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Well i have been reading up on this swap when you change to disco brakes to swap out the master cylinder to a 1" bore one to give your rear brakes more pressure to stop. Well I thought I would give it a try and share what I found.
first I found this write up for a Mazda 929 MC and then one for Subaru. I did the Subaru swap.
Issues with braking?
sami/yota swap with disco - not stopping?
The one thing I see missing is Why?
Basic Hydraulic System Theory:
Your pump (Master Cyl) to your cylinder (Caliper / Wheel cylinder) gives a mechanical advantage by volume / ratio.
In order to understand this better. Look at it like a Transmission or even simpler a 10 speed bike. The small front sprocket makes it easy to pedal but turns the wheel slower. Just like the smaller bore MC has a greater mechanical advantage over the brakes at the wheels.
This mechanical advantage must be maintained when you swap parts. If you install a large bore MC with small bore cylinders (Caliper / Wheel Cylinder) then you will loose some of your mechanical advantage and require more force to lock your wheels. If you have already upgraded to larger Calipers / Wheel Cyls ~ then the larger bore Master cylinder is a great upgrade to keep everything proportional.
Likewise on the other end if you install a Small bore MC and large bore cylinders (Caliper / Wheel cyl) then you may run out of piston travel / fluid displacement before you lock the wheels. OR you may lock the wheels too easily.
While Brake system power is a scientific calculation, using similar size pieces (Subaru) can get the results you seek.
Also remember that calipers generally require more fluid then wheel cyls, and Disk Disk MC's should be kept with Disk Disk applications.
Brake MC swap for sami/yota disco stopping issues..
Subaru Master Cylinders
1998-2003 Legacy
2001-2003 Outback
1998-2002 Forester
2000-2004 Imprezza
with ABS
plunger needs lengthed..The only tweak that needs to be done is the sami plunger needs to be lengthed 14mm out to a total length of 82mm....
Some say a 93 mustang also will work - plunger mod
1980 Firebird MC w/ 4 wheel disks, ($17 AutoZone w/ $9 core) just slotted the holes in the m/c's ears and the bore fit the zuk perfect and the push rod fits great. Be sure to plug the vac port on the bottom of the m/c. I filled it with solder and used a rubber gasket between the m/c and the power boster.
http://bbs.zuwharrie.com/content/topic,31112.0.html
UPDATE:
Late model '94 and '95 Sammy's have a different booster and M/C, and this is not a near-direct fit like on earlier years.
3 different write ups..
http://bbs.zuwharrie.com/content/topic,96888.0.html
http://bbs.zuwharrie.com/content/topic,57063.45.html
http://www.pirate4x4.com/forum/showt...932&highlight=
how to:
1.Remove original master cylinder. Save gasket if possible (use old gasket as a template for a new one).
2.Reach into booster and remove the booster push rod.
3.Remove the “tip” of the pushrod.
4.Cut the head off the new 6mm bolt. Clean up threads by “chasing” with a die.
5.Round off one end with a grinder to make the new booster push rod tip. Note:As an option, you can use a 6mm acorn nut, grind off the corners of the hex, then loctite it on.
The original push rod length was too short, so the new push rod will have to adjusted to the proper length(82mm or 3.55012 inches). There needs to be zero tolerance between the tip and it’s mating surface inside the master cylinder. This will take a couple of minutes to adjust properly.
6.If the Subaru master cylinder doesn’t have an “O” ring on it, swap the Suzuki one onto it.
7.Once the pushrod is adjusted properly, Bolt up the master cylinder after you’ve bench bled it. Use the gasket you cut or RTV.
Here the swap using a Mazda 929 MC. he had to shorten the push rod. The Subaru you will need to lengthen to 82 mm.
I see that in this guys build that he shortened it...????
http://zukikrawlers.com/showthread.p...aster+cylinder
his original was 2 3/4" inches from base face to the end of plunger which would be 69.85 mm in lenght not 82mm like other had said.
82mm = 3.228 inches which is way longer
cus i will have to measure like he did before the swap and make it equal that lenght on the new mc..
his pics he posted with a Mazda 929 mc but im using a 98 suburu forester 1 1/16 bore and i dont have the plastic nipple that sticks out on mine.
Everything about this bolts-on... but you do have to adjust the plunger in the booster - but thats easy.
Here is what the plunger looks like from the stock sami booster. To remove this from the booster, it just pulls right out.
You then unscrew the end of it and trim off 1/4".
Screw it back on and set it to 2 3/8" long.
Then for a test fit you can double check that to the MC which should be 2 3/4" long from the mounting surface of the Master Cylinder which is what the orignal dimension was with the Sami MC - but I just forgot to take a picture of it.....
this is the pic I was talking about it is shorter than others say to be 82 mm
98 Subaru forester
ok here is what i got from :
Original sami mc – 69mm from face to end of plunger
Original plunger length – 75mm
New Subaru mc w stock plunger of sami – 58mm
Make new plunger length equal 69mm when it is in the new mc???
Measure the entire plunger and bolt OUT of the master. Mine was just under 3.25 inches. If you take the O ring off the master and test fit it you can feel when it's too long or too short. You want just a little play before the peddle touches the rod.
I did measure it out and it was 75 mm from the pics above. So i need to make it 82 mm then?
Yes. Just make sure it let's the master completely return to an open state where ther is a little play with the rod fully released from the brake pedal.
as you will see the 88 mc is different plug than the 87 that came off my sami..
i bought a m6 x 1.00 x 50 screw and cut the head off right behind the head.
also got a acorn nut and locked tight it on.
Here are the old screw length and new one.New on bottom.
o ring i pulled off the old sami master cylinder to used on new subaru one.
New subaru MC plug wires i need to splice into the old plug to get it to work.
I did black to black
green to red/black
taped it all up after check it out on rig.
I needed to make a new gasset for the new mc so used just the back of a note pad carboard and cut out the new mc on it.. also you can see the acorn nut sticking out of the brake booster in the pic with the o ring installed.
here it is installed. I notice that i have the brake lines higher than the mc so i had to bend them down some so they are below the MC so the lines dont bleed back and loose pressure on the pedal. you see all the wires taped up too.
All in all i had to adjust the new push rod about 4 times and add a jam nut to other end of the push rod because I needed to lenght ti and wanted it to stay put (nut does not get in the way when using it.
OVer all length of the push rod ended up being about 83 mm and gave me 1/4 " pedal play and then rock hard brakes after that... Love the response of them...
first I found this write up for a Mazda 929 MC and then one for Subaru. I did the Subaru swap.
Issues with braking?
sami/yota swap with disco - not stopping?
The one thing I see missing is Why?
Basic Hydraulic System Theory:
Your pump (Master Cyl) to your cylinder (Caliper / Wheel cylinder) gives a mechanical advantage by volume / ratio.
In order to understand this better. Look at it like a Transmission or even simpler a 10 speed bike. The small front sprocket makes it easy to pedal but turns the wheel slower. Just like the smaller bore MC has a greater mechanical advantage over the brakes at the wheels.
This mechanical advantage must be maintained when you swap parts. If you install a large bore MC with small bore cylinders (Caliper / Wheel Cylinder) then you will loose some of your mechanical advantage and require more force to lock your wheels. If you have already upgraded to larger Calipers / Wheel Cyls ~ then the larger bore Master cylinder is a great upgrade to keep everything proportional.
Likewise on the other end if you install a Small bore MC and large bore cylinders (Caliper / Wheel cyl) then you may run out of piston travel / fluid displacement before you lock the wheels. OR you may lock the wheels too easily.
While Brake system power is a scientific calculation, using similar size pieces (Subaru) can get the results you seek.
Also remember that calipers generally require more fluid then wheel cyls, and Disk Disk MC's should be kept with Disk Disk applications.
Brake MC swap for sami/yota disco stopping issues..
Subaru Master Cylinders
1998-2003 Legacy
2001-2003 Outback
1998-2002 Forester
2000-2004 Imprezza
with ABS
plunger needs lengthed..The only tweak that needs to be done is the sami plunger needs to be lengthed 14mm out to a total length of 82mm....
Some say a 93 mustang also will work - plunger mod
1980 Firebird MC w/ 4 wheel disks, ($17 AutoZone w/ $9 core) just slotted the holes in the m/c's ears and the bore fit the zuk perfect and the push rod fits great. Be sure to plug the vac port on the bottom of the m/c. I filled it with solder and used a rubber gasket between the m/c and the power boster.
http://bbs.zuwharrie.com/content/topic,31112.0.html
UPDATE:
Late model '94 and '95 Sammy's have a different booster and M/C, and this is not a near-direct fit like on earlier years.
3 different write ups..
http://bbs.zuwharrie.com/content/topic,96888.0.html
http://bbs.zuwharrie.com/content/topic,57063.45.html
http://www.pirate4x4.com/forum/showt...932&highlight=
how to:
1.Remove original master cylinder. Save gasket if possible (use old gasket as a template for a new one).
2.Reach into booster and remove the booster push rod.
3.Remove the “tip” of the pushrod.
4.Cut the head off the new 6mm bolt. Clean up threads by “chasing” with a die.
5.Round off one end with a grinder to make the new booster push rod tip. Note:As an option, you can use a 6mm acorn nut, grind off the corners of the hex, then loctite it on.
The original push rod length was too short, so the new push rod will have to adjusted to the proper length(82mm or 3.55012 inches). There needs to be zero tolerance between the tip and it’s mating surface inside the master cylinder. This will take a couple of minutes to adjust properly.
6.If the Subaru master cylinder doesn’t have an “O” ring on it, swap the Suzuki one onto it.
7.Once the pushrod is adjusted properly, Bolt up the master cylinder after you’ve bench bled it. Use the gasket you cut or RTV.
Here the swap using a Mazda 929 MC. he had to shorten the push rod. The Subaru you will need to lengthen to 82 mm.
I see that in this guys build that he shortened it...????
http://zukikrawlers.com/showthread.p...aster+cylinder
his original was 2 3/4" inches from base face to the end of plunger which would be 69.85 mm in lenght not 82mm like other had said.
82mm = 3.228 inches which is way longer
cus i will have to measure like he did before the swap and make it equal that lenght on the new mc..
his pics he posted with a Mazda 929 mc but im using a 98 suburu forester 1 1/16 bore and i dont have the plastic nipple that sticks out on mine.
Everything about this bolts-on... but you do have to adjust the plunger in the booster - but thats easy.
Here is what the plunger looks like from the stock sami booster. To remove this from the booster, it just pulls right out.
You then unscrew the end of it and trim off 1/4".
Screw it back on and set it to 2 3/8" long.
Then for a test fit you can double check that to the MC which should be 2 3/4" long from the mounting surface of the Master Cylinder which is what the orignal dimension was with the Sami MC - but I just forgot to take a picture of it.....
this is the pic I was talking about it is shorter than others say to be 82 mm
98 Subaru forester
ok here is what i got from :
Original sami mc – 69mm from face to end of plunger
Original plunger length – 75mm
New Subaru mc w stock plunger of sami – 58mm
Make new plunger length equal 69mm when it is in the new mc???
Measure the entire plunger and bolt OUT of the master. Mine was just under 3.25 inches. If you take the O ring off the master and test fit it you can feel when it's too long or too short. You want just a little play before the peddle touches the rod.
I did measure it out and it was 75 mm from the pics above. So i need to make it 82 mm then?
Yes. Just make sure it let's the master completely return to an open state where ther is a little play with the rod fully released from the brake pedal.
as you will see the 88 mc is different plug than the 87 that came off my sami..
i bought a m6 x 1.00 x 50 screw and cut the head off right behind the head.
also got a acorn nut and locked tight it on.
Here are the old screw length and new one.New on bottom.
o ring i pulled off the old sami master cylinder to used on new subaru one.
New subaru MC plug wires i need to splice into the old plug to get it to work.
I did black to black
green to red/black
taped it all up after check it out on rig.
I needed to make a new gasset for the new mc so used just the back of a note pad carboard and cut out the new mc on it.. also you can see the acorn nut sticking out of the brake booster in the pic with the o ring installed.
here it is installed. I notice that i have the brake lines higher than the mc so i had to bend them down some so they are below the MC so the lines dont bleed back and loose pressure on the pedal. you see all the wires taped up too.
All in all i had to adjust the new push rod about 4 times and add a jam nut to other end of the push rod because I needed to lenght ti and wanted it to stay put (nut does not get in the way when using it.
OVer all length of the push rod ended up being about 83 mm and gave me 1/4 " pedal play and then rock hard brakes after that... Love the response of them...
discount given for a good sami windshield and frame!
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