Mark 2 brakes binding what to do

I have a 1967 Mark 2 3.4 which I’ve owned a long time. About 8 years ago the servo went bad. On the advice of another Mark 2 owner I purchased an aftermarket servo unit with a stronger boost ratio (4.3.1) (I’m not certain) from SNG . I remember the size of the booster or reservoir required the Jaguar specialist I was dealing with installation at the time to make a few modifications to accomodate the slightly different shape of the aftermarket unit. From that time all those years ago when driving in hot weather in busy traffic I would occasionally experience the brakes slightly ‘sticking’. Tapping the brake pedal lightly a few times would make the problem go away. I’ve lived with this inconvenience all this time assuming this condition was just one of the quirks one had to deal with when dealing with aftermarket parts. Today, however, the ‘inconvenience’ has entered a new phase which is untenable. When pulling out of the garage the ‘binding’ feeling began once again but this time no matter how many times I tapped on the brake pedal the problem would not go away completely. I drove the car around the block and put it back in to the garage while gently applying energy to the accelerator and clutch pedals to finally maneuver the car back inside. I read on previous posts mention of items like "reaction valve’ and “pressure valve.” SNG on their site even sell a valve repair kit. Before purchasing a myriad of parts which may or may not be useful I’m asking fellow listers for advice on what to do. Some posters even suggested the problem might be remedied by simply clearing out some vacuum hoses. My mechanic, if he would choose to take this on always asks that I bring the necessary parts to make the repair. What to do now? Advice welcome. Thank you

Mel R

Go step by step. First disconnect the vacuum hose and then you will have non power assisted brakes and if it continues, you can pursue the master cylinder as being problematic. The tapping to release pressure is a problem.

Be careful with out boost as it will take a lot longer to slow down.

There is a easily removed valve on the vacuum tank. Make sure your hoses have been connected correctly to each nipple on that valve. The Manual shows one way and SNG brochure indicates exactly the opposite. GO with the manual. I’m actually not really sure if it matters? Others can chime in.

The booster can be a bear to R&R, as your mechanic prolly had to cut a bit of metal to make it fit. It’s not a project one wants to do lying on their back ( I know).

The hoses are easily replaced as they may have a leak. I routed mine up and behind the fender to avoid clutter near the other linkages.

Keep us informed.

Since the booster installed years ago was and is an aftermarket item, I don’t know if the factory manual is relevant. I do remember when the mechanic ( unfortunately is no longer in business) installed the aftermarket unit he did have to cut a bit of metal to make it fit. As I noted in my earlier post, the system has not been working 100% as it should for some time. Are you possibly suggesting the cause of this problem might be leak in one of the hoses and perhaps the booster itself is not defective? If so, I’d like to know if that’s possible before I would spring unnecessarily for a new booster.
Thank you for your reply.
Mel R

I had a problem with the booster in my MK IX. I took it out, cleaned and polished the bore, and installed a rebuild kit. I then re-installed it, bled the brakes and took it for a test drive. I had almost made it back to the house when the car started slowing down and the brakes got hot. By carefully reading the manual I found that there is an air valve on the servo which is supposed to allow atmospheric air into the vacuum chamber when you press the brake pedal. Mine was obviously doing that on its own, and it sounds like yours is too. I took the unit off again, replaced the rubber hose that connects the valve to the chamber, cleaned the valve and reassembled the unit, re-installed it and bled the brakes again. This time I left it in the driveway with the engine running, and sure enough the brakes slowly locked up. I was not willing to go through all that rigmarole again with no guarantee of success, so I simply bought a replacement servo, and while I was at it a new vacuum reservoir that came with a check valve. Problem solved! Valves are not available for the original unit but if you can get a replacement valve for your replacement servo that could be your answer.

I would go with servo. I had same problem with the servo in a 420 Compact sedan I used to own. The problem would come and go.
Replacing the servo solved the problem.

British Parts NW has a servo at a good price.

I think your method makes the most sense. I’ll call SNG tomorrow and ask if they still sell the same after market unit and accompanying reservoir and check valve. Thank you. :blush:
Mel R

Looks like you have some good answers to your situation.


Thank you for your reply Gerard
Your detailed explanation helps me to understand the possible nightmare I may be in for here. However, based on what you described and my detailed summation of what I have experienced gives me hope. When I had the servo replaced 7 or eight years ago by a Jaguar mechanic no less, from what I remember he did not mention anything about having to replace the vacuum tank check air valve. On the very day after he replaced the booster he had me take a test drive. Since I wanted to subject the car to a variety of test conditions, I drove around the neighborhood subjecting the car to a variety of conditions including accelerating hard following by having to make near sudden stops. The first few times all was good. Then suddenly, on the last rapid deceleration the brake pedal felt hard as though it was almost fighting me back. I pulled over, waited a minute, then started out again. Everything seemed to be ok. When I returned to the shop and told the mechanic what I had just experienced, he seemed to be clueless as to why this happened. I brought the car home, and everything seemed to work as they should. Several years later after a rapid deceleration when approaching a traffic light which had just changed, I experienced the same condition. If I waited a few seconds and then tapped the brake pedal once or twice, a normal condition returned. Over the years this same condition occasionally reappeared usually on warm weather days. A light tap or two on the brake pedal usually cured the problem. But several days ago returning from a 14 mile drive, as I was literally pulling up to the entrance of my garage, I felt the brakes seizing up on me and had to give more gas to the engine as I backed into the garage. I figured I would give the car a few days rest after which I hoped the problem would be gone. Today when I went back to the car hoping to go for a pleasant drive I could barely get the car to leave the garage. This was something new. My current Jaguar mechanic is located 25 miles away. He has been servicing my car for the last seven years. He actually allows and encourages me to bring my own parts. I wait for him to let me know when I can bring the car in so I can sit and wait while he works his magic. This arrangement has served me well until now but after reading your last description, I don’t know if our arrangement would work out. As you correctly suggested, I have no desire to purchase a multitude of parts I may not need nor do I want to have him ascertain I need to bring him other parts which would necessitate leaving my car overnight parked in his outdoor lot . So that is where we are at this point. The expression on your face sitting near the front right wheel of the Pontiac replicates the feelings I’m having today regarding the brake servo difficulty. What do you think?
Any more advice would be more than welcome.

Mel R

What this sounds like is the piston in the reaction valve sticking.

This is a common problem with aftermarket servos on E Types and the reaction valve on your new servo looks like it’s the same design.

1 Like

Considering this has been an intermittent problem for awhile is there a solution for my current situation to ‘unstick’ the unit without having to take it out and replace it?

I would disconnect the pipe from the inlet manifold, thereby depriving the servo of it’s power source. If the problem goes away (you will need to push much harder on the brake pedal without servo assistance) the problem is with the servo or (less likely) the vacuum tank.

You can then reconnect the servo to the inlet manifold, and this time bypass the vacuum tank to find out which it is.

If it’s the servo it should be easy to find someone who can fix it, or just buy a new one - but take some time to make sure a new one will fit and give you the assistance you want - I replaced mine because it had a fault similar to yours but I would have preferred more assistance than I get from the one I was sold and it fouled the radiator cowling.

1 Like

What Andrew said…
The reaction valve is a known offender, and causes this very problem. I would go for the low-hanging fruit and rule that out first before I started working with the servo. Go over to the E-Type forum and search the archives for reaction valve posts, and you will find more information about this problem than you can believe.

Good luck, and keep us posted,

This morning I went to my collection of receipts for parts and services since I purchased the car back in 1989. Time passes by more quickly as we age. It was not 8 years ago but rather 12 years ago exactly, May 04 2012 that I had the upgraded LR 18230 booster replaced. I called the folks at SNG from where I purchased the current unit in 2012 to ask a few questions. They were most helpful. They said the LR18230 unit already includes all the necessary components; reaction valve et cetera. I told them the mechanic 12 years ago needed to make some adjustments in the inner fender to make it fit and asked if the new LR18230 would be the same shape and size to enable an easy fit. He wouldn’t guarantee it would be EXACTLY the same shape and size but he wouldn’t rule out that possibility either. From the various replies I’ve received from listers on this forums page I’m now more inclined than ever to believe the 12 year old servo is the culprit causing my current dilemna. I’ll call my mechanic today to see if he is available and willing to perform the installation and if he agrees I’ll order the new ‘all inclusive’ servo from SNG today. Thanks to all the lister who have opined. I will provide updates.
Mel R

Thank you for your detailed recounting of the nightmare you endured. After reading your response along with others, I am now convinced the servo is the culprit here. I’ve owned the car (1967 Mark 2) since 1989. I went to my drawer full of receipts and found that exactly 12 years ago, May 04, 2012, I purchased from SNG the Lockheed LR18230 ‘upgraded’ servo which my mechanic at the time installed. Even though the original servo and the new ‘upgraded’ one were both manufactured by Lockheed, the mounting points were different and I remember my mechanic at the time had to make new ones . I spoke with the folks at SNG this morning and the good news is the new units should have the same mounting points as the one I bought 12 years ago and the reaction valve et cetera are incorporated in the unit. My current mechanic assured me he would be able to install it for me so I put in my order with SNG, should be here by the end of next week. I’m feeling cautiously optimistic and will provide updates.
Thanks again.
Mel R

1 Like

This could also be a problem with the master brake cylinder.
Often they do not release fully, preventing to release the pressure.
Be sure you have enough free play in the pedal.
The spring in the master cylinder is often to weak, then the seals will stick.

When the brakes ‘froze’ on me several days ago there was still enough free play in the pedal. This time no matter how many times I hit the pedal the brakes refused to release completely. Yesterday I went down to the garage to check on the car which is parked on a slight incline. When I put it in neutral it began to roll forward. When I put my foot on the brake pedal it stopped as it usually has. On other cars I’ve owned in the past when the master cylinder gave trouble the problem was either the pedal sinking closer to the floor or the pedal pushing 'up ’ and freezing. This was not the case in my current situation. Do you still think the master cylinder is the culprit here?
Mel R

I have had identical symptoms on my mk2 -63. Brakes have been dragging slightly especially the more the brakes are used and the warmer they get. When I bought the car 15 years ago the brakes were overhauled with an aftermarket replacement servo. I tried many anctio including new brake hoses and new seals in the master cylinder. It did not make any difference. Then new rubber seals and polished reaction valve piston in servo. That improved the situation but brakes still binding when used much and getting very warm. Finally I bought a new standard replacement servo from SNG last year and the problem is from then completely gone.
Br Svante

1 Like

Some folks have suggested perhaps the master cylinder could be problematic but I don’t think so,I do believe the problem here is the servo. I ordered one yesterday from SNG. The folks there assured me the new unit includes everything, reaction valve, hoses and reserve tank. I had the original Lockheed unit from 1967 replaced with an upgraded Lockheed unit 12 years ago. I guess 12 years is as good as it gets. At least the mounting points for the new unit should be the same as the one installed 12 years ago.
I went in to the garage today and without starting up the engine I pumped the brake pedal several times. There was no assist without the engine running, but no binding either.
Thanks for confirming my suspicions.
Mel R

1 Like

Here we are six weeks later. I ordered the newer Lockheed replacement servo last month and yesterday my mechanic finally had time for me to have the car towed to his shop to remove the defective 12 year old unit and install the new replacement. When he removed the 12 year old unit and held it up next to the new one, the new unit had an extra valve I believe perhaps pressure release valve with a short hose which attaches to the servo. Other than the new unit being copper color versus black painted old servo, dimensions of both servos appeared to be the same. Over the next two hours, they installed the new unit and bled the entire system. The result? The brakes now work as they should, better than over the last 35 years I own this car. Thank to all for your sage advice.
Mel R


As I posted several days ago, the installation of the new servo cured the problem. Now I have an interesting question on a new development which is actually a good thing. Yesterday I took the car out for a drive and noticed that when I stopped to put the car in reverse, gear change was smoother than it had ever been. In the past on several occasions, when gear change to reverse appeared a bit difficult, I would have to move the gear shift lever (this is an all synchro gearbox) in to 4th gear followed by moving it to the left and down to engage reverse. Not any more. Engaging reverse now is easy every time. On the day of the installation of the new servo I noticed (yes the mechanic actually allows me to set up a folding chair outside the service bay to watch), it appeared to me he was running a new hose from the servo to the intake manifold. I noticed the brake master cylinder and clutch master cylinder are located next to each other on the firewall. Do they share the same source of vacuum as well? I’m pleased with the improved performance, just wondering if one could be related to the other? Thanks.

Mel R