[alfa1318]

Recently rebuilt my 1990 Alfa Spider Quad. Had to work on brakes as well. Replaced Master Cyl, Brake Booster and rebuilt all calipers and proportioning valve as well. Brakes went from super soft and not working to hard. Have driven car to break in but still having problems. When I press on the brakes they feel fine at first but if I have to press on them right away...not touching the accelerator the brake pedal gets very hard making it difficult to stop. Have already tested everything including replacing brake booster hose....and yes brake booster is holding a vacuum and tested booster valve. All I can assume is the one of the calipers might have a stuck piston but unable to determine which one did "wheel drag Test as well" I am very experienced mechanic just can't seem to find the "gremlin" in the brake system.
Any one have any ideas?

 

[alfaparticle]

To check the booster: with the engine stopped pump the brake pedal and hold it down. Then start the motor. The pedal should go down some more if the booster is working.

 

[ghnl]

There should be a one-way valve in either the fitting at the brake booster or the fitting at the intake plenum. Does that valve work? They can stick closed (or open). No vacuum = no brake boost.

 

[alfa1318]

ghnl,

Thanks for reply but hoping for ideas above the typical. Everything has been tested and all is working.

 

[alfa1318]

alfaparticle

Thanks for reply but hoping for ideas above the typical. Everything has been tested and all working.

 

[Gubi]

Well, I know it's holding vacuum, but from the symptoms it sure sounds like you got a bum booster.

...hoping for ideas above the typical.

Here ya go...

 

[aldo]

Everything has been tested and all working.

Maybe you have a weak ankle.:whistling:

 

[ghnl]

Everything has been tested and all is working.

If that were true then it'd be working correctly.

 

[Boccaccia]

Recently rebuilt my 1990 Alfa Spider Quad. Had to work on brakes as well. Rep.. When I press on the brakes they feel fine at first but if I have to press on them right away...not touching the accelerator the brake pedal gets very hard making it difficult to stop...

This is sort of difficult to understand. Do you mean the pedal gets very firm? Travel reduced? Hard to push? Or that you have to push hard?

Be clear and you shall receive good advice.

And don't say this again: "Everything has been tested and all working."

 

[alfa1318]

Tom,

Booster is new and old one was ok...not 100% but ok. Going to check actual vacuum with gauge see i have enough...don't think that's the problem though. Might need to crack open the calipers again.

 

[alfaparticle]

Glazed or contaminated brake pads will give you a hard pedal.

 

[alfaparticle]

Going to check actual vacuum with gauge see i have enough

You can have good vacuum and a bad booster. The simple test in post #2 tests the booster, measuring the vacuum only tests the integrity of the diaphragm.

 

[brewtech]

I had the same issue with a car I still have. Opted to not replace my brake hoses, since they looked good. Well I figured they were probably collapsing on me when I pressed the pedal. So I replaced them, it took care of my issue.

 

[alfa1318]

Thanks everyone.

Took rear left caliper apart and found inside piston rubbing and getting stuck. Found wear on one end of contact surface"half moon" roughly around .024mm. Machined down to a tolerance of .001mm for now...until new pistons arrive. Braking better now but can't wait for new pistons.

 

[Boccaccia]

.. Found wear on one end of contact surface"half moon" roughly around .024mm. Machined down to a tolerance of .001mm for now...

In order for the brakes to work effectively and quietly, Alfa designed a stepped (recessed) area on the portion of each caliper piston which presses on the back of its pad.

Setting Correct Piston Alignment for 115 series cars