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 #380718  by StealthM
 September 15th, 2019, 10:52 pm
Howdy gang. I have a mushy brake peddle. I have replaced all the brake lines, calipers, brake hoses. Rotors and pads. Flushed the system with new fluid. But still mushy peddle. Master cylinder??
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 #380719  by LUNAT1C
 September 15th, 2019, 11:29 pm
I’ve never had the issue myself, but I’ve seen this solved in the past with a master cylinder, the booster, or both. My first thought would be booster.
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 #380720  by M-Pressive
 September 16th, 2019, 7:07 am
Ryan ended up doing the booster and master cylinder to fix the issue.
 #380723  by StealthM
 September 16th, 2019, 12:50 pm
Well ordered the master this morning. Booster seems to be working properly. Guess we will see... ugh.
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 #380724  by Sneke_Eyez
 September 16th, 2019, 1:55 pm
I fought a mushy brake pedal for a long time on the Special after doing my brake lines last year.
It turned out to be a bad booster and a bad master. In the process, I went to the bigger bore master cylinder, which seems to have helped as well.
 #380726  by StealthM
 September 16th, 2019, 11:05 pm
Bigger bore? Please school me...
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 #380727  by Sneke_Eyez
 September 17th, 2019, 8:16 am
So Autozone (and possibly others, but I bought mine at Autozone) sells a 1'' bore "heavy duty" master cylinder for our cars, versus the 15/16 they originally came with:
https://www.autozone.com/brakes-and-tra ... 2558_89618

I believe Brian (Mottman) mentioned it to me in a brake thread I had posted, but I cannot locate where he talked about it.

However, I installed it on my Special, which in my opinion has had poor braking performance since I purchased the car in 2013 with 86k, and it seems to have helped.
One thing that you need to make sure you do is adjust the pedal travel on the master - that will control brake feel to some degree.
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 #382069  by Phoenix
 January 26th, 2020, 4:48 pm
I'm having similar issues even after my mechanic installed new brake lines, master cylinder and brake booster. I just noticed today that the booster he installed is rusty. 😤

What do you mean by adjust brake pedal travel? How is that adjusted?
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 #382074  by Sneke_Eyez
 January 27th, 2020, 8:39 am
There is a rod in the booster (behind the master) that you can screw in and out to adjust pedal travel. I found that even small adjustments to it made a huge difference.
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 #382086  by Phoenix
 January 27th, 2020, 8:24 pm
Thanks for that. One thing I noticed after the new parts went in is that the pedal never gets solid after pumping the pedal in park with the car started. I can just keep pumping. With the car off the pedal will get solid after pumping, then drop when the car is started. One sign that the booster is good. I've also noticed that the two brake lines to the MC were routed with bends above the MC cylinder. Would that trap air causing the spongy pedal? Mechanic said he would replace the parts but I don't want him to waste his time replacing parts again if they're not bad, especially the booster.

He used an unpainted Cardone and it was flash rusted after only 3 weeks. Any advice would be greatly appreciated. Route lines to come out of MC and drop down? Replace MC or booster again? Other problem?