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Hi everyone, recently I got a 1976 K20 Scottsdale with the 400 engine. When I first got the truck I noticed the brakes were very soft but still able to stop the truck. The brake warning light was also constantly on With help from my Dad we bled the system and replaced the master cylinder and for awhile it seemed to work. Then about a week later the brakes started to feel soft again. The brake light would come on but when Id pumop the brakes itd go off. I adjusted the back drum brakes and again this seemed to correct the problem. Its been a few days and the brakes are getting soft again and the brake warning light is almost constantly on. I do still have brakes. I have been watching the brake fluid levels and havnt seen any losses. I checked the brake lines and havnt seen any leaks, the calipers look good. I havnt been able to get the drums off to inspect the wheel cylinders because they are the hub/drum assembly which I dont think I have the right tools to pull them. My question is without a loss of brake fluid do I have a bad component or do I just need to re-bleed the brakes? My dad is questioning weather or not the hydro-booster in bad although from my reading if that fails then the pedal becomes very hard due to loss of power brakes essentially.
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If you didn’t bench bleed the master cylinder, you still probably have air in the system. You can remove it to bench bleed it or, you can crack open the brake line fittings at the master cylinder and bleed that way.
If the rear wheel cylinders are leaking, you should see a wet residue on the inside of your wheel and tires.
I still wouldn’t rule out a leak.
Does the vehicle stay stationary with the brake pedal all the way to floor after a few minutes? If it stops fine, then starts to creep forward, that is usually a sign of a bad master cylinder.
Keep us posted.
Hi dreamer. Usually the pedal is soft but at a ceartin points the brakes will take hold and stop and hold the truck. Thyre just very soft and I dont have very good stopping power so I keep my speeds low and following distances long for the time being.
Did you bench bleed the master? If not, you might be surprised how long you have to bleed the brakes to get all the air out. I would also figure out some way to get the drums off to be inspected. If you don’t have the tools, you might have to bite the bullet and pay to have it done.
Thanks Beefy, we did kind of do a bleed on the MC tho because we didnt do it per the manual I suspect air might be trapped in there still. On the drums Im trying to figure out if you have to pull out the locknuts which would require the tool or if just pulling the axle shaft should work.
I did a master on an 1970 Chrysler 300 I had back when I was a kid. I thought I had all the air out, then felt the pedal. I had to spend another hour redoing it, because I hadn’t bench bled the thing. Found HUGE bubbles still in there. Was all good after that though.
You could also try this method from Eric is you are 100% sure you have no leaks –
http://www.youtube.com/watch?v=KIQIBLGo … aZg_RzOjFW
Dreamer would that method work on the truck? Right now Id have to jam on the brakes super hard to get them to lock up
Good news guys, I bled the master cylinder (disconnected the lines and bled it with it bolted in the truck), then i bled the rest of the tires out as best I could. So far so good. The brake warning light went out and the pedal is much more responsive. During my test drive at some points the pedal would feel a bit soft but would come back to normal if I let off the brake and reapplied them. It couldve just been my opinion. Ill watch it over the next few days and let you know if it looks like a good fix
Sweet man, good to hear. I would again recommend finding some way to get the drums off the rear, just to make sure you don’t have anything leaking back there, but I have a feeling you’ve found your fix. If that’s the case, please mark the traffic light ‘green’, before dreamer sends some of his goons over to your house 🙂
Thx Beefy and Dreamer, Ill Check tommorow and see how the truck does. Ive noticed when I adjust or bleed them before after a day or two they run soft again so I want to make sure its a permanent fix. If not next task will be to pop off the drums and look at the cylinders
In order to properly bleed those brakes you need the special tool for the proportioning valve, it has a valve on the inside that when there is a brake fluid loss it closes off to prevent a complete loss of braking. It’s a very cheep tool as all it does is hold the prop valve open to allow fluid to pass through it freely. I would recommend getting this tool and bleeding the brakes again to make sure you got all the air out.
http://www.amazon.com/OTC-OTC7853-Propo … B000K1FVLW
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