924Board.org

[Feltron]

Hey guys, long time lurker first time poster, I've been working on restoring my 78 and I've finally gotten it up and running and out on the road. I have two problems with the car though, one as noted in the subject is the brakes act up. Any time I come to a stop and apply the brakes one of two things happens, A) the revs go to about 2 grand and stay locked there untill I release the pedal or B) the revs dive and the car stalls. Normally the car stalling wouldnt be a problem but that leads me to the other issue, if the car has been hot for a while so that the fan (singular as the passenger side is broken right now) is on, the starter gets stuck engaged. Even with the key out of the ignition the car continues to turn over until I keep flicking the key and it disengages. However when the fan shuts off the car starts right up frist try no problems. I have been guessing that the brakes could be a bad booster (which is ok becasue in december I plan on doing the 944 brake upgrade got all the hardware and Fuchs from my local scrap yard for a steal) but I have no way to test that, also I feel that the starter issue may be due to the one fan not working and there being a draw issue from the battery. All of that is just speculation and it has been troubling me for a while now, anything you guys could offer would be of great assistance. Thanks

[datatrain]

I'm no expert but it sounds a though one problem is a faulty ignition switch. They are cheap and a quick fix after you do it once.

High revs.....I think maybe you have a leak in the Vac brake system when you press the pedal.

The others..... no idea.

There are more knowledgable people here that can probably point you to the cause.
_________________
'78 924 NA with Collector plate
33 year old car, with me for 21 yrs
Mint '92 318i BMW
Near mint '98 Buick LeSabre
VE7HFR

[Ozzie]

Ok, one long paragraph usually dont work for us old techos.

Break it up a little into different problems.

Brakes- sounds like the booster is duff causing vacuum leaks

The starter on these cars is right next to the exhaust.
Check your heat shields.
I will guarantee you will need to pull the starter out and clean up the internals of the sticking solenoid.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

[Ozzie]

Ok, one long paragraph usually dont work for us old techos. Break it up a little into different problems. Brakes- sounds like the booster is duff causing vacuum leaks. The starter on these cars is right next to the exhaust. Check your heat shields. I will guarantee you will need to pull the starter out and clean up the internals of the sticking solenoid.


Which is easier to read?
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

[Feltron]

thanks data, the only reason I dont think its an ignition switch is Ive tried 2 other ones as an early troubleshooting tactic and that didnt help. But I'll look into the vac leak

[Feltron]

Big help Ozzie, I was hoping someone else would echo my thoughts of the booster. Didnt really know the convention for listing problems, though I didnt mind so much reading your solid paragraph I understand that seperating the problems would be better for troubleshooting. I'll try to keep it in mind for future posts.

Thanks for the help

[Slam]

Check valve in brake vac line faulty?
_________________
'88 944 Auto - may or may not resurrect

[Smoothie]

I'd suspect the brake booster itself since the stall or high revs occur only when the brake pedal is depressed.

+1^ on cleaning the starter solenoid. When dirty (gunked-up) they're known to not operate correctly - usually in the opposite way to your current experience, in that the solenoid won't even move to activate the starter.. -But it's easily conceivable that one might fail differently, and slide into the activate position, then get stuck there instead.
Very unlikely that there's a direct corrolation between fan running and starter malfunctioning. More likely just coincidence as both tend to occur when the engine is hot.
_________________
"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Feltron]

The only reason I thuoght the fan may play into it was becasue I read on a mustang board that some guy was having the same problem with his 68' 302 and he said it was only when the fan was on that it would get stuck.

My rationalization for this was that with only one fan operating and the fans being wired in parallel all the current is directed to one fan causing more draw on its wire from the battery, this added load would heat the wire increasing resistance and putting even more load on the battery. With more draw on the battery from the fan less curent is allowed to the solenoid causing the solenoid to close partially then arc and heat up causing the stick.

Long winded explination I know but it seems reasonable. I will deffinatly be cleaning the terminals and I have a 77' that I'm using as a parts car so I'll take the fan off that (and get a little creative rewiring it as the plugs for the fan changed post 77.5.

Also good to hear all this agreement on the brake booster as I was replacing it when I do the brake upgrade this winter anyway. Thanks again for the help guys.

[!tom]

[gohim]

You have several issues here.

#1, I would not continue to start the engine and drive the car unless you have the cooling system working properly. So figure out why the 2nd fan is not working, whether it's a bad relay or bad fan motor, you need to fix it immediately. When you shut the engine off and the cooling fan is running at high speed, then the cooling should continue to run at the slow speed. If the cooling fan continues to run at the high speed with the engine off, then the cooling fan relay is sticking and needs to be replaced. If the cooling fans do not continue to run at the low speed when the engine is shut off, then the cooling fan resistor is probably defective. On your model year, it may be located on the radiator core support, or under the dashboard on the firewall behind the instrument panel. If you haven't already, you can test the 2nd cooling fan by jumpering it directly to the battery. If it doesn't work, then the motor is no good. If it does work, then you probably have a bad relay. There are three relays related to the ventilation and ac systems, and the failure of any one could affect the operation of the cooling fans.

On the brakes, do you have an automatic transmission? A transmission that's going bad could cause symptoms like this (defective torque converter?). If not the transmission, I'd guess that you have a bad brake vacuum booster. You don't have to switch to the 944 vacuum booster to install four wheel disc brakes, the late 1980 or newer 924 master cylinder and vacuum booster work fine with four wheel disc brakes. Porsche used the same parts for both disc/drum and four wheel disc brake 924/931 cars from 80-85. If you switch to the 944 master cylinder, you also have to replumb the brake lines front and rear circuits from cross circuits.

As to your engine not shutting off when the key is turned off. Is the engine still running at full speed, or is it sputtering? Sputtering would indicate that the engine is dieseling, which is not an ignition switch problem, it's a detonation problem (excessively hot cylinder temperatures and/or timing problems). If the engine runs at full speed with the key turned off and removed, I'm guessing that the problem is in the steering column housing and ignition lock cylinder, and not the electrical portion of the ignition switch. These cars are old, and some/many parts are mechanically worn out.

[Feltron]

@tom
Yea youre right V=IR dunno why I ignored the math and just went with intuition.

@gohim
1: The fan is broken becuase th previous owner snapped a terminal off the passenger side fan plug and I am in the proscess of replacing the whole fan.

2:Its M/T, and the reason I'm switching the booster is becasue I have all the parts from an 84 944 to switch to the 4 wheel disk. And I am aware that teh 924 has x style brake circuts where the 944 has front to back.

3: And when the starter solenoid sticks the engine is not running, its only the starter that sticks and if it does the engine will not start just turn over. And I took apart the steering column when I first got it to change ignition swtiches becase the one that was in it was cracked, so its not that.