Question about '86 master cylinder and booster swap

Willybill32

But at least it's tight!
Jul 16, 2019
488
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Lexington, KY
I have a 1986 Mustang GT 5.0/5 speed. The car sat inside for at least the past 12 years or so. About nine years ago I re-did the suspension, including swapping in a front suspension from an '87-'93, new shocks/struts, new springs and a rear disc conversion kit from Stainless Steel Brake Corp. According to SSBC's catalog at the time, their '86 kit worked with the stock master cylinder, and that's what I have, and the stock proportioning valve is still in place. After all this time, I have the engine freshened up and back in the car, and I've had an opportunity to drive it.

I'm finding the brakes are not nearly as strong as I expected, and the pedal isn't as firm as I'd like. I'm looking about a master cylinder swap, and I'm seeing all kinds of recommendations in the posts I've read, including the '86 Mustang SVO master cylinder (1 1/8" bore), '93 Cobra master cylinder (1" bore), '94 master cylinder (15/16' bore). and more talk about the brake booster. I now realize I need, at a minimum, to remove the stock proportioning valve. Can anyone give me any insight on what is the most appropriate bore size and master cylinder to use? If I use a new master cylinder, do I need to change the booster? If so, to what?
 
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I'm finding the brakes are not nearly as strong as I expected, and the pedal isn't as firm as I'd like.

This sounds like you may still have air trapped in the system.

If your cylinder or booster is under size the pedal should be stiff as hell (and [then] stopping power or lack thereof would come into play).
 
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You need to gut the proportioning valve and I would add a adjustable proportioning valve.
Here is some help:
And:
I should ask, 4 lug or 5?
 
You need to gut the proportioning valve and I would add a adjustable proportioning valve.
Here is some help:
And:
I should ask, 4 lug or 5?
It's still 4-lug.

Regarding the link immediately above your question:

Screen Shot 2020-02-01 at 7.53.25 AM.png
 
try this link

 
Lots of stuff in here.
 
The SSBC is pretty much a 93 Cobra rear setup right? Not sure why they would claim it would work with stock MC?

Anyway, with front stock 60mm calipers and rear 45mm calipers from the 93 cobra, you want the 1” bore MC. On an 86, the fittings are SAE, so ah easier swap is to use an 85 town car MC as its also 1” bore.

Booster is optional. You might want the added assist, or not. Depends on your leg strength and personal preference.

Oh any as soon as any non-stock brake setup is placed on a car, you need to gut the stock prop valve and install and adjustable
 
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You need to gut the proportioning valve and I would add a adjustable proportioning valve.
Here is some help:
And:
I should ask, 4 lug or 5?
Thanks, General karthief!
 
try this link

Thank you!
 
The SSBC is pretty much a 93 Cobra rear setup right? Not sure why they would claim it would work with stock MC?

Anyway, with front stock 60mm calipers and rear 45mm calipers from the 93 cobra, you want the 1” bore MC. On an 86, the fittings are SAE, so ah easier swap is to use an 85 town car MC as its also 1” bore.

Booster is optional. You might want the added assist, or not. Depends on your leg strength and personal preference.

Oh any as soon as any non-stock brake setup is placed on a car, you need to gut the stock prop valve and install and adjustable
Thanks, Mustang5L5!

My ‘86 has the stock booster. Is it adequate for the new master cylinder?
 
The SSBC is pretty much a 93 Cobra rear setup right? Not sure why they would claim it would work with stock MC?

Anyway, with front stock 60mm calipers and rear 45mm calipers from the 93 cobra, you want the 1” bore MC. On an 86, the fittings are SAE, so ah easier swap is to use an 85 town car MC as its also 1” bore.

Booster is optional. You might want the added assist, or not. Depends on your leg strength and personal preference.

Oh any as soon as any non-stock brake setup is placed on a car, you need to gut the stock prop valve and install and adjustable

Mustang5L5, my apologies that I keep getting lost in the forum threads...but I posted a question to you on another thread where you recommended the use of a 1985 Lincoln Town Car master cylinder on an '86 Mustang GT, and I'll post the same question here.

I purchased the '85 Town Car master cylinder. I was hoping for aluminum, but got cast iron, but guess that doesn't matter. The new master cylinder came with a new pushrod. Do you have experience with whether or not I need to replace the original pushrod with the new one, or is there enough adjustment on the original pushrod to allow me to reuse it?

Thanks in advance!
 
You shouldn't need to swap the pushrod. You do need, however, to measure that the pushrod makes proper engagement with the MC's piston. It can' extend out too far, or not be close enough.
 
my apologies that I keep getting lost in the forum threads.


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