Hardly no brakes!

[Chevvy SS]

After installing a mild cam, my 2008 VE Auto nearly have no brakes when putting it in Drive. The pedal goes right to the floor and it hardly stops the car. It gets better when at speed, but is not great at all.

I understand that a bigger cam delivers poor vacuum to the brake booster. Any suggestions how it could be solved with tuning, and how it is done?

[Tre-Cool]

how big exactly.

[Chevvy SS]

Compcam

269/285 adv
219/235 @ .050
.607 .621
113 LSA

[Tre-Cool]

i wouldnt have thought that waould cause you any grief. what sort of map pressure do you have at idle in neutral and in-gear?

[Chevvy SS]

It was not determined yet.

However, after I Googled the problem, I came up with lots of of people on forums with tthe same problems. The general opinion is that a big cam produces less vacuum. Solutions provided are canisters, with or without electric pumps.

4 friends did the same mods on their manual cars, with no problems at all. It also seems that the torque converter plays a role.

Maybe more timing at idle?

[Tre-Cool]

well i have a 224/228@112 in a 6.2, same cam come from my 6lt and it idles at 60kpa and brakes are fine. my drag car idles at 67kpa and again is perfectly fine.

i would check the hose to the booster or replace the valve. doesnt seem right.

[macca33]

Something wrong - other than the camshaft size. As Tre-Cool says, much larger cams in L98s without dramas over here. There will be a vacuum / brake booster line leaking, or not seated correctly.

cheers

[Chevvy SS]

Thanx guys. Havefitted a canister and small electric pump without joy. Will try this.

[swingtan]

As already mentioned, the cam will not cause a "pedal to floor" issue with the brakes.

The brake booster uses manifold vacuum to help "suck" the pedal movement, applying addition braking force. So when it's working, the pedal feels "softer" to push. If there was a vacuum issue, then there would be in sufficient vacuum to help apply braking force to the hydraulic system and the pedal would feel "hard". This can easily be tested by repeatedly pressing the brake pedal with the engine off. The first couple of presses will feel normal, subsequently, the pedal will get progressively harder to push as the vacuum is depleted.

The only time that the brake pedal will go to the floor is if there is insufficient brake fluid in the system to maintain a solid hydraulic coupling from the pedal to the caliper. In other words, there is air in the system. The air will compress and allow the pedal to travel further than it should. The only other thing that may come in to play is the ABS / stability control systems that also modulate the brake pressure. in any case, additional canisters and air pumps will not help. If it was cam induced "low manifold vacuum", you could increase the vacuum simply by revving the engine and snapping the throttle shut. This would provide sufficient vacuum to allow the brake booster to work a few times before the vacuum was depleted.

Maybe check for DTC's and perhaps do an ECM reset to see if things come good.

Simon.

[Chevvy SS]

Pedal goes down and gets as hard as rock. It is then with fully applied brakes at idle in gear that the car hardly stops.

Its idling at 11Hg, and with a blip goes up to 18.