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View Full Version : 1970 Master Brake Cylinder rebuild


Bullshark
04-18-2010, 08:13 PM
What is the proper proceedure for replacing the brake line seats in a 1970 master brake cylinder. The kit included these brass seats and a spring/rubber seat of some sort. I'm guessing it goes behind the brass seat. I have never tried replacing these. Just left the old ones in and hoped they were good. Any guidance guys?? Drilling them out seems to be the most straight forward approach, I'm guessing.

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Bullshark

Stpman
04-19-2010, 12:41 AM
Those things with the springs are check valves and check valve springs, they go in behind the tube seat inserts. IT looks like the inserts just press in. I would think if your not using the inserts again you might use a screw threaded into the insert to pull them out.

Steve

Bullshark
04-19-2010, 01:11 AM
Thanks Steve, Yes, I thought that they were probably check valves. I tried screwing a drywall screw in the brass inserts but it pulled out striping the hole larger. Then thought I would try heating the cylinder cast iron and retry. Next option i considered was just drill them out. Thought I would ask you guys what the best approach might be.

Bullshark

mrvette
04-19-2010, 01:13 AM
Thanks Steve, Yes, I thought that they were probably check valves. I tried screwing a drywall screw in the brass inserts but it pulled out striping the hole larger. Then thought I would try heating the cylinder cast iron and retry. Next option i considered was just drill them out. Thought I would ask you guys what the best approach might be.

Bullshark

Auto Zone exchange 20 bux....

:yahoo::flash::devil:

Bullshark
04-19-2010, 01:23 AM
Thanks Steve, Yes, I thought that they were probably check valves. I tried screwing a drywall screw in the brass inserts but it pulled out striping the hole larger. Then thought I would try heating the cylinder cast iron and retry. Next option i considered was just drill them out. Thought I would ask you guys what the best approach might be.

Bullshark

Auto Zone exchange 20 bux....

:yahoo::flash::devil:

That's whats in the car now. :crap: My floorboard has my footprints in it. :D

saudivette
04-19-2010, 06:52 AM
You should get it powder coated before you refit it :D

BBShark
04-19-2010, 10:59 AM
Interesting, I thought the check valve (residual valve) was only used with drum brakes.

mrvette
04-19-2010, 12:00 PM
Interesting, I thought the check valve (residual valve) was only used with drum brakes.

HUMM...I think U right....

:smash::cool:

Bullshark
04-19-2010, 12:10 PM
Interesting, I thought the check valve (residual valve) was only used with drum brakes.

Larry, how do I find out? I purchased the kit as a rebuild kit for 70 Corvette with PB. Was this Master Cylinder used on drum brake apps? It is the original MS for the car. It wouldn't suprise me if the kit had a few extra parts just to confuse me. :lol:

BBShark
04-19-2010, 12:36 PM
Bob, I suppose your kit could be generic and include parts you don't need. Doing a Google search on residual valves, I came up with this info:

There are two different residual valves. A ten pound residual valve will maintain a line pressure to the rear to keep the drum brake shoes out close to the drums giving a higher firmer pedal. Without a ten pound residual pressure to the rear you will experience a spongy pedal. A two pound residual valve is required whenever the master cylinder is lower than the calipers to prevent backflow of fluid from the calipers to the master.

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Twin_Turbo
04-19-2010, 01:26 PM
Yes, our MCs don't have a residual pressure/hold off valve, that's only for disc/drum applications where the fromt wheels get held off until the rears grab, this is done for stability so you don't spin out in the wet :)

Bullshark
04-19-2010, 01:35 PM
This is interesting. I think I will go ahead an try to extract the seat and find out what's in there. My brakes on the 70 have been giving me a fit for a while now. The symptom is exactly what you describe. No firm pedal at the top of the stroke, but as you apply more pedal they grab and damn near put you through the windshield. The travel delay drives me crazy as you can imagine. I have been chasing my tail trying to figure out what the problem might be. I crimp off the brake hoses and have a solid pedal so I figured it might be the calipers. The system is power bleed so no air as far as I can tell. I am in the process of rebuilding a set of o-ring calipers to replace the auto-zone rebuilds that are on the car now, but I really don't understand how they can be bad. No leaks and not sucking air. Stay tuned.

Bullshark

Bullshark
04-19-2010, 01:37 PM
Yes, our MCs don't have a residual pressure/hold off valve, that's only for disc/drum applications where the fromt wheels get held off until the rears grab, this is done for stability so you don't spin out in the wet :)

Just saw your post Marck, guess I should focus back on the calipers :thumbs:

DWncchs
04-20-2010, 02:11 AM
Maybe you can tap the brass insert ,put in a machine screw with a nut and washer,tighten the nut and it should pull the insert out.

68/70Vette
04-27-2010, 07:36 PM
What is the proper proceedure for replacing the brake line seats in a 1970 master brake cylinder. The kit included these brass seats and a spring/rubber seat of some sort. I'm guessing it goes behind the brass seat. I have never tried replacing these.


Bullshark

If you're rebuilding an old master cylinder, I'd think you'd have it resleeved since the original cast iron bore is probably pitted from rust. I think that Stainless Steel Brake Corporation resleeves them with stainless steel. I think some others resleeve them with brass.

Maybe yours' has been resleeved? I had my 68 MC restored by Paragon and in the process it got resleeved. Don't know if it was stainless or brass. Works fine. Came back looking good. It was a NCRS quaity restoration (even though I didn't particularly want NCRS) and it came back in natural unpained cast iron. I painted it. Just used a normal paint, since I use silicon.