 "The Beast"

Lizzard d id
san jose, ca, USA   USA
In reply to # 1501143 by RobBB HI Lizzard,
so your saying,

A), not to bother with bench bleeding,
and
cool smiley, this is normal .

If so, I'll move ahead and install the MC and continue with assembling /finishing the brake job.

I've just never seen that before.

rob
If you put a little fluid into a new master to wet the surfaces , that's not so bad . It will help the seals slide along the masters wall .
I'd install the thing and then bleed it myself .

clshore Carter Shore
Beverly Hills, Florida, USA   USA
In reply to # 1501163 by dplass Out of curiosity, does this apply to clutch master cylinders too?

In reply to # 1501159 by clshore Yeah, coming up on 50 years with Spitfires/GT6
Have NEVER bench bled them.

Ever wonder why the MC are mounted at an angle, instead of horizontally like many 'regular' cars?
It's to make the MC self bleeding, the air bubbles all collect at the high end where the MC reservoir is located.

Brake lines and slave cylinders do of course require regular bleeding.

Sure, I never bleed clutch systems. Too much work to get the interior out of the way.
Make sure that you install the slave cylinder with the feed pipe at the top and the bleeder at the bottom.
They will then self purge by repeatedly full travel stomping of the pedal.

As a young man, my Spitfire was my only car.
I carried a spare can of brake fluid for when clutch inevitably would start leaking and the MC would go empty.
Just open the hood, top off the MC, then stomp, stomp, stomp, stomp ... until the pedal came back up, and drive home.

Install a new slave, and drive for another year or two (Miami weather was bad for clutch and brake systems).

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Bpt70gt Avatar
Bpt70gt Brian T
Westmoreland, NH, USA   USA
Same here, never bench bled the brakes or clutch.

Tonyfixit Avatar
Tonyfixit Tony M
Duncan, British Columbia, Canada   CAN
I never even heard of bench bleeding until I came to North America. I still do not do it, and have never seen the point.

On a Spitfire it seems like a sure way to get brake fluid all over the bulkhead, and you still have to bleed the brakes when the lines are connected.

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RobBB Rob H
Burbank, California, USA   USA
Thanks Tony,
I have one car, that the Master came installed when it shipped to me from the manufacturer and painter. I didn't bench bleed that one either. Hmmm now that i think about it, it was fine.
And the Bentley book doesn't mention bench bleeding either. I have the book that covers the 72 spitfire. All good points. Interesting that you never heard of bench bleeding till you came to the states/North america.

The only thing that perplexes me is the fact that the fluid in the reservoir just ran out of the outlet ports like a faucet. like i mentioned in the earlier post, I have Never seen that.

Well, till next weekend,
Thank you gentleman All!!!
Rob

Tonyfixit Avatar
Tonyfixit Tony M
Duncan, British Columbia, Canada   CAN
Some owners gravity bleed, that relies on the fluid free flowing from the master.

spitfire50 Avatar
spitfire50 Paul Mugford
Rochester, N.H., USA   USA
In reply to # 1501207 by RobBB
The only thing that perplexes me is the fact that the fluid in the reservoir just ran out of the outlet ports like a faucet. like i mentioned in the earlier post, I have Never seen that.


Rob
Rob,
The fluid has to be able to flow freely from the reservoir to the cylinder when the piston is in the rest position. When the piston moves slightly the port is sealed so the piston can make pressure.
All the best,
Paul

RobBB Rob H
Burbank, California, USA   USA
Hello Paul,
belated reply, long work week.
Yes, of course!! Fluid must get to piston at rest! I was visualizing it in my head, and visualized it wrong. Your absolutely correct. Thanks, when i do this as a hobby, there is just knowledge I overlook or get wrong.

As soon as I get another weekend to myself, I'll have the brakes done and functioning.

I really appreciate your reply.,

rob

Born Loser Avatar
Born Loser Silver Member Matthew Taylor
Land O Lake, Florida, USA   USA
"Bench bleeding" is an American thing, our big boats from the late 60's and 70's do require it. Our LBC's from the same time period get zero benefit from it. Its a common misconception when us Yanks "cross over".

Thanks for the tip on flipping the slave for the clutch Carter - never considered that! But, it should work all the air out eventually, and like you said, make roadside "get home" much better! Will give that a try next time I swap a slave...(hopefully years from now...).

Rob, in my opinion (its worth what you paid for it), the TRW is the finest Master for sale today - well worth the extra beans. And yours is reacting correctly, as others have pointed out.



Matthew
1960 Triumph TR3a
1970 Triumph Spitfire MK 3
2012 Mini Cooper SS Convertible

tmpass Avatar
tmpass Tim P
Medway, MA, USA   USA
1970 Triumph GT6+ (MkII) "Capo"
1970 Triumph GT6+ (MkII) "Blue Oxide"
The only thing you need to worry about when bleeding masters/brakes "in situ" is bottoming the clutch pedal against the floor. I've heard this can damage the plastic spring retainer of the internal piston/spring assembly...

just put a block of wood under the pedal or be cognizant of pedal travel.

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