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brake questions...

9

90blzr

1/2 ton status
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Okay, how do you tell if a master cylinder is going out? Got my brakes bled, but the pedal is still spongy and when I jam on the brakes, the truck just slows down, no way in hell they would ever lock up. The master was sitting for about a year or more :o . I bled them the normal way pumping and cracking the bleeders while holding the pedal down. Cracked the lines at th master first to bleed any air trapped in there. Oh yeah...90K5, 1 tons, rear disk.

I am gonna try pressure bleeding them next with one of those home made garden sprayer bleeders. Maybe that will help out more. On a 90, is the the front resevoir for the front brakes and rear for the rear or? Stupid question, but on searching, I came across some saying the rear was for front and front was for rear so now I am confused :crazy:

Also, seems most people leave that little pin in the combo valve alone, so I will do the same when bleeding. Not sure what that does to aid in bleeding the system.

Now, if I do get another master cylinder, should I get a booster as well?

With searching I've seen people upgrading to a 3/4T master cylinder or JB7. Will they use the same push rod as my 1/2T? Do I get the 3/4T booster as well?

Thanks.
 
Are saying currently you're running with non-power brakes? If so, I'd get the booster anyway whether the master cylinder's good or not.
 
I'm gonna take a crack at this, I know you know that a spongy pedal is a symptom of air trapped in the system. I wonder if you can "pump up" the brakes to get a pedal. If you can "pump em" up and get a good solid pedal your M/C is fine, you just need to get the air out. If your M/C is bad your brake fluid bypasses the seals and dosent build up pressure in the calipers or cylinders. I had a M/C that had so much dirt in it that it was intermittently losing pedal. The dirt was holding one of the little bypass flaps in the M/C open.
Bleed from drivers front to passenger rear, Shortest line length is bled first. I've never had to power bleed anything in my life so I don't think the "garden hose" thingy is necessary.
Also consider "gravity bleeding". I just did a M/C on my '72 and never pumped the pedal at all, just open em up and let em run. ( I had brake fluid in my system that looked like coffee) just don't let the reserviour run low. I was suprised at how well it worked. I can lock up my M/T 35's
I've got no idea about any of your conversion questions, (sorry)
 
Did this combo work right in the past, or are the 1t's and rear discs new?
 
1 tons are new as are rear disks, etc. The brakes worked fine on the 1/2T stuff before :D But then its been sitting for at least a year, maybe two... :crazy:

And also, the front resevoir is for the front and the rear for the rear? Is it only on 3/4T and 1T that they are opposite?

Maybe I'll try the gravity bleed thing. Basically just open the bleeders and let the fluid come out? Do you leave the calipers installed? At what point do you know they are fully bled? Pull up a lawn chair or milk crate have a seat and just wait it out?
 
Yea, you leave every thing installed on the vehicle. I had some clear hose hooked up to the bleeders, and I had it running into a pan or something. I opened the bleeders (slightly) and let it run until the brake fluid came out clear.
I probably ran through about the same quantity of fluid that the reservior holds. DO NOT LET THE RESERVIOR RUN DRY or you'll be bench bleeding the M/C again.
Anyway, I could see the bubbles in the line as the fluid ran through it.
I hear its a good idea to flush out your brake system once in a while anyhow.
 
90blzr said:
1 tons are new as are rear disks, etc. The brakes worked fine on the 1/2T stuff before :D But then its been sitting for at least a year, maybe two... :crazy:
Click to expand...
Changing to rear discs significantly increased the rear piston diameter which changes the whole Hyd system balance. Usually you need to increase the m/c bore size to restore the balance. Search threads on this topic.

And also, the front resevoir is for the front and the rear for the rear? Is it only on 3/4T and 1T that they are opposite?
Click to expand...
IME the rear res is always the front brakes. The reason for this is that the pedal pushrod act directly on the rear piston. The front piston is actually moved by a compressed "slug" of brake fluid and not by the pushrod.
 
yeah, I searched....3/4T master is what alot of people upgraded too. But can you use the existing 1/2T booster or 'should' you use a 3/4T booster ?
Thanks for all of the input.
 
You very well may have a bad master cylinder. Sitting around dry doesn't help seals, nor does pushing the seals into the crud that has built up in the bore.

Changing the entire brake system (essentially) adds more variables, it could be the master cylinder, could be the new rear disks, or it could be a combination.

When my master was bad I never did get rid of the spongy pedal, and the braking effectiveness in a hard stop was never as good as it could have been, but eventually the brake light tripped and the pedal hit the floor. I could pump up the brakesThen I changed the master and all was well.
 
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