TomSmy

iTrader: (11)

Hey Guys,

So here is the situation; just finished replacing my entire braking system with new parts and something is not right.

When the engine is off and I press on the pedal the brake pedal is firm and the brakes bite (as I would expect and it all feels normal).

When the engine is turned on the brake pedal is super soft and goes pretty much right to the floor before the brakes engage to stop the vehicle.

From my understanding this can only be caused by a few things:

1) Air in the lines
2) A leak in one of the connections
3) A leak in one of the pistons
4) Bad Master Cylinder

So I have bled the brakes a lot and my plan is to try again this weekend just in case. I cannot find a leak and the master is new.

Does anyone have any other ideas? Or any tips for checking the above that I may have missed?

As an FYI here is what I replaced:

Brake Booster
Brake Master
All Hard Lines
All Flex Lines
Rebuilt Front Calipers (re honed and used atkins rebuild kit)
Rebuilt rear drums (includes new cylinder pistons)

Any advice would be appreciated! This is my first brake job and would love to get it fixed!

Thanks
Tom

7aull

iTrader: (2)

Hi Tom-
When you put the Br Master in, did you "bench-bleed" it before the install? These can be notoriously tough to bleed completely if they are mounted to the car right out of the box. With a Bench-Bleed you put the loose Master in a Vice, attach a line/hose to the output and loop it back into the reservoir, then start adding fluid while working the rear piston. This "pre-bleed" makes the actual bleed process easier.
Something else I have added to my SA is Speedbleeders, which make one-man flushes a LOT simpler.

Also be sure your handbrake is correctly adjusted, both at the lever, and its adjustment on the rear drums.

Stu Aull
80GS
Alaska->AZ

t_g_farrell

iTrader: (1)

First off, vacuum power assisted brakes will act just like you describe. If the booster is working you should feel the pedal drop and become softer once you start the car. That said, I'm betting you still have lots of air in the brakes. The other issue is did you adjust the master cylinder rod to the right specs when installing it? That rod isn't always at the right length. You could be short and its just not pushing in the rod until you push the brake pedal far enough down.

TomSmy

iTrader: (11)

Thanks for the fast response!

So I have to admit i did not bench bleed the master... ...i knew this would make bleeding the brakes take longer but i assumed it would be good once fluid was pushing out the bleeder valves.

I think I will remove and bleed the master tonight and start again!

Hand brake works great - i very carefully dialed that in so that i had knew i would have some braking capacity before test driving!

TomSmy

iTrader: (11)

So I did spend a fair amount of time looking at the push rod adjustment. I couldn't figure out the correct way to do it so I did the following:

First I made it too long, then I slowly shortened it until it was right on the edge of me being able to "feel" it when i mated the master to it.

Does that sound logical or did i miss something really obvious? I figured worst case my method would cause the brakes to drag?

Thanks!

Tom

Banzai

iTrader: (13)

I wouldn't think the pushrod adjustment would be that far off if the brakes worked previously, but I guess you never know what a previous owner or "mechanic" might have done.

I'm in the "still too much air in the lines" camp. Looking at your original list of 4 possible problems, two of them lead you right back to your number 1 suspect, air in the system. If it is a leak, not sure how you would isolate and find it. I would probably have to go back and inspect everything I replaced or touched in the system.

As far as bleeding, I invested in a small motorcycle vacuum bleeder about 12 years ago and it has been a blessing on several occasions. Makes bleeding the lines a snap and eliminates a lot of fumbling around. Using it, I'm confident that if I still have trouble after bleeding, it's not in the bleeding process itself and I can concentrate on other possible problems.

t_g_farrell

iTrader: (1)

Its a new master cylinder. They don't come pre-adjusted, so you have to make sure its at the right length. If its too short it never fully engages one end of the brakes and if its too long it never relieves all the pressure back into the MC when the pedal is unloaded.

GSLSEforme

A little tip that may make diagnosing this a little easier. I've swapped/upgraded mastercylinders/boosters on different types of vehicles and pushrod freeplay adjustment can be a pain. I purposely set the pushrod to have play in it,before attaching and bolting up i put a small dab of strip caulk on end of pushrod,install and remove and check the depth of pushrod. Fairly quick,rule of thumb,shoot for about.020" clearance. When everything is up to temp,expansion may take up some of that clearance but there will still be enough freeplay. Didn't notice which model you have disc/drum,disc/disc. Proper mechanical adjustment of rear brakes is integral to proper pedal travel.
Also use a Mityvac for bleeding clutch/brake circuits,makes this a one man job. With car in air wheels off,brake,clutch fluid can be purged/bled in 15 minutes. This should be done approximately every two years and is an excellent preventive maintenance procedure,sometimes cures weird pedal issues due to air getting in system.

misterstyx69

iTrader: (142)

I don't know if this pertains to your problem BUT on an FC the hose that is attached to the Booster has a check valve IN it.So if you accidentally reverse that hose you will have Rock hard pedal and no stopping power.
It has an arrow with "Engine -->"stamped on the hose..sometimes hard to see.

TomSmy

iTrader: (11)

Hey All, thank you for the advice so far

So yesterday I finally got time to look over the braking system again.

I lifted up the car and did the following:

• Checked every line connection for leaks – found none.
• Lifted up the front brake calipers and checked the piston area – all dry including the dust boots.
• Removed the master and tried to bench bleed. I made short lines that went back into the reservoir and pumped it a lot.
• Adjusted the booster push rod to stick out further
• Re installed the master
• Bled the rear drum – pushed 1 litre of fluid through.
• Bled the front passenger caliper - pushed ½ litre of fluid through.
• Bled the front driver caliper - pushed ½ litre of fluid through.

I then rolled the car out the garage and stopped no problem with engine off, pedal felt good.

Turned engine on, back to super soft and to the floor.

I then made the push rod even longer, this made the brakes bite VERY HARD and early in the pedal travel, but the pedal feel did not improve,still very soft.
So yes, the push rod may not be set right, but it should only effect when in the pedal travel the brakes bite, not how the pedal feels.

I am now totally out of ideas and very frustrated now. Booked into my local mechanic on the 28th…..

Does anyone have any suggestions what I can do while I wait?

Thanks!

GSLSEforme

Are your rear brake shoes adjusted correctly,parking brake adjusted correctly? You make no mention of that...see my previous post.Did you,are you getting air out of system?

TomSmy

iTrader: (11)

Park brake works great - I made sure of that before I test drove round the block.

As for rear shoes, I pushed them out with the adjuster until they started to drag on the drums. They fit very snug and make removing and installing the drums difficult but doable.

I also reversed a few times to self adjust as well.


Yes I did get some bubbles at the start of my bleeding but they stopped quickly and I got clean clear fluid for many many cycles after that.

Tom

GSLSEforme

You state you tried to bench bleed m/cylinder,were you successsful,did you get air out? Sounds as if you've got the brakes adjusted mechanically correctly.

TomSmy

iTrader: (11)

I did get air bubbles but very few and stopped quickly. Could just have been what was in my short lines........


Problem was when I reattached the master and the lines it was leaking fluid everywhere so I may well have added air back in.....


I was hoping pushing 2 litres of fluid through it would remove any air


Thank you for your help - it is appreciated!




I am hoping that the shop will bleed with some form of machine that will eliminate the chance of any air in the master, then at least we will know where to look.....

GSLSEforme

Try this,you said you replaced all your hard lines,do you still have them? If so cut about an inch behind fitting from line,crush about1/4" of line in vice,bend it over on itself and smash flat,make two. Remove brake lines from master cylinder and install your "plugs". Get someone to pump pedal,crack fitting loose to get air out,no more air-pedal should be rock hard-not move at all. If it does,master cylinder is bad. Start car,feel pedal. Should be able to push some,but not much, if good remove plug and hook up line to front brakes,rebleed and test again. If master is good,will be able to push pedal slightly,start car and recheck,pedal should move but not much. Your hydraulic problem may be related to rear brakes. You can block off the front brakes with the plug,hook up and bleed the rear,repeat the test. The idea is to isolate the complete system from the master cylinder til you prove it good/bad then isolate front/rear system to determine where problem is. Hope this helps...go get some more brake fluid.
Tip: get an old windex spray bottle and fill 50/50 dish detergent & water. Spritz the area where you have brake fluid seeping down from bleeding. The detergent/water will break down brake fluid before it gets a chance to damage paint &start rust. Read my prior post on how to set master cylinder pushrod freeplay.

TheRX7Project

iTrader: (3)

How do you adjust them at the drums ('80)? Mine is really weak and is adjusted all the way tight at the handle.

t_g_farrell

iTrader: (1)

Rear drums on an SA require you loosen 2 nuts on the lower backing plate and
rotate the pin to tighten the shoes up to the drum. I usually make it do both just
drag. Then tighten the locking nuts back down. The trick is when tightening to not
unadjust the adjustment you just made. Takes a few tries usually to get it just right.
Once you do, it make a huge difference in the brake feel and the balance of the
braking.

The procedure is pretty well documented in the FSM. If you don't have it, get it
here or get a hardcopy from ebay. Foxed.ca

TheRX7Project

iTrader: (3)

Yeah that I knew, I thought there was some kind of parking brake adjustment at the drums as well. Thanks anyway.

GSLSEforme

Loosen parking brake adjustment to get some slack in cable/mechanism first. Adjust brake shoes then adjust parking brake to hold car.

midnight mechanic

"Bench bleeding........Problem was when I reattached the master and the lines it was leaking fluid everywhere so I may well have added air back in." is this everyone elses' experience? I never tried bench bleeding, because I thought this might happen. Is there a trick to it?

TheRX7Project

iTrader: (3)

The trick is to do it while the master is in the car, with a hose and a cup full of fluid attached to the bleeder.

t_g_farrell

iTrader: (1)

On the SA the master has its own bleeder which is very handy.

TomSmy

iTrader: (11)

So it turns out i got sent on a giant wild goose chase......

I got sent a brand new master that was faulty - dammit!

Thanks for the help everyone,
Tom

GSLSEforme

Happens,a lot. Sometimes more than one bad part back to back...have to keep yourself focused AND calm to work thru stuff like this.
Doing this for a living,have encountered this often,quality of parts today is abysmal. I make it a point to buy new and brand name when i can to try to minimize this. No one compensates you for doing the job 2x...AND the diag time to figure out the replacement part is faulty. Can't charge the customer for it,lost time can't be gotten back.
Glad you persevered and worked thru it to a successful end.

TomSmy

iTrader: (11)

Yeah I always buy good brand name parts to try to avoid this, bad luck I guess.

Due to lack of time I ended up having to pay my local mechanic to look over the entire braking system, so it was his skills that found the issue!

Thank you for your help though

Car is sorted now and unfortunately up for sale