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  1. #21
    Join Date
    Mar 2019
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    Sevenoaks
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    124
    The 2 pauls. Paul Bannister was making the notes
    Quote Originally Posted by V8 BCC View Post
    Who did you have at the testing station Jules?
    AK Cobra started 06/19
    Chevy 383 Stroker, TKO 600
    See my build on instagram: Julesdm14

  2. #22
    Join Date
    May 2004
    Location
    Cowbridge, United Kingdom
    Age
    62
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    10,102
    I may be completely wrong (it has been known, ask the wife) but surely fitting a limiting valve in the front brakes is going to exacerbate the problem not cure cure it?
    The fronts must lock up first or it's a fail and can be dangerous.
    I get the logic about the weight transfer though.
    Main stream manufactures have always fitted them in the rear circuit for a reason.
    So unless your choice of brake size front to rear is completely out of balance I'd go that way.
    Kev Davies
    South Wales Area Rep. UKCC Membership Secretary
    DAX Mk4, 383 Chevy Stroker, Tremec. SOLD
    Contemporary CCX 3-4028, 445ci Big Block FORD FE,TKO 600, Old School IVA'd and SOLD
    Dax De Dion LS2 and T56 IVA'd June '17 SOLD
    1965 Ford Mustang 289 Convertible SOLD
    In build- Hawk 289 Sebring Awaiting IVA

  3. #23
    Join Date
    Jan 2006
    Location
    Chelmsford Essex
    Posts
    1,366
    The reason why you need the brake pipes going to the correct location is clearly explained in the video for tandem master cylinders. Circuit one will operation at a different stage of pedal pressure to circuit 2 allowing a two stage operation. The reason why the correct front and rear section pipes need to be run to the correct port on the master cylinder.

    https://www.youtube.com/watch?v=Xk2zGvKfrhc
    Dax 351 Cleveland T5 2.88 PL

  4. #24
    Join Date
    Jul 2012
    Location
    NW England
    Posts
    526
    Quote Originally Posted by jon1d View Post
    The reason why you need the brake pipes going to the correct location is clearly explained in the video for tandem master cylinders. Circuit one will operation at a different stage of pedal pressure to circuit 2 allowing a two stage operation. The reason why the correct front and rear section pipes need to be run to the correct port on the master cylinder.

    https://www.youtube.com/watch?v=Xk2zGvKfrhc
    Staged? I don't see any mention of that.
    Lets apply a bit of logic. As soon as you get any pressure in the rear chamber it will be applied to the front piston (and with that spring in there you don't even need any hydraulic pressure). You may get a very small initial braking force to the line attached to the rear port but it is going to be negligable and gone long before enough pressure is developed to lock any wheels. Once any significant pressure is developed (and the ports to the reservoirs closed) pressure will be equal in both cylinders. There is also a possiblity with the assembly shown in the video that the rear cylinder will develope more hydraulic pressure due to the rod down the centre reducing the piston diameter. The same force will be applied to both pistons but the effective area is different, not clear where that rod goes so can't tell for sure, in any case I don't believe that is the case in my Jag master.

  5. #25
    Join Date
    Oct 2017
    Location
    Oxford
    Posts
    932
    Quote Originally Posted by Julesdm View Post
    Ben i followed you the day after!!
    They managed to break my xjs handbrake lever and the rears locked up first. On my car i have been told to inflate the fronts to 62psi and drop rears to 20psi. Booked the re test in a week and we shall see. Off to put some miles on teh brakes tomorrow weather dependant.
    Are you sure those proposed tyre pressures are the correct way round?
    Can you explain the reasoning for that?
    Happy to be corrected!
    Classic Replica Viper currently in build

  6. #26
    Join Date
    Jan 2006
    Location
    Chelmsford Essex
    Posts
    1,366
    I think that is 26psi lol .
    Dax 351 Cleveland T5 2.88 PL

  7. #27
    Join Date
    Jan 2006
    Location
    Chelmsford Essex
    Posts
    1,366
    Quote Originally Posted by GDCobra View Post
    Staged? I don't see any mention of that.
    Lets apply a bit of logic. As soon as you get any pressure in the rear chamber it will be applied to the front piston (and with that spring in there you don't even need any hydraulic pressure). You may get a very small initial braking force to the line attached to the rear port but it is going to be negligible and gone long before enough pressure is developed to lock any wheels. Once any significant pressure is developed (and the ports to the reservoirs closed) pressure will be equal in both cylinders. There is also a possibility with the assembly shown in the video that the rear cylinder will develop more hydraulic pressure due to the rod down the centre reducing the piston diameter. The same force will be applied to both pistons but the effective area is different, not clear where that rod goes so can't tell for sure, in any case I don't believe that is the case in my Jag master.
    At 1.29 into the video clearly states the second cylinder comes into operation as the two open holes to the reservoir are closed at different stages so pressure is applied at different times depending of the stroke of the piston. This allows a delay for front to back braking so the feeds need to go to the correct port. The original question has a Marina Master cylinder.
    Dax 351 Cleveland T5 2.88 PL

  8. #28
    Join Date
    Mar 2019
    Location
    Sevenoaks
    Posts
    124
    correct, the fronts will have less contact with the road surface and thus less friction the rears will have more in contact and thus will grip harder......leading to the fronts locking up first and the rears following......thats the theory.
    Quote Originally Posted by KugaWestie View Post
    Are you sure those proposed tyre pressures are the correct way round?
    Can you explain the reasoning for that?
    Happy to be corrected!
    AK Cobra started 06/19
    Chevy 383 Stroker, TKO 600
    See my build on instagram: Julesdm14

  9. #29
    Join Date
    Jul 2012
    Location
    NW England
    Posts
    526
    Quote Originally Posted by jon1d View Post
    At 1.29 into the video clearly states the second cylinder comes into operation as the two open holes to the reservoir are closed at different stages so pressure is applied at different times depending of the stroke of the piston. This allows a delay for front to back braking so the feeds need to go to the correct port. The original question has a Marina Master cylinder.

    But he makes no mention of it being 'staged' or importance of which line goes where. Just think of what happens.
    Force applied to the pedal starts to move the rear piston.
    No pressure will build up in this line until the port to the reservoir is covered, reduction in volume will simply push fluid back to the reservoir.
    As the port becomes covered the fluid in front of the rear piston (which is uncompressible) will move, some will attempt to move down the line to the caliper, some will try to move wth piston in front of it.
    Motion will occur wherever there is least resistance with the stiction of caliper pistons or the forward master cylinder piston.
    Pressure will only build once motion stops (pads touching discs) and it will equalise in both cylindere.

    Depending on which parts of the system exhibit the most resitance to movement you may get one set of caliper pistons moving before the other but my 50p would say that (on a properly working system) the master cylinder pistons will have less resistance to motion than the caliper pistons. That is irrelevant though because even if you did have the caliper pistons moving first they would stop on contact with the disc and then the pressures will equalise.

    If you really think this amount of pressure would result in the rear brakes locking the wheels before the fronts apply (or vice versa) then fair enough but I'd suggest there was a problem somewhere if so.

    Please poke a hole in my logic if there is one, I'm always happy to learn, but not by saying Mr/Mrs X on YouTube says so therefore it must be right.

    On mine both lines are on QR couplings so I can swap the front & rear connections without any disassembly of the system, loss of fluid or need to bleed the system have done so several times and have not noticed one jot of difference to the behaviour.

  10. #30
    Join Date
    Aug 2004
    Location
    Christchurch, NZ
    Age
    59
    Posts
    2,441
    Agreed, the closing of one or the other port first would have negligable effect.
    Cheers

    Myles D-W

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