renault 15 brakes
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  1. #1
    Tadpole
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    Default renault 15 brakes

    heyy...

    some of you may remember a post a month ago in relation to trouble with a renault 15's brakes.

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    the proportioning valve has been replaced. the master has been resleeved and rekitted.

    yet the pedal is still too soft and the rear brakes lock very easily. if i move the little arm (with the spring) away from the valve so that it isnt exerting pressure, the brakes appear normal.


    ideas?

  2. #2
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    Sounds like the previous owner may have adjusted the brake valve to suit their particular driving style, or the suspension ride height has altered (or been changed with different springs) which will affect the the settings of the arm which actuates the proportioning valve.

    Try adjusting the threaded rod which actuates the arm operating the proportioning valve to see if that limits the pressure that is going to the rear brakes. To do it properly may require taking the car to a brake specialist so they can accurately measure the pressure going to the rear brakes.

  3. #3
    Tadpole
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    hello,

    i thought about this... but, the pressure on the valve is not from the arm, but from the little lever and its spring....

    is there a special bleeding procedure or will the normal way suffice?



    Quote Originally Posted by Simon
    Sounds like the previous owner may have adjusted the brake valve to suit their particular driving style, or the suspension ride height has altered (or been changed with different springs) which will affect the the settings of the arm which actuates the proportioning valve.

    Try adjusting the threaded rod which actuates the arm operating the proportioning valve to see if that limits the pressure that is going to the rear brakes. To do it properly may require taking the car to a brake specialist so they can accurately measure the pressure going to the rear brakes.

  4. #4
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    When the car is on the ground though the arm presses on the lever. As the rear end of the car rises under braking, the pressure on the lever by the arm is reduced. I'm wondering if the arm has been bent or adjusted so that it no longer contacts the spring under braking? Perhaps the spring has gone soft, but I've never heard of that happening before.

    As far as I know the proportioning valves for that type (early 12/AUS spec 15/17) are all the same but I'll check my info to be sure.

    I've never had problems bleeding brakes before, in other than the normal way (starting with LHR, RHR, LHF, RHF). How long had the car been standing before you refurbished it or did you just rebuild all the brakes? Is the servo functioning correctly?

  5. #5
    Tadpole
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    hi there,

    thanks.. understood, but the problem is that there is too much pressure from the spring. when i unhook it, so that the piston in the valve is able to withdraw, the pedal feels normal.

    the brakes were bled with the car on the ground, not jacked up.

    with the spring and small relay lever in place, the rear brakes lock up prematurely and there is excessive pedal travel.

    this is so with engine on or off, so doubt there is an issue with the servo.




    Quote Originally Posted by Simon
    When the car is on the ground though the arm presses on the lever. As the rear end of the car rises under braking, the pressure on the lever by the arm is reduced. I'm wondering if the arm has been bent or adjusted so that it no longer contacts the spring under braking? Perhaps the spring has gone soft, but I've never heard of that happening before.

    As far as I know the proportioning valves for that type (early 12/AUS spec 15/17) are all the same but I'll check my info to be sure.

    I've never had problems bleeding brakes before, in other than the normal way (starting with LHR, RHR, LHF, RHF). How long had the car been standing before you refurbished it or did you just rebuild all the brakes? Is the servo functioning correctly?

  6. #6
    Simon's Avatar
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    Quote Originally Posted by mb300sel
    hi there,

    thanks.. understood, but the problem is that there is too much pressure from the spring. when i unhook it, so that the piston in the valve is able to withdraw, the pedal feels normal.
    Do you unhook the spring with the wheels on the ground or wheels off the ground??

    If wheels are on the ground there is likely too much clearance between the arm and the lever. If there is contact it is likely the arm is out of adjustment, and not pressing on the lever sufficiently while the car is braking. Or the car has raised springs in the rear.

    What are the rear brake linings like? This could also be the problem with excessive pedal travel, out of adjustment or self adjusters not operating.

  7. #7
    Tadpole
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    on the ground, i unhook the spring, and all appears normal.

    it doesn't appear to be an issue with the rod (it isnt touching the lever when car is on the ground)... unless this is indicative of problems elsewhere.

    i haven't had the drums off, but as the rear wheels lock very easily when the lever and spring are in place, i took it to mean all is in order.

    i will look, though.




    Quote Originally Posted by Simon
    Do you unhook the spring with the wheels on the ground or wheels off the ground??

    If wheels are on the ground there is likely too much clearance between the arm and the lever. If there is contact it is likely the arm is out of adjustment, and not pressing on the lever sufficiently while the car is braking. Or the car has raised springs in the rear.

    What are the rear brake linings like? This could also be the problem with excessive pedal travel, out of adjustment or self adjusters not operating.

  8. #8
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    I can't remember the full details of your last thread, but what's the state of the front calipers? The reason I ask is that, if you're getting limited actuation of the front brakes (say, the pistons are siezed or stiff) you'd need to stand on the brakes more to stop, giving full pressure to the rears. The rears would then lock because you wouldn't be getting any help from the fronts. What's the braking performance like generally?

    Stuey

  9. #9
    Member Freddie's Avatar
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    The manual clearly shows that the pressure regulator must be set using a pressure guage inserted into the rear line near brake cylinder. My 17 also locks up rears at very slow speed light load and heavy braking (but usually on on dirt or wet road) - the rear of the car will lift substantially hence almost no load on rear wheels

    Pedal travel id "normal" and fronts pull car up well - I'd check hoses again under pressure

  10. #10
    Tadpole
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    hello,

    unsure of the state of the fronts, but though they may be poor, causing the rears to actuate prematurely, wouldn't there be a decent pedal? this is almost to the floor.

    i have a feeling that the new valve may be dodgy. a month ago, when i last looked at it, i found the rear valve to be stuck. i freed it, and braking seemed perfect .




    Quote Originally Posted by Stuey
    I can't remember the full details of your last thread, but what's the state of the front calipers? The reason I ask is that, if you're getting limited actuation of the front brakes (say, the pistons are siezed or stiff) you'd need to stand on the brakes more to stop, giving full pressure to the rears. The rears would then lock because you wouldn't be getting any help from the fronts. What's the braking performance like generally?

    Stuey

  11. #11
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    Hi again,

    That could simply be adjustment of the rear shoes as Simon said above, especially if the pedal is reasonably hard but just long in travel.

    Although the valve pressure is meant to be set with a pressure gauge inserted into the circuit, it can also be set by trial and error. Essentially, you want the front to lock first, but only just first, so the rears are getting enough pressure to be effective. It's easier to set up on a wet (deserted) road.

    For what it's worth, I've just looked under my R12 (very similar system) and the rod has about 8mm clearance from the lever that touches the piston. However, it has higher-set springs in the rear. The brakes on mine are about as good as you could get on a stock 12 (and I know because I have them on the limit regularly). They're actually pretty good. Oh, and I very rarely lock the rears.

    Finally, I wonder if the non-return valve in the master cylinder outlet to the discs is intact? This keeps the pads up to the discs. I'm sure the R15 has this - Simon can you confirm? This might give you excess travel, but won't explain the locking rears.

    Stuey
    Last edited by Stuey; 19th August 2004 at 08:55 PM.

  12. #12
    Fellow Frogger!
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    Default brakes

    If your rear linings are down, or not of the correct radius, you will get a long pedal, if your linings are wet, they will grab, have you had the drums ofF?
    regards, Fish.

  13. #13
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    Quote Originally Posted by Stuey
    Hi again,

    Finally, I wonder if the non-return valve in the master cylinder outlet to the discs is intact? This keeps the pads up to the discs. I'm sure the R15 has this - Simon can you confirm? This might give you excess travel, but won't explain the locking rears.

    Stuey
    Yep, the brake systems of the 12 and 15 are virtually identical apart from a larger master cylinder diameter on the 15 and the smaller rear drums on the sedan 12.

  14. #14
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    OK, so there's a non-return valve in the outlet to the front brakes, underneath the brass cone that the pipe seals against. Some brake places don't replace this. It's like a reed valve that holds residual pressure in the front brakes to keep the pads close to the disc and reduce pedal travel.

    Stuey

  15. #15
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    Quote Originally Posted by Stuey
    For what it's worth, I've just looked under my R12 (very similar system) and the rod has about 8mm clearance from the lever that touches the piston. However, it has higher-set springs in the rear. The brakes on mine are about as good as you could get on a stock 12 (and I know because I have them on the limit regularly). They're actually pretty good. Oh, and I very rarely lock the rears.

    I remember the Brakes on my old 12 could almost stand the bugger on its end (or maybe that was just the soft suspension) and yes VERY hard to lock up the brakes unless you were really punting hard and braking hard while entering a corner

    mb300sel, how many clicks does your handbrake have, I too would be thinking poor rear brake adjustment or perhaps a worn middle seal in the master cylinder...This will not result in a leak, but will result in a long pedal...

  16. #16
    Fellow Frogger!
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    Default brakes

    can also get problems if the 15ts has has a 16ts master cyl fitted, they have different bores, but the drums need to come off 1st

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