# How to tell your gto is / was disc or drums



## Arie-jean (Apr 20, 2019)

Hello everyone 
I own a 1967 gto. The Pontiac heritage paperwork states my car originally had front 4 calliper discs. It has ( new) drums now.
Can anyone tell me what I can see as " evidence " that my car had discs ? Thx


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## BLK69JUDGE (Jun 10, 2010)

Hello !
a couple items come to mind ...
is the master cylinder still a disc master cylinder
do the brake line look tampered with going to the distribution valve ?

were the rubber brake hose stationary brackets on the frame changed out ??
reach behind the tire and grab the hose ... does it rattle and move in the bracket ??

are the U clips in the end of the hose ? the shape of the hole in the brackets are different 
so if you put a drum hose thru a disc bracket it wont seat properly ,,,, and the clip wont go on ... an it will rattle and be loose ....
does it look like the bracket has been removed ? are the driver and passenger mount bolts the same ? if the patina isnt the same as the frame next to it ... theres a clue
has the car been restored ?
it requires a spindle change to go to the drum backing plate also ,,,, has the front end been apart ??
seems silly someone went to drum when the 69-72 stuff bolts right on the 67 and has been
readily available on parts cars for 30 years and now all the repo stuff is available ...

just my opinion

Scott


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## PontiacJim (Dec 29, 2012)

Arie-jean said:


> Hello everyone
> I own a 1967 gto. The Pontiac heritage paperwork states my car originally had front 4 calliper discs. It has ( new) drums now.
> Can anyone tell me what I can see as " evidence " that my car had discs ? Thx



May not be a lot of evidence left if someone removed the set-up to install the drums. They would have had to do a complete swap to include the spindles.

My guess is that trying to find parts was non-existent at the local parts store years ago or the parts to rebuild were fairly expensive. Remember, its only thanks to the internet that we know that parts are available or there are people who can rebuild them. In my younger years, I could only buy what I could afford and no doubt the disc brakes were not common and if I had a problem or it cost me too much, I'd be going to a junk yard and pulling the more common and readily available parts to do the swap-over which may have even been a much cheaper fix to get my car back on the road faster. Then I would have junked the disc brakes. Many of us did not care about "original" as they were not considered the collectables they are today - so cheap fixes were the means of the day.

One thing not mentioned is that the disc brake option used a different rim. My restoration book states that if you have the stamped steel rims (for hub caps), the 14" x6" rim was stamped "DB." If Rally II rims were used, the standard non-disc wheel was stamped "JA" which my book says fit both drum and disc. However, the 1968 the "JA" stamped Rally II was used for disc brakes while the code "JC" was used on drum equipped cars. 

So seeing that the 1967 Rally II rim, "JA" was the only year it was used on both disc & drums may not be of much help as I had thought IF you have the Rally II's. In 1968, the two different Rally II wheel codes would have been a way to identify.

Continuing on with other identifiers, it appears that the 1967 disc brake option was only available with the power brake booster, while the 1968 option was offered with both a power and manual front disc brake system. So if you have power brakes, this may indicate the disc option.

The power brake set-up with the disc option (RPO 521) used a different master cylinder, Part #5445784 , instead of the drum brake master cylinder, Part #5458522 , used on both manual and power drums systems. The disc brake master cylinder was slightly larger than the standard dual-reservoir master cylinder used for drum brakes.

The 1967 disc brake set-up used a "pressure-metering valve" that is located just below the master cylinder having bracket that is bolted to the same bolt that attaches your master cylinder to the power brake booster. The front reservoir brake fitting has a small steel line that goes to this valve, with the out going steel line from that valve going down to the brake line "distributor and switch assembly." The rear reservoir brake fitting has the steel line that also runs to this switch assembly and you will see an electrical connection found on top where the wire/plug attaches to activate the in-dash brake warning light should either the front or rear braking system fail.

It appears that the 1967 power and manual drum breaks do not have the "pressure-metering valve" under the master cylinder, so this would also identify the disc brake option as only the disc brakes had this valve.

Hope that helps. :thumbsup:


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## Arie-jean (Apr 20, 2019)

PontiacJim said:


> Arie-jean said:
> 
> 
> > Hello everyone
> ...


Hello Pontiac Jim

Thank you very much for the very well documented reply. That really helps a lot.
You are right about saying that a long time ago you didn't care about originality. 
Now I do . And big time. Being a car restorer myself I ( pre war cars ;www.arie-jean.com )care a lot about the originality. 
Not only for the car itself , but also for the " chase " and the process ( just like your reply ) to get the story behind the car and its former owners. 
I still need to dig further. My car should have an WS engine in it , it has a YT engine in it ( but is correctly dated...) 
Thanks again. Greatly appreciated


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## Arie-jean (Apr 20, 2019)

BLK69JUDGE said:


> Hello !
> a couple items come to mind ...
> is the master cylinder still a disc master cylinder
> do the brake line look tampered with going to the distribution valve ?
> ...



Dear Jim

You could be right.
I am looking into it.
Thx for your reply


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