# 1968 GTO master cyclinder????



## rob40999 (May 18, 2018)

Hello All: Still working on braking system on the GTO. I got one smart mechanic and one dump mechanic. One mechanic says the front reservoir works the back brakes and the rear reservoir works the front brakes????

The other mechanic says the front reservoir works the front brakes and the rear reservoir works the rear brakes????? 

I have disc brakes on the front and drums on the rear... I had a conversions kit put on by the other owner. I got no paper work at all when I bought the car.

Which mechanic is right???? Why me, Why me..... LOL LOL

Bobby  LOL LOL


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## PontiacJim (Dec 29, 2012)

rob40999 said:


> Hello All: Still working on braking system on the GTO. I got one smart mechanic and one dump mechanic. One mechanic says the front reservoir works the back brakes and the rear reservoir works the front brakes????
> 
> The other mechanic says the front reservoir works the front brakes and the rear reservoir works the rear brakes?????
> 
> ...



On most GM cars, the front reservoir supplies front brakes. Rear reservoir supplies back brakes. Additionally, each line has a different sized threaded fitting so you cannot install it incorrectly IF the original brake lines are used. The '68 dual master appears to have the same size reservoirs. I have seen other master cylinders which have a larger and smaller reservoir. The larger reservoir typically goes to the disc's. Other makes may be different.

Seeing you have a conversion (non-stock?), it could go either way and would be best to know who the conversion is by and get their recommendations.

The '68 Service manual shows front reservoir going to front brakes & rear-to-rear. The Master cylinder is also a different size. The drum brakes used a master cylinder having a 1" dia cylinder bore while the drum/discs are shown using a 1 1/8" dia cylinder bore. Not having the correct sized master can present problems as well. 

And, if the master was added to an existing power brake booster, (not purchased as a complete power brake master/diaphragm set-up), there is a push rod that comes from the booster diaphragm that activates the master cyl. From the Service Manual, pg 200, "This has to be adjusted correctly to work with the master cyl. If not, the primary cups of the master cyl can overlap the compensating ports and there will be no flow of air or fluid when the pedal is "stroked" and can trap fluid in the hydraulic lines and cylinders and cause brake drag."


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## BearGFR (Aug 25, 2008)

On my 69, the front reservoir goes to the front brakes, the rear reservoir goes to the rear brakes - for certain. Unless someone has been fiddling with your connections you should be able to follow the brake lines from the MC and figure it out.

Bear


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