On other thing here...how much stroke does the master cylinder have if you push the piston in all the way, when it's not plumbed into the system? Does the pedal pushrod have that much stroke, or is it not able to push the piston in all the way? If it won't move the piston all the way, then the "dual" feature of the master cylinder won't be doing anything for you... You might just need to change the pedal ratio to get less leverage, and more travel.
i would try rebleeding the master this way, bleed like you are bleeding the brakes normally, but instead of cracking the bleeder screws crack where the lines run into the master, also there's a book out there that tells in which order you should bleed everything, might wanna see if you can find that, I have seen brake systems be really picky on how you bleed them. but seeing as pumping doesn't bring the pedal up i dont think its an air issue. i think its adjustment. why not get a pedal box from a f-body?
"31 Vicky" ... I understand you now ... I am not really "bottoming out" the master when I am benching it by hand. I am simply reaching the end of the pistons travel ... However, if I was to apply pressure using the pedal (here the leverage factor come into play) I could very easily go beyond the "allowed/expected" piston travel with the result being a damaged master cyl. Thanks, I was worried I was doing something wrong when I was bench bleeding.
Don't know who or where "bottoming out the master would cause damage" came from, but it's totally wrong. Some vehicle tests require several hundred pounds of pedal force, and that's multiplied by the pedal ratio, and applied to an open circuit master cylinder! In production or custom applications, you HAVE to be able to bottom the master to make sure the pedal does not bottom first. System bleeding, including "bench", also requires the pedal to be fully stroked. If the master could be damaged, there would be a pedal stop on all production vehicles, yes? Convinced?
Alright fellas. I have replaced the master with no change in pedal pressure. So I went and did some research. I found out that for the pedal assembly I am using (88' S10) it requires a 1.416 size bore master cylinder for both power and manual setups. Could this be the problem? I just dont have enough travel? Ill be pissed if I am right because Ive dicked with this things for 3-4 full days. The pedal assembly has two holes. One for power lower on the pedal and one for master, higher on the pedal. I havent measured pedal ratio yet, but I will tomorrow night. Thanks for any input.
Also, I think maybe the larger diameter bore might be for the low drag front brake calipers... And I am using the regular 1 piston type from the 70s era camaro. So... what bore size should I be using is the main question.
Make sure the arm off the pedal travels the same as it would for a Camaro, the rest should not matter. Is your prop valve a combo valve with the button on the side of it? Those are impossible to pedal bleed without tripping. My '89 Suburban had one and I paid to have it pressure bled ($20 at the muffler shop) when even following the directions in the factory service manual it would still trip over. Hook a light up to the lead on it so you know if it's tripped or not. What may be happening is you've got front brakes but no rear, those lines being longer would have more air and the valve is more likely to shut off that side. When I drove mine with it tripped, you didn't have a lot of pedal to work with to get stopped.
Holy sheet I think I know what my problem is. Rookie mistake I guess. I plumbed in the prop valve the same way that the original master was plumb in, the rear port goes to the front brakes and the front port goes to the rear brakes... But if what I am reading is correct, the larger reservoir should go to the front brakes right? Well the front reservoir on the camaro is the larger one and the rear port is the smaller one, so I have them hooked up backwards. Please tell me I am on to something. lol.
It does sound like the bore is too small. This would cause the pedal to move more but feel easier. BTW, sorry, I lost your last thread when I took measurements.
The manual master cylinder bore for a nova/camaro, which is what my front and rear brakes are from is a 1 inch bore, that is why I choose that master. But the pedal assembly and prop/combo valve are from the 88 s10, which has a 1.417 inch bore size for their manual brakes. That, and they have whats called a quick up take I think, front calipers to keep the front pads from dragging. Now, the difference between the primary and secondary bore sizes are .5625 for the primary and .5 for the secondary. Right now I have it install with the primary going to the rear drums and the secondary going to the front brakes. Could be my problem, but I am no expert. Just a young punk trying to learn WTF I am doing. lol.
So, finally got to take the truck out for a test drive and I have limited brakes. The pedal is almost to the floor before it gets hard but at that point the truck starts to stop. Think this is a bore size problem or air still in the lines?
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