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Bought an 84 before xmas, its been off the road years as a project car but has had the engine rebuilt and the brakes have been overhauled at some point, ive found receipts for new calipers, hoses, and when the car arrived i noticed its had new brake lines made too, all very tidy etc. I took the drivers front wheel off just out of curiosity and it all looks good behind there.
once i got the engine running and moved the car a little bit it was obvious the brakes are crap. the pedal is quite firm constantly and i have to push it real hard right to the floor just to hold the car still if i move into drive or reverse.
The big vacuum line from the back of the carb is there which runs to a valve thing and then into the brake booster.
The fluid in the resevoir is full and looks nice and clean too.
Could be the Break Booster......
There is a hose that goes into the front of the booster that has a rubber grommet.
Could need to be replaced. Or even need the entire unit replaced.
Last edited by Ron U.S.M.C.; 01-22-2017 at 01:25 AM.
Sounds like you have no brake assist, in other words the booster is bad, as mentioned.Does the brake pedal feel the same as when the eng is off?Its also possible there is no vacuum reaching the booster.
Air in the lines would make it easy to push pedal to the floor.
Yeah its the same all the time. the pedal is quite near to the floor as it is, and i have to really hold it down to keep the car from moving when shifting into drive.
on my 87 the pedal is spongy when the car is off but if i pump the pedal a few times it firms right up, then eases back off when i start the car.
so vacuum problem then ? the brake booster looks like it was removed from the car when the engine bay was painted as its nice and black and clean with no overspray anywhere, surely the previous owner wouldnt of put a junk booster back on the car
Vac line comes out the centre of the carb at the back then goes to this valve thing then goes to the booster. im not sure what the valve is for ? on my 87 it just comes out the back of the intake and straight to the booster.
That is a one way check valve. Try for giggles flipping it around to have the flow go the opposite direction and see if that makes a difference also while you have the house off check to ensure you have good 18" or more of vacuum with the engine idling
Last edited by daferris; 01-23-2017 at 01:36 PM.
Reason: Add with engine at idle
How do i check the vacuum i dont have a gauge or anything, if i pull the hose off should it be sucking against my hand with much force if i put the palm of my hand on it ?
I will try turning the valve around though. Does it need this valve though or could i just replace the entire hose with one straight pipe like on my 87 ?
If the pedal is near the floor when fully depressed, that to me sounds like air in the lines. If they removed the master cylinder, but did not bench bleed it, there could be copious amounts of air in the master cylinder. Additionally, the lines will need to be bled thoroughly after bench bleeding the master cylinder. That should firm you right up.
Normally when a booster or lack of vacuum is an issue, the pedal will not have much travel and sit high (ie, not depress much). It'll also be really hard to stop (worse than manual brakes).
How do i check the vacuum i dont have a gauge or anything, if i pull the hose off should it be sucking against my hand with much force if i put the palm of my hand on it ?
I will try turning the valve around though. Does it need this valve though or could i just replace the entire hose with one straight pipe like on my 87 ?
for the vacuum with your finger capping the line it should with that size of line leave a small welt on your finger if it were pressure it would be like 10-15 psi to try to give you a clue. Vacuum have as someone said I very useful if you have the funds for it. As long as you have vacuum on the booster side of the check valve no harm in keeping it. Also if you can " pump" the brake pedal and it gets harder and does not go down as far than you also have air in the system. If you have drum brakes in the rear and they are really loose ( not adjusted) that will cause the pedal to travel far and be weak as well. If parking brake works apply it see if that helps. Also try jacking the rears off the ground apply the brake and have someone spin the rears well your applying the brakes to see if they are working...
I was tinkering with the car tonight, while it was running i pulled the hose off the brake booster and its getting decent vacuum just by putting my finger over the hose.
I had to move the car too, first time i had actually moved it since getting it, all i wanted to do was turn it around so its facing the other way in the garage and yeah the brakes are terrible, i had to pull the seat forward a bit just so i could ram my foot right into the floor to stop the car moving lol
I cant pump the pedal, its constantly low to the floor regardless of if the engine is on or off.
The car has calipers at the rear. its had new brake pipes from the master cylinder to all 4 corners, new brake hoses front and back and new calipers at some point, and as i previously said the fluid in the resevoir is full and clean.
Ive got one of those one man brake bleeder kits which attaches to my air compressor, it made doing the brakes on my 87 a piece of cake so i can try bleeding it through.
You say the lines are new, but how new? The PO of my '86 stated that the lines were new on it when I bought it, but didn't tell me that "new" was new lines put on five years ago and the car sat outside and didn't move. Come to find out the lines were cheap and had gone bad on the inside.
Once I put new braided lines on and bled the system that car stopped quick!
Thanks guys, looks like the car was last on the road in 2008, then i guess the guy that done all the work started on it then so im not sure how old the brake lines are, they are copper pipes and everything looks nice, he even removed the K member from the car and its been powder coated !
We dont really have any places like that which rent equipment out over here in the England, I will have to look for something to check the booster then.
Its obviously been removed from the car when the engine bay was painted, aside from the big vac line that goes from the booster to the carb are there any other hook up points on it thats i can check ? Im wondering if something is missing or not installed properly like where the pedal meets the booster inside the car. Ive never looked into a brake booster at all
Hey, m8. You're describing the lines going from the master cylinder to all 4 corners.
They DO go from the master cylinder to the prop valve in your car first, right?
Just asking to be sure.
And just in case you don't know how a brake booster works:
In there is a membrane with positive air pressure on the firewall side and negative pressure (vacuum) on the front (inside the booster).
Once the engine is running and generates vacuum for the booster, it eases the force you need to push the brake pedal down.
This is because you have the additional "weight" of the atmosphere pushing with you, because the vacuum inside the booster offers no resistance.
So if your booster were shot (no vacuum due to clogged valve, membrane rupture or damage to the housing), you'd have the same pedal resistance with the engine either off or on and pumping with the engine off would change nothing.
IIRC there should be a slight hissing sound a couple of times when you push the brake pedal after your engine ran (created vacuum) and you turned it off.
Now sound = leak in brake booster?
A moving pedal without hardly any resistance means air inside the lines or master reservoir.
If there were air in the lines AND you still had your prop valve, that tiny sensor in the prop valve would likely cause a light in your dash to turn on, as the sensor reacts to pressure differences between the front and rear break line circuits.
Unless you had the same amount of air in BOTH circuits or no brake fluid at all.
booster replacement isn't a terrible job, but you will be spending some time under the dash. do yourself a favor and pull the driver's seat so you can stretch out whilst down there.
Yeah thats no problem as the seats arent even bolted in anyway, lol.
Ive been under the rear of the car for the first time tonight, and it has indeed got all new brake lines going to the back too and the rear calipers have new brake hoses on. also new handbrake cables, i thought the handbrake was seized as it was really tough to pull on but i guess its just new and actually works !
Anyway, back to the main problem. So we think its the booster for sure and me trying to bleed the brakes is a waste of time ?
I bled the brakes and there were a couple of little bubbles here and there but nothing unexpected. Anyway that didnt help really.
the pedal has good travel but is really firm all the time still. I took the car to the end of the street and back to try and the braking doesnt happen until the pedal is really close to the floor
i also noticed the car isnt shifting gear. It held onto first for ages so ive got the cable to adjust now too. Providing it is just the cable ! Ugh...
Man, that sucks! You could ask a shop if they can vacuum the air out of your lines, master cylinder and prop valve, but that's about all I can suggest regarding pedal travel.
If your master cylinder has air in it, you'll have a hard time bleeding it without bench bleeding it.
The prop valve can be bled by opening the fat bolts up front and rear of the valve itself. Remove the rubber caps if they're still present and have someone stand on the brake, while you carefully open one bolt at a time.
You can adjust your t.v. cable real easy. push in the metal tab to the side of the mounting bracket at the throttle body, shove the black part of that cable towards the rear until it seats against the bracket.
Release the tab and open the throttle body manually and completely (!) until it hits the WOT stopping point.
Your cable will ratchet into position.
Im chasing 3 problems at once now. Trans still wont shift after tv cable adjistment and fluid and filter change so i have a guvernor replacment kit on the way.
brakes still suck. So i have good pedal movement. I was really concentrating on the pedal today when i tried it. It doesnt ease off with the engine running though and as i said i have to really force it down to bring the car to a stop.
It does sound more like air in the system now. You know... air compressing until you can't compress it any further, so the force then applies to the fluid?
A different thought:
Can you push the brake pedal down EASILY by HAND? Do you get the feeling the pedal is pushing into nothing at first, then suddenly making contact with something?
Our cars don't have adjustable rods that connect the pedal to the master cylinder, but perhaps something's broken there?
Edit:
Look at all this gunk that can clog up passages:
This is the back side of my old master cylinder. The rod from the brake pedal joins it there.
And if the seals in the interior deteriorate, it will have a hard time creating the necessary pressure, so this might also be the cause of your issue.
Thanks for the reply man. I can press the pedal with my hand all the way down yeah. I am comparing this pedal to the pedal in my 87. In my 87 the pedal is fairly soft with the engine off, i can pump it 3 times until it goes really firm. Then doesnt ease off until i start the engine and vacuum kicks in.
on this 84 though i can pump the pedal all day long and it feels the same regardless. Thats why i am leaning toward the booster. Its got good vacuum going to it. I have to really mash the pedal to the floor for the car to stop and even then it just sort of comes to a stop.
i bled 3 corners last week, couldnt get the front left caliper bleed valve open. But the other 3 corners were fine, just a few bubbles here and there.
i will have to get under the dash and check where the pedal meets the back of the master cylinder
Replace your master cylinder. Probably bleeding past the piston seals which explains why you can't enough stopping power. They are cheap to buy and easy to replace. Even without the booster you should have a firm pedal.
The pedal is firm, it has good travel but the braking doesnt happen until i really press it into the floor. really feels like its getting no assist.
and also the fact the pedal doesnt become solid when you pump it with the engine off like it does on my 87. then when you start the engine it eases back off with the vacuum.
i havnt looked at the car for a little while now, work, kids then ive been ill all this week, like properly ill. urgh.
If the brake booster is good, but the master cylinder has air in it would i get the same symptoms ? the couple of times ive drove the car to the end of the street and tried the brakes it just sort of gradually slows down when press the brake quite firmly to the floor. If i braked like that in my 87 it would no doubt come to an abrupt stop
I moved the car today actually to see if it was shifting gear and I did have to stamp on the brakes after giving it some gas. It does come to a stop. The rears are squeeling all the time now which is a new thing
When you press the brake pedal with the engine off for the first time..or while its running and press it once as if you panick braked...do you hear a whooshing sound of air? my booster was doing this as a clear sign it was done. Is easy to swap out a new booster..I get a swivel..long extension and my cordless impact and can unbolt it pretty quick now.Unclip the pedal rod and then unbolt the master and slide the booster out and drop the new one 1.Its a quick job and at this point Id replace it anyway for peace of mind if I were you and its been sitting a long time.1 less thing to have to factor what could be wrong.
Replacing the master inst a bad idea also if its the original piece.
When you press the brake pedal with the engine off for the first time..or while its running and press it once as if you panick braked...do you hear a whooshing sound of air? my booster was doing this as a clear sign it was done. Is easy to swap out a new booster..I get a swivel..long extension and my cordless impact and can unbolt it pretty quick now.Unclip the pedal rod and then unbolt the master and slide the booster out and drop the new one 1.Its a quick job and at this point Id replace it anyway for peace of mind if I were you and its been sitting a long time.1 less thing to have to factor what could be wrong.
Replacing the master inst a bad idea also if its the original piece.
I don't get a whoosh of air no. I moved the car again the other day and there is a rattling noise coming from the left rear wheel just going about 10-15mph down my street and back. I put the car up on stands and went through the gears and that wheel wouldn't come to a stop. Well it did....then started moving again even though my foot was on the brake. Wtf ! The right rear wheel sped up and stopped properly though wirh it being the drive wheel.
Did you make sure the pads and/or rotors aren't glazed over?
This could be just a friction surface thing. I just finished redoing my 89' brakes and I had to replace rotors/drums and pads to get that proper feel again. I had just replaced pads and that didn't do squat. Also, I originally started with AC Delco ceramics. I think the Centric stuff looked WAY better.
Last edited by Tootie Pang; 03-26-2017 at 01:59 PM.
I don't get a whoosh of air no. I moved the car again the other day and there is a rattling noise coming from the left rear wheel just going about 10-15mph down my street and back. I put the car up on stands and went through the gears and that wheel wouldn't come to a stop. Well it did....then started moving again even though my foot was on the brake. Wtf ! The right rear wheel sped up and stopped properly though wirh it being the drive wheel.
I tried freeing up the dodgy caliper but it was seized. I've got two new calipers on order. I don't think that will cure the lack of assistance though but it needs done regardless.
Did you make sure the pads and/or rotors aren't glazed over?
This could be just a friction surface thing. I just finished redoing my 89' brakes and I had to replace rotors/drums and pads to get that proper feel again. I had just replaced pads and that didn't do squat. Also, I originally started with AC Delco ceramics. I think the Centric stuff looked WAY better.
The pads arent clean, they have the surface type stuff on them like when you leave a car sitting outside for a while but they arent all rusty. trouble is i cant drive the damn thing to clear the discs, the most ive been is down to the end of my street and back with crap brakes lol.
and also because its not running right either, trying to figure out a fuel issue with the carb while im waiting on the new calipers and other bits coming.
This is what the rear discs both look like pretty much, ive been tidying up the rear by wire wheeling it all and then stone chipping it, done the springs and installed new shocks, just waiting on some new U clamps coming to refit the swaybar with all new stuff. this is the side with the useless caliper too, i just stuck it back on so its out the way for now
Nah they are just marking from the car standing I guess. I've replaced the discs on my 87 so it's no problem but I think the discs are fine. They just need cleaned by the pads when driving basically. I could even look for a local garage that skims discs as it only takes a few minutes
those rear calipers are the Delco Moraines. they are notorious for failing to properly adjust (which requires frequent operation of the parking brake lever). it's not unusual to find one that is locked up and especially to find a rotor rusted up from lack of pad contact.
there was a recall for them (only applicable to manual trans models) and a recall kit that could be acquired to upgrade them. a rebuilt set may, or may not, have the upgraded piston installed. the consensus is 'probably not'.
Once you install the new calipers, ensure they are initially adjusted correctly, religiously use your parking brake and inspect your rotors frequently to ensure the pads are making good contact (no surface rust after a drive).
like me, if you have access to a known good booster, I wouldn't hesitate to swap it out to note any change. you can also apply a vacuum source to your 'suspect' booster to see if it holds a vacuum.
since the master has been replaced by unknown peeps, a proper bench bleed may be in order. the MC MUST be removed from the vehicle to accomplish this.
Thanks man. From what I can gather I don't think the master cylinder has been replaced but it looks like everything was removed from the engine bay for paint then reinstalled and it's had new copper brake lines made going to all 4 corners of the car.
I'd hope the amount of work that the previous owner put into this car he bled the brakes when re installing etc
I might just order 4 new discs now.....but this parcel is going to be heavy as hell that my friend has agreed to bring back from America for me lol
So applying vacuum to the booster and checking to see if it holds how do I do that? I did have to check the pull off on my choke by using my brake bleed kit as it's a one man vacuum thing and that worked great. But you can obviously see the pull off come downward. How do you know the booster is holding vacuum, just by the brake pedal ?
On my other car I can pump the pedal a couple of times wirh the engine off and it goes really firm. Then when I start the engine it eases off. Is that what I'm looking for here ?
If you can pump the pedal forever and it never stiffens, or only stiffens slightly, there is air in the system. Your task is finding out where the air is contained, or in a worse case scenario, entering the system.
Start with the master cylinder. Remove it. Inspect it for leaking seals (mostly evidenced by brake fluid surrounding the piston). If good, bench bleed it and reinstall. If it's leaking, replace it. Then bleed the rest of the system starting at the point farthest away from the master cylinder (in terms of length of brake line) and then move closer. This will take you an hour or two with a friend or speed bleeders, assuming nothing breaks.
Don't spend hours troubleshooting this needlessly. The brake systems on these cars are very simple. Don't overthink it or start throwing parts at it. Once you've bled everything and you're sure there's no air in the system, at that point you should have a firm brake pedal after a pump or two with the engine off. Of course, you should test the booster first and foremost before taking off the master cylinder, as it makes sense to only have to take it apart once. Do this by using a vacuum pump connected to the booster vacuum line, pull down some vacuum, and wait a bit. If you lose more than a couple of inches of vacuum, it's probably shot. If you don't lose more than a couple of inches of vacuum, don't worry about replacing it.
If you can pump the pedal forever and it never stiffens, or only stiffens slightly, there is air in the system. Your task is finding out where the air is contained, or in a worse case scenario, entering the system.
Start with the master cylinder. Remove it. Inspect it for leaking seals (mostly evidenced by brake fluid surrounding the piston). If good, bench bleed it and reinstall. If it's leaking, replace it. Then bleed the rest of the system starting at the point farthest away from the master cylinder (in terms of length of brake line) and then move closer. This will take you an hour or two with a friend or speed bleeders, assuming nothing breaks.
Don't spend hours troubleshooting this needlessly. The brake systems on these cars are very simple. Don't overthink it or start throwing parts at it. Once you've bled everything and you're sure there's no air in the system, at that point you should have a firm brake pedal after a pump or two with the engine off. Of course, you should test the booster first and foremost before taking off the master cylinder, as it makes sense to only have to take it apart once. Do this by using a vacuum pump connected to the booster vacuum line, pull down some vacuum, and wait a bit. If you lose more than a couple of inches of vacuum, it's probably shot. If you don't lose more than a couple of inches of vacuum, don't worry about replacing it.
I havnt got a vacuum gauge to check. But I can pump the pedal forever and it doesn't go solid like my 87. I'm sure I can hear a hissing from the booster area when I'm in the car pumping the pedal though.
All the problems are starting to mount up so I will get back on the brakes once I get it running again
The reason the brakes suck is because the system is not building hydraulic pressure when you push the pedal. That is also the same reason the pedal is super soft because there is very little force (almost none) pushing back on the pedal. And the only reason the pedal goes hard at the bottom of travel is because it literally runs out of travel and is hard up against the physical limits. Don't misinterpret this as brake feedback because you already know your brakes aren't working. All this has nothing to do with the booster.
So the question is, why is the system not building hydraulic pressure?
1. There is so much air in the system that hydraulic pressure cannot build (because air is compressible). This is kind of unlikely after bleeding brakes over and over again. Usually a little air in the system results in spongy brakes that can be pumped a few times to improve feel temporarily, whereas you have virtually no brakes all the time.
2. Massive leak somewhere. Easy to detect because there would be a loss of fluid from master cylinder. In contrast, a small leak would feel fine after bleeding brakes but decline as you use the brakes and air is introduced to the system.
3. Master cylinder not moving enough fluid. This could be a bad master cylinder, or it could be because the brake pedal isn't actually pushing on the master cylinder. There is a push rod between brake pedal and master cylinder. If the gap between parts is too large then there will be a lot of free pedal travel before anything happens. Or maybe there is something wrong with the pedal linkage under the dash.
4. Brake pads are too far away from rotors. In this case the master cylinder is moving fluid but all the effort is being used up just trying to close the distance between pad and rotor. You would be able to bleed the brakes fine (move fluid through the system) but pressure won't build because the caliper pistons are not meeting up against a hard surface. Remember, to build hydraulic pressure you need to move fluid AND the calipers need to meet up hard against rotors.
I would place my bet on poorly adjusted brakes (item 4) or a physical geometry problem with the brake pedal (item 3). You can test item 3 by plugging the outlet ports of the master cylinder and pressing on the brake pedal. If the pedal is suddenly firm at the top of travel then the geometry is fine and so is the master cylinder. You can test item 4 by blocking off the rear brake line so that you have only front brakes. If the pedal feels good and you have brakes, then you know the problem is isolated to the rear. The rear brakes are far more likely to have adjustment issues, which somebody mentioned below.
Thanks man. Ive just put my carburetor back together to see how it fairs, so if i can get it running again i can move the car and start back on the brakes ! im not going to have the new calipers for a while now but i think i will pull the master cylinder and check that over
I know you said that everything was removed to paint the engine bay. Sense you didn't do this work, it is possible that the push rod between the master and the booster was lost or forgotten to reinstall leaving you with no connectivity between the 2. look at the picture on post #25 you can see the indent were the rod pushes Just a thought?? You would have to unbolt the master from the booster and take a peak. this can be done with out interfering with fluid loss.
01-19-2017, 05:51 PM
