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  • Eric S
    replied
    I finally got the car out in the street. It brakes but I am sure it can be better. I drove at about 50 Mph and it stopped well although not as good as with the OEM master cylinder and booster !
    I talked to MBM and it looks like they can't give out any information, probably they fear to be sued in case of an accident ! I don't know but there is no way to get replies as to the questions I asked regarding expected pressure.
    So in the end they preferred to send the 1" master cylinder they should have sent at first so I will try it when received !
    From their chart, going from 1" 1/8 to 1", I estimated I could get from 700 to 900 Psi.

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  • Eric S
    replied
    John
    I read somewhere that the master cylinder cover was to be off and as we need to check and top the fluid level while bleeding I thought it was more convenient to have it opened.
    But anyway, I have been told the master cylinder's piston was not supposed to push inside the reservoir so I may have something wrong there.

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  • jopizz
    replied
    Originally posted by Eric S View Post
    Another concern I have is when we bled the brakes, with cover off, the front reservoir was making a geyser out. Should you press the pedal fast it might have gone 1-2 feet high so we pressed gently.
    I don't think this is normal.
    Why are you bleeding the brakes with the cover off? The only time the cover should be off is when you are bleeding the master cylinder and then you should have hoses from the outlet ports going back into the master cylinder. The brake lines should be disconnected.

    John

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  • Eric S
    replied
    Hi Terry
    I had the tool but it came with no manual !
    I had everything apart so I checked the ports as you said and it was fine, everything was in line (I had the master cylinder open) to measure.
    Then I checked pressure at the master cylinder, 710 Psi front and rear.
    I checked out of the proportionning valve and it was same.
    I connected the wheels and rather than testing at the wheels I tested the car in my yard and it was breaking MUCH better and I was able to lock rear wheels with max pression on the pedal (2 feet) from +/-20Mph.
    Now MBM says 450-500 Psi here : http://mbmbrakes.com/how-to-diagnose-a-problem/

    MBM's tech said "When there is a 100 lb. load on the brake pedal, there is 805 psi for drum/drum and 1025 psi for disc/drum."
    So either the 1" 1/8 master cylinder is too small and they will have to send the correct 1" but I would like to give it a gentle road test around the block to see how it works in real life (with cautious of course)
    Pressure seems low but seems to brake.
    Another concern I have is when we bled the brakes, with cover off, the front reservoir was making a geyser out. Should you press the pedal fast it might have gone 1-2 feet high so we pressed gently.
    I don't think this is normal.
    Last edited by Eric S; June 7th, 2020, 12:22 PM.

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  • BEVS BIRD
    replied
    Hi Eric..sorry for late reply...I hardly ever come to this site any more. 19 inches of eng vac is GOOD..and as long as you get some flow from each reservoir compensation port, you shd be OK......Pressure at FRONT caliper MUST be 1000PSI ...or more.... with a full on panic type application of the brake pedal...and around 600 PSI at REAR brk cylinders....Try with eng running as well as off. you only need to CHECK WHEEL PRESSURES FIRST, then, if pressures low, decide your next action..[ HARD PEDAL LOW PRESS probable master cyl bore size OR SOFT SPONGY PEDAL LOW PRESSURE probable air in system }.both FRONT calipers shd be the same...... and the REAR cylinders shd equal each other as well. if you find that all pressures are low, with good pedal travel and hard pedal I would suspect incorrect master cyl bore size OR TOO SMALL BOOSTER OR BOTH??. you DO NOT REMOVE combination valve from the system to check the pressure at wheels. ... I don't know if you researched "compensating Ports, master cylinder.." this will give you a ton of good info regarding your master cyl operation, and probable causes of front brakes coming on by themselves....good info to know when doing a disc brake conversion. Good luck Those pressure guages never lie.....they will tell you if the system is working or not. CHEERS TERRY
    Last edited by BEVS BIRD; May 16th, 2020, 09:54 PM.

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  • Eric S
    replied
    Well again no news from MBM.
    I am getting a pressure testing equipment designed to check pressure at the wheels. I hope to be able to test pressure at the master cylinder, proportionniung valve and wheels.
    What kind of pressure am I expecting there?
    Probably the manual that comes with the tool will say that but it's not here yet.

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  • Eric S
    replied
    Made thorough testing today.
    I realised I have a vaccum gage in my tools, Vacuum is 19+ at idle.

    Now as you advised Terry, I checked for Dot flow in the master cylinder reservoir when pedal was pressed.
    I assume in normal use liquid is driven from reservoir to the lines when pedal is pressed. Then when pedal is released, liquid comes back in reservoir.
    BUT, when I PRESSED the pedal the liquid blow off (reaching above the top of the reservoir with a gentle soft press) from the front lines port in the reservoir and much less but a little bit from the rear line reservoir.
    I did not saw the piston passing the holes. I was alone and tried to film with my phone. Image was bright and clear but the first pedal press pushed Dot5 on my phone !
    Earlier I opened the master cylinder to clean as I was converting to Dot5 and I may have put something backward (or it came backward and reinstalled it the same way !?)
    I guess that the master cylinder is working backward.

    Your thoughts?

    Edit : opened the master cylinder and there is nothing that can be put backward; Position of the parts relative to the ports seems good. I sent a bunch of pictures to MBM for their advice.
    Last edited by Eric S; May 2nd, 2020, 02:17 PM.

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  • BEVS BIRD
    replied
    Hi Eric....you can easily check your pedal travel in the master cyl as I mentioned in an earlier post....Remove m/cyl cover.....have someone move the brake pedal slowly through it's full travel , up and down...You can look into the reservoir, down thru the fluid and see the compensation ports. SMALL HOLES IN THE BOTTOM OF BOTH RESERVOIRS.........you can see the piston move back and forth.....as the piston covers/uncovers the ports you SHOULD see fluid flow into the reservoir, from this port....you shd see it in both the front and rear reservoir. ....if you see this....it indicates the pedal travel and proper relationship to the Master cyl is good. you really should look up Compensation ports, Master Cylinder...This is VERY GOOD INFO that explains a lot about master cyl operation. also Jopizz is correct on some Combo valves...Make sure you look up YOUR SPECIFIC VALVE, for the proper procedure.. Stay healthy, we are good here { so far} in the interior of BC Canada..CHEERS TERRY

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  • Eric S
    replied
    Terry

    I will check with this combination valve bleeding. Jopizz said here that this valve do not need any special attention to be bled : When you bleed the brakes after everything is back together that will bleed the proportioning valve.
    Booster is 8", MBM brakes also said that the pedal ratio at 6+ should overcome the size difference (1" Vs 1.125")
    Vaccuum has been plugged using the same hose the original set up (that did worked) used.
    Looking forward to read further from MBM and will check how the pedal goes with master cylinder removed from the booster. So I can make sure nothing prevent the pedal from moving !?

    Thank you for your help so far Terry.
    (Forums are quiet these days, everybody is stuck at home worldwide, I was expecting a surge in messages but all forums are quiet... Probably some garages/houses/gardens are being attended at (my case !))

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  • BEVS BIRD
    replied
    Hi Eric ....I see you have had some good suggestions on this problem ...I would put a press guage on the front Caliper AND rear brake cyls. {adaptors screw into bleeder screw ports } You must have around 1000 psi at the caliper to lock up Disc brakes..{Full pedal pressure applied} ..A pressure guage kit is about 60 to 80 bucks from a parts house....with the amount of trouble you have had , this would be a good investment.{.then you can loan it to a friend, and never see it again.}.......The rear brks lock at 600 psi....The Combination valve controls the press difference front to back...if you are using a GM style combo valve it must be bled with the PIN under the rubber cover plug HELD IN. A two person job,,, Or you must use a tool that screws into the electrical warning light port on the top....Easier to see a better explanation if you go online and read about Combination Valves. how to bleed...I dont know the diameter of the booster you are using, it must be at least 8 to 9 inches, double diaphram booster , to work properly with around 16 to 18 inches of eng vaccuum.. and of course you must be taking the vacuum from a separate port in the intake manifold, or full vac port on the carb..Hope this helps you.....A custom brake setup can be apain, as you are finding out...I think a 1.125 master cyl would be ok . with your pedal ratio, if the Booster is sized ok with good vacuum....BUT...the brake pressures will tell you for sure.The brake pressure check NEVER LIES ...CHEERS TERRY

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  • Eric S
    replied
    Hi Terry
    I finally just made it out to measure my stock pedal. It is 33/5cm for a 6.6 ratio. MBM Brakes asks for 1:6 on power brakes.
    I can confirm it's tricky to measure the pedal in place !
    MBM made a mistake and sent a 1.125" M/C. I told them 2 times and they overlooked it and sent it so I thought they knew what they were doing and it should works.
    This being said they will replace it but they also think that a 6.6 ratio should overcome the size difference so they are looking at other possible problems.
    The car just do not brake, it takes it several meters/yards to stop from 20 M/h with 2 feet on pedal !
    All normal troubleshooting checked (bleeding, vacuum, ...)

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  • BEVS BIRD
    replied
    HI ERIC....My 59 has been modified for a Disc Brake kit as well...This car had the Kelsey hayes power brake assist package..which means a very complicated brake pedal assmbly. ..The measurement from pivot to pedal pad center, is 14 inches . and pivot to master cyl rod is 2 inches, {very hard to measure as car is all together.}.. for a ratio of 7 to 1. this ratio is a little high { I think it shd be around 5 or 6 to one for power brks}...But soooo hard to modify stock pedal master cyl rod attachment point on this car. New Master cyl bore is 1 inch... This set up works very well. the pedal feels stock and this kit has been an unreal addition to this car....Hope this helps you CHEERS TERRY

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  • Eric S
    replied
    Locked home with limited access to the car, anybody could give me the dimension of the brake pedal from the pivot point to the middle of the pad (where the foot push) and from the pivot point to the hole on the pedal where the link attaches.

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  • jopizz
    replied
    No, you don't need the engine running.

    John

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  • Eric S
    replied
    Rookie question.
    When we bleed the brakes, do we need to have the engine running (to get the vacuum action from the engine) or is it just fine to use the pedal with engine at rest?

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