Loss of Braking

[IAmTodd]

I'm in a bit of a pinch, I've done some quick searching but don't have a lot of time so please pardon if this is an easy one. I was on my way to see a friend in the hospital. Someone was braking in front of me, I applied my brakes (not hard, I've hit them harder before) and there was a slight pop/pulse in the pedal and I lost most of the braking pressure. They will bring it to a stop but very slowly. Emergency brake (lived up to its name this time) appears to work normally from what I can tell. I can hear some noise in the drums when I apply the normal brakes. When the vehicle is off and I pump the brakes they were return to the normal hard pedal one would assume with no vacuum pressure.

Sorry if this is poorly written but I'm out the door in the trusty Saab.

 

[Tony H]

Pedal goes to the floor when car is running?
Hard Pedal with car off.. does the pedal slowly drop to the floor?

Look under car by Drivers rear tire for brake fluid leakage.

 

[IAmTodd]

I'll check when I get back home. The fluid level hadn't dropped and I didn't see any immediate pooling of fluid on the ground.

 

[Tony H]

try this too:

Step on the Brake fairly hard.. then start to let up a little, see if it drops to the floor as you take pressure off the pedal. If it does, that's a sign the Brake Master is failing.
This can be done with car running or not.

 

[IZwack]

a slight pop/pulse in the pedal and I lost most of the braking pressure. They will bring it to a stop but very slowly. Emergency brake (lived up to its name this time) appears to work normally from what I can tell. I can hear some noise in the drums when I apply the normal brakes. When the vehicle is off and I pump the brakes they were return to the normal hard pedal one would assume with no vacuum pressure.

Definitely check the vacuum/booster part first as hoses and the booster itself sometimes does fail (leak).

I had somewhat the same thing happen to my 7.3L bus (vacuum pump failed as diesels dont have an intake vacuum) and it was a ton of fun bringing that thing to a stop.

 

[IAmTodd]

My first thought was the booster as well. How do you test that? With a vacuum pump?

 

[Jason94sport]

Damn you & your brakes.....
I'd say the brake booster too. I had one go out on a 454 suburban at HW speeds. That was a hairy experience.

 

[Spook]

No fluid loss, easy to see I had the line to the rear go south. Front brakes still worked but the pedal went way down before working.
I had the master cylinder go in a Montego I had, the O ring was letting fluid past. It would work if you let off the pedal completely after braking, but partial release of the pedal and reapplication would result in pedal to the floor . This was a little unnerving as it was coming down the Pacific side of the Continental Divide while pulling a U-Haul trailer with everything we owned in it. Thank heaven for trailer brakes :notworthy

 

[R&T Babich]

My first thought was the booster as well. How do you test that? ...

With the engine off, depress the brake pedal firmly.
Start the engine, the pedal should go down a bit more since the booster now has vacuum.

 

[Anime]

A change in braking pressure felt through the pedal with the engine running usually says hydraulics. Check for leaks, at the calipers, rear cylinders, and the connections at the master cylinder, as well as the rear junction above the differential, and of course the connections at the front/rear hoses, as well as the condition of the hard lines and hoses themselves.

If you find nothing, I'd say master cylinder.

 

[IZwack]

A change in braking pressure felt through the pedal with the engine running usually says hydraulics.

Or pneumatics

 

[IAmTodd]

Damn you & your brakes.....

Tell me about it. Thank the Explorer gods for a properly adjusted emergency brake and a manual transmission!

A change in braking pressure felt through the pedal with the engine running usually says hydraulics. Check for leaks, at the calipers, rear cylinders, and the connections at the master cylinder, as well as the rear junction above the differential, and of course the connections at the front/rear hoses, as well as the condition of the hard lines and hoses themselves.

If you find nothing, I'd say master cylinder.

No leaks. Checked all lines and junctions. Fluid level is staying consistent. I will double check the wheel cylinders but the other night they looked good.

Or pneumatics

I'm not real sure. The current master cylinder says Bendix on it so I don't think it's OEM. Could a seal blow in it? Autozone has a booster and master cylinder for $120. I may go that route since my current booster is quite rusty.

I won't have a conclusion until after the holidays. I'm not dumping any more money into it as it is begging for a new radiator as well. I've hit the brick wall and I'm tired of dumping money into it.

Thanks for all of your replies.

 

[IZwack]

I'm not real sure.

Sorrry, what I meant to say is that the vacuum part of the brake system / booster, is pneumatics. Hydraulics is the master cylinder and slave cylinders / calipers.

But to get back on topic, with no leaks, all signs point to the booster/MC.

 

[IAmTodd]

I understood. Just not sure which one is suspect. It's puzzling because I would think with a firm pedal with no vacuum the hydraulic system would be ok. But a pedal that goes to the floor with vacuum and little braking force would point to either an internal or external fluid leak. As I said above nothing external. So fluid escaping around the piston(?) in the MC?

 

[IZwack]

I understood. Just not sure which one is suspect. It's puzzling because I would think with a firm pedal with no vacuum the hydraulic system would be ok. But a pedal that goes to the floor with vacuum and little braking force would point to either an internal or external fluid leak. As I said above nothing external. So fluid escaping around the piston(?) in the MC?

That definitely could be the case. But if I were you, and although it may be a bit more expensive, I'd just replace both. Looks like you can get a MC from RockAuto for $30-$40 and the booster for $65 (with $10 back for the core).

 

[huntman58]

I understood. Just not sure which one is suspect. It's puzzling because I would think with a firm pedal with no vacuum the hydraulic system would be ok. But a pedal that goes to the floor with vacuum and little braking force would point to either an internal or external fluid leak. As I said above nothing external. So fluid escaping around the piston(?) in the MC?

If the fluid system is good and no leaks you should be able to still stop an auto with it just like an old none powered brake auto from days gone by firm peddle feel and no going to floor.

A soft peddle no pressure but also no leaks as has been said MC or booster.
1st one I would go to would be the MC as yes they can blow and leak internally and act just as if you blew a line / wheel / caliper.
If so you may or may not be able to pump the brakes and get some working pressure.

If you pull the MC and the back of it is wet it blew the rear seal. (Just went threw this on the car was losing fluid but that area is hidden and did not show tell it built up enough to finally drip!) Any way pulling the MC will also show you if the back seal blew or if it is the booster.

take the MC off and try to do a bench bleed and see if you get a pressure build. (I like to use plugs for this and hot hoses) if it bleeds and dose not leak you will not be able to push the brake push rod at all. If it passes the bench bleed test and there is no leaks at any wheel / fitting or line joint you are then down to the booster.
All this will cost only time and some brake fluid as you will have to bleed the system.

 

[Nomad767]

Just a thought....I had something close to this happen to me. Of all things, it was the front brake pads on one side. The pop and pulse was apparently the brake pad almost completely peeling away. I did not do much other than inspect the brakes after it happened, noticed half the pad missing and limped it home using the emergency brake to stop. I do not remember it ever squealing, just a pretty limp brake pedal. Just thought I would put the experience I had in there.

 

[IAmTodd]

That definitely could be the case. But if I were you, and although it may be a bit more expensive, I'd just replace both. Looks like you can get a MC from RockAuto for $30-$40 and the booster for $65 (with $10 back for the core).

Most likely I'll replace both. I can get both for $100 at Autozone so it's a draw with RockAuto and I don't have to ship the cores back, just trade that at the POS.

If the fluid system is good and no leaks you should be able to still stop an auto with it just like an old none powered brake auto from days gone by firm peddle feel and no going to floor.

A soft peddle no pressure but also no leaks as has been said MC or booster.
1st one I would go to would be the MC as yes they can blow and leak internally and act just as if you blew a line / wheel / caliper.
If so you may or may not be able to pump the brakes and get some working pressure.

If you pull the MC and the back of it is wet it blew the rear seal. (Just went threw this on the car was losing fluid but that area is hidden and did not show tell it built up enough to finally drip!) Any way pulling the MC will also show you if the back seal blew or if it is the booster.

take the MC off and try to do a bench bleed and see if you get a pressure build. (I like to use plugs for this and hot hoses) if it bleeds and dose not leak you will not be able to push the brake push rod at all. If it passes the bench bleed test and there is no leaks at any wheel / fitting or line joint you are then down to the booster.
All this will cost only time and some brake fluid as you will have to bleed the system.

I'll pull the MC out and do some troubleshooting on it. If I can determine that's the issues I'll just pop a new one of those in. There's definitely no firm pedal when the engine is running which leads me to believe the booster is working correctly.

Just a thought....I had something close to this happen to me. Of all things, it was the front brake pads on one side. The pop and pulse was apparently the brake pad almost completely peeling away. I did not do much other than inspect the brakes after it happened, noticed half the pad missing and limped it home using the emergency brake to stop. I do not remember it ever squealing, just a pretty limp brake pedal. Just thought I would put the experience I had in there.

Thanks for the suggestion. I plan to do a full inspection of the braking system when I get some extra free time. I'll make sure to look at the linings on all 4 wheels.

 

[IAmTodd]

Ok gentlemen, I've done some work tonight. I ran it around the block as is to see how it's running. Still the same problem obviously only one obsevation; if I hit the brake hard as in a panic stop there is no change in braking speed but the e-brake light comes on as if there is low fluid. Fluid level is great otherwise.

Came back home and pulled the check valve, it's good. I plugged the vac line and ran it around the block again. The pedal is obviously harder to push but still goes to the floor with minimal braking.

At this point I believe I ruled out the brake booster and am down to the master cylinder. Doesn't this sound correct? I'm really hoping as I can get one locally for $40+some fluid and have it back on the road again.

Is there a special way to replace the MC without getting air into the ABS pump? I really don't want to have to deal with that!

 

[sport97]

I had my mechanic do mine (just for piece of mind, my brakes still worked) I think he did it for 110 bucks, part and fluid included. That was worth it to me because I did not want to deal with getting air in the abs pump.