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Brakes grabbing hard after replacement of manifold and carb.

 
dherman
I love my Chevy Chevette!
Posts: 1
Joined: 08/12
Posted: 08/13/12 09:26 PM

I replaced the stock manifold and 2 barrel carb. on my 72 Impala with an Edelbrock manifold and 4 barrel.  At the same time I had the master cylinder replaced as it was leaking between the m.c. and the booster.  After these changes / repairs I can barely touch the brake pedal without screeching to a stop.  Is this a vacuum issue related to the manifold/carb change or something else? Although I had the m.c. leak the brakes worked fine before the change in manifold and carb.  Any suggested fix?  

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Dave632
I mow my lawn and find Chevys
Posts: 2253
Joined: 07/08
Posted: 08/14/12 06:38 AM

I would suspect the master cylinder. Check your vacuum at the booster and see if it reads normal.  
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pepsi1
I mow my lawn and find Chevys
Posts: 1718
Joined: 09/11
Posted: 08/14/12 10:47 AM

Welcome aboard dherman:

Just for HAH,HAH's spray some carb or brake clean all around the parts that were replaced. This is to eliminate and vacuum leaks. I don't think you have any, but there's always a first for anything.

Make sure the correct Master Cylinder was installed on the vacuum booster. The M.C. for drum brakes has a smaller resivoir, then the M.C. for a disc brake system....

I have never seen an intake manifold change and/or carb change effect the engines vacuum. The only thing that effects the manifold vacuum is a cam change. Plus any rocker arm ratio change. But there is always a first time for everything!...LOL...

Check to see if your master cylinder Push-Rod is not stuck in the back side of the M.C. or may not be connected to the M.C. It may not be releasing all the way. If the brake pedal has more then one hole in it, was the rod put in another hole. This will change the push-rod ratio to the M.C. It may not be releasing the M.C. completley and holding some hydraulic pressure in the M.C. Then when you step on the brake pedal you will have the stored pressure and now the pressure when you step on the brake pedal...with the vacuum assist...

Check your manifols vacuum you should be around 16" to 18" of vacuum, this will indicate a good running engine....I don't think that is the problem, but it doesn't hurt to check it anyway....

let us know how you made out. Good Luck

Bob  

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waynep71222
I have an SS396 tatoo
Posts: 448
Joined: 03/12
Posted: 08/14/12 01:03 PM

i vote for the WRONG master ...  

bore size...

depth of hole in the back...

failed booster do to brake fluid leakage into the booster main body..  this has happened many times..

how the booster works..    when the pedal is up.. there is equal amounts of vacuum created by the engine on both sides of the diaphragm...

when you apply the brake.. the movement of the pushrod closes the passage between the front and back half...  but as you depress farther. it starts to release vacuum from the rear half...  so air comes in..  the air pushes against the back side of the diaphragm.. there is vacuum on the front side..

if the valve / regulator that releases vacuum into the rear half is damaged..  you will have really twitchy brakes...

i would double check the size of the master bore first..  smaller bore size will cause issues.. bigger bore sizes will cause issues..

the depth of the hole in the back of the master cylinder piston can vary slightly between applications.. this effects the opening of the vacuum release valve...  if the push rod is too short.. move air will be allowed in and extra assist will be applied..   if the push rod is too long..

you will have brakes that may NOT release fully..   that can have issues also ... as the brakes are partially applied all the time..  touch the pedal.. and you have instant brake...    makes you glad you had seat belts on..   the smily face is supposed to go on the back window.. not your smily face on the inside of the windshield..   you will scare the bugs that normally get smashed on the outside..  

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topline03
I love my Chevy Chevette!
Posts: 2
Joined: 08/12
Posted: 08/15/12 06:18 AM

I have problems with my late 07 model silverado since 20,000 miles the rotors turned, rotors and barrens replaced now the rotors need turned again. The rear wheel cylinders are leaking.Less than 50,000 miles. I have been in contact and GMAC gave me 3000.00 towards a new chevrolet, plus all the other incentives. This truck has been nothing but a money pit taking care of the brakes. I am obtaining a lawyer. LEMON
My silverado is not the most dependable truck on the road. It Sucks  

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Dave632
I mow my lawn and find Chevys
Posts: 2253
Joined: 07/08
Posted: 08/15/12 12:44 PM

I have heard that the Silverados of those years have brake problems. I am suprised that the factory does not have fixes for that. I just got something in the mail for my S10 that indicates they will fix a tailgate problem for free if I bring the truck in for it.  
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