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73-87 Chevy _ GMC Trucks => 73-87 Chevy & GMC Trucks => Topic started by: SinisterC10 on November 22, 2016, 04:03:44 pm

Title: Brake bore size?
Post by: SinisterC10 on November 22, 2016, 04:03:44 pm
I have a 1981 2wd truck and am wanting to know what bore size the master cylinder and brake booster is? I don't have the ID sticker in my glove box so I can't look it up. I'm going with 4 way Wilwood discs and want to replace the old booster and master.
Title: Re: Brake bore size?
Post by: zieg85 on November 22, 2016, 04:43:06 pm
in 81 the sticker is on the drivers side inner fender well under the hood.
Title: Re: Brake bore size?
Post by: SinisterC10 on November 22, 2016, 05:23:20 pm
in 81 the sticker is on the drivers side inner fender well under the hood.

Mine is missing.
Title: Re: Brake bore size?
Post by: zieg85 on November 22, 2016, 05:38:43 pm
The forth digit (letter) tells you what brakes you have
http://www.73-87.com/7387info/8187vin.htm
Title: Re: Brake bore size?
Post by: SinisterC10 on November 22, 2016, 05:45:11 pm
The forth digit (letter) tells you what brakes you have
http://www.73-87.com/7387info/8187vin.htm

My vin has a "D", but that's not going to tell me what bore sizethe MC is. I took a dial caliper and the inside bore measures about 40mm or 1.57". I still need to know if this is considered a jb3 or jb5 system.
Title: Re: Brake bore size?
Post by: Irish_Alley on November 23, 2016, 03:27:26 pm
http://forum.73-87chevytrucks.com/smforum/index.php?topic=28592.0
Title: Re: Brake bore size?
Post by: zieg85 on November 23, 2016, 04:07:36 pm
The forth digit (letter) tells you what brakes you have
http://www.73-87.com/7387info/8187vin.htm

My vin has a "D", but that's not going to tell me what bore sizethe MC is. I took a dial caliper and the inside bore measures about 40mm or 1.57". I still need to know if this is considered a jb3 or jb5 system.

JB3 will have 1" rotors and JB5 will have 1.25" rotors, both share the same master cylinder it seems.
Title: Re: Brake bore size?
Post by: Irish_Alley on November 23, 2016, 04:24:41 pm
jb 1 had the 1.417" bore while jb 3 and 5 had the 1.574"
Title: Re: Brake bore size?
Post by: SinisterC10 on November 23, 2016, 05:48:35 pm
Thanks for the info guys. I've decided to put a Hydratech Hydroboost system in the truck. I have one that I had on my Camaro and am going to have Hydratech change out the mounting plate and pedal rod. Gonna cost me about $275.