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Noise from Brake Pedal  Rating:  Rating
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 Posted: 09-20-2014 03:48 pm
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UKJames
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OK the brakes are now pretty much modern car feel, ok not 4 pot calipers like my BMW but then the JH is a lot lighter so they feel pretty good.
The one issue remaining is the servo/booster. I have attached vacuum gauges to the four Dellorto take-offs in order to balance them, but when I apply the brake, No. 4 vacuum signal drops to zero. This is also the manifold port that the vacuum to the servo/booster is taken from. So although the booster holds a vacuum, there seems to be a leak ONLY when the brake is applied. I am wondering if the rubber around the push rod has failed in some way and I am leaking vacuum at the join with the MC. It can't be the diaphragm internally as the leak would be permanent.
The pushing action of the rod appears to be opening up the leak?

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 Posted: 09-20-2014 06:02 pm
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Jim Ketcham
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Interesting. I have never checked vacuum under those conditions.
Does the vacuum eventually recover while your foot is on the brake or does it remain zero until you release the break? Just trying to determine if it's a temporary surge or vac drop with diaphragm volume change or an actual leak being exposed when the pedal is depressed.
If temporary it might be normal. I guess I can try the same test on my car when I return home next week.

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 Posted: 09-20-2014 06:38 pm
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UKJames
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The vacuum doesn't recover, drops off sharply for the duration of the full down brake pedal (that's the noise I was hearing). Recovers immediately the brake is released.
I suspect the output seal is partially worn, and only lets go when the push rod is extended. I guess these seals must get a fair bit of wear in normal use, they're not lubricated. Visibly the seal looks in very good condition... I'm not sure if you can replace it easily.

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 Posted: 09-20-2014 11:40 pm
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Jim Ketcham
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I noticed a listing on the UK ebay for JH brake servo seals repair kit. In includes an internal schematic of the booster that I can't view well on my mobile device. Might this be of help?

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 Posted: 09-22-2014 10:35 am
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UKJames
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I think that's the seal I need included with this kit. With the MC off I should be able to access well enough to remove the old seal. I'll clean up the push rod while I'm at it and lubricate with some brake lubricant for good measure.

I am quite surprised at how quickly the vacuum is lost though on pedal pressure, I would have expected a faulty seal to 'seep' air not 'dump' it. Maybe the whole seal is lifting of the flange it sits on. I'll have a closer look tonight.

 

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 Posted: 09-23-2014 07:41 pm
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UKJames
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Probably wishful thinking on my part but after driving it around a bit it seems the new MC has helped with the feel, but the boost is only there on hard braking.
The vacuum leaks out so quickly, progressive braking (normal driving) is still not good. I thought the servo was only leaking through the front seal but I think it is generally shot, looking inside there is no obvious large ingression of fluid, but it does look 'damp'. My thoughts are that at some point the bad output shaft seal has created a vacuum between the servo and an old MC, and sucked brake fluid into it.
I've now removed the servo and pedal box and will use the opportunity to clean up and paint the box & bulkhead area before I get a new (old but good) servo this Saturday.....

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 Posted: 09-28-2014 05:36 pm
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UKJames
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A quick update. Took the servo off and on the bench looked through the valve hole with a torch to see the condition- on one side, the diaphragm was shot. Got a new (old) servo from Rejen on Saturday, replaced the foam filter (perished), cleaned and lubricated the rods, gave the thing a spray over. Installed in this morning and bled the brakes. What a difference. Together with the TR6 master cylinder this thing now has some good stopping power.
Bonus is that now I don't have a vacuum leak every time I touch the brake pedal I was able to balance the carbs and colourtune the mixtures properly as well. Now the engine doesn't rock, and as the 4th cylinder isn't constantly getting leaned out I no longer have any spit back through the Dellorto either.
All in all some good progress...

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