My 65 Mk2 has a strange issue.

When I apply the brakes, they stop well. But, after each application they don't release right away.

I have the GM V6 conversion and possibly the vacuum for the servo is hooked up in the wrong place. I'm researching that also.

I'm going to bleed the entire system in the near future also.

Any ideas other than mine?

 

If you are using the standard servo from the MK2, the vacuum should not effect the release, there is a valve inside the servo that is lifted when brake pressure is applied this then allows the vacuum to act on the diaphragm to provide the assist.

I would look at sticking pistons in the brake calipers first, if you can jack all 4 wheels up at once this will be quicker. Apply the brake, and then release, see if one , more, or all the wheels are affected. If only 1 or 2, then remove the wheels and check the calipers, you will find the pistons are sticking.

If no wheels are affected with the engine off, do the same thing with the engine running, if it affects all wheels then you will be looking at the servo, I'd be surprised if it is the vacuum, I would look at the valve first in the case of all wheels being affected.

 

Thanks.

I'll put it up on the lift this week and see what I find and I will report back.

 

if you have not replaced hydraulic lines to brakes, see if they are ballooning or collapsing, not letting fluid return from calipers.

 

Will do.

 

Good point, but usually ballooning wont affect fluid return, and collapsing normally affects braking, not the return after the pressure is taken off.

Just for clarity. collapsing is when fluid gets under the inner skin of the flexible pipe and the pressure then pushes this "out" which effectively closes the internal bore of the pipe stopping fluid passing, which is why it usually shows up more on braking in a poor brake on 1 wheel, or both rear wheels if the hoses is collapsing going to the rear axle, you will not see this effect on all 4 wheels (well highly unlikely) as you would have to have several pipes collapsing at the same time.

 

I bled the whole system yesterday. Hoses are like new.

I haven't had a chance to do much more.

The car will be on the lift for a bit wile I sort out which driven gear i need to correct the speedo reading.

 

I have to say that I believe you have a problem with the air control valve that sits on the side of the servo cylinder. When you lift off the pedal, the outer air valve should close thus reducing the pressure difference across the servo diaphragm as the inner part of the air valve opens. It sounds like the air valve may be sticking closed.

If you have the original servo, it is possible to repair it - there aren't parts available AFAIK, but you might be able to get away with a cleaning. Some vendors offer a rebuild/exchange service but it it a quite expensive process.

In my case I installed a new servo LR18230 as a precaution against using 50+ year old hydraulics. I took my old original servo apart out of curiosity and actually it seemed pretty good except for some congealed grease around the main diaphragm which did lead to some stickiness. However I did not notice any malfunctioning when I had it installed.

The new servo as supplied does not fit properly in the available space and I had to reorient the vacuum line tap on the diaphragm cylinder and also rotate the air valve assembly to get the pipes to line up. Also you must figure out how to attach the servo to the sheet metal housing.

After all this I did a test measuring brake pedal displacement vs brake line pressure and air pressure across the main diaphragm. You might be interested in the result, attached.

 

As I said in an earlier post a sticky valve could be the case , but I would rule out the pistons first.

However again for clarity, the outer air valve is mechanically opened by the air valve piston acting on the air valve diaphragm, it is highly unlikely this is sticking closed, and if it did you would not get any assist from the servo, if it sticks open the servo would be acting on the slave cylinder, but without pressure from the master cylinder this would not apply much hydraulic pressure.

If anything is sticking it is likely the air valve piston, the seal does get soft and sticky over time. The good thing is this seal comes with the servo repair kit from SNG Barret part no 8055 together with the gasket connecting the air valve assembly to the slave cylinder and the seals for the slave cylinder and gasket from the slave cylinder to the diaphragm case.

Take a look at the link below which describes how the servo works very well, it is easy to make an error when attempting to describe this in words alone, and I may well have made an error myself, but hopefully with the details below you can understand how the servo works fully.
http://www.mgb-stuff.org.uk/servo.htm

 

I got a new unit from John's cars in Texas. Car is up on the lift.

Any tips or tricks from someone who has made this repair?

 

I assume you mean you have a new servo unit.

It's pretty straight forward, the worst part is feeding the vac hoses through, remove the servo cover within the wheel arch, disconnect the vac lines from the res tank, disconnect the main brake pipe, and air vent pipe, then swap the units over, obviously you will need to bleed the brakes again. It's a fairly straight forward mechanical job really so you should have no trouble.

 

Well, it wasn't that bad of a job.

Replacing the servo/master solved a couple of issues.

First was the brakes hanging up. Second was the touchiness of the brakes upon application.

This will be my last post here as I sold the car last week.

Thanks for all the help guys.

Back to my 1978 Alfa Romeo Spider project................

 

Glad you got it sorted, sorry to see you sold the car, hopefully you will still check in on the forum, and good luck with the Spider.

 

Thanks for all your help. What a wonderful forum!!

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