vaccume brake issue

[iamjeff]

i replaced my power master setup with a vaccum unit i got out of the junk yard and it has honestly never really worked all that great. The brake pedal has always been hard and the brakes kinda sucked but it seems to be getting worse(not that im always trying to do this...but as a reference, it is impossible for me to lock up the brakes). i have bleed the line who knows how many times and i really dont think that is the issue. there is a check valve right off of the booster and it is functioning. i was thinking the problem would be either in the booster or the master cylinder, but im definitely no brake expert. any advice would be greatly appreciated

-Jeff

 

[TR6]

I assume you got the correct brake pedal when you got the parts? If not, start there. I also assume you are not leaking fluid anywhere, otherwise find it and fix it, and the problem is likely solved.

To check the booster, start the car and let it run. Check to make sure you have vacuum at the booster with engine running. You should be able to tell right away, and the car may even die, as this is such a large vacuum line. Hook er back up and let it run long enough to build vauum back up in the booster. Turn off car, then slowly press brake pedal a few times. It should be fairly easy to depress for the first few times, then get harder as you deplete the vacuum reserve. If is hard right away, your booster is gone. Another way to check is pull the check valve/vacuum line off the booster after the car has sat for awhile. You should hear/feel air rush out of the booster, indicating that it is building/holding pressure.

The master cylinder would give you an erractically spongy or hard pedal without notice. If you are pushing the pedal while braking and it all of a sudden drops, or is unusually hard, your master cylinder could be bad. There are other symptoms as well. I did my conversion with junkyard parts, but bought a remaned master cylinder for it. I don't trust a junk yard cylinder, since you don't know what is in there. If the lid was left open at the yard, you likely had moisture in there that ruined the seals. If your booster checks out, I would put on a new or remaned master cylinder, just on the priniciple of the matter, but it will likely help your problem anyway. Another possibility is the combination valve under the driverside frame rail. I think there was a recall on these, but I don't know what the issue is.

If you have access to a lift (or jack stands or something suitable-don't use cynder blocks), you might put the car on a lift and get it up to speed, then have someone watch while you lightly hit the brakes. All 4 wheels should slow/stop at about the same rate. If not, you should be able to determine if one is not applying, or if one (or more) are hanging up.

Hope this helps. Good luck.

 

[iamjeff]

i did swap out the correct pedal. we actually replaced the master cyclinder when we put all of the vaccuum stuff on. i dont think it is holding pressure when the car is turned off, but i will need to verify that.

this may be a completely dumb question, but i wanted to ask anyway... i have a known good booster off of a 96 (i think) camaro. obviously the master cylinder is different, but the booster itself looks to have the same dimensions as the booster i am now using. is it possible that i could swap my boster out with this one as long as everything matches up?

thanks for any input

-Jeff

 

[iamjeff]

the booster was pretty much hard right away, as it always is. i get a little bosting action, but not that much. i got the pedal about half way down on the first pump with the car off. 2nd was basically nothing. does anyone know anything about using the camaro booster. not that its a huge deal, but i would prefer to not have to spend the 80 some dollars on a reman unit.

 

[TR6]

After the car has run for awhile, you should be able to turn it off and pull the vacuum line off the booster. You should hear the vacuum rush out if the booster has built pressure. Double check to make sure your check valve is good, and that you don't have any other check valves in the line that could be installed backwards.

There are several variables with the camaro booster, and you will have to take your old one off to see if it will work (or find someone that has used one that can confirm).

You need to make sure the rod that attaches to the pedal is the correct length and attachment. You then need to make sure the studs are correct to bolt to the firewall. You then need to check the rod travel that goes into the master cylinder. You may want to/be able to use the rod from your old booster here, but still double check. You also may need to shim the rod to get it the right length. If all these check out, it should work, and probably better than any from a regal anyway.

 

[bilt2run]

Why

You can buy the correct (85 regal works for ours) brandy new booster/ master combo from Autozone for $149 Kills me that people use junk yard boosters especially the guys on here selling them used for $150

 

[Red Regal T]

A hard pedal with no stopping power would indicate a bad booster.

 

[iamjeff]

i checked and it seems to be holding vaccuum. when i pull the vaccuum line off the bosster i hear the rush of air

 

[Rodney87GN]

I agree with Red. Check for vacuum leaks where the master cylinder bolts up to the booster. That's where mine was leaking but it was hard to hear it. I got a new dual diaphragm MC/booster assy for an 87 Monte Carlo from Napa. My brakes work great.

 

[Red Regal T]

i checked and it seems to be holding vaccuum. when i pull the vaccuum line off the bosster i hear the rush of air

All I can say is I've checked boosters that hold vacuum, but the plunger was not assisted. If a MC is bad, the symtom is you have to pump up the pedal. It doesn't cause a hard pedal. The problem has to be one or the other.

 

[thenash79]

I have just converted to vacuum also after leaking PM and i am having the same problem hard pedal with poor braking performance,i can't even lock brakes up with all new rears,11" bear fronts,all new lines,brass meteing valve,master cylinder,two new different boosters with different check valves,18 inchs of vaccum at end of booster hose,and bled them till my fingers bled.After a couple of days going crazy i found my new master cylinder is a 36mm bore size.i bought 2 brand new booster/mc combos from napa,both came with 36mm bore mc.come to find out most of the na cars have a 24mm master cylinder.A bigger bore master would give u more flow(hard pedal) and less pressure(poor stopping power).With the 36mm mc i can't even hold a # of boost before car creeps.They feel so bad i bet I couldn't even skid in dirt.In all the posts on this problem everyone keeps saying the booster/vacuum source is bad.In gmhightech conversion article they used (master brake parts) 1"1/8 (30mm)bore master.As stated in article they can smoke tires on command with brake pedal at 100mph.I originally got an entire setup from a 85 grand prix with a na v8.I didn't want to use old parts on my baby so i went to napa for booster/mc combo.My stupid butt didn't check what size the grand prix mc was before sending them back as core.If u purchase just a mc from them they should ask u what size mc but when u buy combo they don't askI am going to install 24mm master tomorrow and see what happens.if this dosen't work i'm going to start throwing out an anchor when i have to stopI will post results when done.EVERYONE WITH SIMILAR PROBLEM CHECK MC BORE SIZE,AFTER READING 100'S OF POSTS I HAVE NOT SEEN THIS MENTIONED IN A SINGLE ONE

 

[thenash79]

Well tried to get 24mm master today but the only one i could get was from a 80 regal with a NA 3.8l.5 different parts stores around here all say its a 24mm but they give me a 36mm.I installed 24mm,stopping power is better but pedal goes down 1 inch then gets hard(like i'm hitting brick wall)If i take vac hose off booster i lose 1inch of inital travel and pedal is a rock from the start.I went out and tried to skid in dirt,at 10 mph i gave it everything my 140lb butt had,front only slightly locked up.rears didn't do squat.When vehicle is on lift and u slowly depress pedal,as soon as i touch pedal fronts start grabbing,about an inch down the rears start but thats when i hit that brick wall in pedal.My original system had PM ,new metering valve,lines,and all stock brakes.When i did the conversion i changed PM to vac booster/mc setup,11" front bears,and installed line lock after metering valve.After these 3 things they went to crap.I have tried another new vac booster,check valve,2 different bore size MC's,disconnecting line lock,all with no change.Metering valve piston is moving,I'm ready to burn this MotherF#*$er .I have seen parts stores have bad batches of parts before,anyone got any suggestions.Again i have about 18inches of vac at idle and i have correct NA pedal installed.I'm going to take another good look at metering valve,maybe i need adjustable valve?Or a bullet in the head

 

[iamjeff]

i feel your pain. i replaced my vac booster and it seems to have helped a little bit, but im still not satisfied. i am interested to see if anyone else has any input.

 

[slant 6]

Don't know if this will help or not. I'm not a brake expert, but I had similar issue with not being able to build boost or lock up brakes. Turns out my pads and shoes were kind of glazed over. So I turned both, put new pads on, and had a local brake guy put in his custom soft shoes. That really helped quite a bit.

 

[Hot Air]

Guys,
Just bite the bullet and get a Hydraboost system from 84 or 85 and be done with it!
Conrad

 

[87GNSteve]

I bought a reman booster and brand new MC for the N/A Regal.
If I slam the brakes it will put you into the dash. :biggrin:

 

[sbbpwr]

one big thing i have seen on the g-bodys is rear brake shoe adjustment issues.everybody remember how the rear shoes adjust themselves?

 

[Red Regal T]

Jeff, have you upgraded to the S-10 wheel cylinders? Organic rear shoes? Braided brake lines are also a good upgrade. They have no give as do the rubber lines. Also, I found an increase in braking by using Z-Performance pads for about $50. Also, be sure rear brakes are adjusted up tight, and the adjusters are on the correct side. Another worthwhile upgrade would be to replace both front calipers. They are for nothing almost, at $10 each & core. This is good move for anyone with old calipers.

 

[thenash79]

Well i rechecked vacuum to booster in gear with different vac gauge and i am only showing 12inchs of vacuum.I can't find any vacuum leaks even with smoke test,that would have to be a big vac leak.my cam is comp cams 212/212 110 roller with gn1's.Anyone have similar sig? What are u guys reading?With only 12 inchs the booster ain't workin.I don't understand when i go down the highway in decel my gauge shows 20inches but the booster still feels the same.My check valve and booster hold vac for days. Booster should hold the 20 inchs and feel different.I'm on the second new double diaphram booster.