Blog kirkE

Sign in to follow this  
  • entries
  • comments
  • views

1970 240z brakes will not bleed

Sign in to follow this  


I have a 70 240z and the brakes have always been soft from when I originally restored the car. I finally decided to upgrade and fix the issue. I just put on the new Toyota front calipers but I still have the drums on the rear. I have pulled a gallon of brake fluid through the lines but I still get air bubbles out of the rear wheel cyclinders and the pedal remains as soft as ever. Here is what I have replaced

1.) New 1" MC from Datsun Parts - figured the 30% extra fluid would fix it. Nope

2.) New vacuum booster from O'riely's - checked the old vacuum boost for reaction disk- fixed that - it didn't help and so I bought a new one - no help

3.) Took off and cleaned the proportioning valve

4.) Hooked up my air compressor to the brake lines trying for force fluid out (somewhere - anywhere) and find what I assume is an air leak - no help

5.) Found a leaking rear wheel cyclinder, fixed that, no leak now but still get air out of the rear

6.) I have bleed the MC multiple times, gravity feed, vacuum pulled, and even done the old two man method and I can't get these things to firm up?

Any advice??

Sign in to follow this  


Recommended Comments

Try this:

If you still have a spongy pedal, try this trick that a racer taught me a long time ago. Bleed the rears properly first. Then on the right front caliper, remove the outside brake pad. Use some padded channel lock pliers and press the piston carefully into the caliper. It will travel farther than with the pad installed. BE very carelful when you push the pedal down, that you don't push the piston out past the seal. Do that a couple times till you get all the bubbles out. Replace the outer pad. Then remove the inner pad and repeat the process. Then move onto the drivers side and repeat.

Every time I would put new calipers on my race car, I could never get a firm pedal until I did this extra step. After doing it once, it was bleeding as usual.

I don't know why the rears would still have air in them, unless you have them on the wrong side? Don't know if that is even possible.

Good luck,


Share this comment

Link to comment


Thanks for the advice. I will give it a shot this weekend. I am at wits end on this? I think I will pull the rear wheel cylinders and just clean them up as well, although I can't find any leaks and they are only a couple years old, That said the brakes have never been firm? I also tried to backfeed the fluid and push it from the rear wheel forward, but the system must have a check valve or something because I could not get it to take fluid?

Thanks again for the suggestion

Share this comment

Link to comment

Have you started with the master cylinder itself first?

Make sure the calipers have the bleed nipple on the top and not the bottom. Most common mistake right there

Secondly, you should have never thrown those calipers on there. The stock brakes with nice pads, rebuild calipers and some brembo blanks will bite real hard. The bigger calipers mean u need to upgrade your master cylinder to a 280zx or something that is bigger.

Make sure ur nipples on the calipers are facing up and not down...if they are down...switch the inner part of the caliper right to left, left to right.

Share this comment

Link to comment

Here's my experience with "brakes that won't bleed."

Start completely over. Assume NOTHING that you fixed, replaced, tightened is OK, because, OBVIOUSLY, at least one of them isn't. Don't say to yourself, "Well I already tightened that fitting or replaced that slave cylinder!" Sometimes even a new part is no good.

It helps if you can isolate your problem to front or rear, consider disconnecting and PLUGGING the line to the rear to see if you can figure out which end has the problem.

If you want MY GUESS, you probably have a line on the proportioning valve or MC that isn't sufficiently tightened down. Hopefully you have a set of brake line (flange) wrenches and can really snug the crap out of them right to where they're about to strip off, as that's often necessary to get a good seal.

I've torn my hair out over brakes that won't bleed, but a slow, start completely over, methodical approach is the only one I've found that works.

Share this comment

Link to comment


the brakes are better....but...still not as firm as I would have expected. After isolating lines, I finally took it to a mechanic who said that he could not find any air in the lines? He said he adjusted the rear drums and while the brakes work better, I still get about half a pedal of travel before I get any brakes? I still think most brakiing is at the end of the pedal travel. I think I am going to increase the length of the vacuum boost rod to see if there is something with the engagement at the MC. Maybe I am expecting too much "modern" performance out of these brakes. They do stop well but I would just expect that at about 25% pedal travel I would get some kind of braking action???

Share this comment

Link to comment

Are you using the stock brake hoses? If yes, replace them with stainless steel braided hoses. They will also help get a firmer pedal. Make sure the brake pedal itself is adjusted to the correct height. Is the reaction disc in the booster in place?

Just some additional thoughts I had. You can get these old brakes to perform very well. The pedal on my track car was quite firm. It had Toyota 4x4 calipers, with 300 Zx vented rotors, braided lines and Axxis Ultimate pads. That thing would throw you through the windshield if you weren't harnessed in. and that was with the stock rear shoes.

Keep working on it, you'll get there.

Share this comment

Link to comment

Marty has given great advice. make sure the rubber hoses have been replaced. I have also done the old racer trick of reverse bleeding to find trapped air- it works!

Share this comment

Link to comment

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Blog Statistics

    • Total Blogs
    • Total Entries
  • Blog Comments

    • I'm still waiting on a hoist to free up before I can start bolting the new brake parts on my Z, but I did make the drill jig today.  I started with a 12mm thick Mustang wheel spacer with a pilot.  I then made a drawing to layout the holes needed.  I transfered the drawing onto the spacer and I drilled three new 1/8" holes through the jig (spacer) so I'd have the correct 4x114.3mm holes.  One hole is shared from the original 5 lug rotor.  I then bolted the jig onto the Mustang rotor and simply dr
    • Local radiator repair shops used to be plentiful but getting harder to find.  Some of them just specialize in big truck-heavy equipment radiators.  I will be needing to do the same for my project.  I have heard good reports on gas tank RENU but there are none of those franchises in my area.  Good luck, John-Lugoff, SC
    • Decided to go with the 240sx conversion. Main reason is it’s strictly for the street and the parts were easy to source. What I didn’t realize was the 14” wheels won’t clear the caliper. Now looking for a set of 4 lug 15” rims and tires I can use during the build process. Can anyone recommend a temporary solution as far as make and model preferably a steel wheel that I can use until I’m ready to buy the wheel and tire combination at the end of the project? Thanks again for all the help out there.
    • There are several reasons to use the S197 rear brakes.  The rotors are larger diameter than the SVO rotors and they are vented.  The calipers have larger pistons to give them more power.  The big beef with the Maxima rears is that they don't offer as much stopping power as the stock drums.  The S197 rears allow the addition of an adjustable proportioning valve.  The Maxima rears cannot utilize an adjustable prop since the prop needs to be all the way open to get close to enough rear bias. 
    • Any particular reason to use S197 Mustang 5-lug brakes?  The Fox body SVO Mustangs had rear discs with 4-lug.  It's a popular swap to use SVO or T-bird Turbo Coupe rear brakes to retrofit discs to other Fox body Mustangs.  These parts are still pretty common (probably available as a kit).  Might be worth checking to see if they'll fit.