Hi,

For 1986 Trans Am with rear disc brakes:

I'll replace the stock proportioning brake valve spring for the 1NCR5 Grainger or similar spring.

For this "upgrade" I must bleed rear brakes pushing air/fluid from proportioning valve to passenger side rear wheel (first) and driver side rear wheel (second).

What could be the necessarry number of pedal pumps in order to complete this bleeding process?


Thanks

It takes a little over half a beer (or glass of wine, if that's your preferred adult beverage) to sit back and watch the fluid dribble out of the right bleeder (being careful of course to refill the master cyl between sips), and then the rest of it while you watch the left.

Not sure why you'd want to get involved with "pedal pumps". That sounds a little like "work", which is best avoided whenever possible.

According to Mr. Owl, , three.

But, since he cheated, the world may never know.......

Lol, don’t cheap bleed until the brakes are firm . All the wheels

"Pumping" the brake pedal is not necessary for bleeding the brakes, and when there is air in the lines, you're just pumping air. If you have another person there to assist you, have him/her (that's right; it's one or the other) depress and hold the pedal while you crack the bleeder open. Close the bleeder and have him/her let the pedal up and then depress and hold it again. Crack the bleeder open again and then close it again. Repeat this process several times until the brake pedal is firm, in which case all the air will have been purged (be sure not to let the master cylinder reservoir run dry during the process). No "pumping" necessary...

:: I too have always used the gravity method. It really the best way to get the air out.

The reason for this scientific question is because I do this job alone.

So, for each pedal pump (depress) I put a piece of wood between pedal and seat for hold the pedal, then I go to the rear wheel, open the bleeder, and the brake fluid flows about 15 cms. ( aprox. 6 inch). Close the bleeder, go to the driver seat and repeat again.

Then, if the distance between the proportioning valve to rear wheel is 3.5 meters (aprox. 138 inch), I'll need to repeat this process 350/15 = 23 times in order to remove the last air bubble.

If someone can help me with a "mathematical calculation" of this question, it would be of great help.

Thanks again

Buy a mighty vac bleeder or ask for help

You are making it very complicated. Open bleeder. stick a tubing onto bleeder valve stick other end in a jar. Let it dribble out until you see no air in the tubing, close bleeder valve check master cylinder keep top up. Replace master cylinder cover after each refill.

^^^ This ^^^

Although to be honest, you don't even really NEED the tubing, especially if your old fluid is all brown and funky; you can just watch it until clean fluid starts to dribble out.

No need for "pedal pumps". No point in worrying about it unless (a) you are in a hurry, and (b) you have an assistant. Sounds like neither of those 2 things apply here.

Or get yourself a pneumatic brake bleeder and call it a day.

https://www.harborfreight.com/brake-...der-92924.html

33 bucks!

I prefer the one man bleeding method with a soda bottle and 3/16 fuel line, its easy and worked great.

https://www.1aauto.com/how-to-bleed-...lf/video/46296

I was really impressed with the gravity method also.

Get a Mityvac, or a pressure bleeder system.

I use a Mityvac that pulls the fluid into a gatorade bottle, I use a 1 way check valve in between the brake bleeder and the gatorade bottle, and I connect the Mityvac to the gatorade bottle. The vac creates vacuum in the gatorade bottle, which pulls the fluid from the caliper into the bottle. While itpulling fluid, I keep the reservoir topped off.

Its significantly cheaper than the Motiv option below, but the Motiv option is definitely better.

Mityvac.
https://www.harborfreight.com/mityva...AaAp7uEALw_wcB

Or a Motiv pressure bleeder.
https://www.summitracing.com/parts/m...oaAu93EALw_wcB

+1 on the mighty vac. i recently installed all new brake components on a car i'm building (master cylinder, rotors, calipers, lines, etc... - i mean everything!) so there was no fluid anywhere in the system. for the life of me i couldn't get the rear brakes properly bled. there was fluid back there, but couldn't get all the air out of the new lines. i even let it sit for a whole day and periodically checked it / added fluid. gravity method just wouldn't work for me. got a mighty vac and made this job super easy.

I didn't start with the clean system on my GTA, but about 5-6 years ago, I completely flushed it.

Use a turkey baster (or the mityvac) suck all the fluid out of the open reservoir, taking care to keep enough fluid in there so the ports on the bottom remain submerged.
Fill it with clean fluid.
Repeat as necessary till the fluid is spotless and any debris is removed from the reservoir.
The, do the brake flush.

This way you aren't pulling old/dirty fluid from the reservoir through the lines, and instead are just pulling nice NEW fluid through the lines.

Heck, you could probably do the suck/fill onto master once a year if you really wanted to ensure the fluid was always super clean.

The Harbour Freight pneumatic bleeder is cheaper still.

https://www.harborfreight.com/brake-...der-92924.html