Issues With The Brakes

[rikoseth]

Hey guys. New to the forum. Just got my first GMC project truck:) Yep, there goes all my money and future monies earned. I bought it last week. In really good shape, body wise. Engine needs rebuilt, and the interior looks pretty bad. Anyway. Its a '91 GMC Sierra SLE 6cyl 2wd. I decided to put a new master cylinder for the brakes on this past weekend, cause it looked like fluid might be leaking from the seals between the resevoir and the master cylinder. The brakes are really spongey. So, changed out the master cylinder. Bench bled and all. Used the old resevoir, think this is okay? Then proceeded to bleed the brakes. Ran into more issues. The automatic adjusters and the adjuster lever just fell out when I removed the hub. So, I had to work on getting those back in. Ended up just buying new ones. Noticed that one of the wheel cylinders may have been leaking a little. But, I bled the brakes anyway. I know I know lol. It was dark and I was tired! I'm always detailed and like to do things right. Anyway, finished all four, and brakes, still spongey. So, then I decided to replace the rear wheel cylinders as well. Bled them again. STILL spongey, and now my brake light is on. Before while bleeding the first time, it would come on. But when I finished bleeding them, the first time I pumped the brakes, the light went off. After this second time though, the light has stayed on. Also, which is odd, the A/C light on the heater/A/C control panel is flashing too. I checked out the master cylinder and to me, it still looks like it is leaking a little around the seals at the bottom of the resevoir. Just a little. But there is a huge amount of suction when I remove the lid. I checked the resevoir when removing from old master cylinder, and putting it on the new one. It was in good shape with no damage. Any help or input would be greatly appreciated. I'm still learning a lot. I can't understand why my brakes are still so spongey! Thanks!

[Draenor]

GMs tend do get like that after a while.

 

you can also replace the brake lines at each wheel with a braided style line. Another problem is that you could have a vacuum leak or a bad booster.

[rikoseth]

GMs tend do get like that after a while.

 

you can also replace the brake lines at each wheel with a braided style line. Another problem is that you could have a vacuum leak or a bad booster.

 

 

Ugh:) Yeah. I am worried that its the booster. Those are a real pain to replace from what I hear, and kinda expensive. Thanks for the input man!

[rikoseth]

GMs tend do get like that after a while.

 

you can also replace the brake lines at each wheel with a braided style line. Another problem is that you could have a vacuum leak or a bad booster.

 

 

I'm going to research it a little more, but how would I test for a vacuum leak?

[mcreyaufmiller]

for the leak, spray a starting fluid around the vacuum lines, if you get an odd idle, there is a problem with that connection (or Line). I would replace the flex brake lines on the front and diff. These can collapse and cause problems. Also, you should not have a vacuum on the master cyl, it should have a vented cap to allow air to enter the to make up for the fluid moving out.

[gmtech4]

for the leak, spray a starting fluid around the vacuum lines, if you get an odd idle, there is a problem with that connection (or Line). I would replace the flex brake lines on the front and diff. These can collapse and cause problems. Also, you should not have a vacuum on the master cyl, it should have a vented cap to allow air to enter the to make up for the fluid moving out.

 

 

he's talkin about vacuum leaks at the booster not the master cyl.

 

remove all air in the booster by pushing pedal repeatably or pull the hose off the booster ,reinstall hose ,with brake pedal applied slightly ,start the engine,the brake pedal should drop down slightly ,the booster is working and also you could hook up a vacuum gauge to the engine and see 18 inches vacuum,(i think),and or spray stuff aound like buddy said .

[rikoseth]

for the leak, spray a starting fluid around the vacuum lines, if you get an odd idle, there is a problem with that connection (or Line). I would replace the flex brake lines on the front and diff. These can collapse and cause problems. Also, you should not have a vacuum on the master cyl, it should have a vented cap to allow air to enter the to make up for the fluid moving out.

 

 

So I shouldn't have a vacuum on the master cylinder? Because I notice that when I take the lid off of the resevoir, it has suction and is really tight. That might explain why it looks like some fluid is leaking out of the seals from the pressure. How can I remedy this?

 

Thanks everyone for your help and ideas! I looove this damn truck. I'll post before pics soon.

[gmtech4]

the lid should have a little channel in it for air to come and go like buddy said ,to create that much vacuum ,the pads and shoes have to wear a lot to move the fluid out of the reservoir,so don't worry about it .make sure the channel is clear of course