brakes stays slightly applied after stop

Talk about the E-Type Series 2

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elliottS
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#1 brakes stays slightly applied after stop

Post by elliottS » Tue Apr 24, 2018 7:40 am

I'm new here and my '69 series 2 is also new to me. After a stop the brakes are slightly applied. I can feel that when pushing the pedal, after stopping there is some distance until it hit the piston in the master cylinder and after about 1 minute the piston returns to it starting position and the brakes release to a normal feeling. Like it is sticking and is sluggish in the cylinder.

I am thinking the initial solution is to change the brake fluid and bleed the system. And check for proper operation of the master cyl. The brake fluid doesn't look to good and I think it has not been driven much in the last few years. Time for changing the fluid anyway.

I am learning about my Jag after 8 years with a TR6 and doing all my out mechanical work including engine rebuild.

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Gfhug
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#2 Re: brakes stays slightly applied after stop

Post by Gfhug » Tue Apr 24, 2018 7:59 am

Elliott, it sounds like you may have sticking master or slave pistons. You can confirm that if you jack up the car, apply the brakes and see if any wheels are free. If all are tight it might suggest it's the master at fault. A complete flush of the brake fluid would be in order as it's hydroscopic and will introduce water to cause rusting of pistons. Try that first.

If the car hasn't been driven for a few years, then an overhaul of the brakes, new seals, pistons etc. would be sensible. How old are the tyres (tires)? If more than seven years then might be time to get them changed, too.

Let us know how you get on. And ask all the questions you wish. This is a very friendly and helpful forum.

Edited to add: see also this response:
viewtopic.php?f=6&t=12421

Geoff
S2 FHC Light Blue

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abowie
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#3 Re: brakes stays slightly applied after stop

Post by abowie » Tue Apr 24, 2018 8:10 am

Andrew.
881824, 1E21538. 889457..oops
http://www.projectetype.com/index.php/the-blog.html
Adelaide, Australia

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Mark Gordon
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#4 Re: brakes stays slightly applied after stop

Post by Mark Gordon » Tue Apr 24, 2018 1:08 pm

This symptom is very common and the problem frequently resides in the vacuum side of the braking system. The diagnostic test is to disconnect the vacuum line at the intake manifold and plug the intake manifold connection so that you don't have a vacuum leak. This will disconnect the vacuum boost assist to the braking system but still leave the unboosted hydraulic side working normally. Now go for a test drive; you will still have normal, unboosted braking and can lock up the brakes with harder pedal pressure in an emergency if needed. If the problem disappears, you know that the problem is on the vacuum side, most often with the small piston between the MC and reaction valve sticking. The solution is to remove the reaction valve and pull out the small piston, lube it with red rubber grease, reinstall and Bob's yer uncle! If the problem persists with the vacuum disconnected, look for problems in the hydraulic system such as sticking MC, brake caliper pistons, etc. My money is on the piston between the MC and reaction valve.
Mark

67 OTS 1E14988, 2002 VDP

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elliottS
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#5 Re: brakes stays slightly applied after stop

Post by elliottS » Wed Apr 25, 2018 7:33 am

Thanks for those tips. The club I belong to is having a tech session Sat and I will address the problem then when there is the use of a lift. I need to look for oil leaks as it seem to have more that one place that is leaking.

Elliott

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nefematic
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#6 Re: brakes stays slightly applied after stop

Post by nefematic » Thu Apr 26, 2018 11:28 am

elliottS wrote:
Wed Apr 25, 2018 7:33 am
I need to look for oil leaks as it seem to have more...
Elliott,

welcome to the forum and as has been said by Geoff this a friendly place to ask questions. Don´t let a leak here or there get in the way to enjoy your car!

Martin
Martin Scherz
Late S2 1970 OTS US LHD

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elliottS
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#7 Re: brakes stays slightly applied after stop

Post by elliottS » Tue May 08, 2018 7:39 am

I’m going to test the reaction valve and expecting to find it sticky. Looked through the docs and it is mentioned in the written part but not pointer out drawn diagrams. Where is this valve and how easy is it to clean it up.
Thanks
Elliott

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42south
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#8 Re: brakes stays slightly applied after stop

Post by 42south » Tue May 08, 2018 8:27 am

Hi
the reaction valve is the white plastic item attached to the front of the master cylinder.
The little piston that can be sticky is in the body of the master cylinder behind the reaction valve.
If you have either the parts manual or the service manual for the car, or check the knowledge base, there is an exploded diagram of the master cylinder which shows the little piston. Part number 31, it has a rubber seal around it.
clamp off the reservoir hose prior to removing the piston.
to remove press the brake pedal very slowly whilst someone keeps finger over the piston till it pops out.
make sure you note its orientation.
lube it with plenty of red rubber grease.
cheers
mark
Mark Brown
1971 S3 Etype
Son: when I grow up, I want to be a pilot
Dad: You’ll have to choose.

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ENX
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#9 Re: brakes stays slightly applied after stop

Post by ENX » Wed May 16, 2018 5:25 pm

I am new to the forum and came across this thread which gives me much relief. I have taken the car to three separate mechanics and each time they either cannot find an issue when they drive the car or tell me it's fixed. The brakes do not fully release when the car has been driven for a while and it is particularly noticeable when driving slowly in traffic with constant stopping. I have Coopercraft front callipers and the master cylinder is new - does anyone know if this is likely to be an issue with the reaction valve?
BRG S1 4.2 OTS
Howard

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mgcjag
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#10 Re: brakes stays slightly applied after stop

Post by mgcjag » Wed May 16, 2018 6:22 pm

Hi..whats your name..please try to add it in the signature area....re your brake problem..could very well be the small piston sticking in the master cylinder as in the post above yours.. Steve
Steve
1969 S2 2+2 & Building a C type replica

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elliottS
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#11 Re: brakes stays slightly applied after stop

Post by elliottS » Sun Jun 24, 2018 1:29 am

Thanks everyone for the inputs. I removed the reaction valve, cleaned the reinstalled. The brakes are now working as designed. I did have one suggestion from a local restorer. If the rubber hydraulic lines are used and getting old they will balloon out when the brakes applied and squeeze in when the pedal is released. This also makes sense but this cost $$$ so I went with the reaction valve which cost 0$ (Or pounds for you guys). So I save some money for this problem.

Thanks
Elliott

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