Help ! How do you bleed the master cylinder on a 1991 S10 Blazer SUV with 4WAL ABS brakes? Don't say "Just like any other master cylinder."

The master cylinderprimary port on a 1991 S10 Blazer SUV 4WAL ABS brakes requires a9/16"-18 inverted flareline fitting(or appropriate inverted flare plug to bench bleed)whichis IMPOSSIBLEto find.Since you cannot findthe appropriate brake tubing, or a 9/16'-18 inverted flare fitting or a 9/16"-18 inverted flare plug, how canyou bench-bleed a newmaster cylinder without those items?

I have never bled a master cylinder when it was mounted on the vehicle. A counterman at NAPA told me theonly wayyou can blled the master cylinder on that type vehicleis as follows:
1. Mount the new master cylinder on the power brake booster.
2. Attachbothbrake lines.
3. Attach a OTC 7853 valve depressor tool on the rear stem of the combination valve.
4. Fill the master cylinder with fluid.
5. Crack open the primary and then the secondary fittingsto let air out as your assistant depresses the brake pedal until it goes to the floor and repeat untilall air is purged.

Is that the only way thatmaster cylinder can be bled?

 

If you cannot get the fittings or even force a plastic plug into the port, then that is how I would do it.

 

The plastic plugs that come with the new MC are push in type and are notthreaded. They will pop out under brake pressure when you try to bleed the MC.

A 9/16"-18 inverted flare fitting for the front outlet on the MC can still be purchased at any Chevrolet dealership and they are steel fittings. I cantake it to a local welding shop and weld or braze up the hole for a few bucks and make a plug out of it. I would do that but I am going to bleed the MC this morning an don't have time to cobble up a plug. A 1/2"-20 inverted flare brass plug is available at parts stores for the rear outlet port on the MC. The best, simplest and less messy way to bench bleed the MC is with both outlets plugged rather than rerouting the fluid to the MC reservoirwith two short pieces of brake lines, even if you can find a brake line with a 9/16"-18 inverted flare fitting on it.Both ways will work.

I may order a few 9/16"-18 inverted flare fittings from GM and make plugs out of them and sell them on e-bay to the highest bidder.

 

The GM part number for the unique 9/16"-18 inverted flare steel brake line fitting for a 1/4"brake line. It fits the front outlet port on the S10 Blazermaster cylinder. Part number 15724650....MSRP is $4.25 each.

It will take a week to get one from the nearest warehouse...Memphis TN. I will weld up the brake line hole and make a plug out of it so I can bench bleed a master cylinder which is always the best method. That is in case I have to bleed a master cylinder again.