Brake Master Cylinder, what adapters do I need to make this work? Pic's inside.

[Nasty-LSX]

I looked all over online to find out what size front and rear brake line port size is for my 85 K20
and my 86 stepside. NO LUCK FOR INFO!! The k20 has a all cast steel body and steel lid. the 86 has a aluminum body
with a plastic resevoir. I bought the brake master cylinder on amazon and it said to fit the K20. I figured all was good
since the stepside had one identical to the one I bought. When I got it and went to install it the line fitting are different.

I know there has to be a flare adapter for the brake line fitting. I could just send it back for a refund but would like to see
if I can make it work with adapters. Anyone know the size difference? here are some pics.

So this is the one they sent me. its the same as on my 86 stepside.

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this is the one from my K20.

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whats so funny is the 85 and the 86 are leaking like crazy from the rear.

 

[Nasty-LSX]

Here is the one on my 86 stepside leaking like crazy also. Yes I have a new one for this one also!

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is there a brake company I can call to find out adapters size's?? I was going to call MASTER POWER BRAKES tomorrow and see what they say and call inline tube also.

 

[CountKrunk]

Id just start calling all decent companies and see what ya get

 

[RanchWelder]

You kinda need to be careful with the diamter of the hydraulic shaft in the center of the master cylinder.
The all cast iron unit looks like it might be 1-1/8" main shaft, which has a completely different pulse rate or compression to the system than the stock 1" shaft the aluminum housing unit you recieved has. It will not likely function unless you can determine the specs of the main shaft are the same. Then there's thread size difference.

Brakes are high science. The proportioning means a lot.
If you put the incorrect rear size master cylinder to proportioning, your rear wheels might lock up and spin you out, during high speed cornering or an emergency stop.
Front's are supposed to brake first, because of engine weight and angle of steering, while avoiding impact.
Rears should continue sticking to the road around a corner. If they lock up first, your off a cliff on Hollandale.

Toonsis the driving cat.

Quality adapters are not cheap. Getting tough to find good brass or stainless fittings.
Matching the tube nuts can get infruriating, switching from stock.
Adapters lower the flow ratio. Not a good idea, unless you really have done the math.

Here's what I found:
https://www.rockauto.com/en/catalog...052109,brake+&+wheel+hub,master+cylinder,1836


ACDELCO 18M1884 Gold / Professional; Includes Reservoir Info with 13 IN Brakes
Guess you have 13" brakes? This answers two threads.

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I think you just helped me identify the new Master Cylinder for my 14-Bolt swap, as well.
Looks like the front is 1/4" and the rear is 3/16" tubing?

Guess I'm running a new home run to my heavy duty 13" brakes on my new rear axle and this unit has the smaller sized tube nut so my fronts remain the same. Resolved three threads at once?

Will you try and grab a picture of your proportioning valve, if you have one inline to the rear?
R/A does not list one or the number for 3/16" tubes and 13" brakes.

I might have to buy one off eBait for my swap, to match yours, unless somebody here has one for sale.

 

[RaisedK5]

Fyi guys.

1/2 ton masters have front res to front brakes and rear res to rear brakes.

3/4 and one ton is opposite. Front res is rear brakes and rear res is front brakes.

Make sure you plumb correctly.

 

[Blue Ox]

Fyi guys.

1/2 ton masters have front res to front brakes and rear res to rear brakes.

3/4 and one ton is opposite. Front res is rear brakes and rear res is front brakes.

Make sure you plumb correctly.

Not all. Mine is front to front. The bigger reservoir is the fronts.

 

[Nasty-LSX]

You kinda need to be careful with the diamter of the hydraulic shaft in the center of the master cylinder.
The all cast iron unit looks like it might be 1-1/8" main shaft, which has a completely different pulse rate or compression to the system than the stock 1" shaft the aluminum housing unit you recieved has. It will not likely function unless you can determine the specs of the main shaft are the same. Then there's thread size difference.

Brakes are high science. The proportioning means a lot.
If you put the incorrect rear size master cylinder to proportioning, your rear wheels might lock up and spin you out, during high speed cornering or an emergency stop.
Front's are supposed to brake first, because of engine weight and angle of steering, while avoiding impact.
Rears should continue sticking to the road around a corner. If they lock up first, your off a cliff on Hollandale.

Toonsis the driving cat.

Quality adapters are not cheap. Getting tough to find good brass or stainless fittings.
Matching the tube nuts can get infruriating, switching from stock.
Adapters lower the flow ratio. Not a good idea, unless you really have done the math.

Here's what I found:
https://www.rockauto.com/en/catalog...052109,brake+&+wheel+hub,master+cylinder,1836


ACDELCO 18M1884 Gold / Professional; Includes Reservoir Info with 13 IN Brakes
Guess you have 13" brakes? This answers two threads.

You must be registered for see images attach

I think you just helped me identify the new Master Cylinder for my 14-Bolt swap, as well.
Looks like the front is 1/4" and the rear is 3/16" tubing?

Guess I'm running a new home run to my heavy duty 13" brakes on my new rear axle and this unit has the smaller sized tube nut so my fronts remain the same. Resolved three threads at once?

Will you try and grab a picture of your proportioning valve, if you have one inline to the rear?
R/A does not list one or the number for 3/16" tubes and 13" brakes.

I might have to buy one off eBait for my swap, to match yours, unless somebody here has one for sale.

Thanks Ranchwelder. I went to every auto parts looking for the ACDELCO 18M1884 and no one carries it.
I went ahead and ordered from RockAuto. Same one you have listed here. I'll get you a pic of the proportioning
valve within the next 3 hours! Thanks again.

 

[RanchWelder]

Edited: Man do I feel dumb, I thought you were in Los Angeles, Nasty-LSX?

Pardon me for insulting you, Mr. Producer!
I asked the guy rebuilding the white and green pickup for the part number on the proportioning valve.

Hope you'll pardon me for the mix up!