1979 GMC C7000 - brakes require 2-3 pumps

I use my 1979 GMC C7000 primarily in the spring and summer to core bins. Can't remember if 2 - 3 pumps of the brakes were the norm to get good braking. I think that is too many. I did just replace the left front wheel brake cylinders earlier in the week. Thought I brought the brake shoes up to the brake drum with the adjusters enough in that left front wheel. Brake shoes were thick. Is 2 - 3 pumps normal or could I have still have air in the system?? Do the other shoes need adjusting up??? I am not losing any brake fluid now since the wheel cylinders were replaced. Any ideas appreciated. Thanks.

No that is not normal. Adjust the brakes,all of them.

Brakes that need to be pumped indicate air in the system. No pumps is normal. You should have hard pedal at 1/3 of the way down on the first push.

Sound like air in the system. You probably need to bleed all the brake cylinders starting with the one that is as far from the master and work closer

Forgot to mention the brake system has the booster behind the left front wheel.

If the pedal raises with each of the 3 strokes,and it is hard,your shoes need adjusted.If it is soft and stays low,or drops you have air or a leak.When you adjust the shoes tighten them against the drum until the wheel won't turn,and then back them off until you can rotate the wheel,but still has drag against the drum.A big tire like that should only turn maybe a 1/4 of rotation to a half. You should feel drag,or the adjustment is too loose.Mark.

I suspect there is still air in the system.

But check the adjustment, especially the rears. The rear should be self adjusting, but real common for the adjusters to freeze up. To check the adjustment, you can pry the adjuster forward and backward through the adjuster hole. There should be minimal movement. It it moves more than about 1/8" they are too loose. Try turning the adjuster, it should ratchet one direction, toward the tight position. If they won't turn they will need to come apart and be freed up. If stuck for a long time there may be a worn spot on the teeth, the adjuster components will need to be replaced. While in there be a good idea to replace or service the wheel cylinders. Even if not leaking, at that age they can't be good for long.

A good way to tell if there is air in the system, have an assistant pump the brakes up to good pedal. Open the master cylinder and look in with a flashlight. Release the pedal and watch for a fountain of fluid to come up in the reservoir. A small swell of fluid is normal, but an ongoing fountain is the result of expanding air in the system.

There should be a bleeder on the hydro boost unit, where the line out to the wheels connects, and there may be a bleeder on the master cylinder. Bleed those first, then go to each rear wheel, then the fronts.

my grand dad ran the late 70 and 80 GMC trucks 366 gas motor...we always had to pump the brakes 1st time you hit brake it went down a lot then you hit it a 2nd time and you had good brakes...new truck or truck with 150000 miles did not matter.... I learned how to drive in the trucks..I started driving at 15 with my granddad sitting right beside me....My granddad treated you like a grown man if you could work like a grown man and paid us like a grown man when we did a days work

2-3 pump brakes is the adjustment. Air usually causes spongy pedal. The GM fluid brakes are notorious for freezing up the "automatic" adjusters (their term, not mine. I've never seen any stay adjusted.) The hydrovacs under the side tend to fail from sitting seasonally too.

air is a spongy pedal, out of adjustment is what you are experiencing.

So I assume you know there is also a bleeder on the booster. I not sure if ...old...got confused in his reply but when bleeding work from the bleeder closest to the master cylinder ..on the booster..and work away. Why would you bleed out a far away bleeder when a line portion closer to master still has air in it it could push out to a wheel cylinder you just bled? Problem wise, generally air in these systems is only a touch ahead of lack of proper adjustment. Each wheel must be adjusted to where the shoes are tight against the drum and then backed off until they just turn. This includes the adjuster for each rear shoe, four per axle. These brakes have automatic adjusters that may not let the adjuster turn in the loosen direction. If that happens an awl or properly bent weld rod will need to be placed in the adjuster slot to release the automatic adjuster lever from the adjustment star wheel. Now all this is great if the adjuster aren?t rusted and stuck. Which them requires to open Pandora?s box of wheel/drum removal. Good luck!

Brakes on those have to be adjusted tight. Just barely can turn wheel. Adjust till can't turn. Then back off just enough to turn a little by hand.

Every service manual I've ever read agrees with Old on this one. You always start at the far wheel and work your way toward the master cylinder. Fluid won't compress so if you get the air out of the far line, air won't push back in.

Not much point in setting them that tight. They will just burn the drag off in the first hundred miles and you have just wasted that much wear on linings and drums.

I had a bunch of those trucks. You are out of adjustment somewhere. They normally have good brakes.

(quoted from post at 19:34:38 03/02/18) So I assume you know there is also a bleeder on the booster. I not sure if ...old...got confused in his reply but when bleeding work from the bleeder closest to the master cylinder ..on the booster..and work away. Why would you bleed out a far away bleeder when a line portion closer to master still has air in it it could push out to a wheel cylinder you just bled? Problem wise, generally air in these systems is only a touch ahead of lack of proper adjustment. Each wheel must be adjusted to where the shoes are tight against the drum and then backed off until they just turn. This includes the adjuster for each rear shoe, four per axle. These brakes have automatic adjusters that may not let the adjuster turn in the loosen direction. If that happens an awl or properly bent weld rod will need to be placed in the adjuster slot to release the automatic adjuster lever from the adjustment star wheel. Now all this is great if the adjuster aren?t rusted and stuck. Which them requires to open Pandora?s box of wheel/drum removal. Good luck!

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I was taught at a very young age to start bleeding at the wheel farthest from the master cylinder.Always worked well for me and my friends.This ,provided there are no other problems like a bad master cyl. or leaking lines or wheel cyls.

I've been thinking about this all day and actually went and checked a couple service manuals I have. Chilton manuals all seem to follow your train of thought to bleed working from the bleeder the greatest distance from the master cylinder and work back. The "Motor" brand manual I have for 62-71 truck and diesel which would cover this type of truck did not specify a sequence to follow. I just would not want to try to bleed a wheel on one of these systems if the bleeder on the hydro-vac was trapping a lot of air in that area of the brake system. I would agree that if you are doing a complete system rebuild that all the cylinders should have an initial bleed to remove the trapped air which can be quite a lot on these type of systems with the larger wheel cylinders, then move to a final bleed. I generally tried to do the initial bleed with gravity if possible by opening the bleeder once the shoes and springs were assembled. Keeping the master cylinder full, once the bleeder started flowing I would close it. Well I digress, I will say I agree to disagree on the bleed sequence. Hopefully the OP has the issue solved.

One of my favorite sayings, "There is more than one way to do just about everything." I agree that gravity bleeding is the way to go if you have time. Let nature do the work. I'm doing a complete brake rebuild on my old '50 Ford pickup now - new master cylinder, new lines, new wheel cylinders, the works. The master cylinder is below the floor boards on it so I'm afraid it might not gravity bleed. I'm considering buying one of the pressure bleeders. Easier for one man bleeding.