Do I need to change my master cylinder with this 5 lug conversion?

Jawbone

New Member
Jan 17, 2010
21
0
0
B.C., Canada
I'm going to replace my front spindles, rotors, calipers, with those from a /94 Mustang. The rear brakes are going to remain stock drums with axles from a Aerostar and Ranger and drums from an Aerostar.
Do I need to change my MC or is the stock one okay? Thanks for any input.
 
  • Sponsors (?)


Change it to what master cylinder? You should only need to upgrade your master cylinder to the cobra master cylinder and power booster when upgrading the rear to disc. I did the 5 lug conversion but I am having braking issues, but nothing dangerous or uncontrollable.....just uncomfortable.
 
If I need to change the M/C, it would be to a /94 or /95 Mustang. The SN 95 spindles came out of a /94 Mustang. The technical article that detailed the conversion said nothing about changing the master cylinder if you leave the rear brakes stock.
 
You can keep your stock M/C with rear drums. Only when upgrading to rear disk do you need the bigger bore M/C.

The more I read and hear from people, if you upgrade to rear disk the booster is the only optional part, it depends on what your plan is for the car. A road course car uses a lot of brakes and you'll need a bigger booster. But I left my stocker in and it's fine for normal driving.
 
Thanks for the input Repostyle. I'll be keeping my stock M/C since I'm only interested in improved handling for my somewhat "normal" driving. My convertible also happens to be green with a white top. Hated the white top and interior initially but it works great to reflect the heat on those hot days.
 
From all I've read, you only need a /94 or better M/C if you change your rear drums to discs. With 80% of your braking done by the front brakes, for me it's overkill to go to rear discs not to mention the PITA.
 
so the booster is optional? (dont mean to hijack thread)


Your situation is different. With rear disks, you should do the booster as well.

If you only change the fronts, you can get away with a lot more.

Basically MC selection is dictated by hydraulic ratios. It's a calculation of caliper piston (slave) area vs. the Master cylinder piston area.

If you leave the rear drums, there really is only one MC that works - the stock one. Saving grace with this is if the pedal feels a little stiff after the conversion, you can install a booster to give you more assist.

But when rear disks are involved, different mentality. Now you really should look into a booster and a new MC since there is much more piston area to move.
 
Is there a MC out there that has the right proportions for front/rear 5 lug disk brake conversion --AND-- the use of the stock booster?

In other words: One that has a better mechanical advantage and doesn't need the larger boster?


The reason I ask is that I'd HATE to have to alter the shock tower in any way if it's at all avoidable. To me... that's ghetto.
 
Just to toss it in, I have the stock 87 Cylinder/booster with a complete set of Cobra Disc's around my car. I love the feel, and it's not too assisted. May try the 94/gt booster/cylinder in the future, but I like it, and the car stops plenty better than stock 11" brakes.
 
Is there a MC out there that has the right proportions for front/rear 5 lug disk brake conversion --AND-- the use of the stock booster?

In other words: One that has a better mechanical advantage and doesn't need the larger boster?


The reason I ask is that I'd HATE to have to alter the shock tower in any way if it's at all avoidable. To me... that's ghetto.


Depends on what brakes oyu put on. You can only downsize the MC bore so much though.


You don't need to alter the shock tower. I didn't even touch mine in my '88. Looking at it, you wonder how i got it in there, but to be honest, it wasn't any big deal really. I just cut down the studs and slotted all 4 holes to the pass side. Went right in. Start to finish time of 2 hours. :shrug:
 
Is there a MC out there that has the right proportions for front/rear 5 lug disk brake conversion --AND-- the use of the stock booster?

In other words: One that has a better mechanical advantage and doesn't need the larger boster?


The reason I ask is that I'd HATE to have to alter the shock tower in any way if it's at all avoidable. To me... that's ghetto.

To get mine in, all I had to do was notch the holes also. I didn't touch my shock tower.

Someone told me that 92 and newer cars had a little more clearance. I can't confirm that though.
 
Sorry it took me so long to get back to this post. Thanks though, for the answers to my questions.

The brakes I'm using are:

Rears from a 96 V6
SN95 Spindles
Dual piston PBRs on the front (Non-Cobra)

A buddy of mine (who's done a ton of these) tells me that a Cobra MC ontop of my stock booster will be fine while see others who have said that the pedal would be hard.

Either way, I only want to have to do this one time. hehe

I'm all for leaving the stocker booster in there if it will do the job.
 
It'll work, but a "stiff" pedal is also subject to opinion. If it was me, I would swap the booster. When you spend this much time and money swapping to rear disc, might as well get a nice pedal feel to go along with it.
 
I did a 5 lug disc conversion upgraded the booster master cylinder. But also gutted the proportioning valve and replaced the plug with a solid one and added a adjustable proportion valve
 
Last edited: