Tweet
The Marlin Cabrio V8 is a pretty fiery beast, particularly with a modified engine, so if, like me, you’ve been using it with the Cortina Mark IV servo and master cylinder, you will know that uneasy feeling that the brakes are not quite up to the job. I understood the Cortina gear was necessary because the larger engine took up more space under the bonnet, but you need better braking with the more powerful engine, not worse!
When I saw on the Marlin Owners Forum that Mike Garner was offering a 7” dual servo, I lost no time in obtaining one. From the comments on the website, it seemed the best way to improve my braking, but I was hoping that it was not too complicated to install. In the event, it was surprisingly easy. Installing the servo on the bulkhead only required some easing of the holes I had drilled for the Cortina servo in the first place and the Cortina master cylinder (I had purchased a new one on the internet) required the same easing to fit neatly on the front of the servo. Mike included an adaptor plate with the servo, but I did not need this. As the new servo was only ¾” longer than the Cortina one, I was able to fit the existing pipe work. This was all accomplished quickly and easily and on my first test drive I was astonished by the improvement in the braking. I was able to lock the brakes with fierce braking, but with normal pressure, the braking was very powerful, smooth and well balanced. The only problem was that there was excessive brake movement to activate the brakes. The reason for this, I believe, was that the Cortina master cylinder had a bore of 18mm, compared with 22mm on the Sierra. This creates greater pressure, but takes longer pedal travel to achieve it.
Mike also supplied a clevis with the servo, which would have been very useful to attach to the brake pedal via a threaded rod, as it would have made the pedal linkage adjustable, but I could not find a way to do this. I had a bolt welded to the side of my brake pedal, rather than a hole, so in the end, I adapted the Marlin block used in the original build, but shortened it in order to raise the pedal to the same level as the other instruments. This works perfectly well, but it is not adjustable.
In order to reduce the pedal movement, I turned my attention to the front end of the servo, removed the existing pushrod and replaced it with a 40mm long 4mm dome-headed bolt. I adjusted it so that about 20mm was showing and replaced the master cylinder. I was afraid I had overdone it so that the brakes would not release when the pedal was eased, but, as luck would have it, it worked beautifully. My brakes work just as well as before, but with reduced pedal travel. I had planned to make this the first stage of a two stage plan; the second stage being converting the rear brakes to disc, but quite frankly, I think the installation of the new servo had done the job quite without further modification.
I cannot comment about using the 7”dual servo with other components used in the braking, but for owners with the Cortina servo and master cylinder, it is very effective and is quite easy to install. I am extremely grateful to Mike Garner who gave me some invaluable “after sales” advice and for putting me in touch with other Marlin owners who had dealt with similar problems in their conversions.
One last comment; I know some owners with the V8 engine has experienced some problems as the master cylinder (being a little further forward) fouls the air filters on the SUs.. I had no such problem because I have Holly carburetor which sits happily between the rocker boxes!
When I saw on the Marlin Owners Forum that Mike Garner was offering a 7” dual servo, I lost no time in obtaining one. From the comments on the website, it seemed the best way to improve my braking, but I was hoping that it was not too complicated to install. In the event, it was surprisingly easy. Installing the servo on the bulkhead only required some easing of the holes I had drilled for the Cortina servo in the first place and the Cortina master cylinder (I had purchased a new one on the internet) required the same easing to fit neatly on the front of the servo. Mike included an adaptor plate with the servo, but I did not need this. As the new servo was only ¾” longer than the Cortina one, I was able to fit the existing pipe work. This was all accomplished quickly and easily and on my first test drive I was astonished by the improvement in the braking. I was able to lock the brakes with fierce braking, but with normal pressure, the braking was very powerful, smooth and well balanced. The only problem was that there was excessive brake movement to activate the brakes. The reason for this, I believe, was that the Cortina master cylinder had a bore of 18mm, compared with 22mm on the Sierra. This creates greater pressure, but takes longer pedal travel to achieve it.
Mike also supplied a clevis with the servo, which would have been very useful to attach to the brake pedal via a threaded rod, as it would have made the pedal linkage adjustable, but I could not find a way to do this. I had a bolt welded to the side of my brake pedal, rather than a hole, so in the end, I adapted the Marlin block used in the original build, but shortened it in order to raise the pedal to the same level as the other instruments. This works perfectly well, but it is not adjustable.
In order to reduce the pedal movement, I turned my attention to the front end of the servo, removed the existing pushrod and replaced it with a 40mm long 4mm dome-headed bolt. I adjusted it so that about 20mm was showing and replaced the master cylinder. I was afraid I had overdone it so that the brakes would not release when the pedal was eased, but, as luck would have it, it worked beautifully. My brakes work just as well as before, but with reduced pedal travel. I had planned to make this the first stage of a two stage plan; the second stage being converting the rear brakes to disc, but quite frankly, I think the installation of the new servo had done the job quite without further modification.
I cannot comment about using the 7”dual servo with other components used in the braking, but for owners with the Cortina servo and master cylinder, it is very effective and is quite easy to install. I am extremely grateful to Mike Garner who gave me some invaluable “after sales” advice and for putting me in touch with other Marlin owners who had dealt with similar problems in their conversions.
One last comment; I know some owners with the V8 engine has experienced some problems as the master cylinder (being a little further forward) fouls the air filters on the SUs.. I had no such problem because I have Holly carburetor which sits happily between the rocker boxes!
Comment