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Thread: Front brake problems

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    Registered User chefman1's Avatar
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    Default Front brake problems

    Hello All, Need major help with this last problem. I have restored entire bottom part of this z. Suspension, brakes, brake lines, bushings, rotors, calipers, rear conversion. I can not get brake peddle to rise. New brake lines including new booster and master. no leeks, but peddle will not rise? I'm getting bubbles in both reservoirs for front and rear? I have a peddle but it sucks? Please help me, this car is too perfect to let sit in garage.

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    There's a spring that brings the pedal up. Can you pull the pedal up by hand?
    1976 280Z, with some minor modifications

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    Quote Originally Posted by Zed Head View Post
    There's a spring that brings the pedal up. Can you pull the pedal up by hand?
    Hey Zed Head, Spring is there and pedal comes back up but pedal is still soft. This is even after a two man bleed? Master is after market and getting a bubble affect during bleeding but no excess air at the front or back calipers? I did replace the booster and believe that there might be too much free play between the master and booster but not sure at this time? Please help? I have two portioning valves on this car, do i really need two? I have been told by datsun z that upgrading to wilwood 1in and new p-valve that issue would be solved? but i really do not think so? you advise please? Thanks

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    So what you mean is that you can't get a firm high pedal. The pedal drops too low before you get any braking action, or you have to pump the pedal to get any brakes. ???

    One pretty common error that people make is to put the calipers on the wrong sides. They will fit either way. The bleed screw needs to be at the top of the caliper, not the bottom.
    1976 280Z, with some minor modifications

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    soft pedal, but no air in lines during car on or car off. pump pedal the same. bleeder screws on top always.

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    I'm thinking new booster stem has too much play between the master and booster? there are no leeks and bubbles are coming up form each reservoirs while pumping brakes? whats your thought?

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    Registered User grannyknot's Avatar
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    Have you bled the master cylinder? There are 2 bleed screws on the side of the m/c
    1970 240Z HLS30 01955 March/70

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    Yep, bled the master. Bled the lines back to front. Every thing a z needs. I have come to the last two problems, which is p-valves, master or brake booster adjustment. Please advise?

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    That's three problems

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    Quote Originally Posted by chefman1 View Post
    rear conversion.
    Many, many people have problems bleeding the brakes after installing calipers on the rear. Many. Quite often they have to remove the caliper, install a block of wood between the pistons and hold the caliper so that the bleed screw is at the top. There are people on this forum who have spent weeks. maybe even months, trying to get their rear caliper conversions bled.
    1976 280Z, with some minor modifications

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    rears are great, just having problem with the fronts

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    Quote Originally Posted by chefman1 View Post
    I'm getting bubbles in both reservoirs for front and rear?
    Hard to tell what's really going on then. How do you know the rears are great? They lock up but the fronts don't? That's typical of air in the front calipers. Can you pump the pedal to get it high and the brakes working? If you can pump them up then you have air in the system. If they just start braking with the pedal low and there's no change with pumping, then you have an adjustment problem.

    But you should not have bubbles in the reservoirs.

    Did you install a different master cylinder also? The stock system shouldn't have any problems bleeding the brakes.
    1976 280Z, with some minor modifications

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    Don't know if this relates but a month or so ago there was a lot of discussion about a rubber disc between the mc & booster rod that tends to fall down in the booster. & forgotten. Without it the pedal has a lot of travel. Possible that the mc piston doesn't have enough stroke to bleed the air out because the stroke is too short?

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    I had a heck of a time adjusting the brake booster pushrod to the correct length. Setting it up like the factory service manual stated left a very long peddle throw. I kept adjusting until I liked the peddle feel. The rear brakes will drag and lock up if you go too far but just back up 1/8 turn and it should be perfect.

    I would lose the second proportioning valve. Should only have one.
    Last edited by 30 Ounce; 07-07-2014 at 07:33 PM.
    74 260Z late
    3.0 liter Rebello kit
    Rebello mod. SU's

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    Quote Originally Posted by chefman1 View Post
    Hello All, Need major help with this last problem. I have restored entire bottom part of this z. Suspension, brakes, brake lines, bushings, rotors, calipers, rear conversion. I can not get brake peddle to rise. New brake lines including new booster and master. no leeks, but peddle will not rise? I'm getting bubbles in both reservoirs for front and rear? I have a peddle but it sucks? Please help me, this car is too perfect to let sit in garage.
    Bubbles indicate air in the system. Bench bleed the master again and then move to the wheel cylinders.

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    Registered User EuroDat's Avatar
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    Why are you running two proportioning valves. Is the original still in place and an extra aftermarket in the rear line?

    Your pedal problem could be the reaction disc in the brake booster fell down inside the booster. Or the rod adjustment to the master cylinder. That can cause your problem.
    Some aftermarket mc are not put together correctly. Should check that as well.
    Chas
    5/77 280Z HLS30 403100 with some modifications
    Original colour: 305 Light Blue. The PO changed it to Red

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    Thanks to everyone for your help and or advise. I'm hitting it hard tonight and will update everyone on my findings. Cheers

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    Really? Thanks brother i will try that as well. Cheers

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    chefman,

    I live in Austin as well and would be happy to help out a fellow Z owner if you continue to have problems.

    Just let me know and I'd be happy to lend you a hand.

    Mike.

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    Too Cool. Nice to know there are a few of us left in Austin. Ed with the z-clinic and David and Dan Tucker from Jap tech dropped off the radar? I have pulled master and all front brake lines as well as both portioning vales. I will adjust the new booster and replace the lines and see what we get? Keep your fingers and toes crossed for me. Thanks brother. Seeing that your in Austin we will have to connect and revive the z. Thanks

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    chefman, I'll be down in Kyle next week and would be happy to help turn a wrench if you need it. Won't have my Z though.
    75 280Z almost done
    49 Chevy 3100 p/u next project
    96 Dodge 2500 4X4 tows my 5th wheel

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    Default sorry i missed you bro

    I was out of town for the weekend. I still cant figure out why i don't have pressure with the front brakes? I have tried everything listed except for changing out calipers and brake hoses? Anyone have advise?


    Quote Originally Posted by mjr45 View Post
    chefman, I'll be down in Kyle next week and would be happy to help turn a wrench if you need it. Won't have my Z though.

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    One thing that people have done to isolate a problem is to convert one of the fittings in to a plug. For example, take an old fitting with a piece of metal brake line, cut the line short, then bend it and crimp it so it won't leak. Then take that plug and block off various parts of the system. Block the fronts and see if the rears are solid, and vice-versa. Block one caliper, block the other, see if there's a difference. Block the proportioning valves, etc. You can even build two plugs and block the ports from the master cylinder to see if the MC is the problem.

    Have to say though that you haven't really given a good description of what the pedal is doing. Is it high or low, will it pump up, does it drop if you just hold constant pressure on it... etc. Al I see is soft pedal (what does that mean?), air bubbles in the reservoir, and the rear brakes "work great" (no details on what "great" means). Plus you said the rears work great, but you're reporting bubbles in the rear reservoir. The solution is in the details, but you have to provide those.

    Good luck.
    1976 280Z, with some minor modifications

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