Ok, a little background before we get started. I am doing a Toyota 4 piston caliper upgrade to my '71 autocross car. The brakes actually worked really well before I started, but the car is going to be doing high speed autocross at the track, so I wanted something even better.

All the parts went in pretty easy. Finding longer metric bolts for the hubs was a trip though. Re-bending the caliper hard lines was a little tricky too. I put in new Speed Bleeders too.

So, I start bleeding. Started with RR, LR, RF, LF, and then Master. I put 3 quarts of Valvoline DOT 3/4 Synthetic through and the pedal goes stright to the floor. Bleed the MC and all corners a dozen times each.

Then I found Rick's racer trick. Took the front brake pads out one at a time, stepped on the brake to get the pistons out, and then pushed 'em back in with channel lock pliers. Did this probably 10 times on each piston, till I didn't see any more bubbles coming out. I was amazed at how much air was still in there. The pedal feel improved SLIGHTLY. Still feels soft, way softer than I want for an autocross car.

I have gone though 4 1/2 quarts of fluid now and the brakes feel worse than before the upgrade. I haven't even felt confident enough in them for a test drive. So, what do I do now??? Any new tricks or suggestions would be appreciated.

Marty

Originally posted by Marty Rogan

So, I start bleeding.

What technique are you using to actually do the bleeding? There are a number of products out there designed to make it a much easier job (speedbleeders, vacuum pump, etc.) especially if you're having to do it all by yourself. It sounds like you've gone through an awful lot of fluid.

Guess the obvious question is how old is the master cylinder? If it's fairly new, then the next obvious thing would be the adjustment on the pedal.

If the master could be suspect, I'd go with a 15/16th's master from the ZX. You're asking the stock master to pressurize the lines now with 2 extra pistons in front, which will need a bit more fluid than the originals.

Try pulling the handbrake up a notch or two, and see if the pedal feels better, if it does, then the rear shoes aren't adjusted correctly and need to be tightened up.

Those are the most obvious things that I can think of.

Mike, as I said in the post, I installed SpeedBleeders. Won't do this without them.

2Many, The Brakes actually worked great before, and I know the MC was replaced by the PO. I would not think the MC would just go bad on you during an upgrade.

When you say, pull up the hand brake a notch or two, do you mean from completely off? Or in addition to where it normally pulls up to?

How do you adjust the pedal? Would adding the 4 pots put that out of adjustment?

Keep the ideas coming.

Thanks,

Marty

The parking brake trick works from the "off" position, it will take up the slack in the rear shoes (if they aren't adjusted tight enough) and give you a harder pedal feel as the shoes won't be moving as far to contact the drum.

The pedal height should be 8 inches from the floor at rest. Measure it to the flat of the pedal pad, and make your adjustments on the piston at the pedal clevis.

If the adjustment was off just a little before the change, it could be that it's affecting the travel just enough that it isn't moving enough fluid due to having the 2 extra pistons to pressurize.

The MC woudn't "go bad" during an upgrade, but it could be the MC wasn't 100% and needing the extra fluid movement has only exaggerated the slight problem it may have had.

IMO, upgrading to the larger MC is always a good idea when you upgrade to the 4 piston calipers or swapping for rear discs, or both.

Thanks for the explaination. I am taking tomorrow off from work and will give these a try.

If you go with the ZX Master, would you have to reverse the lines, like you would on the 72/73 MC? Any other mods required to make that one work?

Marty

In your first post you said that you bled them in this order, RR LR RF LF MASTER, Bleed the master first then go in your order of the brake ends. It may be that you are introducing air into the lines when you do the master last. Just a guess, if it worked before it should work now...

Thanks Lance. I thought of that later too. Later in my journey, I always started at the Master and then went to the corners.

Marty

Originally posted by Marty Rogan

Mike, as I said in the post, I installed SpeedBleeders. Won't do this without them.

Ah, that's what I get for trying to read too fast; sorry about that. I've never used speed bleeders but I have used a vacuum pump and it worked great for me. Hopefully some of the other suggestions get you further along.

Hmm, I did the same thing as Mike, read it so fast I completely missed where you said you did the MC last.:stupid:

MC has to be done first or any air that may be trapped will either stay in the MC or end up in the lines, calipers or the rear cylinders.

In no particular order......

The 15/16 on the 83 and 4 is backwards (it also has a single reservoir divided internally). 15/16 from 79-82 are the same orientation as 7/8.

Did you install a proportioning valve?

Bleed both masters and then work from nearest to furthest wheel away from MC.

Take the spring off the brake pedal and see if it 'drops'. I doubt it, as the brakes worked before and you didn't muss with anything.

Reaction disc?

Save the fresh bled fluid, let it sit in the bottle--covered--a while until the tiny bubbles dissipate. It is fine to re-use for major bleeding excercises. If you have run that much through, you've got all the cooked stuff and crap out.

Get a vaccuum gun. Buy a nice one. Spend more than $50.

Poor-man's 'speed bleeders' are: Wrap teflon tape around the threads of the bleeder screws. Quite a bit cheaper and performs the exact same function.

steve

Originally posted by Zvoiture

Poor-man's 'speed bleeders' are: Wrap teflon tape around the threads of the bleeder screws. Quite a bit cheaper and performs the exact same function.

steve

Not to steal the thread but how does that work? My understanding is that speed bleeders are like one way valves alowing fluid to pass out if loosened but air not back in, teflon tape on the other hand, if it held together, would block the bleed hole, if it came apart like it usually does it would probably block the bleed hole and gum up the works????

Maybe I'm missing something here....