GSF - difficulty starting/solid brake pedal

[Pielight]

On a handful of occasions GSF very recently, I've had a trouble starting my GSF. On each occasion, when pressing the brake pedal to allow the car to start, the pedal is rock solid as if mechanically locked in place. This I believe, is preventing the contacts of the brake pedal micro switch being made and hence the issue with starting. I had to press the pedal VERY hard for the car to start. Any ideas...thanks.

[ColinBarber]

Normally you would have a little pedal travel before the brakes engage, are you saying there isn’t any movement at all?

[Spock66]

Get an assistant to check if the brake lights come on when you have this problem.

[Steve]

sounds like servo has lost vacuum

once car starts it will have vacuum, but obvously you cannot.

if you do manage to start and it does it again then probably leak in servo etc.

[Pielight]

6 hours ago, ColinBarber said:

Normally you would have a little pedal travel before the brakes engage, are you saying there isn’t any movement at all?

Yes that's right...when the issue occurs there seems to be little to no perceivable movement. 

There car had stood idle a week and I tried starting it... It started no problem at all. I'm beginning to wonder if the switch is adjustable and has gone out of adjustment requiring the pedal to be pressed harder than before. Thanks for reply.

[Pielight]

7 hours ago, Spock66 said:

Get an assistant to check if the brake lights come on when you have this problem.

Good call thanks...I will try that.

[Pielight]

6 hours ago, Steve said:

sounds like servo has lost vacuum

once car starts it will have vacuum, but obvously you cannot.

if you do manage to start and it does it again then probably leak in servo etc.

Thanks - I've just started the car without issue after it had stood a week - if there was a leak you would expect you'd expect a problem after that length of time...unless the problem is intermittent. Very strange.

[4969_LXS]

It could be the brake booster check valve is not operating as it should be. It's documented on the ISF. Could be a similar set up on the GSF maybe ?

[ColinBarber]

Even if you lost all vacuum assistance you would still easily have enough movement for the brake lights and starter to operate. 

 

INSPECT BRAKE PEDAL FREE PLAY

Stop the engine and firmly depress the brake pedal several times until no vacuum is left in the brake booster assembly.

Depress the brake pedal until a slight resistance is felt. Measure the distance as shown in the illustration.

 

Brake Pedal Free Play
1.0 to 6.0 mm (0.0394 to 0.236 in.)

 

 

On 11/12/2023 at 6:23 PM, Pielight said:

I'm beginning to wonder if the switch is adjustable and has gone out of adjustment requiring the pedal to be pressed harder than before.

Both the pedal height and brake switch can be adjusted but would never need to be done once set up. It is worth looking at the brake pedal mechanism itself just to make sure nothing is fouling the pedal and everything looks correct.

[Pielight]

On 11/12/2023 at 8:10 PM, 4969_LXS said:

It could be the brake booster check valve is not operating as it should be. It's documented on the ISF. Could be a similar set up on the GSF maybe ?

That's a good call....it could well be that the servo is not holding the vacuum as long as it used to and I was used to just pressing lightly on the brake when starting. I guess the check valve would allow the vacuum to leak off rather than sealing it in.

[Pielight]

On 11/12/2023 at 8:11 PM, ColinBarber said:

Even if you lost all vacuum assistance you would still easy have enough movement for the brake lights and starter to operate. 

 

INSPECT BRAKE PEDAL FREE PLAY

Stop the engine and firmly depress the brake pedal several times until no vacuum is left in the brake booster assembly.

Depress the brake pedal until a slight resistance is felt. Measure the distance as shown in the illustration.

 

Brake Pedal Free Play
1.0 to 6.0 mm (0.0394 to 0.236 in.)

 

 

Both the pedal height and brake switch can be adjusted but would never need to be done once set up. It is worth looking at the brake pedal mechanism itself just to make sure nothing is fouling the pedal and everything looks correct.

Thanks Colin this is really useful. There is definitely play on the pedal (certainly more than the 1mm stipulated minimum). I got the brake lights checked and they only come on when the pedal very lightly applies the brake, i.e. they are not actived within the travel of free play. My drive is on a slight slope, so I was able to use that to see how hard the brakes needed to be applied to activate the brake lights...the minimum needed was insufficient to stop the car on the slope, so deceleration would be negligible when the brake lights activate. I'm satisfied that they are working correctly. That situation is the same both without vacuum present or with the engine running.

I believe that the issue may be that vacuum is not being maintained as well as it was and I now need to press the pedal significantly harder to operate the switch than I'm used to. If the pedal is pressed hard enough it starts every time.

[Pielight]

Just a quick update.... strangely this fault seems to have resolved itself and I've not had the issue since my last post.