front disc-master cyl. help needed (1 Viewer)

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I bought my cruiser with disc brakes on the front and its a 71' so i figure the axle is from a later year cruiser or has been converted to front discs by the PO, it has the stock master cyl. and I was certain i was putting a non-ABS master cyl on it until reading further posts that drums need a residual valve to put a constant 10lbs? of pressure on the drums, so if i have a stock master then wouldn't it be putting constant pressure on the front discs? I need to put a bigger master cyl on for sure because i couldn't make that thing stop for the life of me if i needed to....


so what do i run, i have discs up front and drums in the rear i need something around 15/16 bore or 1inch , i was planning on going 80 non abs but i would need to put a residual valve on it? i'm going for simplicity

so what do i do???? this thing will be on the road soon and i was just wondering if i could get some help...


i've checked out the tech links but nothing really answered my question so I triedddd......thanks...
 

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Oh...Durka Durka Durka.
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Your drum brake master cylinder, with the residual pressure valve removed from the front circuit should provide ample stopping power for your truck, provided it is functioning properly. I have used these in many a disc brake swap, both front disc, drum rear, and disc front and disc rear, with a proportioning valve to control the flow/pressure to the rear calipers.


Good luck!


-Steve
 
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normally when the discs are fitted the RPV is removed from the front circuit. Easy to do - unscrew the big nut the front brake pipe goes into. Remove springs and rubber washer. Replace big nut. Bleed.
 
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alright thanks, but i was thinking more along the lines of a master slave upgrade, i heard this works alot better so it couldn't be that much of a myth....

so which one do i upgrade to ?
 

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When installed in a properly functioning system…


Seems to me you have something going on other than a master cylinder issue if " i couldn't make that thing stop for the life of me if i needed to...."


Are you 100% positive that your booster is operating properly? I thought you were looking for a hissing sound a couple weeks back, and a check vavle for the booster that you have in there currently...

Post up a pic of what you currently have...


Have you tried to bleed the brakes, to verify that the master is moving fluid, and that there is not any restrictions in any of the hoses or lines, or that the calipers and wheel cylinders are operating properly?


It is very possible that you could bolt on a new master and not resolve your braking issue....


Good luck!


-Steve
 
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i have all new rear wheel cyl's.. i properly adjusted the rear brakes, the front brakes are in decent shape, i just bought all new brake hoses and have bled the system 2-3 times to make sure i can get all the air out of the system. the master is moving fluid because it bled the brakes fine....

i resolved the hissing, it was not the brake booster it was the weber carb and i have resolved the problem with it....

when i press the brake the rpms jolt a tinyy bit, is that ok? i realize replacing the master may not resolve my problems but my master is a bit old and rusty right now and figured it was in do time to replace it soon....


i can get a toyota mini truck booster and master for free from a friend.... any thoughts would be great... thanks poser for always chiming in for me... and the rest of us...
 

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Thank you for the background/clarification on your situation....


Seems to me, I would try the booster from the mini with your current master cylinder, since you only mentioned exterior corrosion, and not that it was leaking. Pay attention to the length of the actuation rods between the two booster assemblies, as to not bottom out the master cylinder. You will see where this is adjustable in multiple places when you have them removed and side-by-side. You should not need to open the system up again, and have to bleed it, if you only change the booster. Just be mindful of your lines and do not pull on them too hard. IIRC, you will need to mount the mini booster upside down, putting the vacuum hose on the bottom, and most likely that hose will need to be lengthened.

If you have fluid flow, and have to pull the steering wheel to your chest in order to get enough leverage to actuate the brakes, I would look at the booster, so long as EVERYTHING else is adjusted properly. But that is just me...I am sure that others have different opinions.

:beer:


Good luck!


-Steve
 
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thanks man.. .i'll give it a whirl...

any other suggestions would be awesome... but i'll go get the booster tomorrow...

i figure if the booster is equivalent to the one i have now, thats fine because its still 10+ years newer...
 
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If you have fluid flow, and have to pull the steering wheel to your chest in order to get enough leverage to actuate the brakes, I would look at the booster, so long as EVERYTHING else is adjusted properly. But that is just me...I am sure that others have different opinions.


i have to agree with Poser, the booster is what creates the power in the power brake system, your master even if its old is probably still fine if it isnt leaking and fluid still flows. try the booster
 
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When I switched to discs, I found the pedal was VERY hard with the std booster.
I put a 60 series booster in - huge difference.
No issues with the brakes and 37s.

You have checked you havn't got a seized caliper piston?

Also, a common m/cyl fault is the failure of the seal between f & r circuits, which basically means the rears dont work properly.
Can you lock up the rears if you push hard enough?
 
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nope i can't lock up anything.... just kinda slows down then creeps to a stop... i'm gonna go with another brake booster...thanks guys...

how do I see if it hase a seized piston?

i can tell that the proportion of the front and rear brakes is almost right on... but it just isn't stopping quick enough....i'll go get the booster today and post up tonight....

thanks all again....your all very helpful..
 
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bandy rooster said:
how do I see if it hase a seized piston?
Pull the caliper. Get someone to gently push on the pedal - GENTLY!
all 4 pistons should move. If one doesnt, it may be seized.
You should be able to push them bacvk with a large multigrip - again, if not, seized piston.
 
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:UPDATE:
i got a booster and brake master off a 81 yota truck, it has discs up front and drum in the rear so the rear has a residual valve, from what i can see its a 13/16th bore and is AISIN

(off the yota truck) the booster - has been replaced sometime in its life, its a BENDIX MASTER VAC: unit number: 223-01031, although the master is a alittle rusty the inlets to the rear and front lines are clean... so i think it should be ok?

i think it would be best to use the 81 master/booster setup because it has only one residual valve which would work for the rear brakes... your thoughts???

should i keep them together and use the hole unit that i got off the yota truck?? or incorporate my 40 master with the 81' booster????whats your thoughts, so far thats what i have to work with ... thanks all...
 

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your existing master has a 15/16 bore....I would use it.


change out the booster, and see what happens.


Good luck!


-Steve
 
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ok, its on and i turned the engine on for a little, the pedal already felt better went a couple feet stopped...boom bang clang!!! needles to say, a rock or something hit my fan and spun it into the radiator! i swear just when i get something done another problem bites me in the a$$, it wasn't a tool or anything that i left there, so i suspect a rock

but the brake booster seemed to work good for the 30 seconds it was tested


so how do you replace a small leak in the radiator about this big:

-------
-------

its like cut through two fins and was leaking quite a bit of anti freeze...should i try some bars radiator stopleak or something more drastic... thanks all i'll do a post up of everything when i get a real test drive.......
 

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