Thread: Dual 7" Servo
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Old 15th March 2014, 05:48
Mike Mike is offline
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Default Rose Joint Now Fitted

There have been 49 Marlin members who bought one of our dual 7" servo upgrade kits - which must be a high percentage of all the non Ford engined Sportsters and Cabrio/Hunters, and says a lot about what the they thought of their original brake set up.

There has been one issue which affected a small number of owners, where the servo would continue to apply a gentle force to the brakes after taking their foot off the pedal, causing them to over heat.
It seemed to affect the Zinc plated servos more than the black powder coated ones. Initially these were returned to the supplier as faulty, but through time I have come to believe that it may have had more to do with the way the Marlin servo is aligned with the pedal in the Marlin designed pedal box.

Marlin offset the angle of the pedal pivot and the servo mounting face, to create more space in both the footwell and the engine bay. The angle is evident in the above photo: the pedal box is lined up with the grout lines in the tiles, highlighting the servo angle in the foreground......

Whilst this did not seem to affect the Metro servo, which would tolerate a significant offset, the vaccum seal in the rear of the new dual 7" servo seems much more sensitive, and if it does not seat correctly appears to lead to brake binding complications.

I drilled, and then slightly elongated, a hole through my brake pedal, and fitted a clevis around the pedal using a clevis pin to achieve the alignment I wanted. Other owners left the Marlin welded in bolt and chose to mount the clevis to one side of their pedal.

Patrick and a couple of others used rose joints which are a much better solution ( and I wish I had thought of this when putting the kit together). It allows the push rod/pedal connection to bolted up tight, yet freely accepts the offset angle, and also accommodates the change in angle as the pedal travels through its arc.
So, when my clutch master cylinder failed (due to poor alignment - caused by me!) and I had to remove my pedal box yet again! - I chose to replace my brake clevis with a rose joint at the same time.

For anyone interested in adopting the rose joint solution, the servo has 3/8" UNF threads, but the bolt that is usually welded into the Marlin pedal is 10mm. If you buy a straight forward 3/8" rose joint, it will come with a 3/8" hole in the rose joint (which is slightly less than 10mm). Also all the rose joints I have located were all just too short to screw onto the servo and allow the pedal to be set where I wanted it.

My solution was to buy a 10mm rose joint, and a 3/8" x 20mm collar, and to spot weld them together.
I have been very careful to then allow the rose joint to locate laterally against the pedal in its central rest position, and used a couple of washers on the pedal pivot to ensure they lined up perfectly laterally.
Job done.
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