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New Brake System Fluid and Bleeding
#1383633 Fri Nov 06 2020 12:56 PM
Joined: Nov 2009
Posts: 60
D
Wrench Fetcher
I finally have all the replacement components for my 1956 Chevrolet 6100 brake system.

All new brake lines, wheel cylinders, master cylinder, brake hardware, reconditioned hydrovac, relined shoes, turned drums, etc. Basically if a part could be replaced or reconditioned it was, so the system is going to be bone dry.

My question has to do with adding fluid and bleeding the system. I know the preferred method is pressure bleeding, but do I add fluid to the master cylinder first, then try to bleed non pressured (ie just pump the pedal) to get fluid in the system? Or just go right to the pressure method?

Any tips for this would be greatly appreciated.

Thanks

Re: New Brake System Fluid and Bleeding
DougH6100 #1383634 Fri Nov 06 2020 01:16 PM
Joined: May 2017
Posts: 344
S
Shop Shark
I always bench bleed the master, before installing it, so that it can be tipped to ensure all air is out. Sounds like you have already installed it so that might be tough.

Beyond that, I would go straight to the pressure bleed as that has a steady flow of fluid uninterrupted by pedal movements. That seems to result in fewer chances for trapped air and no chance of reverse flow of air back to the master. There would also be fluid in the cylinder of the master at the first stroke of the pedal for proper lubrication. That might not be the case with straight pedal bleeding.

Sounds like you are going to have a brand new, first rate system, nice going!


Mac :{)

1962 K10 short step side, much modified for rally
1969 T50 fire truck, almost nos, needs a few things
Re: New Brake System Fluid and Bleeding
DougH6100 #1383647 Fri Nov 06 2020 04:05 PM
Joined: Nov 2005
Posts: 5,826
3
3B Online
Master Gabster
Hy DougH6100, as Sweepleader said bench bleeding the master cylinder is the best way to achieve a good bleed of the system. There is also a proper sequence in which to bleed, your truck has a Hydrovac so it is to be bled first, according to the maintenance manual the uppermost bleed screw should be bled first and then the one at the end of the tubular projection, then depending on which rear brake system your truck is equipped with, Twinplex (Bendix) or FR-3 (Wagner). Twinplex have only one bleed screw per rear wheel brake, FR-3 have two bleed screws per rear wheel brake. After the Hydrovac bleed left rear brake, if two bleed screws are present (FR-3) bleed the lower one first, then the right rear, if your truck has Twinplex rear brakes the next wheel cylinder to bleed is the one bleed screw on the left front, then the right front. If your truck has FR-3 rear brakes then bleed the right front lower then upper then left front lower then upper bleed screws. The maintenance manual says that pressure bleeding is the only method recommended for trucks larger than one ton or equipped with a Hydrovac. Hope that helps, finger tips sore now.

Re: New Brake System Fluid and Bleeding
DougH6100 #1383653 Fri Nov 06 2020 05:36 PM
Joined: Nov 2009
Posts: 60
D
Wrench Fetcher
Thanks for the tips, I have read the shop manual and my truck is equipped with the Bendix brake system. Nothing is installed yet so I will absolutely bench bleed the MC.

Re: New Brake System Fluid and Bleeding
DougH6100 #1383711 Sat Nov 07 2020 02:31 AM
Joined: Feb 2016
Posts: 440
7
Shop Shark
Doug, when I did my brake work I also had a totally dry system. I rebuilt the master and wheel cylinders, all new rubber hoses, all new cupro-nickel hard lines. I bypassed the hydro-vac due to internal leakage. I had no problems filling and bleeding the entire system after everything was installed. I did it the old fashioned way with a helper working the peddle and me at the wheels. I did adjust the shoes real close by jacking up one corner at a time and having a slight drag on them before bleeding. At this point I am not using the hydro-vac, just manual brakes. It does a good job and I've had it loaded three trips with 100 bales of hay. I know the hay is not as much of a load as the truck was spec'd for but it's a good start.


1957 Chevrolet 5700 LCF 283 SM420 single speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto
Re: New Brake System Fluid and Bleeding
DougH6100 #1383717 Sat Nov 07 2020 03:51 AM
Joined: May 2017
Posts: 344
S
Shop Shark
When bench bleeding a master I use a syringe with a rubber snout on it in the brake line ports. Fill the reservoir about half way and draw fluid out the port, then tilt the syringe to keep any air in it and push most of the fluid back. Repeat with the other port. Re-do until no more air comes out. Cap the port not bleeding, keep fluid in the reservoir. I tilt the master so that air inside it will be forced out the reservoir when fluid is pushed into the port.

This is the one I use but there certainly are others out there:

https://www.napaonline.com/en/p/NMB...fZU3S3UlNqXiPyahJC7wF3a8xgsaAsZQEALw_wcB

A pressure bleeder or just manual operation of the master can be used too. Keep the ports plugged as best you can while the master is installed to help keep air out. Usually fluid dribbling from the reservoir out the ports will keep air from coming in.

Last edited by sweepleader; Sat Nov 07 2020 03:54 AM.

Mac :{)

1962 K10 short step side, much modified for rally
1969 T50 fire truck, almost nos, needs a few things
Re: New Brake System Fluid and Bleeding
DougH6100 #1383720 Sat Nov 07 2020 05:17 AM
Joined: Dec 2015
Posts: 2,142
Big Bolt Forum Moderator
read and follow your manual carefully, on the rear shoe adjustments, the adjustment on the upper shoe on each rear wheel needs to be backed off all the way. Otherwise it can trap air in that wheel cylinder.


Mike

1955 Chevy 6400 ex-flatbed (no bed now!)
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