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68 chevy truck soft pedal

 
Nesto
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Posts: 4
Joined: 12/10
Posted: 12/05/10 11:29 PM

I have a 68 chevy c20 3/4 ton 2 wheel drive pickup with drums all the way around. I was driving my truck home from work and the pedal seemed to fall at a red light. It feels real soft and I have to pump it to stop. I bled my entire braking system several times and fluid is coming out of all four bleeder valves. Still not fixed. I then put a new master cylinder on it and bench bled it, rebled all four and still the same issue. I took all the drums off and replaced all shoes and wheel cylinders, still same issue. Any suggestions? Any help you guys may have is greatly appreciated.  

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chevelle83
I mow my lawn and find Chevys
Posts: 2280
Joined: 11/09
Posted: 12/06/10 06:18 AM

are you loosing brake fluid??? if not,,, the only thing that will allow the pedal to sink while you have foot pressure on it is simply the master cyl.

Otherwise you have a leak,

1 I have seen brand new, and reman master cylinders not work right.

2 I have also seen brand new wheel cylinders and new/reman calipers leak.

SO new or replaced dont necessarily mean problem solved.  Oh and I have got 2 master cylinders back to back defective too!!  BTW I went to another part store after that!

Just a thought,,,,,when you replaced the shoes, did you have the drums turned/redressed at the same time?????

Problem is if the drums are out of spec (too large inner diameter) this will keep the shoes from making full contact with the drums.  The shoes will act like springs and will flex when the pedal is applied and make for a spongy pedal.

Keep in mind this would be a case where the drums were quite worn or turned way out of spec to cut all the groves out combined with the already existing wear.

Hope you get it fixed, good luck.  

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Nesto
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Posts: 4
Joined: 12/10
Posted: 12/06/10 06:54 PM

I am not leaking any fluid. The master cylinder remains full after use of the brakes. I have not turned the drums, I had them checked out and was told they were still good to go.  Could a bad rubber line cause this? I have a lifetime warranty on the master cylinder so I'll replace it and see if that helps. I wouldn't think to replace the booster in this scenario. Thanks for the help I hope I get her fixed too.  

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chevelle83
I mow my lawn and find Chevys
Posts: 2280
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Posted: 12/07/10 09:03 AM

The power booster only affects pedal effort.   Old rubber hoses will only have minimal affect on the pedal. If they are cracked just change them anyway.  

Just a thought,,,, I assume you did make absolutely sure that you got the wheel cylinders with the exact same bore size as your originals???? Also same thing on the master cylinder bore size.   I have seen many parts boxed wrong, and most of the parts on chevy brakes will interchange and bolt right up  

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Nesto
I love my Chevy Chevette!
Posts: 4
Joined: 12/10
Posted: 12/07/10 03:34 PM

I know that the parts are the exact same as the original equipment. Potentially a bad master. I'm going to get another one and some rubber hoses just in case. What affect would a bad proportion valve have on my brake performance. I don't think that's the issue here but out of curiosity I looked for one and came up empty handedit was hard enough finding one for an all drum setup but all I found was one for a 1/2 ton pickup.  

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chevelle83
I mow my lawn and find Chevys
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Posted: 12/07/10 04:46 PM

the prop valve just balances the pressure from front to rear, if you are getting plenty of fluid out of all 4 wheel cyls when you bleed the brakes the prop valve is most likely fine  

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68scott385
I mow my lawn and find Chevys
Posts: 1994
Joined: 10/09
Posted: 12/07/10 05:22 PM

http://www.lmctruck.com/

here's the place you need to shop to get parts for your truck  
68scott385 68scott385 68scott385

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Nesto
I love my Chevy Chevette!
Posts: 4
Joined: 12/10
Posted: 12/08/10 12:04 AM

Have the catalogue they don't stock that valve either. All other parts are readily available at auto parts stores. I am going to swap the master again and change out those hoses this week and see how she does.  

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waynep7122
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Posts: 1130
Joined: 08/09
Posted: 12/08/10 09:30 AM

lets take a step back...

you sound like you had a problem with the master cylinder having an internal leak between the sections...

i have had a hand full of replacement masters that had problems...

i have found the internal ports that were drilled in from the side were not properly deburred so it caught the seals as the they went by... but.. this is 3 out of hundreds i have installed...

i am taking that you have a pair of wrenches to loosen the lines into the master....   have someone pump the brake pedal a few times.. then hold it ... count to 10.. then loosen the lines at the master..  do you get an even amount of fluid from both sides when you ***   if you only get fluid from one side...  you might still have an internal leak...



on turning the drums...   was there a noticeable ridge on the inside of the drums ...  if so.. you need to have them turned or replaced...

the drums as they wear.. they bell mouth as they expand from heating during use... this when new shoes are installed..  allow the shoe friction material to only contact part way... then try to deform the shoe to contact the entire face of the drum.. this gives one a soft pedal and reduced braking effect as there is less surface area in contact with the drum ...




investing in a brake bleeder vacuum kit... like this..   the brass bodied versions like shown are sold at many parts stores and tool stores..

http://www.harborfreight.com/brake-bleeder-and-vacuum-pump-kit-92474.html

just one thing...  before using it.. while setting it up...  hook the little tank to the pump.. and block the open port on the tank.. and squeeze the handle to create vacuum in it..  make sure that it holds vacuum.. i have run into a few.. that the seal was damaged by the zip lock back containing the additional parts crushed the seal.. preventing it from being used...

one last thing..

how is your brake adjustment....  i normally don't just turn the wheel until it drags.. i  go in with a screw driver and push the star adjuster forward.. then backward... NOT TURNING IT...
forward... (______|_)  and
backward (__|_____)    if i get more than  
this much movement..  (__||___) movement.. then i know the shoes are out of adjustment...


there are a few places online that will have the valve you are talking about.. they usually don't cause to much of a problem..   if you have one end that won't bleed... the valve may be shifted....


this is one of the places that i have found that has a good selection of them with pictures.. just incase you need more info on it...

http://www.piratejack.net/index.php?option=com_virtuemart&page=shop.browse&category_id=30&Itemid=6  

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AbleSmith
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Posts: 5
Joined: 08/10
Posted: 01/16/11 10:44 PM

There might be issue with your bearings, clean the bearings or replace them, kindly check Brake fluid level, if it is low then fill it to the mark.  

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