Spongy brakes (1 Viewer)

[robnicko]

Would this not be against the common sense? Not saying it didn’t fix your problem, but what would the logic explanation be for the booster being the problem?

i know it sounds odd but this is what the faulty booster in the Mazda did.
I never examined the old booster, just replaced and brakes came good instantly.
Prior to swapping it out the pedal would seem hard with the motor off however once started the pedal would sink to the floor and braking was pretty much non existent
It did happen after I had the car apart for repainting so whether something worked its way loose or other I dont know, it just failed

 

[flintknapper]

i know it sounds odd but this is what the faulty booster in the Mazda did.
I never examined the old booster, just replaced and brakes came good instantly.
Prior to swapping it out the pedal would seem hard with the motor off however once started the pedal would sink to the floor and braking was pretty much non existent
It did happen after I had the car apart for repainting so whether something worked its way loose or other I dont know, it just failed

I can believe it. It would be an odd failure of the booster to do that....but certainly possible. Boosters can fail in a number of ways....resulting in different issues (not always just hard braking).

 

[clx16]

Did some more testing today, I found that when I press the brake pedal, the brake fluid level rises up, when releasing, it drops again.
is this normal behaviour due to a compensating port from cylinder to reservoir, our does it automatically mean leaking seals? Anyone could check this on his ABS equiped 80?

I still have abs and I don't see that happening. Maybe it is at a very small amount that is hard for me to see. Is it pretty drastic for you? Air can compress so wonder if that is just indicating air still in the lines.

 

[NielsC]

Here can you see the rise and drop of the fluid level.



To me it looks normal as when the piston gets pressed, the Front piston seal moves passed a tiny compensating hole wich connects the body of the MC to the reservoir, but still not too sure about it.
An OEM rebuild kit is ordered for the old MC.
Today I removed the ABS pump, and bypassed it, bleeding it was hell, ran 4 bottles trough it on different ways, 2 man pumping, pressure bleeder,…
Still the same!
While in there I made plugs to blank off the holes of the master cylinder. Blanked off it’s solid as a rockand cannot be depressed, neither with the engine running. Does this rule out the MC and the booster?
If not I might order a new booster and rebuild my OEM master, possible replace al calipers with new ones as mine have been rebuild and might be faulty?
I’m sick of diagnosing and bleeding this thing over and over.

 

[clx16]

Well just by what you are saying, seems like you ruled out ABS pump as the issue. Also master cylinder. What you describe. at least to me, does not sound like a booster problem.
calipers..... rebuilt should work like new. They are VERY simple. (not sticking not leaking usually = good) Just checking since I've removed mushy brake calipers before... they were installed on the wrong side so the bleeder was not at the top, they trapped air. Are your bleeders the high point on your calipers?

I hear you on being tired of working on brakes. I really don't enjoy bleeding them on the 80 series at all.

 

[NielsC]

Yep the bleeders are pointing up, had a friend make that mistake before
Yes Everything checks ok, and yet still this mistery remains unsolved.
I’m gonna try plugging front left , then front right, and then the rear brake linea one by one and see if it makes any difference in pedal feel.
And verify again all caliper pistons can retract easily.

 

[NielsC]

I’ve plugged the line to the rear calipers and bled, no difference.

Then I plugged the line to the front left side caliper and bled, this gives me solid pedal!! No more spongy pedal!

Connected again and bled, plugged the line to the front right caliper, gives me a solid pedal aswell!!

Connected everything again and bled once again, resulting in the same spongy pedal as before what the hell?

How can disconnecting one of the front calipers give a solid pedal, but both connected makes the pedal spongy and make it dropping to the floor when pressed?? Any toughts on this as I’m at my end here?

 

[flintknapper]

Just trying to be sure I understand all the connections and procedures, so please excuse the following questions.

I’ve plugged the line to the rear calipers and bled, no difference.

So....this was plugged at the M/C? Then system/lines/calipers to front were bled? Pedal still spongy?

Then I plugged the line to the front left side caliper and bled, this gives me solid pedal!! No more spongy pedal!

Line to this caliper was plugged at its termination point? Right side lines and caliper bled? Gave firm pedal?

Connected again and bled, plugged the line to the front right caliper, gives me a solid pedal as well!!

Opposite of above....but again got a firm pedal with ONE front line blocked (and rear port on M/C blocked)?

Connected everything again and bled once again, resulting in the same spongy pedal as before what the hell?

Entire system reconnected, bled and spongy pedal again?

How can disconnecting one of the front calipers give a solid pedal, but both connected makes the pedal spongy and make it dropping to the floor when pressed?? Any toughts on this as I’m at my end here?

I see your methodology (isolating each system Front/Rear and side to side on the fronts). I'm thinking you might benefit from actual pressure tests at each corner to see IF that would give us any direction. It could done both going through the ABS and with ABS bypassed to help eliminate that component being a problem.

This is perplexing to be sure.

 

[NielsC]

Just trying to be sure I understand all the connections and procedures, so please excuse the following questions.



So....this was plugged at the M/C? Then system/lines/calipers to front were bled? Pedal still spongy?

Correct

Line to this caliper was plugged at its termination point? Right side lines and caliper bled? Gave firm pedal?

Correct

Opposite of above....but again got a firm pedal with ONE front line blocked (and rear port on M/C blocked)?

The rear port was reconnected and bled.

Entire system reconnected, bled and spongy pedal again?

Yup

I see your methodology (isolating each system Front/Rear and side to side on the fronts). I'm thinking you might benefit from actual pressure tests at each corner to see IF that would give us any direction. It could done both going through the ABS and with ABS bypassed to help eliminate that component being a problem.

This is perplexing to be sure.

View attachment 3237287
View attachment 3237288

If I could source a pressure gauge with adapter this could be an option.
However this is simple hydraulics, really not complicated.
It really should not be difficult, but indeed this is getting so frustrating and time consuming that swapping out all calipers and master for new ones comes to mind.
I think I can rule out the booster and ABS pump.
The LSPV is tied in the front circuit, could it act up or something?

 

[White Stripe]

LSPV is only for the rear brakes. Where did you plug the line up front? Before or after the brake hoses?

 

[flintknapper]

Correct

Correct

The rear port was reconnected and bled.

Yup

If I could source a pressure gauge with adapter this could be an option.
However this is simple hydraulics, really not complicated.
It really should not be difficult, but indeed this is getting so frustrating and time consuming that swapping out all calipers and master for new ones comes to mind.
I think I can rule out the booster and ABS pump.
The LSPV is tied in the front circuit, could it act up or something?

Yes there is a 'sense line' that goes up there and is famous for holding air along with the LSPV itself.

 

[Somebodyelse5]

The above part of the whole equation tells me you have a bad master cylinder, even though you just installed a new aftermarket one.

Going all the way to the floor is either a leak to the outside or an internal leak allowing it to continue to move to the floor.

If you're exaggerating the going to the floor, then it's still air in the lines. During bleeding did you let the MC get low enough to expose the holes in the bottom?

Sometimes aggressive two man bleeding is better than one man with a pressure bleeder.

Also, the order in which you do this is important.
For a LHD truck:
RR
LR
LSPV
RF
LF
LSPV

I'm going to agree^

I've heard a lot of folks fighting with aftermarket boosters... mine passed on the FSM checks but still ended up being my break issue. New OEM booster did the trick for me.

I've also heard of folks damaging the master cylinder by using the pedal to bleed... didn't see you call that out specifically, but I believe @JunkCrzr89 mentioned it to me when I did my replacement last year. Worth a thought if you're still fighting for ideas.

 

[NielsC]

LSPV is only for the rear brakes. Where did you plug the line up front? Before or after the brake hoses?

The sensing line from the front is the one that has the bleeder on the LSPV, that’s why theres a bleeder.

Before the brake hoses. At the ABS pump.

 

[NielsC]

I'm going to agree^

I've heard a lot of folks fighting with aftermarket boosters... mine passed on the FSM checks but still ended up being my break issue. New OEM booster did the trick for me.

I've also heard of folks damaging the master cylinder by using the pedal to bleed... didn't see you call that out specifically, but I believe @JunkCrzr89 mentioned it to me when I did my replacement last year. Worth a thought if you're still fighting for ideas.

What symptoms did you have with your booster?

I wanted to rebuild the old one but it has the rear part of the piston jammed inside, probably was pumped to the death while bleeding once in it’s life so I needed replacing anyway.
Will rebuild the new one I have and check for marks inside.

 

[NielsC]

So a bit of an update on the problem.
I’ve replaced the master cylinder once again, and replaced the booster with it.
At first it seemed better, but after some driving it’s clearly not any better.
So now every part in the brake circuit, except for the ABS pump, has been replaced or rebuilt. And the ABS pump has been bypassed temporarily without succes.
The only succes I had was with either one of the lines to the front brakes plugged of.
So this leaves me stumped… I think I am just going to keep living with it because I can’t think of a solution any more.

 

[FirstToy]

So a bit of an update on the problem.
I’ve replaced the master cylinder once again, and replaced the booster with it.
At first it seemed better, but after some driving it’s clearly not any better.
So now every part in the brake circuit, except for the ABS pump, has been replaced or rebuilt. And the ABS pump has been bypassed temporarily without succes.
The only succes I had was with either one of the lines to the front brakes plugged of.
So this leaves me stumped… I think I am just going to keep living with it because I can’t think of a solution any more.

Quite old threads but sounds similar. maybe will give you some ideas.

HELP Brake pedal goes to floor slowly

Is master number three from the same source as the others? I’d assume the re-mans are batch produced and could have the same defect (or new guy). First was used OEM. second and third will be same Cardone --- which I have put on two other cars with no issues. Recall that when I plugged both...

forum.ih8mud.com

Spongy and poor brakes fixed (sort of)

Sorry this post is so long, but I wanted to add these thoughts to the board for anyone else who is having the sames issues I had to hopely help them out...... So, after about 2 years, I finally have the brakes working about as good as they probably ever have. although there is a little...

forum.ih8mud.com

booster rod adjustment

Brake Booster Rod Adjustment - What Do I Turn Where?

I have searched for hours on here, Google, and some other forums, and cannot find what I think is probably a dumb question. I have the knowledge on how to measure the rod length in respect to the master cylinder, moving over the brake pedal bracket, and pretty much everything else. But what do I...

forum.ih8mud.com

 

[Inthefive555]

Any update to this issue? Experiencing this same problem, except ABS pump was also replaced and brakes worked fine until truck sat for an extended period ~6 months. Now brakes are spongy with no improvement after bleeding.