VH SLX, Would a V8 master cylinder fit on a 6 cylinder braking system

[Vin999]

Yamaha RD 400 motorcycle

Had to check ... Incase it was Recreational Drugs

 

[Vin999]

RD 400

big difference cars to bikes

 

[Skylarking]

I have experimented with different size MCs and the smaller bore definitely places more pressure on the caliper pistons and pulls you up quicker. The smaller bore also flexs the lines more. The larger bore generally is used on twin piston or more piston calipers. A large bore MC on single piston calipers and standard booster and all else being the same will feel like a rock.

With an OEM setup, for a given brake pedal stroke, you get a given master cylinder stroke, the length of which depends on pedal leverage. Changing the OEM master cylinder to a smaller diameter means that with the given master cylinder stroke, less fluid volume is move compared to the ODM setup. As such you can’t get a higher line pressure than when the OEM master cylinder is used..

Changing and OEM system so that a larger diameter master cylinder is in use will result in a shorted pedal movement for the same braking force which will be interpreted as a wooden pedal.

Either way, your experience doesn’t seem to line up with how I understand it all works.

As is, brake pedal feel and brake control is an interesting subject but these days with ABS/EBD and it’s ilk, designing good peddle feel is becoming less important. It’ll all be electronic braking soon

 

[Skylarking]

big difference cars to bikes

Hydraulic brake theory is exactly the same* for motorbike, motor vehicle, push bike, etc. Unless I’m missing something.

* ignoring proportioning valves

 

[losh1971]

big difference cars to bikes

Happy to be corrected but how can it vary much? I would think the same principle applies? If the MC was identical except bore diam how can a smaller diam one not be higher pressure like it is on a bike? Are the car ones operating in some different way, asides from the booster?

 

[losh1971]

Hydraulic brake theory is exactly the same* for motorbike, motor vehicle, push bike, etc. Unless I’m missing something.

* ignoring proportioning valves

clearly it can not be because on a bike if you run a smaller diam MC your brakes will pull up a lot harder. I have tried it and plenty of other blokes that race use smaller MCs to increase the pressure on the pads. My bike mech runs one off a dirt bike which are really small but the force is far greater than mine and he uses the same calipers as me.

 

[Skylarking]

clearly it can not be because on a bike if you run a smaller diam MC your brakes will pull up a lot harder. I have tried it and plenty of other blokes that race use smaller MCs to increase the pressure on the pads. My bike mech runs one off a dirt bike which are really small but the force is far greater than mine and he uses the same calipers as me.

It just doesn’t make sense what you say as changing to a smaller mc must result in less fluid being sent to the caliper for a given movement of your bike brake lever. As such, less fluid to the caliper means less movement of the pads. How can that create more line pressure?

If what you say is true, taking it to the absurd and going to a smaller and smaller mc means less and less pad movement. So at some point you’ll pull the hand lever until it hits the handle bar and the pads wouldn’t have appreciably moved. How much would line pressure be then?

OOPS

Ok, I should have remembered my pascals law from years ago... Obviously fluid is incompressible and force is transferred in all areas of the fluid. With MC and calliper being where the force escapes, it’s all proportional to area where F1/A1 = F2/A2 in a simple two piston system.

So is mc is 1” and calliper is 2” then applying a 100N of force to the MC will result in 200N of force at the calliper. Subsequently replacing the MC with one of diameter 0.5” with the same 100N force will result in calliper force of 400N.

So smaller diameter master increases force at the calliper BUT volume pushed to the calliper is reduced. Volume is proportional to the square of the diameter so has a big impact. Unless fluid volume pushed into calliper is appropriate for the required operational movement, the calliper piston will run out of stroke.

This just highlights that some deep understanding is required when playing with brakes and probably why it’s a good idea things are engineered when modified from OEM.

 

[losh1971]

Obviously there is a limit but when I run the 9/16 MC it pulled me up quicker than the 5/8. Some go as low as 1/2 but that would be about as low as you would go. Yes there is less fluid but volume doesn't equal pressure on a bike at least. Now i have no idea how the science works., so i can't explain how it works.

 

[Skylarking]

Obviously there is a limit but when I run the 9/16 MC it pulled me up quicker than the 5/8. Some go as low as 1/2 but that would be about as low as you would go. Yes there is less fluid but volume doesn't equal pressure on a bike at least. Now i have no idea how the science works., so i can't explain how it works.

I updated my post above... explains the principle which I misunderstood/forgot/got too old...

 

[Fu Manchu]

I've had all combinations on my VC...single diaphram booster, with both M/C's and double diaphram booster with both M/C's....

The only difference is the bolt positioning on the strut tower.....The bracket is identical, however if you change the booster from one to the other, from what was originally fitted, you'd have to modify the bracket to suit

I got the bracket from the wrecker when I got the booster.

I think the different flares on the brake pipes was more due to a change is design, I think series 2 VP? So pre that would be fine?
Someone mentioned the different rod length. That jogged my memory. I can't remember if I was able to adjust the length or if there was something I did by putting something down the hole of the booster?

This goes back 20 years ago, so I'm rusty on the details. I liked the end result. A few years before I sold the car I put VZ brakes on too.

Overall, the job was straight forward to do, not too time consuming and @OP should go for it.