KITT1983

iTrader: (3)

my rear calipers were replaced 4 years ago with ac delco parts.

who makes good e-brake cables?
but how come the car wont panic stop it feels like it has abs

firehawk1988

I recently started having brake problems similar to what was mentioned before. What happened was i noticed a "suction" or air bleeding sound coming from the pedal area inside the car as i drove it. The pedal became soft and the car was difficult to stop unless you pumped the brakes and pushed it deep to the floor. I figured since i had the car since 2001( my 88 formula) and never changed the M/C, it would be a good idea to start there. I bought a remanufactured on from Advance and installed it...bleed all corners of the cars and it still feels the same. The pedal is soft and spongy but i am still getting that vaccum suction sound coming from the pedal area inside the car.

Also when the engine is shut off the brake pedal is hard and stiff to push. But when the engine is idling and i pump the brakes, you can see the rpms drop with each pump going from 800 rpms down to about 400rpms. Continously pumping the brakes will bring the rpms down to the point where the engine acts like its ready to stall. But once you let off the brake, in a few seconds it goes back to idle.

The "sucking" sound and the pull on the engine has me wondering if its the Brake booster. Has anyone seen this before? I have never seen this happen on any of the cars i've owned(which includes the 2 F-body's i own now and my gf's Firebird).

lonestar7

iTrader: (1)

That certainly sounds like you might have a hole in the booster diaphram or a leaky seal in there. I would also double check that the vacuum hose going to the booster has a tight fit and no cracks.

firehawk1988

The hose was the first thing i checked since i knew it was the only thing going to booster. It took it off which it was tight and had no holes or cracks. I did notice that my Camaro(carbed) had the filter on the line and the Firebird(TPI) didn't which would explain what was mentioned before about the filter being used on carbed and TBI cars to not allow fuel ever getting to the booster.

I priced a reman booster for $100 and i was afraid the booster was the problem since the way the car was acting.

Azrael91966669

ive replaced ever part of the brake system in my car other then the booster
someone mentioned a seal inbetween the mc and the booster

im still dealing with this problem luckly the car stops well just the pedal feel is crap
i just wish i could lock the fronts with the c4 brakes i would think you should

im gonna look into this booster seal but my dads 89 iroc with 33k makes the same hiss and dosnt have the pedal problems but it also still has its stock front brakes and rear drums

Azrael91966669

its hard to say but im gonna look into getting a new seal for there aswell

but what i ment by the hissing and sucking air sound is the
2 rubber "grommets for the master cyl where the res hooks into
the hiss and will also lose fluid there after a few weeks/ months
ie that i know they have gone bad again once the brakes feel like crap and you can feel fluid on the bottom of the res and the "grommets" look wet
it dosnt seem to matter what brand of master i use i end up with the same problem after a few months ive tried 4 differant brands and 5 differant autoparts dealers in the end ive learned its just easier to go to the junk yard for the "grommets" since they last for a month or 2
but even once there replaced i still have a hiss it is comeing from the booster
but every third gen ive been in makes that noise but none have had the brakeing issues i have

Edit i have looked every where i can and i cant find a seal/gasket to go between the master and the brake booster

edit again i just came across these answers related to this thread

brake booster

Q. The brake pedal is low and spongy. I guess I need to replace the booster, right?
A. No. The booster will never cause a low or soft brake pedal, check for air or other hydraulic problems. A defective booster will only cause the pedal to become hard or not return.

Q. I installed a new booster. Why am I hearing an air noise under the dash? this is the noise i hear
A. This is usually a normal noise made during brake application due to atmospheric air entering the booster filter located around the push rod. Tip: Moving the silencer (foam seal) may reduce noise level.

booster is not my problem

master cylinder

Q. Why does it take me a long time to bleed a step bore style master cylinder?
A. Refer to the installation instruction sheet for special step bore bleeding process. Bench bleed first by slowly depressing brake piston then release slowly and waiting 20 seconds before you push again. NEVER pump piston/pedal with a step bore style master cylinder. Follow the same process on the vehicle.

maybe ive been bleeding incorrectly?

Q. The brake pedal is low and spongy. Is it a bad master cylinder?
A. First, check for air in the system. Make sure master cylinder is level when bleeding. Air will compress in a hydraulic system causing a low pedal. Then check for brake hoses swelling/expanding under pressure. Then check brake drums/discs for proper specifications. And then check brake material

Q. How can I test a master cylinder to see if it's bypassing?
A. Simply plug the master cylinder ports and press the brake pedal. If the master cylinder is bypassing, the pedal will go down. If the pedal stops hard, the master cylinder is OK

i would try that but have nothing to plug the ports

im gonna give this another go around since i have warrentys on all the parts still
just gonna replace the master again then im gonna replace all the rubber hoses
then im going to blow out all lines again they blew out last time with no restrictions
as i must say the fluid has turned dark again but the headers do run with in an inch of the lines
im gonna replace all 4 calipers again and new pads all around and new rotors
then if i still have the damn problem im gonna swap spindles and put factory brakes up front just to see and if that dosnt work then i guess ill just have to live with crappy pedal feel

i was also reading about miss aligned rotor to pad distance causeing a mushy feeling and there is a distance even when new pads are installed this is the reason i was thinking about putting stock up front for a test

none of these seem to figure out whats blowing the grommets out

only thing i cant afford to change out again is getting the 1le prop valve so ill just have to assume its working im not spending another 200 on something with no warrenty

RBob

iTrader: (1)

You may be overfilling the M/C. There needs to be room for the brake fluid as it heats up and expands.

RBob.

Azrael91966669

ok so this weekends adventure into fixxing this again has still not fixxed the problem

new master new rotors all around new pads all around i wasnt about to rechange the lines there less then a year old i also put on new rubber line
and 4 new calipers

the brakes have gone from feeling "ok" for 3-5 stops to now never feeling ok

brakeing power starts applying once the pedal is half to the floor there are no leaks
i bench bleed the master cly i had made bleeder lines from metal ones few years back i never knew i would need them this often lol

lucky the master was under warrenty from the last one so it was free
i bought the "cheap" pads semi metallic as ive been told it could be the way my ceramics feel that are killing where my stopping power that is true


i then blew out the lines no restrictions
me and the kid up the street bleed the lines starting rr lr rf rf one brand new fluid

now last night when i finished the job the brakes where fine i did the broke in the pads correctly
the pedal was up all the way

lucky the master was under warrenty from the last one so it was free
i bought the "cheap" pads semi metallic as ive been told it could be the way my ceramics feel that are killing where my stopping power that is true

now one day later its like the master is shot already it returns to the top but its like no fluid is really there

i can now lock the brakes int he front coming to a stop but as i said the stopping power only starts once the pedal is half down

even with the car off and vac gone the pedal has nothing till half way down like the pushrod is to short now and i am annoyed
is it just me or is everything reman/ auto parts junk now
the masters being shot out the box
new duralast gold alt lasting 3 weeks oh and they have to order it so i always wait 2 days before getting anything

my calipers where the same took 7 tries to get ones that where not stripped one of the 2 bleeder or the banjo or th piston seals leaked it started really pissing my off i told the guy order 10 of them for each side and ill swap them in the parking lot till i get a good set sadly it took 3 trys before finding a good caliper and these are out of the box

Azrael91966669

the feeling at the pedal is that the brakes are not even operating till the pedal is half down even when the car is off its rock hard once you hit the middle of travel

the new master is to blame it has 0 pressure for the rear so im basicly only useing front brakes the rears worked with the last master

Nelz

When was the last time you changed out all the fluid in your car? The brake fluid may have absorbed too much water as it is hygroscopic. Drain all the old fluid, flush the sytem and refill it with new fluid. Here is a tool to help.

http://www.speedibleed.com/


You've chased this problem with a bunch of new brake parts, but the root of the problem may by the fluid.

Nelz

Otherwise, is the brake pedal where it is mounted flexing?

Azrael91966669

ive done the fuild swap a few times now how many times do you need to blow out the lines i say ive done a full fuild swap once or twice a year nothing is changing

Nelz

Are you using a pressure bleeder instead of having a friend pump and hold the brakes?

Azrael91966669

ive tried reverse bleeding with pressure at work
i tried one man bleeders
ive tried the mitivac gun
ive tried the 2man pump style
and ive tried gravity bleeding
all ended in the same soft pedal

Nelz

1. Air in the lines or leak somewhere
2. Ballooning brake hose
3. Worn out drum
4. Warped brake shoes
5. New shoes that have not seated.

Usually in that order for spongy brake pedals. Since you've replaced everything and insist the lines are good, try going for stainless steel braided and teflon coated lines. You can get them pretty cheap off ebay from

Silverstone http://stores.ebay.com/Silverstone-M...p2047675.l2563

It's the last thing it seems on your list.

Azrael91966669

4 wheel disc system
all 5 rubber hoses are new ive replaced them twice now no change no leaks

to me it just seem odd that even with everything replaced it always ends up the same if it had an adjustible brake pushrod i would just assume that was the problem but these cars are not adjustible

even our gm mastertech at work is stumped on this problem but he gave me the idea to swap back to stock front brakes saying the vette calipers most likely need more fluid hence more pedal pressure to work he says the lt1 era vettes used a differant master so that could be the problem
i doubt that since many swaps have been done and not many have this or any issues

after recently putting new rotors all around and putting new pads on i can lock the fronts in the rain , but not when its dry

dont get me wrong the car stops well the issue isnt really the stopping power more so the pedal feel is un nerving to say the lest

Nelz

Can you please put a pressure gauge on the brake line and tell me how much psi you are getting at the lines?

A C4 Caliper has a piston area of 3.53 square inches according to this chart:

http://lukeskaff.com/?page_id=333

Using the guidelines in Brake Systems by Mike Mavrigian and Larry Carley on page 165 under racing brake hydraulics you need a Master cyinder area of 5/8 with a Master Cylinder Bore dia. (inch) of .307.

"While the above chart has merit, it is primarily intended to guide master cylinder bore selection for road race and Indy car applications, where smaller pedal ratios are commonly used. However, in Late Model oval applications, pedal ratios of 6:1 and 7:1 are common. If a 3/8" bore piston is used in the calipers (this gives about 3 square inches of piston area), a 5/8 bore master cylinder will provide a too-soft pedal feel and extended pedal travel for a higher ratio pedal setup. This will create too much line pressure, causing rear wheel lockup too easily for a late model car (especially on dir), which can also create engine stalling problems. Road race applications can handle smaller masters cylinder bore size combinations in conjunction with lower pedal ratios. For applications like Late Model, a 5/8 and 3/7" master cylinder setup would provide extended pedal travel and a too-soft pedal, so a larger bore size masters setup would be more applicable, such as a 1" and 3/4" or 1" and 7/8" combination.

So yes, it may be the wrong master cylinder.

You may have to bite the bullet and call Wilwood or Tilton or some aftermarket master cylinder company for a recommendation.

Or who knows, try the GM master cylinder that was matched to your caliper.

Pg. 169.

Recommendations:
1. A larger master cylinder will displace more fluid volume, but will create less line pressure. The result is a HARDER pedal with more braking effort. A smaller master cylinder will displace less fluid volume, but will create more line pressure (Softer pedal with less braking effort.)


It sounds like your master cylinder is too small. You need a larger master cylinder.

Not sure what size though. Call Wilwood or some aftermarket company.

The book says it's a trial and error process which as we know, gets expensive.

On the lukestaff site he cites that the size of Master Cylinder bores. * It also looks like from 89-92 GM used the smaller drum brake master cylinder 18030555 on all f-bodies.

There are part numbers for the bigger 1.42" front/1" rear master cylinder used on older F-bodies instead of what you have-1.25"front/0.945"rear master cylinder. There is even a part number for the bigger B-body cars with 1.575"front/1.126"rear. If your pedal is too soft/spongy, maybe there is too much line pressure and you need to go to the bigger master.

AvantiHall

Do not use rebuilt master cylinder, use new AC delco master cylinder, if 4 wheel disc system. Go to the wrecking yards and take your old booster to master push rod, find an adjustable push rod. Measure and make sure there is about .025 play in push rod master cylinder to booster. Remove cap and you should see a wave of fluid when you let off the brake pedal. When bleeding a old master cylinder do not push all the way down, it will rupture the cups inside. New master can go to floor if you want. Bench bleed the master cylinder, keep dot 3 and 4 off your paint. The pedal operator, must take their time pumping the pedal, also each time their foot must come off the pedal so the master cylinder can gulp a little fluid. The caliper bleed screw must be at the highest point to remove all bubbles properly. If not at the very top, some times you can snap open and closed the bleed screw to try to get the air out. Use copper washers on the hose fittings both sides, like removed, and only new ones. Keep fluid in the master and don't run out, or start over. After going out and seating the brakes in, let cool and bleed one or two shots from each wheel, if air still, continue till only liquid, test drive and check again. Make sure the fluid is never above maximum, oh, if the brakes self apply then the gulp port is not letting fluid back into the reservoir, sometimes the push rod is slightly too long. Buy cheap get cheap. Your brake parts should be the best money can buy, I can find $18.00 rotors and premium ones for $98.00 rotors for the same car. If you use the $18.00 rotors, cut your floor boards out and drag you feet to help stop. If the brake booster hisses when pedal is applied look at the inside push rod and see if the silencer ( piece of foam) is there. On a all 4 wheel disc use dot 4, if dot 3 used the boiling point is too low, if dot 5 is used it must be dot 5.1 and say compatable with dot 4, if your brakes feel mushy add emergency brake pedal some and see if they come up or the pedal feels more solid, if so the rears have a problem with the caliper. If emergency brake is a baby set of shoes then the caliper in the rear are not working correct. If rear ABS the solenoids could be letting fluid bypass inside. The front brakes do 65 % of the stopping, if i drive the car backward at about 35 mph and slam on the brakes the should skid evenly from the front. If I slam on the brakes going forward the fronts may just skid, the rears should never skid on dry pavement. Slotted rotors or holes drilled removes part of the rotor material and the brakes will have less effciency, exception being, 4 piston calipers and a few other special systems. Organic pads will give you brakes right now! When too hot they will fade, more so with thinner pads (worn down to 30 %), simi metallic pads have a strange pedal feeling, while driving on the freeway and not using your brakes for a very long time, when you come off the freeway and hit the brakes, nothing for about 1 1/2 seconds then they work great. Thats normal! To check booster it will hold boost for hours, pump till the pedal is hard, hold foot on the brakes and start the engine, the pedal should drop about 3/4 " if too big of a cam, you may not, no you will not have good power brakes, change over to remote vacuum system. Hope this helps.

Dave

Nelz

Another checklist from pg. 194

1. Air in brake system
2. Calipers incorrectly mounted with bleed screws not in high position (top)
3. Too small master cylinder
4. Faulty master cylinder
5. Calipers misaligned to rotor
6. Calipers mounted equal to or higher than master cylinder. Install 2 lb. residual valve
7. Excessive caliper flex. Check line pressure, which should not exceed 1500 psi
8. Pedal ratio too great
9. Excessive spindle deflection in corners causing piston knock back

So check line pressure before replacing master cylinder.

AvantiHall

Send it to California and I'll fix it! Read, think and read again!!!!

vortec350s10

Just thought I'd share my brake experience. I swapped over to LS1 rear discs a couple years ago and swapped an LS1 master at the same time. My original rear discs did not work at all. I bench bled the LS1 master before mounting. My brakes are weak all the time, I think they have gotten worse though. I have an adjustable prop valve that I have cranked up all the way to give rears max pressure. At one point I could lock up the rears once they were heated up when pushing as hard as I could. I have ceramic pads all around and haven't tried any other pads yet to compare. I also noticed that slamming on the pedal fast is actually worse for stopping power than slowly applying brakes. Seems as though the brakes don't get any pressure till the pedal is down an inch or two. I'm probably going to swap back to my stock master and see if anything improves. I'm going to drive a friends stock iroc to see what his feels like. It'd gotta be a heck of a lot better than mine!

91L98Z28

There is definitely something "indirect" about the GM power brake booster in terms of a panic "slam the brakes" stop vs. a controlled, slower approach to applying the brakes - as you mentioned, you get more effective braking with a slower approach until the pads engage.

With that said - when you swpaped to the LS1 master, did you switch to non-retracting front calipers? If not, then your brakes were not working correctly. The LS1 master does not have the dual bore to move the caliper pistons out (they retract on our stock calipers).

vortec350s10

This is the first thread I've seen where the 4th gen calipers are mentioned as low drag/quick take up calipers. Or is it the third gen ones that are this way? Well either way, maybe that has something to do with the crappy brake performance. So if the front calipers are different between third gen and LS1 cars, what about the rears?? If the rear LS1 calipers are one style and the front 3rd gens are the other style (meaning quick take up or not) maybe they will never work well together on the same car since only one pair of calipers (front or rear) will have the correct master cylinder. Hmmm....
Either way, I want to go back to my stock third gen master and see what that does.

91L98Z28

third gen iron front calipers are low drag and require the quick take up master.