Sportomatic Servo Diaphragms

[72_sporto]

Michel mentioned that he was having some issues with his sporto box when we spoke through the week. His gearbox was rebuilt about 7 years ago but, as far as he knows, the servo is still original. Having owned a 3 sporto boxes, I have also had the odd issue... Starting with a snapped tooth on 1st costing $3500 to repair 25 years ago.

Most of the problems I have had, though, have been with deteriorated diaphragms. I said that I would post a photo of one of these for Michel to have a look at as they don't tend to pop up much on the web.

I tried using vulcanising glue, superglue and layers of DOW silicone to repair it but they all failed within a short time.

[72_sporto]

more photos..

The next photo shows a Sportomatic servo that was rebuilt using a Lockheed brake booster diaphragm as well as different diaphragms Fichtel and Sachs used in two differently marked servos that I have. One from a 72 the other from a 76. There is about 10mm difference in width between the two.

The cases on 2 of my servos are marked 135 x 60 and the other one is marked "Saxomat". (Possibly from a Merc?) All 3 cases are the same diameter.

The white diaphragm is the second prototype of my newly moulded silicone diaphragm. Untested as yet.

I use a small 90 degree o-ring hook probe to initially lever open the locking band then a modified paint can opener to complete the job. These will mark the plating on your servo housing in opening it. (For those that have pristine servos...) The band is 0.5 x 16 mm steel- from memory.

I found some earlier posts by John on Pelican about testing the integrity of the servo. They referred to attaching hoses and pumps but I could not find any further details. All I do- with the servo out of car- is just plug the hose tube outlet and push and pull really hard on the clevis. (Almost stand on it....) If it moves, the diaphragm is cactus...

Normally just holding my thumb over the outlet and pushing/pulling on the clevis is enough to tell if there is a problem.

[9er]

Interesting Bill.

[Merv]

Well done Bill. This kind of information adds to the 901 Encyclopaedia.

[72_sporto]

Thanks Merv.

I forgot to add...that I needed to move the clevis to a number of different positions when testing as small tears can be hard to pick and can temporarily "reseal" still allowing the servo to intermittently work.

Be careful to only apply longitudinal force to the clevis to avoid bending it!

[Michel]

Hey bill

Just what I'm looking for - good info. are you using dental plaster or silicone for the mold?

Perhaps someone needs to twist johns arm so he'll reopen his werks special servo.