Brake problem

[Mark Gordon]

The brakes on my '67 OTS (LHD) are slow to release after I remove my foot from the brake peddle. When everything is cold, they slowly release after about 5 seconds, but as the brakes (and engine) heat up, they take considerably longer to release--about 15 seconds or so. Does that sound like a bad reaction valve? Can the reaction valve be tested by disconnecting the vacuum line, plugging the line to the reservoir and then carefully testing the system? Any other ideas as to what may be causing the problem?
Mark

[christopher storey]

Mark : it is more likely to be the servo sticking. The brake system on 4.2 cars is ingenious but idiosyncratic. The master cylinder does not itself operate the brakes at all : it operates hydraulically the shuttle in the servo master cylinder ( and of course the air spools in the reaction valve) but the brakes are applied by the shuttle in the servo cylinder and released by the big spring in the servo vacuum chamber pulling the shuttle back to its resting position. Over the years there is a tendency for the seals in the shuttle to swell , and this upsets the balance between spring force available, and spring force required to retract the shuttle. An overhaul of the shuttle and new seals is the only real cure, but the first thing to try is thoroughly to flush out the system with alcohol and replenish with new brake fluid

[1954Etype]

The brakes on my '67 OTS (LHD) are slow to release after I remove my foot from the brake peddle. When everything is cold, they slowly release after about 5 seconds, but as the brakes (and engine) heat up, they take considerably longer to release--about 15 seconds or so. Does that sound like a bad reaction valve? Can the reaction valve be tested by disconnecting the vacuum line, plugging the line to the reservoir and then carefully testing the system? Any other ideas as to what may be causing the problem?
Mark

Might be worth checking out your vacuum lines - if they are too soft they will collapse internally.

[Mark Gordon]

Thank you for the advice, as always very helpful. I think this is one I'll leave to my mechanic as I dread the thought of having to bleed the rear brakes. That's why I was hoping that it was a bad reaction valve: repairable without bleeding the brakes! I'm glad to see that the forum is up and running again. Although there is very little that I can offer in terms of advice, I really enjoy reading all of the posts and I have learned so much about these cars that we love over the past two years that I've had mine.
Mark

[christopher storey]

Mark : I have just looked at this on Jag-lovers ( an invaluable resource if you're not acquainted with it) and someone points out that it is worth checking the flexible hydraulic hoses for internal collapse before going to the trouble of master or servo rebuild.(Akin to what Angus suggested on the vacuum hoses) . Try searching on the Jaglovers forum for e.g. "sticking brakes" and you will find a wealth of info

However, to save you some time ( and with apologies for the length) I reproduce edited extracts which I took when I had the same problem - note that the ---- between paragraphs indicates that a new author is involved : -

The servo is controlled by the reaction valve, on the front of the
master cylinder. To test the servo, disconnect and plug the hose
going to the backside of the servo. With the engine running, that
should have the brakes fully applied without you having to touch
the pedal. If that works, then replace the reaction valve, and
you'll probably be OK.
You can test the reaction valve by putting a vacuum gauge in that
same hose. With the engine running, and your foot off the pedal,
you should see full manifold vacuum in that hose. As you depress
the brake pedal, you should see the pressure rise. With the pedal
applied firmly, the hose should be at atmospheric pressure. The
other hose going to the servo should have full manifold vacuum at
all times. If it doesn't, then you may have a collapsed hose
between the maniold and reservoir, or betwee the reservoir and
reaction valve, or a failed check valve on the reservoir.
--

I just completed rebuild of entire brake system on my S1 and may be
able to offer some help.
I'd look at these three areas for likely cause of brake sticking:
1) Air Reaction Valve leaking. Assuming you have boost assist
working, when you release the brake pedal the secondary piston on
the top master cylinder should retract and allow the ARV to close.
In effect sealing the rear chamber of the boost diagphram from
atmosphere and connecting it to vacuum, thus the booster spring
retracts the slave piston cylinder to free the disc calipers.
On the bench, the ARV should seal the side and back ports when the
valve is at rest. When pushed in, the side port should be open to
atmosphere and rear port should be sealed to vacuum.
2) Master cylinder Reaction valve cylinder is stuck in open. With
the reaction valve off, you should be able to push the little
piston back with a small hex key by about 2 lbs force. If it is
very tight then the piston/o-ring/cup is at fault. If reaction
valve seals are bad, then it may not build up enough force to push
the piston back but since the diagphram is so big there may still
be enough vacuum force to close the calipers.
3) Stuck slave cylinder floating piston. Mine was stuck while bench
testing. If there is any stickiness there, the brake fluid pressure
will jam the piston tight and the retraction spring can't unstuck
it. Both master and slave cylinder must slide freely by hand
pressure on bench.

---
*assuming* the engine is running when you're having this
brake problem then the issue is most likely the reaction
valve on the master cylinder. This is not releasing/closing
like it should and as a result the servo is operating when
it shouldnt.

This is common with both new Mcyls and rebuilt ones, some
say one of the seals in the rebuild kits is slightly oversize..

Firstly confirm the servo is the cause by clamping the pipe
to the vacuum reservoir & (carefully) prove to yourself that
the brakes are working OK without servo assistance.

Then re-rebuild the reaction valve, or *maybe* consider a
slightly stronger spring in the reaction valve or polish the
bore of the little piston in the end of the m/cyl.

searching the archives will find you loads of discussions on

------

Not an E owner but the 1967 420 I just bought has a similar brake
setup and it too had self applying brakes. I replaced the (air)
reaction valve and that did not fix the problem. To confirm that it
was related to the master cylinder the problem went away when the
vacuum hose to the reaction valve was disconnected. I remover the
reaction valve and using a magnet pulled the intermediate piston
(tiny piston) from the top end of the master cylinder. A small
amount of brake fluid did drip out. I cleaned the piston with some
denatured alcohol and that fixed the problem for me. Pete

-

You can read a complete discussion of the reaction valve as 12 Oct
2008 posts titled ''Yet another brake master cylinder question.''
You can investigate your rv while it is on the car and without
losing any brake fluid. Careful not to lose the valve spring. If
you must work on the little piston, then of course you will lose
brake fluid. You can rebleed the master cylinder at the left front
wheel cylinder only.


--

There are discussions of how the brake system works, but I've never
seen one that includes the rv. Let me try to explain clearly; ask
me questions where I fail. We should be able to agree.

The diaphragm in the rv works like the diaphragm in the servo.
There is a constant vacuum on the firewall side thru the metal
valve housing. The front side can be evacuated thru a hole in the
center of the plastic diaphragm support or exposed to atm pressure.
This is controlled by the valve system that has a spring.

If you press hard on the brake pedal the valve system allows
pressure into the front of the rv and the rear of the servo at
about 2/3 atm or 10 lbs/sq in. When you release the brake the air
pressure on the front of the 3 or 4 sq in diaphragm pushes with a
force of approx 30 lbs to move the diaphragm into the valve
housing. If the little piston doesnt hang up or bottom out, and
the diaphragm support doesnt bottom out in the housing, then the
valve system opens the hole in the support, evacuating the rear of
the servo. The basic problem is to open the hole in the center of
the diaphragm support to evacuate the servo and release the brakes.
I believe the force of the spring to be small compared to the air
pressure. Also, if the spring were the return mechanism, then the
valve system would still cover the hole in the center of the
support. Something has to move the diaphragm further than the
spring could.

Why do brakes fail to release? In my case it was because the
little piston and the support both bottomed out before the valve
system opened the evacuation hole in the support. I solved this by
using a deeper valve housing. 30 lbs is a lot of force, so I am
suspicious of the sticky piston solution. But I don't really know.
I think people should investigate how far their rv diaphrams move.
Should be at lease 1/16 in past equilibirium. Fussing with the
piston may change something just enough that the diaphragm moves
just little further, opening the hole a micron. These people may
be skating along on the thin edge. The piston fix eventually fails
for some. If you have a beautiful golden metal valve housing, then
it is not very deep. Success will depend on what your plastic
diaphragm support is like.

----------------

Curt, As promised a while ago I have been checking on ( my
perception ) of how the reaction valve ( rv) works. I have
done this by playing with the rv valve assembly on the bench
, by applying a vacuum from a vacuum pump, I.e. NOT on the
car! When the brakes are off the rv has a vacuum in both its
chambers, created by plumbing to the intake manifold. When
the brakes are needed, and the brake pedal is pushed,
atmospheric pressure is caused to press on the diaphragm in
the servo, as well as on the diaphragm in the rv. This
change from vacuum to atmospheric pressure is triggered by
the rv. Inside the brake master cylinder ( mc) the brake
internal piston pushes on the small internal lever, then on
the intermediate piston in the end of the mc, and then also
on the rv diaphragm pushrod. Inside the rv, to achieve this
a number of things have happened. The rv valve in the center
of the rv diaphragm has been closed to seal the vacuum in
the rear rv chamber, and the the front chamber is open to
the atmosphere by the other end of the rv valve. The rv
valve has been moved forward, because the pressure from the
brake piston has overcome the spring in the end cap of the
rv housing.
As pressure on the brake pedal is released, so the rv
diaphragm, pushed by the atmospheric pressure will start to
move the piston back into the brake mc housing. However, at
some intermediate position the vacuum is reinstated in both
rv chambers as the rv valve does its thing. The final
movement in re-seating the intermediate piston I believe is
achieved by a push from the rv spring. This spring must also
be of sufficient strength to seat the central valve to
isolate the vacuum in the rear chamber of the rv valve,
during the time that the brakes are on , when the front
chamber is at atmospheric pressure.
So for the brakes to work as planned by Jaguar, a number of
factors need to be operating
1) The intermediate piston must move freely in its bore,
and it must be in sync with the diaphragm push rod, and the
rv valve.If parts are replaced they must of the precise same
size as the originals. A change of geometry will cause
malfunction
2) The rv valve MUST give a good seal on the valve seat in
the centre of the diaphragm to isolate the vacuum in the
rear chamber. For this to occur the rubber seal itself must
mate well with its seat ( i.e, it must be sufficiently soft,
not age hardened) and the spring pushing it must be strong
enough. If the vacuum is not isolated then the amount of
servo assist is diminished.
3) If the rv spring is not strong enough to reseat the
intermediate piston AND to reseat the air vent side of the
rv valve, then the front chamber does not achieve its full
vacuum, and the brakes that were on stay on!
There are pictures in my Photo Album, and the link is
http://www.jag-lovers.org/v.htm?1224955698

----------------

Curt,
I believe the problem *is* due to ''stiction'' in that little
piston. Air pressure may well be responsible for the final bit of
retraction of that piston, however, if the piston sticks while
extended, *it* will keep the reaction valve open. The reaction
valve will only restore vacuum to both sides of the diaphragm
*after* the piston has reracted slightly. So, if the piston
sticks, from the RVs perspective, the brake pedal is still
depressed, hence it continues to vent the rear of the booster. The
piston movement *always* leads the RV movement, the RV simply
reacts to what the piston ''tells'' it to do.
--

[Mark Gordon]

Christopher, you are truly amazing! Your latest and in depth posting has given me several things to check that are within my capabilities. I had earlier discussed the problem with my mechanic and he suggested as one possibility that the internal surface of the hydraulic hose could have begun to delaminate and was, as suggested, acting like an anti-retraction valve. However, he said that the problem should be there from the start, not getting increasingly worse and would tend to be very reluctant to release the brakes. That doesn't match my symptoms. However, the operation of the booster and/or the reaction valve does seem to suspect. I will give it a shot and let you know what I find. Thank you again for your help.
Mark

[Mark Gordon]

I have tested the reaction valve and the servo and they both have tested OK. No collapsed vacuum lines and 20 in. vacuum from the reaction valve. Full brakes with the servo disconnected. Full vacuum from the vacuum reservoir. It looks like my problem is in the master or slave cylinder, and a rebuild is in order. Again, thank you for your help. I will update you when I get it sorted out.
Mark

[Mark Gordon]

Here's a very belated update on the cause and solution to my brake problem. I was unable to find the source of the problem (brakes failing to release) and had even taken it to a Jaguar mechanic who couldn't find what was going on. Pete Crespin stopped by last Monday and took a look at my car and almost immediately spotted a small kink in the vacuum line where it makes the bend to connect with the servo. A PO had apparently replaced that section with a piece of plain rubber tubing rather than proper vacuum tubing. I was unable to access the clamp which is holding the faulty tubing to a T union just forward of the bulkhead, so I cut the tubing just forward of the servo and spliced in a U shaped piece of copper tubing which makes the bend without kinking (or collapsing) the faux vacuum line. As I believe y'all would say, "Bob's your uncle!" The brakes work like they should with an investment of only about $.25 worth of copper tubing and 30 minutes of my time which is worth about $.02! I was prepared to replace the reaction valve, rebuild the servo or who knows what else when the engine comes out later this fall for rebuild and clutch replacement. Again, thank you to everyone on the Forum for being so generous with their time and expertise and I do apologize for taking so long for posting the solution to my problem.

[PeterCrespin]

Yay! Well done Mark.

Glad to repay in tiny measure your generous storage offer. Not easy to work down there on a LHD, but once we disconnected the manifold vacuum and the brakes worked perfectly (though somewhat weakly) the overall cause was clearly vacuum-related not hydraulic and it was just a case of looking for the culprit. Enjoy the car again, she's a keeper.

Pete

[Mark Gordon]

Final (I hope) update on my brake problem. My joy with the kinked or collapsed vacuum hose problem was short lived. The failing to release problem turned out to be improved but not resolved. I spent some time going over the various components and hoses of the system with a vacuum gauge and then reported the results back to Mr. Crespin. The Professor took some time to clear up some misconceptions of mine on how the system operates and then suggested that the problem might be due to a weakened return spring on the front of the reaction valve. Two minutes of time (if that), stretching of the return spring and now, after two runs of about 75 miles in temperatures of up to 38 deg. C. with lots of braking, everything is working as it should.

[Mad River]

Howdy gents! We just took delivery of our S1 coupe and immediately experienced the brake issue. Let me just say thanks for all of the information in such a concise location!

Also nice to see a few E enthusiasts near the Colonial capital. :D

[Mark Gordon]

Mad River (you're not also a canoeing enthusiast by any chance, are you?), welcome to the Forum and it's good to have another local on this side of the Pond. You'll find the members here to be very friendly and generous with their impressive expertise on the E Type. I would encourage you to go the the "Welcome" topic and post your information on the E Type World Map.

[Mad River]

Hi gents! I finally had the time to look over the servo, at least superficially, and I have a question about which I need sage advice. How is the vacuum hose secured to the reaction valve? The end of the vacuum hose on our car has a metal tube in it, and the hose is secured to the metal tube with a hose clamp. The metal tube sticks out of the hose by perhaps a quarter of an inch. I noticed that the metal tube is threaded on the inside.

That metal tube was then pushed into the round opening on the plastic body of the reaction valve. However, the round opening looks like it has taken some abuse over the years and appears stretched or misshapen. In fact, the metal tube was essentially just sitting loosely in the hole on the reaction valve body, and literally fell out of it when I touched it.

So, I think it's safe to assume that I don't have a good seal (heck, or any seal) going into the reaction valve. I've found an NOS rebuild kit and will replace the plastic body. However, I'm still uncertain on how the vacuum hose is supposed to be secured to the reaction valve.

Thanks one and all!

[christopher storey]

The front cover of the reaction valve should have a plastic spigot which is an integral part of it. the hose pushes over this and is secured by a jubilee clip or , for the purists, a cheney clamp

[Mad River]

Howdy gents,

Thanks so much for the advice and excellent posts about the brake issue generally and the reaction valve specifically. The spigot on the reaction valve cover was indeed broken off, and the spring was also rather weak after years of service. So, I replaced the entire cover assembly, though I retained the original rubber diaphragm/seal since the one included in the Lockheed replacement kit wasn't as good a fit. The brakes are now working perfectly!

P.S. Mark, I'm not an avid canoer, but I grew up in the Mad River Valley when the factory was still in Waitsfield. My first job, though, was indeed with Mad River Canoe. In junior high school I built the scale models of their canoes that they gave away as promotional items, etc. They were about three feet long and the hulls were made from the same kevlar that the actual canoes were poured from. I must have built fifty or sixty of those babies. Indeed, I still have the one that they let me build for myself!

[Mark Gordon]

Cool! I have two canoes in my back yard, one is a Mad River owned by my hunting and fishing buddy (we float fish the local rivers in the Piedmont region) and the other is a cedar strip canoe that I built about 15 years ago. The Mad River model has more rocker than mine (virtually no rocker from bow to stern), so it is a better river canoe, as it name would imply, because it is easier to turn. Mine is a better flat water canoe because it tracks very straight with little correction. There are quite a few E Type owners in the DC area; we should make plans to get together for a run.
P.S. I, too, grew up near the Mad River and once floated it while trout fishing with my dad and brother. However, my Mad River is the one in Ohio between Springfield and Dayton.

[Mad River]

Mark, thanks so much! Your water-bourne craft sound great.

I think a gathering sounds fantastic! Let's see what can be organized.

I often forget that there are other Mad Rivers. Does your river flow the "wrong" way as well (north instead of south)?

Best,

B.

[Mark Gordon]

No, generally it flows to the south until, west of Springfield, it flows to the southwest to join the Little Miami at Dayton. The good canoeing and trout fishing, at least back in the 1960's was north of Springfield.

[Maikel]

Hello,
after having had a scary monent in my S1 I am still afraid to drive it.
What happened.
I was cruising through the hills for about 2 hours and was on my way back. Just in town after a steep decent I was back on the flat when a bus i pulled out right in front of me.

I had to hit the brake, but there was no reaction at all.
The pedal went down without any sort of resistance and stayed there.
Imagine you pedal is down but no sign of braking.
That was like in the James bond movie. But not funny this time.
I pulled the hand brake and slowed down and avoided an accident.
After about 5-8 sec. the pedal cam back but still there was no pressure on the brakes.
I know from my youth when we changed the brakes I had to pump frequently and got some pressure on the wheels. Might have been some air in, but I am driving this car since one year and it was all fine. This time it was impossible to pump as the pedal stayed down.

When servo is not working I still have some resistance in the pedal just less pressure force on the brake cylinders, but what could cause such a total loss of brake?

I checked the car today again with engine off, high pressure at pedal right from the first inch after pressung, with engine on the same. Always very early resitance, in fact as far as I can remember much sooner than it used to be.

Now I am afraid to drive as it can suddenly happen.

My impression is that before I could push the pedal 1/4 of its way to have pressure, now it seems that is it almost immediatly.

Can anymone share this experience and how did you resolve it?

Thank you for assistance.

Maikel

[Mark Gordon]

All the symptoms of boiling the brake fluid either by overuse of the brakes (i.e. hard and frequent braking during a race) or the brakes dragging because of various problems in the system (frozen caliper piston, failed reaction valve, sticking master cylinder piston, etc.). With boiling brake fluid, everything works fine up until the point that the fluid starts to boil then you are trying to brake with brake fluid vapor and not liquid. Don't work so good! Then, once the brakes cool down and the fluid recondenses, the brakes work normally as if nothing was ever wrong. Time to go over the system thoroughly and diagnose the cause of the boiling fluid. Good luck!