Master cylinder ID help needed

[83Stepper]

So a little back info on what I've got. 83 Stepside that was originally a 4.1 I6 3 on the tree. PO swapped the 4.1 for a mild build 350 sbc and moved the column shifter to the floor. Appears that the PO, or one of them, had intentions of hot rodding it and did some funky stuff. Won't get into all the details but yeah it's been a process just to make it a daily again.

TL/DR; doing the brakes and appears that the master cylinder is toast. Pedal is fine to about 3/4 then gets really hard to depress and can't bleed the rear brakes. So I'm leaning towards the master is done for. Believe it's a JB1 system with manual brakes and 11" rear shoes, no RPO on the glovebox door. Casting number on the master is 18006812. Rough measurement of the bore without tearing into it appears to be approx 1 3/16", 30mm-ish.

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Trying to at least find a rebuild kit, but no luck so far online. Swear these things are non-existent or I've got a Unicorn. Canadian built truck if that helps any. Not seeing any signs that this was a power unit that had the old vacuum booster removed. Any help would be greatly appreciated.

 

[Keith Seymore]

For 1983 the base manual system is JB1 and the master cylinder is part number 18006064 broadcast code CU.

Built in Oshawa makes no difference.

K

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[83Stepper]

For 1983 the base manual system is JB1 and the master cylinder is part number 18006064 broadcast code CU.

Built in Oshawa makes no difference.

K

You must be registered for see images attach

Greatly appreciated! Did some digging and found some info but nothing like this. Appreciate you and the info!