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Old 02-14-2020, 07:29 PM   #1
vht
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Master Cyl Upgrade

I am going to upgrade the master cyl on my 1997 Z71, done went through everything else on the brakes. I checked out the thread on here where you can go to a 2002 Tahoe type master, checking the pt numbers he provided I couldn't get the Duralast to come up. Done a search on Autozones site and came up with two, one for a JC5, or the other for a JH5, JH6, or JH7. Which one are you all using? I've found the adapter fitting you need.
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Old 02-14-2020, 10:53 PM   #2
Palf70Step
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Re: Master Cyl Upgrade

Don't know if this is the thread you looked at or another, but this thread lists several models.
https://67-72chevytrucks.com/vboard/...d.php?t=586972


Brake codes are
JC2 11765 P BRK M BRAKE VAC POWER, 17" DISC/DISC, W/RWAL, 6,800 LBS 20205 E T E A
JC5 11768 P BRK M BRAKE VAC POWER, 4 WHL DISC, 7,200 LBS 940211 E T E A

JH5 11948 P BRK M BRAKE HYD POWER, 4 WHL DISC, 7,300 LBS 10921 E 4 E A
JH6 11949 P BRK M BRAKE HYD POWER, 4 WHL DISC, 9,900 LBS 940211 E T E A

I would say by the numbers in the above thread they are using for the JC2/JC5 variation NM8089, which I believe are for vacuum assist brakes, verses the JH5/6 for Hydoboost brakes
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Last edited by Palf70Step; 02-14-2020 at 11:15 PM.
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Old Yesterday, 11:07 AM   #3
speedygonzales
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One last thing you should do first

Have you ever done or had done, the "automatic bleed" process?
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Old Yesterday, 06:58 PM   #4
vht
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Re: Master Cyl Upgrade

Was going to but my Solus doesn't have that option for the earlier trucks. Done several 99 and up with it.
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Old Today, 08:59 AM   #5
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Might want to try before you go to that trouble

I did the MC change. I also did a 2 piston caliper change with slotted rotors. I also made the MC push rod 1/4 longer with a spacer.

Nothing I did compared to a "proper" auto bleed. That is where the complete system is bled manually, then the auto bleed is done and then a manual bleed is done last.

This one auto bleed made a world of difference. Was it as good as other vehicles brake system? NO Was it significantly better? YES

I have a Solus Pro so I'm not familiar with a standard Solus and my pro will do the bleed process but I will say this, the program to do the auto bleed is not where you think it should be. If you're not sure look around.

I am going to some day prove the entire problem with the GMT400's is a restriction on the brake system from the ABS. The way I plan to do so is make a patch brake line to take the MC around the ABS and go straight to the brake lines.

One thing you might also want to do is try using the E-brake to stop with instead of the brake pedal. Obviously you have to hold the release handle up so the pedal doesn't lock. Try it when you are alone on a street that is not fast and try coming to a stop using just that.

This can give you an indication of how well your back brakes are doing without having the fronts influence the feeling.

In the mean time, I suggest you try the auto bleed first before you go the way of the MC change. I'm betting you will be surprised.
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