brake problem - The 1947 - Present Chevrolet & GMC Truck Message Board Network

nvrforgotten52 · 05-22-2006, 04:17 PM

hi, i have 69 cten with all four wheel drum brakes new master cylinder, wheel cylinders pads...etc. i have all new parts except for the booster. the pedal goes almost to the floor. and i just cannot figgure out why. there is not one air bubble in the system... no leaky bleeder screws, wheel cylinders or kinked lines... im thinking it has to be the booster???? any help would be great. thanks...
david

nvrforgotten52 · 05-22-2006, 04:34 PM

anyone??

pharcydekm · 05-22-2006, 09:51 PM

I would say you have a bad master. Do you get good pressure when you bleed the system?

dwcsr · 05-23-2006, 12:03 AM

If you are sure you have no air in it excess travel means its out of adjust ment. First thing is to make sure the brakes are adjusted up properly. Bring them up tight an back off till they just turn with a little drag. If this is a booster you added to get power brakes one of two thing may be wrong.

1. the master needs to be for a power brake system and you got a manual brake one. The hole on the rear of the master where the push rod goes in is deeper on a non power master so you would be closer to the floor when applied if it was the wrong one.

2. The push rods are not adjusted correctly.

If its an original power brake system then you may have the wrong master. The push rod depths are different as I said but the bore on a non power master is smaller and pushes less fluid per application but at a higher line pressure so you would be closer to the floor again when applied because the volume required to push the wheel cylinders out all the way is not sufficient. You may be able to pump them up and get a good pedal.

A bad booster usually make pedal effort harder and does not change the travel very much. If anything it would make the pedal go lower if it were good than if it were bad.

look there first and see what happens.

pharcydekm · 05-23-2006, 08:40 PM

I agree with you up until your last statement. If the master is bad you will have a low pedal and will also feel mushy. If you can pump it up then I would blame the master. It could very well be a push rod problem though and I believe you are dead on as far as trouble shooting it.

dwcsr · 05-26-2006, 06:50 PM

Normally in my experience if you have a bad master it will leak out the back or if you apply constant but light pressure on the pedal it will slowly creep down to the floor. If the seals were very bad in the back it may suck air and get mushy but this does not typically happen on a new master.
But anything is possible.

05-22-2006, 04:17 PM	#1
nvrforgotten52 Registered User Join Date: Jan 2006 Location: Morro Bay C.A Posts: 179	brake problem hi, i have 69 cten with all four wheel drum brakes new master cylinder, wheel cylinders pads...etc. i have all new parts except for the booster. the pedal goes almost to the floor. and i just cannot figgure out why. there is not one air bubble in the system... no leaky bleeder screws, wheel cylinders or kinked lines... im thinking it has to be the booster???? any help would be great. thanks... david

05-22-2006, 04:34 PM	#2
nvrforgotten52 Registered User Join Date: Jan 2006 Location: Morro Bay C.A Posts: 179	Re: brake problem anyone??

05-22-2006, 09:51 PM	#3
pharcydekm Registered User Join Date: May 2003 Location: Englewood, CO Posts: 146	Re: brake problem I would say you have a bad master. Do you get good pressure when you bleed the system?

05-23-2006, 12:03 AM	#4
dwcsr Hollister Road Co. Join Date: Apr 2005 Location: Houston Posts: 6,131	Re: brake problem If you are sure you have no air in it excess travel means its out of adjust ment. First thing is to make sure the brakes are adjusted up properly. Bring them up tight an back off till they just turn with a little drag. If this is a booster you added to get power brakes one of two thing may be wrong. 1. the master needs to be for a power brake system and you got a manual brake one. The hole on the rear of the master where the push rod goes in is deeper on a non power master so you would be closer to the floor when applied if it was the wrong one. 2. The push rods are not adjusted correctly. If its an original power brake system then you may have the wrong master. The push rod depths are different as I said but the bore on a non power master is smaller and pushes less fluid per application but at a higher line pressure so you would be closer to the floor again when applied because the volume required to push the wheel cylinders out all the way is not sufficient. You may be able to pump them up and get a good pedal. A bad booster usually make pedal effort harder and does not change the travel very much. If anything it would make the pedal go lower if it were good than if it were bad. look there first and see what happens.

05-23-2006, 08:40 PM	#5
pharcydekm Registered User Join Date: May 2003 Location: Englewood, CO Posts: 146	Re: brake problem I agree with you up until your last statement. If the master is bad you will have a low pedal and will also feel mushy. If you can pump it up then I would blame the master. It could very well be a push rod problem though and I believe you are dead on as far as trouble shooting it.

05-26-2006, 06:50 PM	#6
dwcsr Hollister Road Co. Join Date: Apr 2005 Location: Houston Posts: 6,131	Re: brake problem Normally in my experience if you have a bad master it will leak out the back or if you apply constant but light pressure on the pedal it will slowly creep down to the floor. If the seals were very bad in the back it may suck air and get mushy but this does not typically happen on a new master. But anything is possible.



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