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1969 K5 - little to no brakes

fear_nothing

fear_nothing

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1969 K5 - Disc brakes in the front / drum in the rear.

Been fighting a problem w/ my brakes for a while. Used the opportunity to replace the calipers and brakes up front. (OEM AC Delco) Ordered new hoses but they were too short. They probabaly need to be replaced, but aren’t cracked and don't appear to be leaking. I'm using a brake bleeder/vacuum pump to bleed the brakes.
* Passenger front doesn't want to bleed - I can build pressure w/ the pump but no more than 15-20 lbs. It leaks down moderate to fairly quick. Just enough time to open / close the bleeder screw
* Drivers side seems to bleed fine. It builds 20+ lbs and slowly leaks down. More than enough time to open / close the bleeder as needed

4 month ago I also replaced my carb. For reasons I can't remember I also replaced the vacuum hard line. This would be the screw in hardline that goes from the back of the carb over to the master cylinder booster.

There is a very small hint of brakes if you stand on the pedal. The pedal feels normal & not spongy. Drove it around today in my pasture, and based on the tire marks - the driver’s side front is working based on the skid marks.

What do I need to be looking at?
 
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Fill the master cylinder and leave the cover off. Pull the lines off of the calipers and see if fluid runs out. If not, line is plugged.

Run the engine and pull the hose out of the booster. Should hear a vacuum noise. If not, hose is plugged or booster has a leak.
 
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If your pressure is bleeding off, on the front right, have you tested the front left? if the left bleeds down also the master cylinder maybe by passing internally.
If the left is holding, then you have a leak, or a hose that is ballooning. It is quite common for gm hoses to fail internally, blockage, or swell.
Is this factory disc or a conversion?
Hard brake linings, cooked or glazed, will require excessive brake effort, even when all else is functioning to design.
 
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ktmoutfront said:
Fill the master cylinder and leave the cover off. Pull the lines off of the calipers and see if fluid runs out. If not, line is plugged.

Run the engine and pull the hose out of the booster. Should hear a vacuum noise. If not, hose is plugged or booster has a leak.
Click to expand...
Good suggestions thanks
 
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Wes Harden said:
If your pressure is bleeding off, on the front right, have you tested the front left? if the left bleeds down also the master cylinder maybe by passing internally.
If the left is holding, then you have a leak, or a hose that is ballooning. It is quite common for gm hoses to fail internally, blockage, or swell.
Is this factory disc or a conversion?
Hard brake linings, cooked or glazed, will require excessive brake effort, even when all else is functioning to design.
Click to expand...
It was converted to front disc brake by the PO. The rubber hoses are in sorry shape, rusted pretty bad where they pass through the frame. They would of gotten replaced today if I had the right ones.
 
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So do you know what master cylinder the PO used in his conversion ? do you still have 10 or 12bolt rear drums? If so I would recommend using a 70 disc brake Chevelle master. I have used them on many conversions and never a problem. I even swapped a wilwood out for a Chevelle and got much better performance. If you have a 14bff rear drum then a mid 70's c/k 20 will do.
How come you haven't gone to steel braid brake hoses ?
 
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Wes Harden said:
So do you know what master cylinder the PO used in his conversion ? do you still have 10 or 12bolt rear drums? If so I would recommend using a 70 disc brake Chevelle master. I have used them on many conversions and never a problem. I even swapped a wilwood out for a Chevelle and got much better performance. If you have a 14bff rear drum then a mid 70's c/k 20 will do.
How come you haven't gone to steel braid brake hoses ?
Click to expand...
No reason for not switching to steel braded lines. Besides the length what size connector do I need or is it universal? The rear is a a ten bolt. Here's the master. The setup is not new.. its worked fine for the 10 -15 years I've had it.20210529_094904.jpg

20210529_094920.jpg
 
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It looks like your front lines must have a T down in the frame, so if you have brake action on one side but not the other, there must be a blockage in the line after the T. I would take the line off at the T and the hose to check for flow. Once opened up on both ends, that line should let fluid run. It could have a chunk blocking it.
Your master cylinder is from an '81 or newer. If it has been working and all you did was replace calipers and pads, then it has to be a fluid blockage. I would bet that even the wrong size caliper would give noticable brake action in a pasture.
I wouldn't think that there would be much brake action from the left side if there was still air in the front lines and the lines to both sides were flowing properly.
OR there is a blockage in the caliper itself.
 
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I've had both a caliper stick and rubber brake line collapse at different times. The collapsed line would hold pressure at the caliper, but not allow fluid to move for bleeding. I'd start simple if the lines were suspect to start with getting new lines. You can't tell the line is collapsed by looking at it.
 
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Wes Harden said:
Should only need to do that when the balance valve need to be recentered. I could be, in this era vehicle you wouldn't have pressure to front or the rear. Not just 1 front.
Click to expand...
If it’s been converted, it may have a different valve setup for disc. Though if it worked fine before and won’t now, does seem like a downstream issue. Sounds like air in the lines to me.
 
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When I converted my 72K5 from disk/drum to disk/disk I swapped in Master/Booster (dual diaphragm booster) from GM 1 Ton K30.
This is what a K30 Master/Booster looks like (double the braking power of 1/2ton setup)
I can lock up all 4 :pimp: :waytogo:

MasterMaster.jpg
 
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Well a year later - a guy finally found some time to work on this. Some observations:
  • It doesn't look like the front brakes on either side are engaging at all
  • In an effort to keep rust down - most of the brake parts are dusted w/ spray paint
  • the brake rotors on both sides still had spray paint - it hadn't worn off
Whether its the culprit or not - the brake hoses on either sides are getting replaced
attempt one was successful - tried Amazon on a Hail Mary as nothing was available locally

Questions
Whats a good source for braided brake lines, they need to be at least 24" accepting a 16 mm bolt in the frame T.
Pic 1 is caliper and the hose that didn't fit - IE the 16 mm bolt to the brake line junction in the frame was to large & didn't fit
hoser.jpg

A guy still thinks this whole deal is self-inflicted. Problem started when I replaced my carb last year. Same model carb - albiet I swapped the jets at some point but thats it.
Pic 2: depict a custom vacum line?
Should I be chasing anything down in this area?

6-24-Antty.png


also going back thru this thread & making sure all the prior suggestions were followed
-IE I took the brake hose off the drivers side and blew it out
-bled brake & no change
-pedal is a little softer but the fronts still don't engage
 
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Wait you can bleed the brakes, but the new calipers won't clamp?

What kind of stream do you get when the bleeder screw is opened under pressure? If both fronts aren't working the proportioning valve. Sometimes the spool valve will only shift reducing flow, but pumping the pedal should still apply adequate braking.
 
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Wes Harden said:
Wait you can bleed the brakes, but the new calipers won't clamp?

What kind of stream do you get when the bleeder screw is opened under pressure? If both fronts aren't working the proportioning valve. Sometimes the spool valve will only shift reducing flow, but pumping the pedal should still apply adequate braking.
Click to expand...
Just cracked the bleeder screw on both sides - not even a trickle. Time to replace the proportioning valve?
 
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