70 pb master cylinder replacement anxiety

[Chris H.]

I'm about to reunite my 70 LS5's original power brake master cylinder with the car. The unit was rebuilt by Whitepost Restorations. I requested that they not restore the exterior of the unit, as I hope to Bowtie the car one day.

When I purchased the car, the seller had recently installed the deluxe Muskegan brake kit (new m/c, rebuilt calipers, new lines, etc.) The car currenlty has a nice hard pedal.

I have a few questions about installing the original m/c.

My first concern is getting all the air out of the system. I've got the Stainless Steel Brake Corporation manual to use as a guide. I'll probalbly go the gravity bleed method. They emphasize bench bleeding the mc in a vice before installation in the car. Is there a bench bleeding kit out there? Do I need to cobble together some setup using fittings / tubing?

Also, the rubber gasket between the power brake booster and the m/c is there, but kind of dried up. This gasket is just to seal the vacuum, right? If I had a bad seal, it would just require more braking effort, not a spongy pedal, true?

Thanks for any insight. I've read lots of brake bleed horror stories and don't want to go there.

[Jim T.]

Re: 70 pb master cylinder replacement anxiety

Chris you can find the master cylinder bleeding kits at some auto parts stores. The kits are usually all plastic that screw into the master cylinder with a tube running up into master cylinder so you can see that all the air is out.
I have taken a prepared master cylinder, mounted it, and loosly fit the brake lines letting the master cylinder bleed fluid into the lines and then tighten them. I did not have to bleed any air out for the brakes to work using this method. I did go ahead and run new fluid through the calipers just to change out all the old fluid. Worked out well the couple times I have done it. This only applies to a previous good working system and just changing out the master cylinder.

[Chuck S.]

Re: 70 pb master cylinder replacement anxiety

Chris,

I believe the gasket you reference between the MC and the booster (Part No 730392) was intended only to seal dirt and grease out the area between the MC and the booster, and is not essential for operation.

After looking for this gasket about a year or so, I realized it did not exist either NOS or repro. Not even the Good Doctor sells it, and this part would be right up his alley. Makes me think that not enough people are demanding this part to make their brakes work.

I don't have my booster in front of me, but I am inclined to believe that the vacuum sealing is done inside the booster.

[Larry S.]

Re: 70 pb master cylinder replacement anxiety

As for your first concern I just purchased a new tool This is a picture of it.It is a power bleeder made by motive products.This is the url of there web site (cut and paste it into your browser)http://www.motiveproducts.com/index.htm

I have always had troubles bleeding brakes (silacone in a vette)and this tool made easy work of bleeding brakes.I highley recomend it to any one with a vette who will work on there brake system more then once.I have described it on a different corvette website/forum I just dont know if its OK to link to the other forum otherwise I would link to the other post exspaining my exspereance with this tool




A picture of a power bleeder.