Dakotaz

1990 L98 pedal has always been soft, tough to lock up / make ABS activate but it can be done. New booster, brakes bled multiple times by peddle and vacuum, new pads, roror, and hoses. Now I have read vacuum below 18 inches can cause this. Running 16 pounds checked with two different gauges.

Thoughts and thanks.

belairbrian

I'm confused on why you're chasing low vacuum for a soft pedal. Low or no vacuum creates a hard pedal.

Try pressing the pedal 3 or 4 times with the car off. The pedal should get hard to press. If it doesn't you if you have air in the lines.

Now with pressure built up hold your foot on the brake pedal and start the car. Pedal should move down with the weight of your foot. If it does the vacuum system is working.

It sounds like your really saying you have poor braking performance.

Dakotaz

Yes i should have said hard peddle. It's like the booster is not doing it's job 100%. I have done the test mentioned above and it did as you stated. I was just wondering if the lower vacuum by 2 pounds would have that much effect on the booster...
That doesn't make sense to me, but multiple brake sites state that 18 to 20 inches of vacuum is needed for the booster to work properly. The car stops alright, it just doesn't feel like true power brakes.
Thank you for your reply.

PatternDayTrader

Say you decelerate from 45 to 15 without touching the brake, just letting engine braking slow you down, do you get one pump on the brake that feels normal ?

belairbrian

The booster stores vacuum so it can work when the engine is in a non-vacuum generating state. Low vacuum would take longer to replace it. But that usually occurs from the engine design. Are you running a stock engine or a modified one?

Do you have any indications of a vacuum leak such as a high idle?

Could be a worn master cylinder, could be the brand of brake pads. Could be the pads were not broken in properly and are glazed.

When my booster was going bad I had a hiss when applying the brakes I sort of had power brakes that faded and made the car hard to stop.

Dakotaz

Pedal feels the same in all conditions. Stock engine 115,000 miles. No vacuum leaks that I have been able to find yet. Have not done anything to the master and pads were broke in per the manufactures instructions. No hiss. One suggestion was to add an electric vacuum pump. May have to look on the net to see what is available. I hate throwing money at parts and hoping. Always believed in diagnosing and replace...

PatternDayTrader

I would install a vacuum gauge and tape it to my windshield and drive the car for a bit. I think you are going to find that when you decelerate with the throttle closed and with whatever engine braking is available, the vacuum signal is high enough to operate power brakes once, the first time you depress the pedal, probably not the second.
The fact that you are saying there's no difference, makes me think there's something wrong with the brake booster.

PatternDayTrader

Now that I think of it the one way check valve at the booster could do the same thing if its malfunctioning. In fact that part better work perfect if you have borderline insufficient vacuum at idle.

Dakotaz

Took it out for a drive with the gauge taped to the window. Never saw it go above 16 inches. I used the actual hose for the booster. The booster is definitely doing at least part of it's job since the brakes really suck without it... Maybe these brakes are just that way. I seem to see a lot of people complain about this. Could the two inches be that much difference. I can get a universal vacuum motor for $145, or maybe try to find one off of a wrecked diesel pickup at the junk yard, but who knows if that would be any good. Only been this way for three years I have owned it so if I cannot figure it out oh well.

PatternDayTrader

Well probably is just low vacuum then. I'm surprised that you cant get a strong vacuum signal on decel. Sucks because it seems like 16 is right on the edge of being able to work ok.

Dakotaz

It does suck but the best I got was 16. I was hoping that someone else might have looked at the vacuum as being the issue and spent the money to try it. I might keep searching on the net. Most the hot rodders that were having the problem were down in the 10 inches of vacuum range due to their cams. I can understand that having an effect on the brakes but two inches is just so close.
Thanks for all or your suggestions!