Sticky or 'detent' in brake pedal

schoward · 04:22 AM

After my 81 SC has been sitting overnight or few days etc., the first push of the brake pedal for the day has a clear ' stick' or 'detent' as you do that first press. After that, all fine and brakes operate perfectly regardless.

I have opened up cluster and that is all fine, bronze bushes done, lubed, etc. I have recreated it pressing the pedal by hand while observing the open cluster. The 'stick' is up top where the rods disappear into the master cylinder and you'll hear almost like the sound of a sticky rubber boot softly 'pop' when it does this.

I have shot some lube into the linkage in the master cylinder housing from the frunk removing the plastic access covers (about the size of bottle caps), but no luck.

Brake fluid has been changed religiously every two years under my 17 year ownership and I have stainless lines in place of the rubber. Brakes work great, no drag, no complaints. I have owned the car awhile and maybe this would happen sometimes that first press after long storage, but not as routine as now.

Is this just age or a sign of master cylinder trouble on the way? No change in brake performance so far.

Did some searches but nothing came up. Thanks in advance.

gazzerr · 09:14 AM

Mine does something very similar to that. My pedal box bushings were quite bad so I replaced them and the slop is out of the mechanism but I still get that detent on the first press (engine off, foot on brake ready to start). I don't feel a "stick" but the pedal stops like it should. The noise is the rubber in the brake booster diaphragm. I've had the booster out, actuated it by hand and heard the same noise. My booster seems to work properly and passes the pump and start engine test (pedal should sink when the vacuum builds). I don't know if this means it's faulty or not or it's just 40 years old and noisy. Hopefully experts will chime in here.

There was evidence of a previous master cylinder leak so perhaps the brake fluid had done some damage. The booster doesn't seem to give a lot of boost like modern cars but my car stops well with new lines/calipers/pistons/pads and rotors. I've never driven another SC to compare with.

schoward · 10-07-2021, 12:40 PM

Quote:

Originally Posted by gazzerr

Mine does something very similar to that. My pedal box bushings were quite bad so I replaced them and the slop is out of the mechanism but I still get that detent on the first press (engine off, foot on brake ready to start). I don't feel a "stick" but the pedal stops like it should. The noise is the rubber in the brake booster diaphragm. I've had the booster out, actuated it by hand and heard the same noise. My booster seems to work properly and passes the pump and start engine test (pedal should sink when the vacuum builds). I don't know if this means it's faulty or not or it's just 40 years old and noisy. Hopefully experts will chime in here.

There was evidence of a previous master cylinder leak so perhaps the brake fluid had done some damage. The booster doesn't seem to give a lot of boost like modern cars but my car stops well with new lines/calipers/pistons/pads and rotors. I've never driven another SC to compare with.

Thanks. Yeah 'stick' is probably not the word - pedal stops where it should and returns fine, but just a little 'detent' that you push through sometimes on the first push of the day, then all fine and pedal and everything operates as it should. Maybe change in season with rubber I dont know. Brakes work just fine and no leaks observed so no reason to pull anything yet.

More so lately than in past 17 yrs so curious if any further guidance or remedies...

gazzerr · 10-07-2021, 02:58 PM

No worries. From memory (might be faulty) the brake rod operates a lever that in turn pushes on the booster rod and then the output pin from the booster pushes on the master cylinder. You can look up under the dash there and see if anything's binding with the lever mechanism.