Let’s diagnose a hard brake pedal

[honeybadger]

Howdy all!

Hoping y’all can help me diagnose a hard pedal I was getting on the track. Essentially, every so often I’d get a hard brake pedal after long straight where I spent significant time at wide open throttle. I discovered that if I lifted and let the car coast for 1-2 seconds, the pedal was there like normal. It also never went hard anywhere but after big straights (how nice of it).

Only trial and error so far was checking the check valve going into the booster - it passed the blow test. Air only went through towards the intake. There was also a or escape sound when I pulled it out of the booster.

Possible causes from what I know:

1. Lockouts are simulating a “big cam” and the engine might not be generating enough vacuum

2. Brake booster could be faulty

3. Vacuum leak

Anything I’m missing? Any recommended course of action?

My plan is to test how much vacuum the engine is pulling, but I’m open to ideas/guidance.

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[Rapid Red]

Most boosters have a plastic check valve. Found where the line attaches to the Booster.

Could be something going on there. Considering the under the hood temps being reached.

 

[svttim]

I had a catastrophic failure that was very similar. I was a cracked plastic fitting on the intake. Several shops missed it. I finally inspected very carefully and found it. I epoxied a steal line inside the plastic line. Anyway, I think you are spot on with your list

 

[honeybadger]

Most boosters have a plastic check valve. Found where the line attaches to the Booster.

Could be something going on there. Considering the under the hood temps being reached.

I checked that and it appears to be okay.

I had a catastrophic failure that was very similar. I was a cracked plastic fitting on the intake. Several shops missed it. I finally inspected very carefully and found it. I epoxied a steal line inside the plastic line. Anyway, I think you are spot on with your list

Was it tied to the line running to booster directly? I have about 4 lines on the intake capped off, maybe they’re leaking

 

[Flyhalf]

Kevin i knwo might be a stupid answer but dis you check the pads?
Is same thung i experience with glazed pads

 

[svttim]

I checked that and it appears to be okay.



Was it tied to the line running to booster directly? I have about 4 lines on the intake capped off, maybe they’re leaking

Yes. It was a small line but at 145 brake pedal was concrete. Hello Canada Corner tires

 

[honeybadger]

Kevin i knwo might be a stupid answer but dis you check the pads?
Is same thung i experience with glazed pads

You had a hard pedal with glazed pads? I’ll go check

 

[K4fxd]

You need a vacuum reservoir like we needed back in the old days.

Like this

https://www.amazon.com/Competition-...s=brake+vacuum+canister&qid=1617158562&sr=8-1

 

[K4fxd]

I discovered that if I lifted and let the car coast for 1-2 seconds, the pedal was there like normal. It also never went hard anywhere but after big straights (how nice of it).

This is what tells me you need a vacuum can

 

[honeybadger]

Kevin i knwo might be a stupid answer but dis you check the pads?
Is same thung i experience with glazed pads

This is what mine look like

Spares look the same to me

 

[Flyhalf]

Those were the previous set. They were glazed. Very similar to yours.
Rule of thumbs
Soft pedal no brakes =boil fluid( or air in )
Hard pedal no brake = glazed pads.
Try to sand them 1-2mm to remove the glazed
(1 ome the pic has half sanded and half still glazed to show you the difference)

 

[ChipG]

Interesting thought, but would the hard pedal really come and go with badly glazed pads? The fact that it happens after long straights and recovers doesn't sound like pad issues - I'm not sure how glazing would get better after a couple seconds off throttle.

 

[Flyhalf]

Interesting thought, but would the hard pedal really come and go with badly glazed pads? The fact that it happens after long straights and recovers doesn't sound like pad issues - I'm not sure how glazing would get better after a couple seconds off throttle.

It might or might not
After long straight is also when you are faster too. So major friction and heat occurs. Sometime I'm able to do 1 fast lap befpre receiving hard pedal due to glazed pads.
I also nptice this problem more with shitty tires. I wonder if the pads are very bit bite pads and overwhelm the tire creatimg also issue with ABS.
Kevin was a cota which use lots of braking too.

 

[K4fxd]

If you listen to the symptoms it is obvious he lost vacuum. 2 ways to fix this.
1 install a vacuum can
2 install a vacuum pump

or

3 go back to TiVVT

 

[honeybadger]

You need a vacuum reservoir like we needed back in the old days.

Like this

https://www.amazon.com/Competition-...s=brake+vacuum+canister&qid=1617158562&sr=8-1

I’ve looked at this. Seems like it might be useful if my vacuum is borderline okay. I have a tester coming to measure. We’ll see.

Those were the previous set. They were glazed. Very similar to yours.
Rule of thumbs
Soft pedal no brakes =boil fluid( or air in )
Hard pedal no brake = glazed pads.
Try to sand them 1-2mm to remove the glazed
(1 ome the pic has half sanded and half still glazed to show you the difference)

So hard pedal - i’d describe it as not moving all the way down and not letting me push it to the floor even with a lot of weight. Does that sound similar?

Not sure what the difference of manual brakes vs. glazed pads would be. The car still stops, just takes a bit longer. But literally, the next corner was always fine - no matter what.

Interesting thought, but would the hard pedal really come and go with badly glazed pads? The fact that it happens after long straights and recovers doesn't sound like pad issues - I'm not sure how glazing would get better after a couple seconds off throttle.

this is what has me thinking vacuum issue. It was super predictable once I figured it out. If I went straight to max brake on the back straight, I could kick in the hard pedal easy. If I waited that extra second, the brakes felt normal

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