Sportomatic problem.... vacuum control valve

[frankposj]

Hi All,

Recently acquired a 1968 soft window target sportomatic to my collection.

Engine runs great, but the clutch does not disengage. Therefore a lot of grinding noises when I try to put it into gear. Guess it is my clutch that is stuck. As far as I know the engine needs to go out for this, is this correct??

I also have to take a look at the lever switch, I have a continues 12V going to my control valve. There is a bit of vacuum on the line....could it be the case that my disengaging problem of the clutch is related to the continues 12V going to the valve??

Does the system need to build up pressure to disengage? If so, that does not happen on my car because of the continuous 12V going to the valve. If this is not the case (building vacuum pressure) I definitely need to pull the engine.

Just trying to understand the principles a bit more.

Thanks for the help..

Thanks, frank

[chrisg252]

There are two threads about Sportomatics that you should review.

This one is a good overview:-http://forums.pelicanparts.com/porsche-911-technical-forum/470611-sportomatic-you-experienced.html

And this one is the most detailed :- Ultimate ?maybe? Sportomatic Gearbox Rebuild

Good luck

Chris

[frankposj]

Hi Chris,

Thanks for your reply. I will take a look at the links.....

Regards, frank

[rodoredas]

Hi Frank,

I wouldn't be removing the engine just yet, there are a some things to test before that. The clutch is operated by vacuum and a switch at the base of the gear lever. Check the switch first.

Take the shift knob off, the gear shift boot and the plastic top from the switch, it's a white plastic moulded fitting. Look closely you will see this contains 2 switch mechanism, one towards the front the other the rear. Make sure these contacts are engaging when move the gear shift lever forward and back an inch or so. Clean these contacts with small piece of emery paper and electronic cleaner. If this switch is not working the clutch will never dis-engage. Make sure it is orientated properly, if the switch is not aligned with the gear shift lever movement it won't make good contact. Imagine that the gear shift lever moves North/South if the switch is aligned East/West (or not exactly North/South) the contacts will never meet properly. Check the alignment and clean it.

Then start the engine in neutral, with cap off the switch. Gently move the gear shift lever (an inch or so) the contacts should touch and you should actually hear the clutch disengage if you listen carefully.

If you have verified that the switch is working but you still cannot engage a gear, you may have no vacuum. Just like on the manual there is a lever that pulls the clutch from the pressure plate, but instead of that lever being operated by your foot it is operated by air pressure and a lower air pressure (vacuum) inside a cylinder called a Servo. This cylinder device had a rubber plate inside it which separates the space in the cylinder into 2 equal chambers. Attached to the rubber plate is a lever connected to the clutch to pull it from the pressure plate. This chamber is open to atmospheric pressure. The two chambers are completely isolated from each other. The other chamber is 'fed' vacuum from the engine manifold via the Solenoid. This chamber can, via the solenoid be at atmospheric pressure also. Obviously if one half of the chamber has 'vacuum' and the other 'atmospheric pressure' the air pressure will push on the rubber separator, pull the lever forward and disengage the clutch.

So is there enough vacuum being generated. Pull the vacuum pipe from the manifold that goes to the solenoid, plug in a vacuum gauge and take some measurements. I'm not an expert in how much is needed but tests I've done indicate you need about 10 or more inch hg. That is about 9psi, atmospheric is say 14psi. That equates to about 150lbs pressure difference between the two chambers - enough to pull the clutch of the pressure plate. I have issues at 8 inch hg.

If you have vacuum, then the Solenoid could be the problem. It has an electo-magnet, operated by the switch. The electo magnet operates valve inside in the Solenoid. The valve simply opens/closes and allows 'air' or 'vacuum' into the chamber in the Servo.

Should you have 12v to the Solenoid all the time - not sure, (but here again I'm not sure, car electrics is something that still gets me thinking!!) which tends to point to the switch. This is first place I look and do regular maintenance on it and have some spares.

There is another switch, the Bypass switch, located on the gearbox, again operated by changing gears, that too may not be operating correctly. I have also found that you must let the engine warm up and ensure your oil lever is at the correct level. Unlike the manual, the engine and gearbox share the oil and I have found that you must allow a few minutes for oil circulation to reach all sections of the gearbox, particularly if you try an move into reverse gear without adequate circulation/warm up time. The reverse gear is a long way from the oil tank!

Try and get it sorted, one step at a time, starting with comprehensive look at the switch, the Sporto is great fun when you know how to drive them properly.

Cheers
Shane

[rodoredas]

Hi Frank,

...had to close that last post before i finished...

I have low vacuum in my Sporto due to some hot cam timing, and i do not rely on manifold vacuum anymore. I've installed a CVR Vacuum pump, one of these which supplies constant 15 inch hg (7 psi) to the vacuum system, the tank and servo. This equates to about 200lbs difference in pressure in the Servo chambers, again enough to pull the clutch away. This might not suite your (i assume) carby engine due to lack of mount points, but if the engine isn't generating enough vacuum this can help.

Obviously if the vacuum tank and servo leak (suck in air) then you have different problems, and there are ways to check if the tank and servo leak. You could get some smoke generating devices and spray it around the tank to see if gets sucked in. I've never done that but I'm sure it's possible and perhaps other Sporto experts may know of ways to check that without removing them. Access to the Servo is difficult though as it sits atop and to the side of the gearbox.

I would imagine that access to the Solenoid on 69? Carby engine may be easier than on my CIS 75, you could always remove that and get auto electrician to test it. I tried that on a spare Solenoid I had and stuffed it up - again my auto electric skills lack a little. If it's working you can hear the valve clicking as it opens and closes when current is applied - I got that far in my test and then blew it!!

below is one of may hand drawn diagrams, I should have included the set of these in my other thread, for some reason forgot to do that, but I will.

You can see that the Solenoid valve (horizontal red valve) simply allows 'air pressure' or 'vacuum' to get into the vacuum chamber side of the Servo, thus allowing the clutch to dis-engage as it is shown in this diagram. There is valve inside the Solenoid at point C that controls the level of 'vacuum' in the tank (no vacuum in the tank means you can't change gears - essentially). It's unlikely this valve is stuck it's very simple mechanism, a spring and plastic valve stopper.

having said all that - start with the Switch!!



good luck
cheers

[frankposj]

Hi Shane,

Thanks a lot for your help and taking the time to write this helpful reply.

My switch is not working correctly. This means, it is sending 12V to the valve continuously. I know where this comes from.

If I take the tubes from the outlet of the valve I feel sucking from both outlets (the one going to the reservoir and the one going to the "box" on the gearbox with the lever attached.

No disengagement of the clutch. I tried to disengage it manually but there is no movement. I was just wondering whether the continuous opening of the control valve could lead to my problem of non disengagement..... In other words: does the system need to build up vacuum in the reservoir before being able to disengage?

If so, this could be causing my problem.

Could my valve be broken? Reason I ask is that with 12V there is vacuum coming from both tubes (aka outlets on the control valve). My gut feeling tell me that this is correct. Both outlets are "open" because the reservoir should help the valve with producing more vacuum for the disengagement, correct??

If so, I need to pull the engine and gearbox to check disengagement box on the gearbox (membrame??) and check the clutch for sticking.

I have also read something about a fuse in the manual. Where is it located and what is it for? Is it for the control valve??

Just trying to fix a problem and understanding the methodology.....

Thanks, frank

[chrisg252]

Frank,

I can only speak for the '75 model year. There is a Sporto only fuse in the engine compartment ( left side behind the removable cover of the regulator plate) I believe it has something to do with the heater blower motor. There seems to be no fuse on the circuit for the selector switch.

Chris

[john walker's workshop]

it always has 12V. the gear shift contact is the ground (brown wire) which completes the circuit to activate the vacuum valve unit which passes vacuum to the release servo. disassemble the shift handle and file the contacts clean and adjust it to move fore and aft with very little clearance between the upper and lower sections. be sure the wire to the lower part is still intact.

[Scott Douglas]

Ya'll might want to look at this thread for a solution I came up with:

Sportomatic switch improvement

[Scott Douglas]

This may help you understand the principles involved with the Sportomatic operation as well...



I hope it's readable...

[frankposj]

Hi Scott,

Thanks a lot for the help.

Do I understand it correctly that the clutch is disengaged when the shifter is in Neutral?

I do have a bid of vacuum, but nu clutch movement. My guess is that I have to look a the membrane of the thing moving the clutch or look at a stuck clutch disc. The car has been standing in the garage for a long time before I bought it.

Before this I will check the amount of vacuum, just to be sure.

Thanks, frank

[Scott Douglas]

Frank
Yes, that is my understanding too. The clutch is disengaged when in Neutral. That is one of the reasons you can't double clutch a Sporto when down shifting.
In order to check the diaphragm you'll need to drop the engine/trans as it is buried up there on top of the trans. At least it was on my SC, your car may be different but I doubt it.
When I had my diaphragm out to test it, I had a hose attached where the vacuum hose connects and used a dowel as a plug to seal it. Remove the plug and manually push the rod coming off the diaphragm 'IN' as if it were being actuated. Install the plug so the hose is sealed. The rod should stay in the 'IN' position and you shouldn't be able to pull it out either. It doesn't take much air pressure to actually move the diaphragm so I would not hook it up to any compressed air source except a bicycle pump.
Hope this helps.

[rodoredas]

Hi Frank

How did you go, have you done any more tests, interested to know what you have found here

Here's my understanding

With the engine off and gear shift in neutral air pressure in the Servo has equalised because the valve in the Solenoid has 'closed' (moved to the right in the Scots diagram above, allowing atmospheric pressure into the top side of the Servo. The 'closed' value is holding vacuum in the tank as is the small Check Valve - 17 in the diagram, atmospheric pressure in the manifold has forced this to close. The small check valve in the Solenoid directly opposite the tank port may well have closed due to different pressure in the system. So there is some vacuum in the tank and the rest of the system is at atmospheric pressure. The clutch is therefore engaged by spring plate pressure.

Start the engine with the gear shift in neutral, the bypass switch will supply power to the solenoid opening the valve and allowing some stored vacuum from the tank into the Servo (really just a reduction in air pressure). The check value will open as manifold pressure changes allowing more vacuum into the system. This will be fed to the top side of the Servo immediately causing the clutch to disengage - if the Servo membrane and lever system is working. As Scot mentioned and the diagram shows, the clutch should be disengaged when in neutral after starting the engine.

But it is difficult to actually see that!

If the membrane and lever system are not working (the membrane is torn or there are vacuum leaks etc) the clutch will still be engaged. If the Solenoid valve has not opened (moved left in diagram) there will be no vacuum at the top of the Servo - same problem, clutch still engaged. I think you said you had vacuum on both ports of the Solenoid (Tank and Servo) so I reckon that indicates the Solenoid is OK and vacuum would be created in the top section of the Servo.

So with engine running and gear in neutral and foot on the brake pedal - can you run through the gears in this state without any crunching noises? I know this is what you said initially but clarifying if this is the case with this simple test, may help with isolating the cause.

As you run through the gears (push into 1st and release gear shift, pull into second and release gear shift etc) you should sense the clutch disengaing and engaging and also notice a slight difference in the tone of the engine when the clutch being engaged and disengaged. In fact just by moving the gear stick forward and backward a little (so the switch closes/opens) you should feel the same sensation without having to actually engage gears. Or you can try this, push the gear shift into 1st and let go, then with your finger push the gear shift forward a little, you should feel the clutch disengage.

In this state (car running in neutral, pushing gear shift forward) there are a couple of things happening. Firstly the Bypass switch is holding power to the Solenoid. As you push the gear stick forward the micro-switch closes while the bypass switch opens and power to the Solendoid is controlled by the micro-switch. If the micro-switch is not working the Solenoid valve will close and you will loose vacumm and the clutch will engage while you are trying to push it 1st. Once you are in 1st and you release the gear shift the micro-switch will open (the bypass switch is also open now) so the Solendoid valve closes allowing atmospheric pressure into the top half of the Servo, equallising pressure. The clutch will engage by the pressure of the pressure plate. Pushing or pulling the gear shift slightly will cause the micro-switch to close and a subsequent pressure difference in the Servo, dis-engaging the clutch.

Cheers
Shane