I have seen references to the the use of a '73 to '79 bus master cylinder as a possible master cylinder upgrade when using larger calipers. Supposedly it has a 22mm bore. Has anyone actually made this conversion? Does anyone have any info on this mod? Thanks in advance for the info.
Full Version: Master Cylinder Upgrade - 22mm bus?
diddn't the bus use a vacume assist for braking? A 22mm MC is going to be STIFF for a 914 w/o power brakes.
Zach
Zach
QUOTE(stevekh44 @ Jul 28 2010, 07:11 AM) 
I have seen references to the the use of a '73 to '79 bus master cylinder as a possible master cylinder upgrade when using larger calipers. Supposedly it has a 22mm bore. Has anyone actually made this conversion? Does anyone have any info on this mod? Thanks in advance for the info.
Could be...
Ya see - MC bores are _really_ specified in 'English' measurements...
The '23mm' MC we all talk about is really 15/16".
Similarly, the '19mm' is really 3/4" and the NLA '20.5' is 13/16.
a 22 would be 7/8"...
You have to make sure this isn't a power brake MC (i donno nothin' 'bout busses...)
You call this an "upgrade". Please describe in your own words exactly how this swap meets the definition of the term "upgrade". More pedal effort? The fact that it's internally set up for front discs and rear drums? The fact that it's designed for vacuum assist? Two brake light switches? All of the above? None of the above?
The Cap'n
The Cap'n
well larger calipers may require a larger master as there is more volume to move about . What reference did you see this being used in a 914, maybe we can read that and follow up.
I guess maybe you need to tell us which larger calipers you are using?
I know that the 911 cars have bigger calipers and they use a bigger master. I belive that is a direct bolt in replacement in the914. you might consider that option if your calipers are simular volume to the 911 ones.
the trick with large calipers is to have a master that move enough volume to move the caliper pistons all the way tight with out running out of master stroke.
the metering of the master is also important, specially if it came off a car that has different types of brakes (disc verse drum)
I guess maybe you need to tell us which larger calipers you are using?
I know that the 911 cars have bigger calipers and they use a bigger master. I belive that is a direct bolt in replacement in the914. you might consider that option if your calipers are simular volume to the 911 ones.
the trick with large calipers is to have a master that move enough volume to move the caliper pistons all the way tight with out running out of master stroke.
the metering of the master is also important, specially if it came off a car that has different types of brakes (disc verse drum)
A real upgrade is the 19mm 911 MC. The real one, NOT the leaky Chinese POS knock off you see on sale for under $100.
it is a little stiffer then the 17mm 914 unit, though only just and you get used to it within the first few miles of driving. And it is considerably cheaper then the 914 unit.
Zach
it is a little stiffer then the 17mm 914 unit, though only just and you get used to it within the first few miles of driving. And it is considerably cheaper then the 914 unit.
Zach
I currently run a 19mm master cylinder with BMW 320i front calipers. The pedal is firm, but the travel is a little more than I would like. I have aquired all of the necessary parts and plumbing to do the Volvo caliper swap, but my problem will only get worse without the proper master cylinder. I know that there is a 23mm Mercedes master cylinder that is suppose to be usable, but requires additonal mods to fit, plus it is a little pricey. I saw on the Pelican forum that someone suggested the bus master cylinder, but didn't give any details. I looked the cylinder up and it does reference a booster application.
My application is a track only (autocross) 914 wtih a 355 small block Chevy. Car weighs about 1875 lbs.
A real upgrade is the 19mm 911 MC. The real one, NOT the leaky Chinese POS knock off you see on sale for under $100.
it is a little stiffer then the 17mm 914 unit, though only just and you get used to it within the first few miles of driving. And it is considerably cheaper then the 914 unit.
Zach
My application is a track only (autocross) 914 wtih a 355 small block Chevy. Car weighs about 1875 lbs.
QUOTE(Vacca Rabite @ Jul 28 2010, 07:44 AM)
A real upgrade is the 19mm 911 MC. The real one, NOT the leaky Chinese POS knock off you see on sale for under $100.
it is a little stiffer then the 17mm 914 unit, though only just and you get used to it within the first few miles of driving. And it is considerably cheaper then the 914 unit.
Zach
QUOTE(stevekh44 @ Jul 28 2010, 02:24 PM)
...I know that there is a 23mm Mercedes master cylinder that is suppose to be usable, but requires additonal mods to fit, plus it is a little pricey.
I paid about $125 for mine from DART in Colorado.
There are at least two flavors of port arrangements - the one I recently bought has the main ports on the opposite side from one I bought 'back in the day' when this was first a popular mod - with 911S aluminum front calipers and standard 914.6 rears.
So you might have to re-run a couple of hard lines - no big deal.
You do need a longer pushrod - easily made from an old cylinder head stud and a couple of minutes grinding a radius on the business end.
'S' caliper 911's originally came with a 13/16" (20,5mm) MC but those have been NLA for a long time.
I run the Mercedes 23mm master cylinder with Wilwood billet front calipers and Carrera rears. The 19mm cylinder didn't move nearly enough fluid to push those calipers. In a few weeks I will replace the rear calipers with two spare Wilwood SuperLite II's just to lose some weight when I replace the 914-6 rear rotors with vented Carrera rotors.
22mm vs 23mm might not sound like much at first, but each mm bigger yields and exponential increase in the area of the piston.
The 22mm is 380 sq mm of area and the 23mm is 415 sq mm
The means the 23mm cylinder moves 8.5% more fluid than the 22, which is quite a lot. It will also add (approximately) 8.5% more pedal resistance, and take 8.5% less pedal travel given the same calipers.
As a comparison the 19mm has a 284 sq mm area, which is 32% less than the 23mm. Essentially that's 1/3 less area/pedal travel. Again, a lot of difference.
The 23mm mods are minor IMHO.
Good luck!
22mm vs 23mm might not sound like much at first, but each mm bigger yields and exponential increase in the area of the piston.
The 22mm is 380 sq mm of area and the 23mm is 415 sq mm
The means the 23mm cylinder moves 8.5% more fluid than the 22, which is quite a lot. It will also add (approximately) 8.5% more pedal resistance, and take 8.5% less pedal travel given the same calipers.
As a comparison the 19mm has a 284 sq mm area, which is 32% less than the 23mm. Essentially that's 1/3 less area/pedal travel. Again, a lot of difference.
The 23mm mods are minor IMHO.
Good luck!
Ron -
I found your posting that had the Mercedes and ATE part numbers. Thanks for posting them. Do you know where I can find the 90º fittings? I think I can get the blue hose from Pelican or Pegasus.
-Steve
I run the Mercedes 23mm master cylinder with Wilwood billet front calipers and Carrera rears. The 19mm cylinder didn't move nearly enough fluid to push those calipers. In a few weeks I will replace the rear calipers with two spare Wilwood SuperLite II's just to lose some weight when I replace the 914-6 rear rotors with vented Carrera rotors.
22mm vs 23mm might not sound like much at first, but each mm bigger yields and exponential increase in the area of the piston.
The 22mm is 380 sq mm of area and the 23mm is 415 sq mm
The means the 23mm cylinder moves 8.5% more fluid than the 22, which is quite a lot. It will also add (approximately) 8.5% more pedal resistance, and take 8.5% less pedal travel given the same calipers.
As a comparison the 19mm has a 284 sq mm area, which is 32% less than the 23mm. Essentially that's 1/3 less area/pedal travel. Again, a lot of difference.
The 23mm mods are minor IMHO.
Good luck!
I found your posting that had the Mercedes and ATE part numbers. Thanks for posting them. Do you know where I can find the 90º fittings? I think I can get the blue hose from Pelican or Pegasus.
-Steve
QUOTE(pcar916 @ Jul 28 2010, 11:45 AM)
I run the Mercedes 23mm master cylinder with Wilwood billet front calipers and Carrera rears. The 19mm cylinder didn't move nearly enough fluid to push those calipers. In a few weeks I will replace the rear calipers with two spare Wilwood SuperLite II's just to lose some weight when I replace the 914-6 rear rotors with vented Carrera rotors.
22mm vs 23mm might not sound like much at first, but each mm bigger yields and exponential increase in the area of the piston.
The 22mm is 380 sq mm of area and the 23mm is 415 sq mm
The means the 23mm cylinder moves 8.5% more fluid than the 22, which is quite a lot. It will also add (approximately) 8.5% more pedal resistance, and take 8.5% less pedal travel given the same calipers.
As a comparison the 19mm has a 284 sq mm area, which is 32% less than the 23mm. Essentially that's 1/3 less area/pedal travel. Again, a lot of difference.
The 23mm mods are minor IMHO.
Good luck!
Rich,
Did you buy the Mercedes MC from DART?
Thanks,
Steve
...I know that there is a 23mm Mercedes master cylinder that is suppose to be usable, but requires additonal mods to fit, plus it is a little pricey.
I paid about $125 for mine from DART in Colorado.
There are at least two flavors of port arrangements - the one I recently bought has the main ports on the opposite side from one I bought 'back in the day' when this was first a popular mod - with 911S aluminum front calipers and standard 914.6 rears.
So you might have to re-run a couple of hard lines - no big deal.
You do need a longer pushrod - easily made from an old cylinder head stud and a couple of minutes grinding a radius on the business end.
'S' caliper 911's originally came with a 13/16" (20,5mm) MC but those have been NLA for a long time.
Did you buy the Mercedes MC from DART?
Thanks,
Steve
QUOTE(ArtechnikA @ Jul 28 2010, 11:12 AM)
QUOTE(stevekh44 @ Jul 28 2010, 02:24 PM)
...I know that there is a 23mm Mercedes master cylinder that is suppose to be usable, but requires additonal mods to fit, plus it is a little pricey.
I paid about $125 for mine from DART in Colorado.
There are at least two flavors of port arrangements - the one I recently bought has the main ports on the opposite side from one I bought 'back in the day' when this was first a popular mod - with 911S aluminum front calipers and standard 914.6 rears.
So you might have to re-run a couple of hard lines - no big deal.
You do need a longer pushrod - easily made from an old cylinder head stud and a couple of minutes grinding a radius on the business end.
'S' caliper 911's originally came with a 13/16" (20,5mm) MC but those have been NLA for a long time.
QUOTE(stevekh44 @ Jul 28 2010, 04:54 PM)
Did you buy the Mercedes MC from DART?
QUOTE(ArtechnikA @ Jul 28 2010, 11:12 AM)
I paid about $125 for mine from DART in Colorado.
yes.
yes.
QUOTE(ArtechnikA @ Jul 28 2010, 12:12 PM)
'S' caliper 911's originally came with a 13/16" (20,5mm) MC but those have been NLA for a long time.
That particular master cylinder isn't in the PET, nor is it in the late '70s IMC catalog. (Gotta throw some of that stuff out!) Furthermore, I've never seen a 911 so equipped, and there've been a bunch of them pass through my service bays over the years.
The Cap'n
QUOTE(Cap'n Krusty @ Jul 28 2010, 06:30 PM)
That particular master cylinder isn't in the PET, nor is it in the late '70s IMC catalog.
I didn't just make it up, so now I've gotta go through the stuff I didn't throw out either and find where I saw it...
I agree it's not in the USA ETKA.
Mighta been a reference in Frère or the ROW ETKA...
Sorry but I haven't needed any in lots of years. But call Rich Bontempi at High Performance House (650-364-6234). He often knows where to get anything I need when I'm stuck.
You might also call V-Craft
http://www.vehiclecraft.com/Brakes/930_upgrade.htm or
Rennsport Systems
http://www.rennsportsystems.com/1-sf.html
and/or SmartRacing
http://www.smartracingproducts.com/
since at least one of them used to sell the kit complete with all fittings and hoses.
Good luck
Ron -
I found your posting that had the Mercedes and ATE part numbers. Thanks for posting them. Do you know where I can find the 90º fittings? I think I can get the blue hose from Pelican or Pegasus.
-Steve
I run the Mercedes 23mm master cylinder with Wilwood billet front calipers and Carrera rears. The 19mm cylinder didn't move nearly enough fluid to push those calipers. In a few weeks I will replace the rear calipers with two spare Wilwood SuperLite II's just to lose some weight when I replace the 914-6 rear rotors with vented Carrera rotors.
22mm vs 23mm might not sound like much at first, but each mm bigger yields and exponential increase in the area of the piston.
The 22mm is 380 sq mm of area and the 23mm is 415 sq mm
The means the 23mm cylinder moves 8.5% more fluid than the 22, which is quite a lot. It will also add (approximately) 8.5% more pedal resistance, and take 8.5% less pedal travel given the same calipers.
As a comparison the 19mm has a 284 sq mm area, which is 32% less than the 23mm. Essentially that's 1/3 less area/pedal travel. Again, a lot of difference.
The 23mm mods are minor IMHO.
Good luck!
You might also call V-Craft
http://www.vehiclecraft.com/Brakes/930_upgrade.htm or
Rennsport Systems
http://www.rennsportsystems.com/1-sf.html
and/or SmartRacing
http://www.smartracingproducts.com/
since at least one of them used to sell the kit complete with all fittings and hoses.
Good luck
QUOTE(stevekh44 @ Jul 28 2010, 12:53 PM)
Ron -
I found your posting that had the Mercedes and ATE part numbers. Thanks for posting them. Do you know where I can find the 90º fittings? I think I can get the blue hose from Pelican or Pegasus.
-Steve
QUOTE(pcar916 @ Jul 28 2010, 11:45 AM)
I run the Mercedes 23mm master cylinder with Wilwood billet front calipers and Carrera rears. The 19mm cylinder didn't move nearly enough fluid to push those calipers. In a few weeks I will replace the rear calipers with two spare Wilwood SuperLite II's just to lose some weight when I replace the 914-6 rear rotors with vented Carrera rotors.
22mm vs 23mm might not sound like much at first, but each mm bigger yields and exponential increase in the area of the piston.
The 22mm is 380 sq mm of area and the 23mm is 415 sq mm
The means the 23mm cylinder moves 8.5% more fluid than the 22, which is quite a lot. It will also add (approximately) 8.5% more pedal resistance, and take 8.5% less pedal travel given the same calipers.
As a comparison the 19mm has a 284 sq mm area, which is 32% less than the 23mm. Essentially that's 1/3 less area/pedal travel. Again, a lot of difference.
The 23mm mods are minor IMHO.
Good luck!
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