I have a 71 Cutlass S. Replaced the entire brake system including conversion to disc on the front (except the distribution block). Before the replacement, my brake pedal seemed harder than normal. Seems like I had to push way to hard given I have power brakes. I replaced the power booster. That helped some. Then I replaced the entire system including new proportioning valve, new master cylinder (correct for discs), brake lines to the front (not rear), etc. Used front disc parts off a parts 71 Cutlass Supreme. I did use Delco? equivalant calipers for the discs, but all the other parts were from the parts car. Rear brakes replaced including brake cylinders. Brake pedal improved. Bottom line - brake pedal is still too hard to push. I even adjusted the elevation of the pedal to get a better angle for more leverage.

I also own a 65 Dynamic 88 with 4 drums. This car brakes way better than the Cutlass.

Any thoughs on how to improve the hard pedal problem?

Thanks in advance. Larry

 

Vacuum problem?

Did you change the camshaft too?

 

I agree that it does sound like a low vacuum or booster problem. Just because the booster is new doesn't mean it's good, especially in the last few years it seems.

Assuming the cam is stock;
Did you replace the check valve on the booster too?
No vac hoses disconnected under the hood?
Brake lines aren't kinked anywhere, rubber brake connection hoses all replaced?
Can you take a vacuum reading at idle?
I had the same problem with my '68 GTO but it was from a hairy cam and I had to install a brake vacuum pump to compensate for the lack of vacuum.

 

The booster was brand new from OPGI (with stamp) and included the check valve. The car does have an aftermarket Edelbrock intake manifold with Edelbrock 4 BBL carb. That seems to be the only modification. I don't think it has a differerent cam. I'll check the vacuum hoses. Brake lines are new for the front including rubber. Not sure about the condition of the rear ones, but I'll check.

Would the aftermarket manifold cause the problem?

 

If I'm reading your first post correctly you are running a distribution block and a proportioning valve? When I converted my F85 from power drums to manaul disks I removed the distribution block and added a proportioning valve. If your running both maybe they are working agaist each other? Just a thought. JKaz

 

Doesn't the distribution block have the sensor that sends the message to turn on the brake idiot light when pressure falls? Any other suggestions from anyone on whether I should remove the distribution block? And, yes, I am running both the distribution block and proportioning valve.

 

Actually, the sensor is a DIFFERENTIAL pressure sensor. It only illuminates the light if there is a significant difference in the pressure between the front and rear brakes. This is intended to actuate if, for example, you rupture a brake line in one half of the system. If pressure in both front and back are low, but the same, the sensor will not go off.

 

You mention in your posting that that before the replacement of parts the pedal seemed harder than normal. tham lets start with the basics I would set in the car put pressure on the pedal then start the car the pedal should drop slightly as the power booster vacuum kicks in . I would also jack up the car apply brake pressure and check to see if all 4 brakes are holding shouldnt take a lot of pressure to hold the brakes. I would also take the lines loose at the master cylinder and check the drop of the brake pedal, should go to the floor with little to no effort. This will give us clues as to where the problem is. If one or more of the wheels doesnt hold maybe a restriction in that part of the brake system if the brake pedal doesnt drop with the lines disconnected we look for a problem in the master cylinder booster area.

 

OK. Good input. I'll need to set aside time to make the checks as suggested by Oldsrallye350. For the record, I am using the same distribution block that was on the car (i never checked its condition). I purchased the CH26775 disc/drum proportioning valve from OPGI and had this installed. I assume my mechanic removed the old 4 drum proportioning valve.

 

Bluevista had it right. My mechanic informed me my power brake booster is leaking. It is a brand new unit from OPGI. Also, I am only using a proportioning valve - no distribution block.

 

I would bleed the brakes again. I like the old way of doing it. Where it takes two people one person pumps the brake pedal five times last time they hold down on the pedal and the other person opens the bleeder the pedal should go all the way the floor. Close the bleeder. Repeat until there is no air in line. Do same to all four brakes. It always works. I like buying brake parts at Oreily's auto parts. They have good prices and good parts. Plus they all the brake parts for my 70 Cutlass.

 

That the way I bleed the brakes too. Did this already, but the pedal is still a bit hard. I'll report back after I replace the power booster. For the record, this is the second part I purchased from OPGI that I will have to return. Other was body bushings. The set did not match what came off the car. I'm beginning to loose faith in OPGI, although the control arm bushings, sway bar parts I purchased from them did work.

 

I had a power booster go bad on me while I was driving once. My brakes where fine. Then the brakes got hard I could only move the pedal about four inch maybe that was using both feet. I change power booster then the brakes where fine.