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  • Marina brakes

    For some time (about 17 years) I have had the feeling that the servo brakes on my 1275cc engined Roadster are far too severe on emergency application, especially in the wet. I don't think the lightweight Roadster needs the servo.
    To test my theory I disconnected the vacuum tube from the manifold and plugged the business end.
    Bearing in mind that it is probably 40 years since I drove a non-servo car I set out to see what it felt like. Obviously the pedal needed more pressure but I think the "feel" was better with less tendancy to lock up. The real test will be when I try it in the wet which is where I have the most trouble trying to avoid lock-up, but brake safely and sensibly.
    The shortened brake pedal with less leverage has to be considered too.
    What I am not sure about is this - is some of the extra pressure required due to having to move the servo mechanism manually?
    Any comments welcome,
    Franklin.
    Franklin, Leicester

  • #2
    Re: Marina brakes

    I've been struggling with the same problem in that my car tends to lock up the front wheels more often than not. What I noticed at the weekend while getting her MOT renewed before the winter was that the breaking effort on the rear axle is quite low. I'm not sure why. This is one thing that I'm going to investigate over the winter.
    Mk2 SWB Marina Roadster with a 2.0L Pinto built in 1986

    Comment


    • #3
      Re: Marina brakes

      Some Marina rear axles used a smaller bore wheel cylinder 5/8" if this is the case then change the wheel cylinders to 3/4" and that should improve the balance. Obviously making sure all the workings in the rear drum including the sliding wheel cylinder are in good condition. What can happen is the wheel cylinder seizes in the back plate so only one shoe is doing all the work.
      Ben Caswell probably not the last word on anything here!!

      Comment


      • #4
        Re: Marina brakes

        As you are no doubt aware, if you don't use the servo you will need to put more pressure on the pedal for the same braking effort. Have you fitted the re-enforcing bracket between the front bulkhead and the adjacent chassis rail. This was a modification suggested several years ago because the bulkhead could crack after a while. I think most Roadster owners will have done this mod but I thought it worth mentioning. The bracket was originally available from YKC but that is obviously not an option now. My own Roadster has a remote servo which is quite small in diameter and doesn't give the same increase in effort as the in-lines one. The car will tend to lock up at the front under high braking if the road is wet or there is loose gravel or mud but otherwise behaves quite well.

        Comment


        • #5
          Re: Marina brakes

          When I bought my current car, a hybrid with a servo, it had a tendency to lock the front brakes. After refurbishing the rears with new cylinders, shoes and drums it's now nicely balanced even in the wet it's giving me a high level of confidence.
          - 9th owner of T693 SSC possibly a factory built Ford based V8 Sportster
          - 4th owner of Q309 RNV, an early Cabrio built by Bob Copping, owned Doug & Liz Billings for 16 years
          - 9th Custodian of JRR 929D, Triumph Vitesse based special Paul Moorehouse built prior to the Triumph Roadster kits.
          - 8th owner of Roadster chassis number 2395. Now owned by Barry!
          - Builder of chassis number 2325 (PKK 989M) in the mid 80's. Now owned by Eric & Lynne.

          Comment


          • #6
            Re: Marina brakes

            The only thing that stops you is the friction between the road and your tyre.
            If the tyres are poor quality, and so for the road there will be a tendency to lock up.

            Equally if your tyres are narrow, you will lose contact area with the road which is where a reduced tyre pressure could help.

            When I fitted Clio vented discs and their calipers, slightly larger pad area, I did play around with brake pressure balancing but never reached a satisfactory medium. I could with my servo brakes lock up the fronts, but it was unusually harsh braking and it was a damp slightly loose surface.

            Of course the best braking effort is just before the wheel starts 'under rotating', cadence braking may be needed to bring the car to a halt.

            So far as bulkhead cracking goes, all the above comments apply. From my analysis the early roadsters with no servo were the greatest victims, so the standard stiffening bracket might be needed. It might be worth standing on the pedal and getting someone to watch for excessive movement.
            MOC member since 05/97
            1984 Marlin Roadster SWB.
            1800TC, Unleaded ported head, stage 2 cam. Ford Type 9 gearbox, Dolomite Sprint rear axle fitted with MGF disc brakes.
            Three core radiator, Renault Clio vented front discs.
            The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man.

            Loads of Marlin Reference can be found documents here or there.

            Comment


            • #7
              Re: Marina brakes

              I was thinking the same Steve and was planning to get some better tyres to improve things but as I said I noticed that the peddle effort required to stop the rollers was significantly higher for the rears than the fronts, I would guess 10x which is why I’m going to be taking a look at the rears over the winter.
              What puzzles me is that Marlin recommended using rubber hoses on the rear to reduce the breaking effort on the rear axle as the roadster would have a tendency to lock the rear wheels… seems odd to me.

              Mk2 SWB Marina Roadster with a 2.0L Pinto built in 1986

              Comment


              • #8
                Re: Marina brakes

                What would be true to say is that the auto adjusters on the rear brakes, when fitted, rarely work efficiently, and that few people remember to check the manual adjusters, (when fitted)
                I am not sure that varying the size of the rear cylinders, given the size of the brake drums, has a significant effect on rear brake effectiveness. I think you would be hard pressed to notice any change.
                MOC member since 05/97
                1984 Marlin Roadster SWB.
                1800TC, Unleaded ported head, stage 2 cam. Ford Type 9 gearbox, Dolomite Sprint rear axle fitted with MGF disc brakes.
                Three core radiator, Renault Clio vented front discs.
                The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man.

                Loads of Marlin Reference can be found documents here or there.

                Comment


                • #9
                  Re: Marina brakes

                  Thanks for all these helpful comments. Good points about poor quality tyres and tyre pressures etc. I will attend to the latter now.
                  Geoff, I remember talk about the strengthening bracket but I have never really considered it.
                  I have just had a look and mine has nothing attached to the aluminium casting on the bulkhead BUT lower down there is a steel triangular gusset about 6"x 6"x 6". It is welded to the top edge of the chassis and the bottom of the bulkhead in the horizontal plane. Is this the bracket you refer to?
                  Franklin, Leicester

                  Comment


                  • #10
                    Re: Marina brakes

                    Hi Franklin, from your description it sounds as though you already have the bracket fitted so nothing to worry about there.

                    Comment


                    • #11
                      Re: Marina brakes

                      I could publish a link to my source material but the last version was deemed to break MOC's opinion on copyright issues.
                      its still there in its original location if you want to go and fond it.
                      MOC member since 05/97
                      1984 Marlin Roadster SWB.
                      1800TC, Unleaded ported head, stage 2 cam. Ford Type 9 gearbox, Dolomite Sprint rear axle fitted with MGF disc brakes.
                      Three core radiator, Renault Clio vented front discs.
                      The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man.

                      Loads of Marlin Reference can be found documents here or there.

                      Comment


                      • #12
                        Re: Marina brakes

                        Hi Franklin,
                        The bracket fits below the brake servo, mine was a little rusty so made a new one out of aluminum.
                        I am in the middle of a rebuild so ideal time to take pictures.

                        1ADD9815-3300-4C7F-B588-00F646A664F4.jpeg

                        Some also put a piece of angle aluminum inside the bulkhead. I have yet to fit mine in place.

                        3AD2864A-0D75-477E-8546-AAA9E38A664E.jpeg

                        Cheers,

                        Comment


                        • #13
                          Re: Marina brakes

                          Sorry, I've borrowed your pic Martin.
                          For what it's worth, my experience has shown that the fatigue crack is usually on the bend marked in green, secondly (perhaps as well as) on the one marked in red.
                          This was on a car without the triangular reinforcement bracket
                          Rgds DC
                          Attached Files

                          Comment


                          • #14
                            Re: Marina brakes

                            Thanks DC, good to know. I have put in both reinforcing (or will be) with the servo as well so should be ok.
                            May think of something to reinforce the lower bend before I fit the angle aluminum to the top bend.

                            Comment


                            • #15
                              Re: Marina brakes

                              Originally posted by David View Post
                              When I bought my current car, a hybrid with a servo, it had a tendency to lock the front brakes. After refurbishing the rears with new cylinders, shoes and drums it's now nicely balanced even in the wet it's giving me a high level of confidence.
                              Nudged by Steve's comments I've remembered that I also renewed all 4(5) tyres as they were at least five years old.
                              - 9th owner of T693 SSC possibly a factory built Ford based V8 Sportster
                              - 4th owner of Q309 RNV, an early Cabrio built by Bob Copping, owned Doug & Liz Billings for 16 years
                              - 9th Custodian of JRR 929D, Triumph Vitesse based special Paul Moorehouse built prior to the Triumph Roadster kits.
                              - 8th owner of Roadster chassis number 2395. Now owned by Barry!
                              - Builder of chassis number 2325 (PKK 989M) in the mid 80's. Now owned by Eric & Lynne.

                              Comment

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