Can u tell from vin if a truck has 1" or 1.25" rotor?
 

see above

Re: Can u tell from vin if a truck has 1" or 1.25" rotor?
 

no sir

Re: Can u tell from vin if a truck has 1" or 1.25" rotor?
 

Pull the wheel off and measure outside to outside of the rotor. You'll know right away.

RIZ

Re: Can u tell from vin if a truck has 1" or 1.25" rotor?
 

Check the RPO codes. Heavy Halfs, fleet trucks and special orders had them.

Re: Can u tell from vin if a truck has 1" or 1.25" rotor?
 

My 87 is a "Heavy Half" with 1.25" Rotors.
It has two RPO codes , "JB5" and "J55"

JB5 Brake System: Power, Front Disc, Rear Drum, 6400 Lbs.
JB5 BRAKE POWER, DISC/DRUM, 6,400 LBS

J55 BRAKE SYSTEM HEAVY DUTY

Desert

Re: Can u tell from vin if a truck has 1" or 1.25" rotor?
 

The best way is to measure.
I had an '86 with the HD rotors and an '83 with the light duty rotors.
I'm not sure what GM was thinking.

I know all the 71-72 front ends are 1-1/4".
I think all the 73-80 front ends are also 1-1/4".
81-87 is anybody's guess,...

Re: Can u tell from vin if a truck has 1" or 1.25" rotor?
 

Based on this I'm guessing JB3 would be the RPO for the smaller rotor.

K

Re: Can u tell from vin if a truck has 1" or 1.25" rotor?
 

I will pull the wheel and check it out. I was in front of the computer at work and was trying to figure it out.

Re: Can u tell from vin if a truck has 1" or 1.25" rotor?
 

JB3 BRAKE POWER, DISC/DRUM, 4,600 LBS

Dez

Re: Can u tell from vin if a truck has 1" or 1.25" rotor?
 

Right. That would be the smaller power brake system.

I know there was a manual system available as well, JB1 perhaps?

It just occured to me that, during our recent move, I found the actual component charts that we use/used to release the specific brake hardware for the various systems - from 1979 or so. I'll see if I can find it again and post it up.

K

Re: Can u tell from vin if a truck has 1" or 1.25" rotor?
 

my 80 big 10 had 1" rotors that some one swap in, but it now has 1.25 rotors front and rear

Re: Can u tell from vin if a truck has 1" or 1.25" rotor?
 

off topic but kinda the same but I went to order front pads for my CC dually and they asked me what size my rear breaks were? the sizes were 13.2 1/2 or 13.3 1/2 where do i measure?

sorry for the thread jack

Re: Can u tell from vin if a truck has 1" or 1.25" rotor?
 

K

Here is one of many resources.

http://www.c2e.info/rpocodes/gmrpocodesGthroughM.html

JB1 BRAKE, MANUAL DISC/DRUM 4300 LBS

Dez

Re: Can u tell from vin if a truck has 1" or 1.25" rotor?
 

Ok - as I mentioned, here are the actual charts that were used by the design engineers to release the various brake components. You can see the hardware sizes, bore dimensions, friction material, etc and breakdowns by part number.

Based on the '87 chart it looks like the 1" rotor was used only on the two smallest systems, the JB1 manual and the lightest JB3 power. You should be able to tell by looking for your truck configuration on here:

1974 and 1987 shown:

http://i1016.photobucket.com/albums/...ase74-1001.jpg

http://i1016.photobucket.com/albums/...ase87-1001.jpg

I'll post the complete set as a reference in a separate thread.

K

Re: Can u tell from vin if a truck has 1" or 1.25" rotor?
 

easiest way is to stick your index finger in the holes that run along the edge of the rotors. I if you finger goes in its 1.25 if it doesnt its 1"

works for me. lol