Brake pedal goes to the floor......

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Posted: Feb/06/2016 at 7:41pm

If my math is correct I need a 1 1/4" bore MC
Front piston 3.375" rear 3.146"

FuzzFace2

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Posted: Feb/07/2016 at 12:34pm

Ok got to ask why a line lock on the rear?
Also you said "ball valve" is this for open/closing the line lock?
Got a picture of this line lock valve so we can see it?

OK using GM? calipers out back is there an adjustment like turning the piston to get it closer to the pad(s)this could be why the peddle needs to be pumped. Like adjusting shoes they have to be close to the drum before you can bleed and get a good peddle.
Dave ----

TSM = Technical Service Manual

75 Gremlin X v8 for sale
70 Javelin 360/auto drag car
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Posimoto

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http://www.mscdirect.com/product/details/86857505

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Posted: Feb/07/2016 at 4:26pm

Thanks for the reply Dave,

FuzzFace2 wrote:

Ok got to ask why a line lock on the rear?

To use as an e-brake. I understand it isn't as safe as a traditional e-brake but it works for my needs.

FuzzFace2 wrote:

Also you said "ball valve" is this for open/closing the line lock?

Yes

FuzzFace2 wrote:

Got a picture of this line lock valve so we can see it?

FuzzFace2 wrote:

OK using GM? calipers out back is there an adjustment like turning the piston to get it closer to the pad(s)this could be why the peddle needs to be pumped. Like adjusting shoes they have to be close to the drum before you can bleed and get a good peddle.
Dave ----

Yes GM,

Posimoto wrote:

I already inspected the calipers and brackets, they work as they should. The piston and pad is positioned correctly against the rotor.

I'm fairly certain I need more volume, the numbers I'm running call for a 1 1/4” bore. I'll make some calls tomorrow to double check.

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Posted: Feb/07/2016 at 7:31pm

What's the application for the master cylinder? Also what's the application for the rear calipers? You say GM but what do they fit? It sounds to me like you're using the wrong master or there's something wrong in the rear brakes. I'm using stock front calipers and Cadillac rear calipers, with the e brake setup in them, a stock AMC master with 1 1/8" bore with no issues so I'm confused as to why your system isn't working right.

"Hemilina" My 1973, 5.7 Hemi swapped Javelin

Posimoto

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Posted: Feb/08/2016 at 1:08pm

Your cadillac rear calipers have a piston diameter of either 2.121" (small caliper) or 2.497" (large caliper). As mentioned I'm running 3.375" in the front and 3.146" rears.

My front and rear calipers work as they should, no issues there. I'm confident the air has been removed from the system, the only thing that remains is volume. When I talk to wilwood the first time the tech recommended a 1 1/8" bore MC.

After looking at my numbers I believe I need a larger 1 1/4" bore MC as I previously mentioned. I called wilwood tech again this morning, talked to a different tech and he agreed it sounds like a volume problem, and after punching in the numbers recommended a 1 1/4" bore MC.

I also found out they don't offer the 1 1/4" bore MC so maybe that is why the first tech I talked to recommended a 1 1/8" bore, or maybe he typed in a wrong number.

I'm running a Chrysler PB, unlike the AMC booster that can run GM the Chrysler runs ford.
MC 78 Mercury Marquis (1 1/8" bore disc/disc application)
F- calipers K30
R- caliper K20

Looking around this morning I found a 97 ford 250 disc/dics w/o cruise MC that should work. I'm sure there is more as well.

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Posted: Feb/08/2016 at 2:32pm

Those are some big caliper pistons (stock KH 2.75" & small Bendix 2.6" used 1" bore master, big Bendix 3.1" had 1 1/8" master).
If you had a 2:1 volume ratio master, not surprised it didn't work. Likely need 1:1 with that combo.

Hope you have an adjustable proportioning valve and severely limit rear pressure or your rears are likely to lock up under medium-to-hard braking and spin the tail around. A smaller rear caliper piston would generally be a better match.
http://tiltonracing.com/wp-content/uploads/98-1261-Brake-Proportioning-Valve_.pdf

Keep it safe,RD.

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