C2 Dual Master Cylinder

[William G.]

Had master cylinder rebuilt --now I want to bench bleed it with denatured alcohol to clean it. After cleaning I will empty it out and bench bleed with silicone dot five brake fluid. What if I can't get all the denatured alcohol out --will it affect the silicone --Do I need to let it all evaporate and dry out before adding the silicone or does it matter??? Any one had any experience doing this?? Thanks, Bill

[Terry M.]

Re: C2 Dual Master Cylinder

I used the alcohol to flush the remains of the glycol-based fluid out of the brake lines on my 1970, and then blew shop air through the lines. That has been 20+ years ago, so my memory is hazy, but I believe I disassembled the brake master cylinder to clean the old glycol-based fluid out. I would suggest disassembly since there is nothing to be gained by bench bleeding with alcohol, and one can be sure of the evaporation of the alcohol if the master cylinder is disassembled. Use the DOT 5 to lubricate the seals during assembly. One should also be sure the wheel cylinders are clean of the glycol fluid also. I put the DOT5 in when I was rebuilding the calipers, so that made the task easier. No issues in the last quarter century or so. I did flush the DOT5 once in that time, just for s)&) and grins.

[William G.]

Re: C2 Dual Master Cylinder

Terry
Thanks for the reply.

The master cylinder was just rebuild and i dont know what they bench
bled the master cylinder with. So i was going to bench bleed it with
denatured alcohol and drain it out and then put in Dot 5 brake fluid and
blench bleed it and then install it on the car.
Is all this nessary.
The system has not had any brake fluid in the brake lines or the calipers.
They have all been replaced. 1965 WITH POWER BRAKES.
Bill

[Terry M.]

Re: C2 Dual Master Cylinder

Well I guess bench bleeding with alcohol will not hurt, I just wouldn't be comfortable with the possibility of residue of the lubricant they used being in there, or the residual alcohol. The only potential problem with the Master Cylinder will be whatever they used as a lubricant when assembling it, and that should be minimal. Did they tell you it was bench-bled before they sent it to you? That is not usually done because of the remaining fluid leaking during shipment.

Since you don't know what they used (at least you don't mention what they used) as a lubricant during assembly, cleaning with alcohol with it disassembled would be best. That eliminates any residual alcohol in it, and gives you the chance to lubricate the seals with DOT5 for reassembly. The master cylinder is not that hard to disassemble, once it is out of the car. The FSM will show how to do that, with pictures.

I don't think there would be any issue doing it the way you propose, but it is a roll of the dice. Perhaps there is someone on this board who has tried that.

BTW: I would flush some alcohol through the brake lines, even if they are new. Then blow them out with shop air before connecting the calipers. Just to make sure nothing crawled in there, or anything fell into the open lines. But that is just me.