The backwards hustle!

[74CustomK20]

I'm wanting to go from power to manual brakes on my 1974 K20, as they never worked right. Also manual is just easier to me... Anyway has anyone ever done this swap? Can I just remove the booster? How do I modify the rod then? Any insight would be great!

[slotard]

You'll need a different master cylinder in order to have reasonable stopping power with manual brakes. I'd advise finding a booster/master out of something modern that's similar bore to stock and swapping that, manual brakes on a full size (I'm guessing on reasonably large tires) aren't much fun.

[74CustomK20]

So find a newer one with manual brakes n use that cylinder? Be easier?

[slotard]

Originally Posted by 74CustomK20

So find a newer one with manual brakes n use that cylinder? Be easier?

I meant to get a complete power setup off something else. Manual brakes on a heavy truck aren't a good idea.

[86c20]

well there are many here that have had brake problems with these trucks. i myself have rebuilt mine many more times then i wish to say i have lol.

what is the problem with the brakes that make you want to change back? may be something simpple to fix that you are just over looking

[enaberif]

Swap to powerboost.. Manual brakes on a heavy truck.. not a good idea.

[D13]

Manual brakes use a different master, rod, and pedal link location.
Having (actually currently) owned both, I can 100% say that you will be well ahead to fix you power brakes. If you must go manual go 100% Wildwood. With a K20, if you ever drive in the city, or have bigger than stock tires, or tow, I would not even consider manual brakes.
As a reference, my dad's 81 C20 was the lightest duty 3/4 ton you could buy, including straight six, 3 speed manual, and manual steering, and GM fitted it with power brakes, and would not let him delete it due to need for braking capacity.
Best bet is to fix whats on it.

[74CustomK20]

When I have it hooked up to my carb like normal, plug in back clamp and to booster... I hit the brakes and they will stay engaged... Like the pedal won't release. I tried with my q-jet, my edelbrock 600, and then 2 different boosters. So I don't know what its deal is...

[Just call me Sean]

Sounds like a bad booster. It would/should be hissing if it's that bad.

[74CustomK20]

It makes no noises... Not sure what's up but I just have left it unhooked so i could drive it. Although I know its not right... Reason why I wana fix it.

[enaberif]

Hook up your vac hoses again properly and run the truck and try using the brakes. Afterwards shut the truck off wait a few minutes and pull the fitting from the booster and see if it held any air.

[86c20]

i would want to say its the check vavle in the line the elbo that goes in the boster.??? try that see what you get. or how old are the rubber brake lines? have had it do that.

now think simple there are no abs in these trucks so that leves you with rubber lines boster check valve and return springs. . rule of kiss man. tell us everything you have done

[74CustomK20]

Originally Posted by 86c20

i would want to say its the check vavle in the line the elbo that goes in the boster.??? try that see what you get. or how old are the rubber brake lines? have had it do that.

I have a new brake everything from between the cab n box. New line going back new cylinders new shoes drums all. I have a new hard line from junction box to driver rubber line, rubber passenger is year or 2 old... New calipers, drilled n slotted rotors, and pads at same time of rear brakes being done... New booster and master cylinder at time of rear n front too...

Filter from carb to booster? I have just a vacuum line no filter? Can you elaborate on this?

[Just call me Sean]

I would pull the master and bench bleed it, to make sure it's good. Bench bleed with plugs not hoses.

[homemade87]

Ok , lets clear up a few things . You say the peddle does not release . Does it come back to the top when you take your foot off. If not then it has to be the booster hanging when vacuum is present, or the master . If the peddle is coming back to the top the problem is most likely past the master cylinder . What does not make sense is when you remove the vacuum the brakes work . Only thing I can think off is you can not press them hard enough to duplicate the problem . Vacuum will not keep the brakes depressed no matter how high the vacuum . Booster can fail .So vacuum is out . Check valve only holds vacuum what the motor will produce . Stop looking for vacuum problems . It will not keep your brake depressed unless a booster failure. An I think you have ruled that out with a new booster .

Is it pulling to one side when you brake . If not then it has equal pressure to both sides on the front . The common denominator is the proportioning valve if all things has been changes . If this is the problem you will still have your problem even if you go to manual . I would look into changing the prop valve . It seems to be the likely problem . While you have it off I would remove the brake lines from the master to the prop valve and be sure they are clear.

Hope some of this helps .

[74CustomK20]

With it running,if I had everything hook up normal,I could push the pedal down and it WOULD NOT release the brakes until I shut the motor off.

They work yes i can drive it fine just give little more stopping room.

No it was not pulling to one side until the rear end went out.

I always thought that manual brakes had no prop valve, just front and back.

Answered the best I could. So you are now suggesting a new prop valve and clear the lines again?

[homemade87]

Originally Posted by 74CustomK20

With it running,if I had everything hook up normal,I could push the pedal down and it WOULD NOT release the brakes until I shut the motor off.

They work yes i can drive it fine just give little more stopping room.

No it was not pulling to one side until the rear end went out.

I always thought that manual brakes had no prop valve, just front and back.

Answered the best I could. So you are now suggesting a new prop valve and clear the lines again?

You did not mention if the peddle comes back to the top when you take your foot off the peddle .You just said brakes will not release untill motor is shut off .

[74CustomK20]

My bad! No. It will only come up when shut off as well.

[homemade87]

Well this narrows it down. I no longer suspect the proportioning valve . Let look at it this way . The master cylinder is a check valve . When it pushes fluid it will not pull that fluid back . It will retract to get some more fluid if needed . So no way a master cylinder will do this unless it is binding , But we ruled it out because when no vacuum present it no longer does it . If it was bad it would do it regardless .

So that leaves us the booster . Apparently something is going on with it . Maybe the wrong booster . Did I see you put 2 of them on . Something is binding to hold the booster on . Try this . Unbolt the master and slide it back . Then pull the pin that presses the master and bolt the master back up to hold vacuum. Crank the truck and see what happens . ( not sure if booster will work proper with the rubber seal boot not sealed , reason for bolt master back up ). This is a simple test . Maybe it will tell us something . This will definitely tell if its the master or booster side.

Also be sure your brake peddle is free and not binding.

[wilkin250r]

I'm not 100% convinced it's not in the master cylinder.

I agree with homemade87's logic, it does indeed sound like the booster, because it sounds like the brakes are mostly functional (albiet stiff and difficult) without the vacuum hooked up. This sounds like a booster problem.

However, the original poster does say earlier in the thread he tried two different boosters, same result. It's not impossible to have the same defect in two different boosters, it's just improbable.

My thought is that the master cylinder may indeed be binding up, but the effects might not be FELT without the vacuum hooked up. It might very well still be occuring, but might not be noticable or significant without the added force of the booster.

[74CustomK20]

I did try 2 one old 1 1 new. But i left the new one on seeing as its "new". Someone mentioned a filter 86c20... About a filter in the line?

[homemade87]

Are you talking about this filter on the booster . http://www.carpartsdiscount.com/auto...FY_m7Aod9xsA1g

74 , Did it do the same thing you are talking about before you changed the booster in the first place . I don't know a hole lot about the c20's but does the brake peddle have a return spring on it under the dash .

[74CustomK20]

Yea that! It had one originally. I got rid of it. Did fine. With old booster. New booster without have this problem... Maybe I need one for the new booster?

[homemade87]

Originally Posted by 74CustomK20

Yea that! It had one originally. I got rid of it. Did fine. With old booster. New booster without have this problem... Maybe I need one for the new booster?

It is possible that gm designed into it something that works to control vacuum . I have never experienced one of those things . Worth a shot for what it cost . I would be skeptical if it works . I still say you have the wrong booster .

Looks like you could pick one up at oriellys or some where like it .http://www.oreillyauto.com/site/c/de...1272&ppt=C0066

Do you still have your old booster . Why did you change it out.

[74CustomK20]

I changed it when. I went from hydroboost to vacuum. I will get one Friday amist the chaos.