Replacing a Sporto Vacuum Servo Diaphragm

[72_sporto]

Several of the guys that have bought new diaphragms from me have asked about the process of replacing these diaphragms. I had posted some pics on TYP901 but you need to be a paid member to see them. So I have combined and elaborated several of my older posts below.

Having owned 3 sporto boxes continuously over the last 30 years, I have had the odd issue or two... Starting with a snapped tooth on 1st- costing a small fortune to repair 27 years ago. (On a RS spec 2.7) Most of the problems I have had, though, have been with deteriorated diaphragms- like the one in this photo. I have tried using vulcanising glue, superglue and layers of DOW silicone to repair them but they all failed within a short time. Mostly due to the overall drying out of the original rubber.



I own five Fichtel and Sachs servos from cars of all different years. The cases on 4 of my servos are marked 135 x 60 and the other one is marked "Saxomat". (Possibly from a Merc?) All 5 cases are the same diameter. The Saxomat- that came from a 76 four-speed- is 10mm wider than the other 4. (My diaphragms still fit this one just fine.)



I found some earlier posts by Fishcop 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 that I do- with the servo out of car- is just plug the hose tube outlet really well and push and pull really hard on the clevis. (Almost stand on it....) If it moves in or out, 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. You can usually hear a "hiss" from the leak- if your ambient environment is quiet enough. The piston should be in the middle of it's travel so that the diaphragm does not temporarily reseal against the case. You should also try moving the clevis conically to a number of different off-center positions when testing as small tears can be hard to pick and can temporarily reseal, still allowing the servo to intermittently work. But be careful to only apply longitudinal force to the clevis when doing this to avoid bending it!

It is possible to work on and adjust most servos without removing the motor or even dropping the oil for many cars. Just by removing the 2 rear engine bolts and lowering the motor a few inches. On my 72 you can lower the motor enough to remove the complete servo. (You may need to disconnect wires or fuel lines on some cars.)

Over the years, many servos have been rebuilt by brake and clutch shops using modified brake booster diaphragms- like the Lockheed one below. My servo lasted about 3 years with one of these....



I don't think that the factory ever offered just the diaphragm as a spare. Probably due to the swagged band clamp. I searched in vain for many years. They did offer the complete servo as a spare for a while and there are several retailers that still list complete new servos for sale. But several guys have told me that, even when they bit the $1300 bullet, they all had no stock when an order was placed.

I was already running a hand cast prototype silicone diaphragm in my car when I first met Fishcop several years ago. His enthusiastic response at finding a newly made diaphragm and that of the TYP901 guys convinced me to develop it further and get it manufactured.

The swagged locking band that holds the servo cases together is 0.5 x 16 wide mm steel- from memory. It is this thin so that it clears the left drive-shaft. Some are continuous and some come in 2 halves. You can re-use it if you take care in removing it. 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 may mark the plating on your servo housing in opening it- for those that have pristine servos- so you may want to use some tape to protect it. You should be able to get away with only prying up one side of the band. If you do destroy it in removing it it is possible to use 2 piece truck servo clamps that have a section removed to clear the driveshaft. (As in the second pic above.)

[72_sporto]

I currently use a $20 pair of nail pincers to re-swage the bands back on. Make sure the vacuum inlet connector is pointing in the right direction before swagging. (I recommend using a permanent marker to draw a continuous line on both cases before disassembling them.) I usually use a carpenter's screw clamp to firmly hold the two cases together which allows me to do the swaging. (Not shown in this pic.) I also use a 10mm by 40mm strip of 2mm aluminium plate to protect the band from the pincers and to allow the correct clearance in the crimp. (You can see this if you look carefully.) Don't over-crimp. You don't need to apply much force when crimping to get a really good seal.

[jbell959]

Thank you.... I bought a couple diaphragms from you and I'm getting ready to rebuild mine. Perfect timing!!!

[93nav]

72_sporto,

Thanks for taking the effort to get these parts made and posting the howto info here. Would the metal band from this VW kit work? Not sure what size the VW servo is.

Thanks

Volkswagen Restoration Parts | New VW Parts | Volkswagon: Clutch Servo Repair Kit, Auto Stick ,Bug & Ghia '68 - '74

[72_sporto]

Originally Posted by 93nav

72_sporto,

Thanks for taking the effort to get these parts made and posting the howto info here. Would the metal band from this VW kit work? Not sure what size the VW servo is.

Volkswagen Restoration Parts | New VW Parts | Volkswagon: Clutch Servo Repair Kit, Auto Stick ,Bug & Ghia '68 - '74

Hi 93nav, I looked into Autostick servo many years ago, as I hoped that the diaphragm would fit the 911 and it would be a quick, cheap repair. It doesn't. The VW is much smaller- 125mm OD from memory.

The nail pincers are not the most elegant solution but they are cheap and they do work. You can get a neater job by rounding off the jaws with a file. You can also use channel lock pliers- at a pinch. (pun unavoidable..)

When I get some time I'm going to look into developing a cheap, can-opener type of swaging tool and offering new locking bands for the concourse guys.....could be a while, though.

[jbell959]

Originally Posted by 72_sporto

I currently use a $20 pair of nail pincers to re-swage the bands back on. Make sure the vacuum inlet connector is pointing in the right direction before swagging. (I recommend using a permanent marker to draw a continuous line on both cases before disassembling them.) I usually use a carpenter's screw clamp to firmly hold the two cases together which allows me to do the swaging. (Not shown in this pic.) I also use a 10mm by 40mm strip of 2mm aluminium plate to protect the band from the pincers and to allow the correct clearance in the crimp. (You can see this if you look carefully.) Don't over-crimp. You don't need to apply much force when crimping to get a really good seal.

I'm finally getting ready to disassemble and rebuild my servo. Do you know what the original finish was on these early 911 servos? Mine has a nice surface coating of rush so I can't tell.

[72_sporto]

Originally Posted by jbell959

I'm finally getting ready to disassemble and rebuild my servo. Do you know what the original finish was on these early 911 servos? Mine has a nice surface coating of rush so I can't tell.

Hi jbell, Sorry to take so long to reply. I've been working away in Sth America.

All my servos have a dark grey metallic coating that you can see in the 4th photo. Not sure what this actually is. I'm about to take a bunch of parts to my electroplater and these include some rusty servo shells. I'll let you know what he thinks it is.

[72_sporto]

Finally got a chance to drop my servo covers- and a whole lot of other parts- up to East Coast Electroplating. It looks like the covers may be Parkerized. This is the same type of finish that is commonly used on guns. The boys at ECE are going to do some samples over the next couple of days....

[Arqueteck]

i just saw all this post. fantastic. exactly what i needed to learn.

what connects the round metal diaphram plate to the rubber diaphram? i presume two plates sandwiched together??

can i buy some diaphrams too??

alex

[72_sporto]

Hi everyone, Demand dropped off last year so I removed the ebay and Gumtree listings. I now only really check typ901 regularly. If you need to get my attention on ESR or Pelican it's best to PM me. I still have a few diaphragms available.

[targa68SPM]

Hello,

@Sporto

Do you still make these or do you perhaps have one left? Have a Sporto -68 that probably needs it...


rgds from Sweden,



//Martin

[camshaft6au]

Hi Sporto,
I'm in Hamilton Brisbane.
I've a 74 911 4speed Sporto and I have a leaking servo diaphragm.
Do you still have any?
Could give me a call 0414964955
Regs
Camshaft