69 Chevelle SS front brake bleeding

['69Novajoe]

Originally Posted by mockingbird812

Been a while since i did the bleeding but I remember it was firm and I think I used a clamp to depress it and free my hands up to do the bleeding at each front wheel. I would put something (piece of wood) between your clamp and the plunger so as not to harm it.

Yep, that sounds like the proper way to do it!!

Originally Posted by mockingbird812

Hey Joe, I reached out to Tom, WilmasL78boy, and he should check in soon.

Thank you so much Sam!!

Originally Posted by WILMASBOYL78

69 Chassis Service Manual states this regarding bleeding front disc brakes:

"The spring loaded end of the pressure metering valve must be depressed while bleeding. This can be done by depressing and holding the plunger in the end of the valve either by hand, or by clamping.

This is all on page 5-29....there is additional information on pages 5-3 thru 5-5

If the plunger won't move, it may be stuck due to age/corrosion...I would check it and service as needed.

I double checked the 70 manual as well...same instructions.

Good luck.

_wilma

**you just reminded me I have to look at the front brakes on the 70 4 spd...I had a collapsed hose and changed both of them...pedal is still a little soft...

Hey Wilma, thanks for checking in!! I actually clamped the metering valve in a vise this morning and the plunger still won't move!! Guess I've got a faulty valve after all. Gee, it's "only" (almost) 51 years old so what do I expect??!!! It will be nice to get her back on the road, especially since I hear gas prices are coming way down!! But, then again, we aren't supposed to go out (in California) anyway!!
Take care, be well and thanks again for all your help everyone!!

[m22mike]

Does this help at all ? I would like to understand how pushing on ,(DEPRESSING ) the exposed piston rod moves anything when the valve seal is already seated ?
Joe , your valve is most likely OK. They are easy to take apart, just used the correct socket. Most I have restored I cleaned and re used the seals.

['69Novajoe]

Originally Posted by m22mike

Does this help at all ? I would like to understand how pushing on ,(DEPRESSING ) the exposed piston rod moves anything when the valve seal is already seated ?
Joe , your valve is most likely OK. They are easy to take apart, just used the correct socket. Most I have restored I cleaned and re used the seals.

Hey Mike, you've raised another question!! I hear that the plunger needs to be "depressed" in order to bleed the front calipers. That has come from a few sources now. With all due respect, since you've actually taken one apart and know how they work, do you think the plunger actually moves but maybe just a very small amount?? In this case, I'm gonna be a "parts replacer" and see what happens. I think something is blocking the flow of brake fluid and this looks to be a good place to start?? The way the pedal was acting (going almost all the way to the floor!!) and the actually braking was performing (not coming to a stop very fast!!) it all points to just the rears doing all the work??!! Anyway, I found a new replacement on ebay for $54.50. I'll keep you all posted.

[m22mike]

IMO, pushing on the shaft only increases the pressure on the piston seal, that is under spring pressure and seated and holding off flow. As the brakes are applied the rear brakes see pressure first, as pressure increases to about 40psi it overcomes the spring pressure in the ROUND HOLD OFF VALVE. Fluid flows into the line at the big nut , passed the piston seal, out the side fitting to the distribution valve, to the front brakes. Sometime watch the shaft move out as the brakes are applied by a helper.
If you wanted free flow through this valve it seems to me one would pull and hold the shaft open to unseat the piston seal.
Open to learning more if this sounds incorrect to others.

Mike

['69Novajoe]

Originally Posted by m22mike

IMO, pushing on the shaft only increases the pressure on the piston seal, that is under spring pressure and seated and holding off flow. As the brakes are applied the rear brakes see pressure first, as pressure increases to about 40psi it overcomes the spring pressure in the ROUND HOLD OFF VALVE. Fluid flows into the line at the big nut , passed the piston seal, out the side fitting to the distribution valve, to the front brakes. Sometime watch the shaft move out as the brakes are applied by a helper.
If you wanted free flow through this valve it seems to me one would pull and hold the shaft open to unseat the piston seal.
Open to learning more if this sounds incorrect to others.

Mike

Okay, I see your point. So now I'm totally confused as to why it says in the manual....."The spring loaded end of the pressure metering valve must be depressed while bleeding. This can be done by depressing and holding the plunger in the end of the valve either by hand, or by clamping." Will doing that relieve the spring pressure somehow?? I've been trying to do this with a hand-held vacuum type bleeding tool which doesn't create enough vacuum (?) to overcome the spring pressure?? Some other instructions mention using a "pressure-type" bleeder. Not sure if that would make a difference or not?? I've ordered a new valve like I said and will let you know what I find. If it still doesn't work I'll have to find a "helper" to help me bleed the brakes the "old-fashioned" way by stepping on the brake pedal!! Thanks again for all your input Mike!!

[m22mike]

I have no comment on the directions in the service manual Joe.
Sorry I don't have any more
I can tell you. Maybe those that have had succes depressing the shaft during bleeding can explain what is happening in the valve.

Mike

['69Novajoe]

Hey Mike, I ended up buying a new metering valve (because I was convinced it was bad), pushed the plunger (which seemed to maybe move a little bit, if at all!!) and then proceeded to bleed the brakes. Actually, before I installed the valve, I checked it with my vacuum bleeder to see if it was allowing air through it and it was! Not sure if pushing that plunger did the trick or not!! I got good flow to the fronts now and the pedal has returned to the proper position and is rock hard!! Guess I got all of the air out of the system!! Everything seems to be working correctly at this point and I'm a happy camper!! Gonna go on a bit of a ride/cruise this Saturday to give it a good test. Thanks again for all your input and suggestions.