74 brake booster question(s)

[OldRoller]

base 02, not Tii. Gunther is rolling now, did the 25 miles from the shop to the house, ran well. I have a odd feeling regarding the booster operation though:

Pedal is hard, no sponginess but less vac assist than I remember (feels like a manual system).

Booster vac tested, holds vac, no leakdown.

19" vac from manifold at idle, check valve correct orientation.

MC checked, no leaks into booster.

No brake drag or lock up after repeated braking.

Brake pads/calipers/rotors/rear shoes all new, haven't been fully bedded yet.

 

If I hold my foot on the brake then start it up, I feel a slight drop in the pedal from the vacuum assist. Driving, the stopping power is good but not on par with expectations.

My next step is to fully bed the brakes with hard braking/cool down/hard cycles and see what develops.

Any input from the more knowledgeable? It just feels like very little assist, but it might be me.... been years since I drove an 02 regularly.

 

Edited May 11 by OldRoller

[2002]

Might be some corrosion on the brake booster allowing leakage between the master cylinder and booster.  Make sure the O-ring seal is good too.  Item 7 below:

 

 

 

[tzei]

Has your squat 1rm dropped?

 

seriously, check this out:

 

and 02 booster does not boost that much imo.

[OldRoller]

5 hours ago, tzei said:

Has your squat 1rm dropped?

😵  You lost me there Tzei... squat 1rm? 

All linkages are adjusted to spec, o-ring mc to booster is new. 

I may be just unfamiliar with the system, and as you suspected there is not much 'assist' from the booster.

I might pull it and verify off-car operation just to be sure. Thanks.

[Chris_B]

There is a fair amount of assist from the booster. Disconnect your vacuum line (and plug the open end) and see how it feels. If your booster is working properly, the pedal pressure to stop should feel significantly increased- really hard.

[TobyB]

You didn't buy MetalBastards, did you?

 

t

 

[tzei]

6 hours ago, OldRoller said:

squat 1rm?

Yes well was trying to be funny. Was referring leg muscle performace (squat - execise, 1 Repetition Max weight). I know my legs are weak (chicken style) as i don’t work em like i should.

[OldRoller]

7 hours ago, Chris_B said:

Disconnect your vacuum line

Yes, tried that and as noted there is some assist, just not as much as I expected.

 

6 hours ago, TobyB said:

You didn't buy MetalBastards, did you?

Not sure of the pad make, they came with the rotors and calipers from an 02'er in CA. A change is likely in the near future.

 

4 hours ago, tzei said:

trying to be funny. Was referring leg muscle

Good on you, Tzei, I should have caught that! My lower limbs are in good nick for an old man, I played soccer for 25 years in the NC Adult League... it's the limb between my ears that might be getting a little tarnished.... 😵

[Paul5801]

Hopefully I am not highjacking this thread.  Seemed an appropriate thread to discuss booster questions.  My booster passes standard checks while in the car (1976 standard 2002).  The pedal depresses when starting the car with my foot on the pedal and the pedal is not hard.  It also holds vacuum when tested with a vacuum pump without pressing the brake.  Since installing an AFR gauge I noticed that when pressing the pedal the AFR remains steady.  However, when lifting my foot off the pedal, AFR goes lean ( ~13 then jumps to ~16 ) then quickly recovers.  I also occasionally hear a slight engine stumble when it goes lean. Is this expected behavior that I never noticed before having the AFR?   

[jimk]

37 minutes ago, Paul5801 said:

Is this expected behavior that I never noticed before having the AFR?

Yes.  There are 2 air chambers in the booster.  Press the brake pedal and a valve at the pedal shaft end opens and atmospheric air rushes in and the pressure pushes the diaphragm - the boost.  Let up on the pedal and the valve closes and a second valve internal to the booster lets the air that entered when the pedal was pushed previously into the 2nd chamber.  That's when the air in the second chamber is sucked into the engine (and the a/f goes lean momentarily).

 

A properly operating booster/check valve will supply some boost when the engine is shut down and the pedal is pumped for one or two times.  This can be tested with the car on a slight incline so it will roll without the brake applied.

Edited May 14 by jimk

[OldRoller]

As a follow up... booster tested off the car revealed all is normal. No leaks, vacuum applied with resulting assist, poppet valve allowing air displacment. So... reassembled and went for a ride to bed the brakes fully. Numerous 60 to 20 hard stops with short cooldown between, then normal driving home. 

Stopping feels much improved over previous drives, so conclusion is the system is working as designed. It's just not POWER brakes, it's power assisted. I can live with it.

BTW, anyone have a brake pad make that they really count on? So hard to cut through the hype....

[oldbugr]

On 5/11/2024 at 11:47 AM, tzei said:

Has your squat 1rm dropped?

 

seriously, check this out:

 

and 02 booster does not boost that much imo.

That was helpful just to know how to test it. Thanks

[Conserv]

On 5/23/2024 at 10:18 PM, OldRoller said:

 

… BTW, anyone have a brake pad make that they really count on?…

 

I really like Porterfield’s street pads — not to be confused with their track pads, which I don’t need. I run Porterfields in both the ‘76 and the tii.

 

But… if I recall, Toby doesn’t care for them, which gives me some pause… 😯

 

Regards,

 

Steve

 

[2002#3]

+1 for Porterfield.  Many miles:  always stop really well, quiet, and surprisingly little dust.

Larry 

[TobyB]

Porterfield DOES make good street/ light track use pads.  

 

I found that the r4-s compound wasn't durable with stock brakes on a car that 

went to the track regularly and was used hard, then driven on the street-

not what 99 44/100ths of people do these days.  I then got over myself

and went to larger brakes, whereupon a good street pad (textar) was enough.

 

But that's a 30 year old compound by now.  If it's still the same, it's still good!

 

Hell, I still use Hawk Blue on the racecar these days, so who am I to grouse?

 

t

can't remember what's on the PRO3 car...