How to identify proper used brake combination valve application (Page 1/1) MRBLUE87 MAY 10, 09:42 PM I have a customer who wants a used brake combination/proportioning valve for a 1986 GT. I have several saved in boxes and several still on parts cars but no 86's. GM used three parts numbers during the five production years. I do not see a part number on the valves but there is a stamped in number starting with either a 2K or 3K. Catalog shows all 84s except Indy used the same valve as a 86-87 2.8 car. So I checked my four 84 parts cars and my 84 driver and they all have a different number stamped on the side of the valve. I would like to use one of the valves I already have off but how do I identify which is part number 10028622 ? fieroguru MAY 11, 05:59 AM Not exactly sure when the change took place, but the early models used a 13/16" nut and the later models used a 3/4" nut at the end of the housing. All 88s should have the 3/4" nut, but not sure if all the 84-87s used the 13/16 nut. There was a bias change for the 88s, so I would expect them to be different.