Brake Bleeding ??

[George Zeck]

I am having modest success so far in bringing my "project" back to life. I took the (2) front calipers off the car and replaced the brake hoses (lines looked fine) and compressed the pistons (l & r for each side). Bled ONLY the front's (assuming that I don't need to bleed the back brakes because I didn't touch them). Topped off master cylinder. Braking "power" was LOUSY !! Probably worse than before I started messing with them

Don't see any leakage (only < 10 min after test run). So I think I have everything tight enough. Is there any special way I need to position the "hollow bolt" connecting the brake hose to the caliper ? I just put it on and tighted it firmly.

Should I bleed the back as well or are my calipers shot (they sure seemed fine and not frozen / rusted together)?

Lousy brakes or not -- the car sure turned heads during my two laps around the block !! /ubbthreads/images/graemlins/patriot.gif

 

[Biff]

George,

Re-bleed the entire system. When you were working on the front brakes air got into the system. Some came out when you bled the fronts, but some air also probably went up and is now traped somewhere (like in the distribution block assembly). All 4 wheels are on the same circuit, so any air in one part of the system will affect the entire system. I made a power bleeder, using a 1/2 gallon plastic tank sprayer and now brake bleeding is a simple, quick one person job. The how to make a power bleeder can be seen at https://www.bmw-m.net/TechProc/bleeder.htm

 

[Biff]

George,

Another thing I forgot to mention was the rear brakes. Are they properly adjusted? If they have to much play it would cause soft brakes in that you would have to double pump the pedal to take up the slack. Once pumped up it would seem fine.

 

[George Zeck]

To be determined on the rear's. Worked fine 20 yrs ago (last driven). The emergency brakes DOES work (quite surprising) so I must assume that the backs work -- just affected by the air in the system.

Since this is my first ever attempt at bleeding a system -- I am waiting on a friend who is very familar w/ LBC's and has done it many times.

Thanks for the help. Glad to have a place where I can "ask away" and not feel I am alone on this project. /ubbthreads/images/graemlins/patriot.gif

 

[screenprinter]

George, I hope you're able to read this.
The single most important system on a lbc is the braking system - a car that won't go is aggrevating, but a car that goes and can't stop is about a #9 out of 10 on the Sphincter Factor - Snakes in a junkyard are the only things that rate higher. Therefor please DO NOT assume that everything is jake without determining it to be so - I'm new here and I want to have the priviledge of posting with you for some time to come.
Any time you open any part of a hydraulic system it's almost a certainty that air is in there somewhere. So if you're to the point of bleeding the front calipers, do youself a favor and pull the rear brake drums and inspect for any nasty little surprises such as leaking wheel cylinders, uneven wear and/or contamination of the brake linings, broken springs, chewed up brake drums, etc.
Also check the condition of the flexible hose leading from the rigid line to the junction block - One time I lost my brakes because the old flexible line had swollen from years of brake fluid and produced what was, in effect a non-return valve - that is when pedal pressure was applied the wheel cylinders expanded but did not release when pressure on the pedal was released because the hose wouldn't let the fluid return to the system - Once it built up enough pressure the wheel cylinders blew out and adios muchachos!

So, assumptions can be okay except when it comes to the braking system - then it's the mother of all A#@biters.
Hoping to read many posted questions from you in the future.

Bob M

 

[Steve]

/ubbthreads/images/graemlins/iagree.gif Could not agree more.....There are several other factors to consider here. Since the car was laid up, twenty years ago now, the rear brakes could well have seized. Just a little dampness in the air can cause this. I have had it happen to LBCs, so if you have escaped then you are lucky.....pays to check them out anyhow. Secondly, brake fluid absorbs water from the air, which is the reason why it is recommended to replace brake fluid every two years. After twenty, I guarantee that the fluid that was in the system will have become contaminated. Even though there is some new fluid in the system, it will not be enough, and the water that is in there from the old will soon contaminate the new. So please:-

1. Bleed the entire system, topping up the reservoir constantly. Continue until you are sure that all the old fluid is purged.
2. After completing this, then check the operation of the rear brakes thoroughly.

Screenprinter is right, we want to have you around posting for some time to come /ubbthreads/images/graemlins/laugh.gif

 

[George Zeck]

I found out the hard way the cylinder's are bad. Have new parts. Hope to be Ok after that. Thanks for the follow up.

 

[Bugeye58]

Well, George, how hard was the impact?
I usually keep a spare set of rear cylinders handy, as I have had them sieze up over a single winter of sitting. But, I tend to keep a decent parts inventory on hand anyway, just in case.
Jeff

 

[screenprinter]

George,
Lemme pass along a neat tech tip I read somewhere on the web about rear wheel cylinders in Spridgets -

That little rolled split pin at the top of the back of the cylinder which protrudes through the backing plate...An easy mod is to remove the split pins and tap the holes for a small fine thread bolt - Screwing the bolt into the cylinder from the backing plate prevents the cylinder from moving any - Reason for doing this? The wierd system of using a spring washer and a circlip to attach the wheel cylinder scares the heck out of me - If the cylinder moves toward the brake drum at all there is a chance that the rotating hub can bear against the cylinder and dust cap and cause another nasty surprise similar to the swollen brake hose gag.

I haven't done this yet, but when i reach the point in the project for the brakes to be redone I'm going to give this one a try - If I screw up a cylinder, they're fairly inexpensive - and available from Advance Auto, AutoZone,etc.

The great thing is is that Spridget rear brakes are about as basic and simple as they come - absolutely a no-brainer.
Glad to see you got things sorted out on your end.

 

[George Zeck]

Happy to say I did not make an "impact" with my car -- I really meant to say that after 90 min of bleeding the brakes with a friend of mie (and not looking at the bak brakes) -- we (eventually) noticed a LARGE puddle of brake fluid coming out of rear / pass brake assembly. Bought new cylinders & shoes. Hoping that is it -- but if not -- it won't be too long before I'm road worthy !!

 

[Steve]

Good news George.......Glad to hear that she'll be roadworthy soon.

 

[Bugeye58]

George, glad to see that there was no "Percussion Test" involved. It's better that way! /ubbthreads/images/graemlins/grin.gif
Jeff

 

[Texas_Cicada]

I am also reassembling the hydraulics on my car. After putting the master cylinder back together, with new washers and gaskets from Moss, and filling the resevoir with fluid (DOT 4), I can't get the pistons to move smoothly. They compress and squirt fluid, but then they return to their resting position very slowly. (All of this is being done on the work bench, with the fluid going through two pieces of scrap tubing into an old jug.) Any ideas? Does the MC have to be connected to the slave cylinders to function properly?

 

[Bruce Bowker]

Not 100% sure but I would think that when the system is fully hooked up they will return. The way you have it now there is no "back pressure" so to speak, nothing to push them back.

Was DOT 4 fluid specified? Nothing to do with the above. Just that some seals do not like DOT 4.

 

[SilentUnicorn]

i would think that the springs in the master cylinder are strong enough to quickly return the valves to the home position . when bench bleeding, a fair amount of force is required to compress the pistons, and generally they pop back rather quickly.
unless ther is some restriction in the scrap lines you are using, and it takes a moment or two for the fluid to be drawn back up in to the resevior?

mark

 

[Texas_Cicada]

This afternoon I pulled the MC back apart. I noticed some small bits of debris in the fluid and a little bit of rust discoloration. I guess I didn't get the system as clean as I thought when I put it together the first time. I flushed the whole thing out with a couple of cans of clean fluid and cleaned out all of the orificies. Tomorrow I will put it all back together and try again.