For those that have used one.Is it possible that the power bleeder could induce air into the fluid.Factory manual says not to use a pressure bleeder without a diaphragm in it because of this very problem.I pump it and it holds pressure on the gauge without leaking down.I have yet to find any leaks but for the life of me I can't get the air out.I see air bubbles in the bleeder hose so I know some air is getting out.I have replaced everything in the system.Beat the snot out of the calibers with a rubber hammer.Makes me feel better if nothing else.

 

I don't think you have to worry a the pressures of the hand pump power bleeders (around 20 PSIG). I think the manual is referring to those bombs filled with brake fluid that run off the shop compressed air. 100 PSI may well cause problems with bubbles, especially if it sits undre pressure for a prolonged period.

 

As long as the pressure bleeder is full of fluid, I agree that you don't have to worry about it.

I think it's more like 10.

 

The ones that use shop air normally have a bladder in them.Just can't figure out where the air is coming from.Fluid leaks around the bleeder but its under pressure.I close it off before I open the tank to add more fluid.There is no sign of fluid around any of the new o ring calibers I just put on.I bench bleed the mastercylinder several times.Im must be missing something somewhere.I pulled the pads to get a better look at the calibers.Dry as bone.No fluid on ground after the car sits for a while.None on the brake fittings around the mastercylinder of brake switch.New brake switch even.I don't get a brake light and it will lock up the brakes but it dose it about an inch from the floor.I blocked off the poets on the mastercylinder and with only an inch of travel the pedal is hard as a rock.I keep getting these tiny bubbles in the mastercylinder reservoir while applying the brakes with the lid off the mastercylinder.It's got all the symptoms of air in the system but like I said no leaks.I have dot 5 in it but guys I work with use it without any problems.I bleed it in the right sequence.I have found a few tiny leaks at some of the connections and tightened them up and double checked them.No more signs of any leakage at the fittings.Stainless braided hoses about 5 years tops.Im not getting any small black specks in the fluid.Im assuming the rubbers still good.

 

Tiny bubbles coming up in the master could be air leaking in the font of the master. I've been pushing the master piston in and spreading fluid on the bore and then releasing the piston.
I also boil my silicone fluid before using it.
When I bleed with a Motive type , I only pump it up to about 8 lbs so the bleeder basically acts as a constant supply of fluid under low pressure and then I use the brake pedal to force the higher pressure. Some very slow strokes to the bottom and some short jabs to dislodge bubbles but with 30 seconds between any pedal strokes.

 

Factory is correct, but the other bleeders work and don't cost 500 bucks.
The Motive type press bleeders are just glorified weed sprayers.They introduce air into the tank at the bottom of the pump assembly and tank so air bubblers are introduced into the fluid and the bubbles are made smaller the higher the pressure. Just pump it very slowly to minimize the aggitation. The only other thing you could do is add a schrader valve near the top of the tank and fill with very low pressure from air compressor so as not to mix air with fluid.


With the mc ports plugged, you should have no more than 1/4" pedal travel (manual or power with the engine off).
When you bech bleed, make sure the master is tilted since the ports are at about the 11 o'clock position and keep going until no more bubbles. I just use the presure bleeder off the car and rotate the master slightly in all directions and then mount the mc with the bleeder still attached.

 

You can purchase bleeders with a check ball in them. They are also known as "speed bleeders" the check ball helps prevent air from being sucked back into the lines. I bled my brake system (three years ago) with a Motive pressure bleeder and replaced the regular style bleeders with the speed bleeders. No bubbles, firm pedal, car stops on a dime and gives you nine cents change.

 

After reading up on dot 5 brake fluid I'm convinced I have been inducing air into the fluid with the power bleeder.I have been pumping it up to 15lbs to help the slow flow in the front caliber bleeders.I found a decent pressure bleeder with a diaphragm and a aluminum plate that gose over the mastercylinder instead of the plastic one that came with mine.It's not cheap 315 shipped.I'm tired of bleeding brakes.I'm going to try the gravity method.If I don't have any luck with that.The motive bleeder at low pressure.If that don't do it.I'm going to POP for the diaphragm press bleeder.It's sounds like its more of a nature of dot 5 fluid problem more than anything.Just not use to dealing with it.

 

Roger do use dot 5 and if so do you get a hard pedal that way.

 

I'm not a real fan of the silicone and use it only if requested by the customer but if I boil the fluid I can usually get a pedal almost as solid as dot 3.

 

I recently changed my calipers and went to dot 5 silicone fluid as well. For a bleeding procedure it was noted in the instructions to make sure the back end of the car was higher then the front end. I gravity bled each wheel for at least 1 minute after the lines appeared to flow clear. Started on the right rear inside half then outside half then to left rear. Then to front right then finished with the left front. Being sure to keep master cylinder full at all times. Once that was complete I had a friend push the brake pedal in half way as I opened and closed each bleeder. Took about 1 hour and everything works great. I wish you luck in getting your system ready. There have been so many horror stories about bleeding the C3 brake system. Guess I just got lucky!
Rodney

 

The po put it in.I had never hurd of it till I bought the car.So boiling it helps get the air and moisture out?I'm at my wits end with this thing.I bet I have put 3 gallons of fluid thru it.First the tiny little leaks letting air back in and now this.It dose seem to have less air the lower the press I use.That diaphragm bleeder is starting to look mighty good right now.I have bleed a lot brakes without any problems at all over the years but this is the first corvette I have ever owned.Love the car. Hate the brake bleeding.I guess I need to step away from it for a while.I have been off for a few days and just wanted to get it done while Im off.

 

I prefer my Motive type over my diaphragm type hands down but I do air my Motive type as Noonie recommended through a port at the top of the tank.

 

The M/C will retain a small amount of air even after "bench" bleeding for two reasons:
1) With the car level, the M/C is slanted front to back
This causes some air to remain trapped toward the front of the car (M/C). "Tilting" the M/C (or the entire car) helps with this problem.

If you "bench" bleed the M/C when it's mounted in the car, then you are really "pre" bleeding... not "bench" bleeding.

We're all pretty much aware of that one.

This one takes a little more investigation... a cutaway view of the C3 M/C...
2) The line ports are not drilled into the top of the master cylinder bore.
This provides an area along the top of the bore where air will remain trapped. "Rotating" the M/C during the bench bleed helps with this problem..... but this is a tricky maneuver due to the fluid in the reservoir. "pre" bleeding cannot address this one.... you would have to rotate the entire car.

Pressure bleeders will not solve these problems... they cannot force the trapped air to defy gravity... brake fluid is heavier than air.

2 cents

 

i dont think its your pressure bleeder.....i dont use any fluid in my pressure bleeder at all.....just air and i clamp the top on the MC with hose clamps and then take several ounces of fluid out of the calipers and disconnect every thing and fill up the MC again and move on to the next caliper....no mess what so ever.....the key is to never take out too much brake fluid and you must mesure what you take out to make sure you leave fluid in the MC.

 

I agree with this and have always done mine using this method. Much less messy than filling the Motive container with fluid and it works like a charm.

 

I notice that my brake pedal is spong after bleeding all 4 calipers. To do it right i'd replace all the calipers, MC, proportion valve and as many lines as i can get to on my 74. But the next owner can do that.


QUOTE=rugerm44;1578049253]The po put it in.I had never hurd of it till I bought the car.So boiling it helps get the air and moisture out?I'm at my wits end with this thing.I bet I have put 3 gallons of fluid thru it.First the tiny little leaks letting air back in and now this.It dose seem to have less air the lower the press I use.That diaphragm bleeder is starting to look mighty good right now.I have bleed a lot brakes without any problems at all over the years but this is the first corvette I have ever owned.Love the car. Hate the brake bleeding.I guess I need to step away from it for a while.I have been off for a few days and just wanted to get it done while Im off.[/QUOTE]

 

Thanks guys.When I rest up I will give another try.