Marina Servo, is it working as intended?

[Robert in Cumbria]

As mentioned elsewhere, my Roadster is now running. One of the aspects which need dealing with is the servo, I suspect the servo assistance is not working.

If I repeatedly and quickly dabb the brake pedal hard, the engine shows signs of weak mixture, running faster and unevenly as I would expect. Simply holding a heavy pressure on the pedal is OK, no weak running. However, if I stop the engine with the brake pedal pressed hard, the feel does not change even slightly. Normally I would expect the pedal to rise slightly against my foot pressure as the engine stops.

Even given the very limited trial run I did today I didn't feel the pedal is what I would expect for a servo brake system.

Is it possible/advisable to open up the servo to check it out for stuck valves, leaky diaphragm or other fault, or is it a simple (but expensive) matter of replacing it out of hand?

Or... Is the servo on a Marlin normally c**p?


A point perhaps worth mentioning, I don't think there is a non return valve anywhere in the vacuum system... Might there be one in the servo?

With my Rovers the non return valve was on the manifold and the tube was a form of reservoir of vacuum, so there was a small reserve.

[Mike]

Re: Marina Servo, is it working as intended?

Hi Robert
I don't know about Marinas, but Metros have the non return valve fitted as the elbow directly in to the face of the servo.
Don't suppose a Metro servo would fit would it? There are at least 50 club members with a spare one, as we have upgraded to a 7" dual diaphragm servo for much improved brakes. I gave my old Metro one away - I'm sure there would be someone willing to do the same if you could make use of it?

Another way to test a servo is to put your foot on the pedal with the engine stopped, and then start it up - if the servo works the pedal will go down further. Doing it the opposite way as you are should make no difference as the vacuum reservoir should hold it.
Another test is to run the engine then stop. You should get three servo assisted pedal travels at least, before you feel the pedal go hard when there is final no vacuum reserve.
Mike

[Robert in Cumbria]

Re: Marina Servo, is it working as intended?

Thanks for the suggestions Mike, I will follow them up when I get home. I will check out the non return valve. Is the Metro servo a direct replacement for the Marina one, there are four bolts at the back and a two bolt horizontal flange on the master cylinder.

[Mike]

Re: Marina Servo, is it working as intended?

Robert, I am not familiar with the Marina servo, but the Metro has 4 studs on 90mm centres, to the bulkhead, and two studs for the master cylinder are at 70mm centres.
Another important factor will be the diameter - the Metro is only 7" measured across the maximum external diameter i.e. across the seam.

[stevejgreen]

Re: Marina Servo, is it working as intended?

Servo check valve is http://www.rimmerbros.co.uk/Item--i-RTC812 is known to fit a Marina Servo.

Its my understanding that there is a similarity between the Marina servo and early Landrovers?
I think a question asked on Fastmarina may have results.

[Robert in Cumbria]

Re: Marina Servo, is it working as intended?

Sorted!

Phew, I was worried about that one... Can't afford a new servo right now.

Having read about servo's last evening I tackled it as soon as I had a bit of a result with the brake flexes. I took the master cylinder off and examined the seal behind the master cylinder. It isn't in the best condition so I got a little Vaseline and applied some to the sealing parts. The servo now works OK. I need to order a kit to replace the seal. The rod which actuates the master cylinder is in good order so I think a new seal will fix it long term.

If I start the engine now with pressure on the brake pedal it goes down and the opposite when the engine is stopped. I seem to have a good pedal so that's another task done.

Marlin front end with brakes.jpg

Another of my interests, flowers. A Passiflora in my greenhouse. It has been obliging me with pairs of beautiful flowers almost continuously for the last four weeks or so.

Passiflora.jpg