maok Posted November 20, 2017 Share Posted November 20, 2017 Has been leaking ever so slightly from the boot (which was just staying together) and finally have had a chance to investigate. There was lots of grime and old hard oil inside the boot (probably from the tail shaft boot spraying the grease around the general area) and in the cylinder. I thought I would post these pics of the Australian version of the master cylinder for you LHD'ers The angle at which ours are mounted on the right hand side chassis rail. 1 Link to comment Share on other sites More sharing options...
maok Posted November 22, 2017 Author Share Posted November 22, 2017 The location where it bolts on to; Link to comment Share on other sites More sharing options...
lozrocks Posted November 22, 2017 Share Posted November 22, 2017 Are new boots and seals available? Link to comment Share on other sites More sharing options...
maok Posted November 22, 2017 Author Share Posted November 22, 2017 My local master cylinder re-sleever had them in stock. The bore was in good shape, it is huge at 1 5/8". Cleaned up well with some tooth paste. It is going to be a challenge to find a modern dual circuit equivalent to replace in the future. Link to comment Share on other sites More sharing options...
lozrocks Posted November 23, 2017 Share Posted November 23, 2017 Pre internet days I replaced my master cylinder (Chrysler 75) with a dual circuit unit from a HQ Holden. It's working a treat. Bore is only 1 inch but she will lock up all 4 wheels without too much problem. Hardest part will be setting it up to get the master cylinder level. Link to comment Share on other sites More sharing options...
maok Posted November 23, 2017 Author Share Posted November 23, 2017 (edited) I would have thought that a regular car master cylinder would not pump enough brake fluid to work with our cars, especially due to the bore size of the MC and the larger diameter of the copper pipes to the wheel cylinders in relation to a modern car brake lines. Was/is your master cylinder similar setup to mine? Edited November 29, 2017 by maok spelling (see edit history) Link to comment Share on other sites More sharing options...
Spinneyhill Posted November 23, 2017 Share Posted November 23, 2017 You only need to pump enough fluid to move the shoes about 0.012" if they are set up correctly. The size of the lines doesn't matter, it is the size of the wheel cylinders that matters, coz that is the required volume of fluid: piston area x 0.012" x 2 per cylinder = 0.5 ml per cylinder, about a tenth of a teaspoon for a 1.25" dia. wheel cylinder. (hope I have got the units right!). So for four wheels, less than half a teaspoon of fluid is pumped to activate the brakes. Yes the master cylinder piston goes a bit further because it is smaller in diameter. Link to comment Share on other sites More sharing options...
lozrocks Posted November 24, 2017 Share Posted November 24, 2017 21 hours ago, maok said: I would have thought that a regular car master cylinder would not pump enough brake fluid to work with our cars, especially due to the bore size of the MC and the larger diameter of the copper pipes to the wheel cylinders in relation to a modern car brake lines. Was/is your master cylinder similar setup to my? Set up is totally different. Plus I think the 62 has external brakes doesn't it? So the slave cylinders actually travel a bit further. The 75 master cylinder sits at about 20 degrees to the horizontal with internally expanding brakes. Yours appears to be about 45 degrees. Link to comment Share on other sites More sharing options...
maok Posted November 24, 2017 Author Share Posted November 24, 2017 7 hours ago, lozrocks said: Set up is totally different. Plus I think the 62 has external brakes doesn't it? So the slave cylinders actually travel a bit further. The 75 master cylinder sits at about 20 degrees to the horizontal with internally expanding brakes. Yours appears to be about 45 degrees. Exactly right there Lozrocks. I have found a master cylinder from a '80s Isuzu truck that may work with not too much trouble. Has a 1 5/8" bore as well and could easily be mount from the side at 45o angle. http://www.ebay.com.au/itm/New-Genuine-PROTEX-Brake-Master-Cylinder-For-ISUZU-SCR480-SCR480-2D-Truck-4X2/122320422570?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649 Link to comment Share on other sites More sharing options...
maok Posted November 24, 2017 Author Share Posted November 24, 2017 On 11/23/2017 at 7:19 PM, Spinneyhill said: You only need to pump enough fluid to move the shoes about 0.012" if they are set up correctly. The size of the lines doesn't matter, it is the size of the wheel cylinders that matters, coz that is the required volume of fluid: piston area x 0.012" x 2 per cylinder = 0.5 ml per cylinder, about a tenth of a teaspoon for a 1.25" dia. wheel cylinder. (hope I have got the units right!). So for four wheels, less than half a teaspoon of fluid is pumped to activate the brakes. Yes the master cylinder piston goes a bit further because it is smaller in diameter. The wheels cylinders on the '28 Chryslers push a fulcrum to apply the brake bands and hence have a fair bit of movement. Link to comment Share on other sites More sharing options...
lozrocks Posted November 25, 2017 Share Posted November 25, 2017 Does the truck master cylinder need to sit horizontal? I'm not an expert on brakes. But, if you split the system you won't need the same size bore master cylinder. Bear in mind that there are essentially two pistons inside the split MC. I'd be dropping down to 1 1/8 or 1 1/4 bore for the MC. Link to comment Share on other sites More sharing options...
maok Posted November 27, 2017 Author Share Posted November 27, 2017 On 11/25/2017 at 6:19 PM, lozrocks said: Does the truck master cylinder need to sit horizontal? I'm not an expert on brakes. But, if you split the system you won't need the same size bore master cylinder. Bear in mind that there are essentially two pistons inside the split MC. I'd be dropping down to 1 1/8 or 1 1/4 bore for the MC. I'm not sure about needing to be mounted horizontal, it does look like it has remote reservoir setup. Unfortunately I cant seem to find much information on it. You are probably right about that it doesn't need to be the same bore size due to the two pistons but I don't think it will hurt to have the large bore size. Just means there will be less foot pedal movement to get full braking. Link to comment Share on other sites More sharing options...
Spinneyhill Posted November 28, 2017 Share Posted November 28, 2017 22 hours ago, maok said: there will be less foot pedal movement to get full braking. It think it also means there will be more pedal force required to get the same pressure in the fluid. 1 Link to comment Share on other sites More sharing options...
maok Posted December 2, 2017 Author Share Posted December 2, 2017 On 11/29/2017 at 5:19 AM, Spinneyhill said: It think it also means there will be more pedal force required to get the same pressure in the fluid. I would have thought the force required would be dependent on the friction required at the brake bands.What happens in between would not matter, unless there is a leverage involved. Link to comment Share on other sites More sharing options...
Spinneyhill Posted December 3, 2017 Share Posted December 3, 2017 19 hours ago, maok said: What happens in between would not matter, unless there is a leverage involved. There's the rub. It does matter. Pedal force is converted to pressure in the fluid (pedal force / piston area = pressure in the brake fluid in the master cylinder). The pressure in the fluid is converted back into force at the wheel cylinder ( force = pressure x area of wheel cylinder piston). In the course of slowing the vehicle, this force (and the work it does in moving the piston and the brake shoes) is converted to heat on the brake drum and dissipated to the surroundings. You will note the difference in piston sizes in master and wheel cylinders. The force exerted at the wheel cylinder is thus related to the force at the master cylinder by (wheel cylinder force) = (pedal force) x (wheel piston area / master piston area). The force applied to the brake shoes (band) on your vehicle is the wheel cylinder force modified by the levers the pistons operate. Link to comment Share on other sites More sharing options...
maok Posted December 3, 2017 Author Share Posted December 3, 2017 The below is a pic of the two systems as a schematic, I have just indicated an arbitrary force required; Link to comment Share on other sites More sharing options...
Spinneyhill Posted December 4, 2017 Share Posted December 4, 2017 I thought dual circuit brakes had one circuit on the front and one on the rear. If one fails as you have it you will veer off or across the road, i.e. it will pull towards the operating side = possible serious trouble. Link to comment Share on other sites More sharing options...
Bloo Posted December 4, 2017 Share Posted December 4, 2017 5 minutes ago, Spinneyhill said: I thought dual circuit brakes had one circuit on the front and one on the rear. If one fails as you have it you will veer off or across the road, i.e. it will pull towards the operating side = possible serious trouble This is correct. Rear wheeled vehicles are split front-to-back and front wheel drive vehicles are split diagonally. I suspect that was just an example of the distribution of force, and not advice on how to hook things up. Link to comment Share on other sites More sharing options...
Spinneyhill Posted December 4, 2017 Share Posted December 4, 2017 33 minutes ago, Bloo said: front wheel drive vehicles are split diagonally. I am surprised by this. It will still pull quite badly towards the operating front side because there is 25% or so more braking effort at the front wheels. Still, something new for today and it is only breakfast time! Link to comment Share on other sites More sharing options...
Bloo Posted December 4, 2017 Share Posted December 4, 2017 It surprised me too the first time I saw it. It does pull. The trouble with a front to back split is that if the fronts are the ones that fail, the rears aren't really worth much if you need to stop.. I think this would be even worse on a front wheel drive car. Link to comment Share on other sites More sharing options...
maok Posted December 4, 2017 Author Share Posted December 4, 2017 Yes, it was just an example of the distribution. The existing setup is left/right and not front/back. Regardless, if there is a major leak anywhere - no brakes. If I was to go for a dual circuit MC I will change the piping so it is front/back setup. Link to comment Share on other sites More sharing options...
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