Brake Booster Problem with friends AE86

scarsofcarma · 01-25-2014, 10:09 PM

Hi everyone, this is an issue with a friends AE86 notchback Corolla.

He needed to replace his brake booster and master cylinder because his master cylinder was leaking fluid into his booster, which in turn was leaking into his interior carpeting. When we removed the booster, it was literally full of fluid to the point that it could've filled a 16 ounce soda bottle.

After replacing the booster and master cylinder with new ones he bought from rockauto.com we are having an issue with the booster not functioning properly. We bench-bled the master before installing it, and we flushed out all the old fluid and bled his hydraulic system 2-3 times in the proper sequence.

Before we started the car, the pedal was nice and firm. As soon as we start the vehicle, the pedal sinks to the floor with no effort whatsover. Pumping the pedal has no effect on raising the pedal or adding pressure when the car is running. But if you turn off the car and pump the pedal, the pressure returns and the pedal doesn't sink to the floor anymore.

Normally I'd say this is just a bad booster... but this one is brand new... and very much a pain to install... so I just want to make sure I didn't miss something before he sends it back and says its defective.

Also, the vacuum check-valve to the booster functions properly we removed that and tested it.

Any suggestions appreciated! Thanks

JL1RX7 · 01-26-2014, 09:46 AM

Bad check valve going to the engine? All the vacuum lines good with no fluid in them going to the engine?

Whizbang · 01-26-2014, 11:35 AM

new doesnt mean it has ever worked either.

id check the valve and the vac lines again. aside from that.... might be a bogus part

scarsofcarma · 01-26-2014, 04:11 PM

Yes vac lines are good. There's only one going to the intake manifold from the booster. We removed it for inspection when we checked the valve. There was signs that some brake fluid residue in it but its clean now and no leaks.

01-25-2014, 10:09 PM	#1
scarsofcarma Rotary Fanatic Join Date: Aug 2013 Location: Antioch, Ca iTrader: (0) Posts: 101 Rep Power: 12	Brake Booster Problem with friends AE86 Hi everyone, this is an issue with a friends AE86 notchback Corolla. He needed to replace his brake booster and master cylinder because his master cylinder was leaking fluid into his booster, which in turn was leaking into his interior carpeting. When we removed the booster, it was literally full of fluid to the point that it could've filled a 16 ounce soda bottle. After replacing the booster and master cylinder with new ones he bought from rockauto.com we are having an issue with the booster not functioning properly. We bench-bled the master before installing it, and we flushed out all the old fluid and bled his hydraulic system 2-3 times in the proper sequence. Before we started the car, the pedal was nice and firm. As soon as we start the vehicle, the pedal sinks to the floor with no effort whatsover. Pumping the pedal has no effect on raising the pedal or adding pressure when the car is running. But if you turn off the car and pump the pedal, the pressure returns and the pedal doesn't sink to the floor anymore. Normally I'd say this is just a bad booster... but this one is brand new... and very much a pain to install... so I just want to make sure I didn't miss something before he sends it back and says its defective. Also, the vacuum check-valve to the booster functions properly we removed that and tested it. Any suggestions appreciated! Thanks

01-26-2014, 11:35 AM	#3
Whizbang Respecognize! Join Date: Jul 2008 Location: Δx = ħ/2Δp iTrader: (5) Posts: 3,190 Rep Power: 20	new doesnt mean it has ever worked either. id check the valve and the vac lines again. aside from that.... might be a bogus part __________________ For current updates and event coverage check out Follow on Twitter! @WhizbangRally Whizbang Rally's Webpage \| Facebook

01-26-2014, 09:46 AM	#2
JL1RX7 Rotary Fanatic Join Date: Feb 2008 Location: Front Royal, VA iTrader: (1) Posts: 487 Rep Power: 17	Bad check valve going to the engine? All the vacuum lines good with no fluid in them going to the engine?

01-26-2014, 04:11 PM	#4
scarsofcarma Rotary Fanatic Join Date: Aug 2013 Location: Antioch, Ca iTrader: (0) Posts: 101 Rep Power: 12	Yes vac lines are good. There's only one going to the intake manifold from the booster. We removed it for inspection when we checked the valve. There was signs that some brake fluid residue in it but its clean now and no leaks.