C3 brake distribution block

[Tom R.]

Have just replaced the main brake distribution block (brass) on my current restoration project (70) along with routing the main brake line down the left side to the rear. After the hard work was done, I discovered the fitting on the brake line to be larger than what the block was threaded for. The top of the replacement block I purchased accepts 1/2"-20. Since I bought both the block and the line from the same supplier, am wondering which is correct? Obviously the block will be the easiest to remove and return but I can also cut and reflare the line.

[Joseph K.]

Re: C3 brake distribution block

Check the threads on the original Block

[Tom R.]

Re: C3 brake distribution block

Good idea, and I would have if I could only find it. Anyone thinking about a full body off never having done one will be amazed at how much room it requires. Not to mention how many plastic bags it takes to store parts. I simply can't find the one I'm looking for.

[Alan S.]

Re: C3 brake distribution block

Hi Tom,
I can appreciae your thoughts about the room required and the tagging/bagging systems needed.
I found that with hundreds and hundreds of bags of parts and fasteners separated into dozens of boxes, I still could 'lose' something because I hadn't been perfectly logical as to just where it should go after coming off the car.
Also, you can't have too many pictures or notes that are too extensive.
It's BIG fun!!!
Regards,
Alan

[Paul J.]

Re: C3 brake distribution block

Good idea, and I would have if I could only find it. Anyone thinking about a full body off never having done one will be amazed at how much room it requires. Not to mention how many plastic bags it takes to store parts. I simply can't find the one I'm looking for.

Tom, everything that I take off of a car is bagged, tagged, then put into a box with the area that all of the pieces came from written on it. In this case, it would say "Frame". I use small boxes and I also include larger parts, as they will take up space and limit the number of bags that go in. I also write the contents of some of the bags on the outside of the box. When I need to find a part, I usually can find it in the first box that I go to, and if its not there its almost always in the next one.

Another thing that I've found over the years is that best way to "bag" parts is not with plastic bags (even though I still use them). The plastic lunchmeat containers made by Glad and others that you get when you purchase sandwich meat at the store are perfect for assemblies, and parts with screws and bolts. I use adhesive labels from the office to write the contents of the boxes on as it is easier to see and the boxes are usually recycled into the next project.

Paul

[Joe L.]

Re: C3 brake distribution block

Have just replaced the main brake distribution block (brass) on my current restoration project (70) along with routing the main brake line down the left side to the rear. After the hard work was done, I discovered the fitting on the brake line to be larger than what the block was threaded for. The top of the replacement block I purchased accepts 1/2"-20. Since I bought both the block and the line from the same supplier, am wondering which is correct? Obviously the block will be the easiest to remove and return but I can also cut and reflare the line.

Tom------


There were several of these brake fluid distribution and differential pressure sensing switches used over the 1967 to 1982 period. Among the 69-77 pieces the size of the various fittings was one of the primary differences between them.

The 1969-only block, GM #3956727, used an upper fitting of 1/2-20 thread size. It's possible that this block was used on VERY early 1970's but I really doubt it.

The 1970-73 block, GM #3980797, used a 9/16-18 thread size for the upper fitting. Some photos of an NOS GM #3980797 are attached. However, the configuration of this block MAY have changed at some point even though the part number never changed. The upper fitting on original blocks may be tapped directly into the brass block. This NOS SERVICE block may use a "cut down" brass block with an attached hex fitting at the top. Why this change was made is completely unknown to me. Functionally, both block styles are exactly the same.

[Joe L.]

Re: C3 brake distribution block

For comparison, the GM #3956727 block used for 1969 is shown below. For 1969, the original block was definitely of the type having the upper fitting tapped directly into the body of the brass block. This SERVICE valve has a "cut-down" brass body and an attached brass hex fitting.

[Tom R.]

Re: C3 brake distribution block

Joe,

The replacement block I purchased is tapped directly into the body @ 1/2"-20 but the brake line fitting has a 9/16"-18 as originally on the 70-73 as you said. That leaves me with having to replace the fitting on the line to match my new block. Thanks for the info.

[Joe L.]

Re: C3 brake distribution block

Joe,

The replacement block I purchased is tapped directly into the body @ 1/2"-20 but the brake line fitting has a 9/16"-18 as originally on the 70-73 as you said. That leaves me with having to replace the fitting on the line to match my new block. Thanks for the info.

Tom-----


Yes, I believe the reproduction blocks use the original configuration.

I think if I were you, I'd try to obtain a block with the correct upper fitting size rather than change the brake line fitting. I think they must have sent you a 1969 block rather than a 70-73. I know that both blocks are reproduced so it's not as if they just had a "one size fits all" sort of thing.