I’ve placed the combo valve on the frame. I assumed the line to the rear was 1/4 inch because Joe P. has mentioned that in several other posts, but it appears in 64, 65, and maybe 66, the line is 3/16. Which brings me to the question of does the line need to be replaced with 1/4 inch or can I use an adapter (IFM to IFF) that converts 1/4 inch to 3/16 inch coming out of the combination valve? The in-line tube website states 4 wheel disc brake cars use 3/16 but this is disc/drum. Does that mean I should run 1/4 inch to rear distribution block and also change the rear lines? That’s going to require more adapters. What is safest to do? Thanks

 

Use the IFM to IFF adapter. Once you bleed the brakes, there will be no functional difference between 1/4" and 3/16" lines. The volume of fluid that moves through that line is too small for diameter to matter.

 

Thanks for your quick reply, Joe.

Btw, for others reading this the IFM to IFF adapter is In-line Tube part # AD3. Converts 1/4 inverted flare to 3/16 line out of the combo valve.

Also, I’m using an AC Delco after market 1972 cutlass Master Cylinder, part# 18M1878, with my original 1964 drum brake booster. You could use raybestos MC36306 as welI. The push rod length needs to be approximately 2 and 3/8 inch. I cut down a spare 4 inch push rod I had from a junk yard car. I initially cut the spare rod down to 2 and 5/8, then used a grinder to make small changes and stopped when I no longer transferred paint from the MC plunger (concave surface) to the push rod tip. If the push rod is not cut down to the proper length and continues to press on the MC, the brakes may drag.

Rather than steel line, I used Nickel copper line. Easy to bend. Lisle 33260 double flaring tool made perfect flares.

 

Those adapter fittings are available at most places. NAPA usually has a selection, for example. Surprisingly, the ILT price seems to be on the low side compared to other vendors, so good job finding that one. As for the M/C, the brakes WILL (not may) drag if the pushrod is too long. Many aftermarket GM-style master cylinders come with a deep hole to allow bolt-up to the long pushrod booster without the need for modifying the pushrod.

 

That’s helpful to know that MC push rod hole depth is different between manufacturers. Buyer beware.
I do not have a Napa nearby. Just an Oriellys and there selection is awful. So, I’ve always ordered from In-line tube. Parts arrive in 3 days, thankfully.

 

I came here to look into this same problem, so I'm thrilled to see such a relevant thread. I have already bought the 1/4 hard line for the rear but realized it doenst fit the rear flex hose (I think it is a 3/8 connection). I do think 1/4" is what my combo valve needs though. So, I ordered a rear hose from a 68 Caprice which is the 7/16-24 thread. Its good to hear that the line size will not affect brake operation.

 

Don't confuse tube diameter with flare nut thread. Flare nuts for 1/4" tube can be either 7/16-24 or 9/16-18 thread. 7/16-24 is the "standard" size that you'll get on a parts store piece of line. GM used the non-standard sizes to prevent incorrect connections on the assembly line. As I noted above, you can get inverted flare adapters to convert threads. You can also cut and reflare with the correct flare nut.

 

Joe, I think we are on the same page. I do have an adapter that I believe is the one you mention, so I could make it work with another roll of 3/16 hard line. While Im not dead set on having to use the 1/4 hard line for the rear, I do have it on hand, and only enough 3/16 to do the fronts. My goal this weekend was to get brakes working.

I too have used the copper nickel lines for my last two projects and this one, and I really like it... I dont have the ability to comment on longevity yet, but forming and flaring it has been a dream.

I will have to remember that I am using a different rear hose forever, but I try to keep a book with notes like that. I never refer back to it, but I do try to keep it.

 

I'm not suggesting using 3/16 line. The factory used 1/4 line. I'm saying that you can get adapters for the straight thread that has nothing to do with the diameter of the line.

 

I guess what I was trying to say is... I have what is supposed to be the correct rear flexline for a 64 (from ILT). But, it is setup for a 3/8-24 thread fitting (this made me assume the line was supposed to be 3/16) I have an adapter that will go between the 7/16-24 fitting for 1/4 line and the 3/8-24. This would work but I didn't know how I felt about using an adapter in my brake lines, seems like an extra place for it to leak.
So at first I tried to find a 3/8-24 fitting for 1/4 line (this would eliminate the adapter), but couldnt find one so, I looked for a flex line that accepted the 7/16-24. The caprice line is 7/16-24 thread, I have those connectors for 1/4 line. For me it just seemed like an easier solution...

I'm trying build it to work correctly with the parts I have on hand. So my plan is to run a single piece of 1/4 line from the combo valve all the way to the back, with no unions and no adapters. This should go straight to the flex line and then the T block, from the T block I was going to run 3/16 line to each wheel cylinder.

 

OK, now I understand. I may have given you bad info, I'll have to check my 64. The front to back line MIGHT only be 3/16 on those cars. I know the one on my 62 was only 3/16. I'm not sure when they made the change to 1/4.

 

Hi Joe, as you suspected, the 64 F85 has 3/16 on all four corners. This is why I needed ILT part number AD3 which is a 9/16-18 male and 3/8-24 female adapter on the rear port of the proportioning valve. No leaks so far.