alexdimen

iTrader: (13)

well i've read some old threads on brake bleeding and from what i've heard the hand vacuum pumps are a waste of time for brake bleeding.

what i've come across is a surplus medical/laboratory grade electric vacuum pump capable of pulling 30 hg/in and an air tight 1+ gallon catch can i put in line.

i've been trying to remedy my spongy brakes (single piston non-abs) for a while now and still cannot always lock the wheels before the brake pedal hits a "wall" about 1/3 to 1/2 down to the floor and feels gross the whole way there.

i have new front rotors, an air-tight booster, 80 dollars worth of pads, and a new master cylinder and am pretty sure that my pushrod on the brake booster is adjusted decently. i think that my problem is that i haven't been able to bleed my brakes properly using the old pedal pumping assistant method, but am open to suggestions on what else it could be... the wall that the pedal hits is really baffling me i guess because i don't fully understand how the booster works.

so... basically what i'm asing is how can i use this vac. pump setup to bleed my brakes... do i just hook the vacuum line to a bleeder nipple, make sure there is fluid in the resevoir and let the pump do the work?

Go48

iTrader: (7)

First of all, you might want to consider installing SpeedBleeders on all your calipers. They have check valves in them that only allow passage of fluid in one direction. With those you can open one up and pump away until no air is seen in the hose.

For the vacum pump you will need to have a hose from the bleeder into a closed container and a hose from the container to your vacuum pump. That way, you are drawing a vacuum within the closed container and that is pulling the fluid into the container while keeping your vacuum pump free of fluid.

alexdimen

iTrader: (13)

that is my exact setup... i have a large sealed stainless catch container with two seperated fittings on it.

what i'm asking is do i just turn on the pump and keep an eye on the fluid level or is there a trick like pumping the brakes or something? i have never used anything close to this method for brake bleeding.

plus the way i see it, the constant vacuum will be as good or better than just a check valve... as well as less money because the whole setup was being thrown out so i got it for free.

Go48

iTrader: (7)

Well, I've never used a powered vacuum pump, so I can't answer your question from my experience. Personally, I would be concerned that the pump would draw too much vacuum, but that's just me. I'm not sure if a high-vacuum applied to the system could create problems with seals or some other internal components. My GUESS would be that it would be OK, but I still wouldn't use one.

As to procedure, hook up the lines and the pump, open the bleeder screw, and turn on the pump. Let it run until no more air is visible in the line and be careful to not let the master cylinder run out of fluid, and also watch your catch can so that it doesn't fill to the point where you suck fluid into your pump. You don't need to pump the pedal since the vacuum is drawing the fluid out of the system. Start with the right rear, then left rear, right front and then left front.

SureShot

I have used a Mity-vac hand pump to bleed brakes, but it is a little subjective.
What happens is the bleed nipple screw threads leak some air so it's tricky to tell if the air in the drain tube is from the system or from the nipple.

As long as the drain tube end is covered with fluid in the catch can, reverse flow is not a problem when bleeding by pumping the pedal.
The only trick is then closing the bleed nipple before any air can get in the threads after the last pump stroke.

Go48

iTrader: (7)

The solution to the thread problem is to coat the threads with the goop that you can buy in a small bottle from the same source as the SpeedBleeders. You paint the goop on the threads and heat them in an oven to cure it. The goop seals the threads even when unscrewed enough to let the fluid flow out.

jackhild59

iTrader: (7)

A couple of wraps of teflon tape will do the same thing, without the hassle of buying some special goop and heating it in the oven.

alexdimen

iTrader: (13)

thanks, great ideas... i tried hylomar but i don't think it did the trick will try the teflon tape on wednesday when i give it another go-around... couldn't tell if the air coming in was from the lines or through the threads.

i bled the rear brakes with the vac pump method and can now lock them up... but not the front ones so the car is out of service for now cuz it was sketchy as hell... though the pads were finally able to polish the rotors again, so i suppose that's a good sign.

my dumb *** forgot to let off the e-brake when bleeding too so i'm just going to reset the booster push rod and then hit all four corners again and run through a ton of fluid. i'm going to blow the car up if that doesn't work.

seriously... well either that or do a 5 lug swap.

classicauto

iTrader: (3)

although this probably is not an issue anymore by the sounds of the amount of bleeding you've done

But sometimes a spony pedal can be old, burnt brake fluid - therefore the entire system needs to have a transfusion.

I bet you've done enough bleeding to do this by now...but just a thought.

Also have you ever checked the ENTIRE sytsem for pinhole leaks? what kind of shape are all the lines in? are there any patched sections of line with compression fittings and things of that nature? if so they are a nice place for air to be sucked into the system

alexdimen

iTrader: (13)

honestly, i doubt there is more than a drop of old brake fluid in the system. and no there are no patches i have noticed (i've been all over this car quite a few times) and have inspected the lines and there are no wet spots, repairs or anything like that. amazingly the lines don't have cracks in the rubber either, thanks to virginia weather i guess.

jackhild59

iTrader: (7)

One other possiblity, is that you have run the reservoir dry during the bleeding process and pulled some more air into the system. Yeah, I know, you would never make that mistake, and niether would I. But then again I did too do it. I learned that the RX7 brake reservoir is frustratingly small when you are trying to flush the brake fluid and/or bleed all the brakes.

Now I just poke a couple of nice size holes in the seal on the brake fluid bottle, then invert the bottle and stick the top of the bottle into the top of the brake reservior. The brake fluid will automatically keep the reservior full for as long as you need it to, or until you empty the bottle. I use a quart when I am flushing the fluid.

FWIW, my "speedbleeder" is a 13 yr old wannabe RX7 driver that is willing to help just to be around. He runs the brake pedal, I run the wrench on the bleeding nipples.

As a reward, I'm going to buy him a Family Truckster when he turns 16.

alexdimen

iTrader: (13)

booster pushrod is perfect at 20 hg/inches and i reset it so it had no clearance and about 1/2 mm of interference with the piston.

then i did the teflon tape thing, which still let in a tiny bit of air until i perfected the technique (only works well if it is wrapped in the right direction, but didn't discover until i got to the front brakes)... but i ran a large bottle of brake fluid through the lines, most to the rear and then the last 1/3 on the fronts.

the brake action showed a minimal amount of improvement, but am now able to lock up the fronts as well... but i still hit that "WALL" 1/3 of the way down to the floor, which is stopping me from getting full pressure to the calipers.

i am thinking that this "wall" may be the booster coming to the end of it's travel from a malfunction. i did test the booster for leaks and it holds a vacuum fairly well, but not forever... as a final precaution i put some high vacuum grease on the booster rod and fittings to ensure a good seal.

any thoughts?

alexdimen

iTrader: (13)

bump