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Username Post: upgraded master cylinder        (Topic#359848)
Posts: 531
Loc: Ohio
Reg: 12-17-06
02-17-20 04:23 PM - Post#2786749    

Hi, Ive upgraded 65 impala brakes to dual master cylinder with disc front and the prop valve has a 1/4" connection for rear line which of course is 3/16" factory. Is leaving the line at 3/16 to the rear axle a problem? I was just going to reduce the line with a fitting at the proportioning valve.
thanks jim


65' Impala SS, 65' Belair, 89' Silverado Z71, 95' Silverado Z71, 12' Silverado, 15' Silverado LTZ, 16' Tahoe LTZ

Edited by 995jim on 02-17-20 04:24 PM. Reason for edit: No reason given.


Posts: 4

Reg: 01-22-20
02-18-20 05:12 PM - Post#2786810    
    In response to 995jim

Hi, I am going to be doing the same thing on my 65, although I am keeping the manual 4 wheel drums.I will be using a 67 dual master. The Inline Tube distribution block I obtained has 7/16-24 ports for the rear brakes.I plan on keeping the 3/16 line and using 7/16-24 to 3/16 line tube nuts when I make up the lines. My original 65 single master feeds the distribution block with 1/4 inch line, but I am going to use two 3/16 lines to feed my new distribution block. Both of these masters have 1 inch bores, so all the research I've done says this should work perfectly. The original single master probably has the 1/4 inch line to the distribution block because it is feeding both fronts and rears through the one line and needs more volume. Splitting the fronts and rears with the dual master using two 3/16 lines should work fine. Larger line flows more volume, but the pressure in the system is determined by the bore size of the master cylinder.

Edited by BillM89 on 02-18-20 05:12 PM. Reason for edit: No reason given.

Very Senior Member
Posts: 4464

Reg: 12-29-02
02-18-20 08:53 PM - Post#2786825    
    In response to 995jim

The reducer should be fine. I've got one on my car and the rear brakes work well.

Posts: 38

Reg: 09-03-18
02-19-20 05:08 PM - Post#2786878    
    In response to 65_Impala

Yes, you'll be fine. I used the reducer on my Inline Tube block when I did the dual master conversion. Inline Tube should really include the reducer since they list the tubes and block as fitting the 65 with the smaller size line to the rear (and as delivered, it doesn't).


65 Impala convertible 327/250 Maderia Maroon/black California black plate car

Edited by jayoldschool on 02-19-20 05:09 PM. Reason for edit: No reason given.

Gold Supporting Member
Posts: 78
Loc: upstate NY
Reg: 11-12-19
02-20-20 06:47 PM - Post#2786956    
    In response to jayoldschool

I agree w/ Jay. when I swapped mine to dual/front disc setup it has the prop valve right off m/cyl. I used original larger line from old master cylinder to the distribution block at the frame, just gently looped it to mate to the rear port at the valve and plugged the 2 ports at the block that went to the front. The original distribution block became my reducer, and I kept as much original as possible!

'65 Impala SS, Crocus Yellow/blk
327 / 300 L74
M11 3 on the tree
12 bolt 3.31 open dif

Edited by docjns1 on 02-20-20 06:48 PM. Reason for edit: No reason given.


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