Stupid master cylinder question ...

[67 455 Bird ragtop]

Ok have a sort of dumb master cylinder question. I'm using the hydroboost system from a 1978 Eldorado on my 67 'Bird. Now "normally" the rule of thumb is the larger reservoir is for the front and smaller rear. Well this master cylinder has the same size reservoirs. But it does have two different size ports. One is 9/16 x 18 and the other is 1/2 x 20. So safe to assume the larger port is the front brakes and the smaller is teh rear???

Like I said dumb question but better safe than sorry.

[Apogee]

Nope, it's not safe to assume that the larger port goes to the front brakes. Since you have symmetric reservoirs, I'm guessing you might have a C3 Corvette MC? If that's the case, the front port goes to the front brakes and visa versa. If it's something else, post up what it is and I'm sure somebody can tell you which port is which.

Tobin
KORE3

[67 455 Bird ragtop]

Ooops .. sorry. It's a 1978 Eldorado MC. The description on RockAuto says the 9/16" is primary and the 1/2 is secondary. Just found that.

[Apogee]

I'm not personally familiar with the 1978 Eldorado MC, so I can't say, sorry.

Tobin
KORE3

[NOGO]

There are two different size fittings, but the size of the fittings does not indicate anything and only prevents mixing the lines up in the stock application. Typically the front reservoir and fitting will be the outlet to the rear brakes.

[ArtosDracon]

Front is front rear is rear, internally they're identical flowing, so make sure you have an adjuster inline for the rear, the bias is bad out of the box.

[67 455 Bird ragtop]

Front is front rear is rear, internally they're identical flowing, so make sure you have an adjuster inline for the rear, the bias is bad out of the box.


So for ease of bending/routing my lines from the MC to the prop valve i "could" run rear-to-front and front-to-rear if necessary since they flow the same ??? Aod I'll keep in mind the bias for the reas once the car gets on the road.

[Hydratech®]

It is actually critical to make sure you get the brake lines connected up to the right ports on the MC. Here is the part detail on the '78 Eldo MC:

http://www.raybestos.com/wps/portal/generic/productDetail?productId=1156414&applicationId=&partNumber=CHILD-BDBL-MC39195&fromCatalog=true&productImageId=&__formSubmitted=true&__resetPortletState=true&imageURLList=&defaultURL=http%3A%2F%2Fimages.affiniagroup.com%2F ai%2Fimages%2FBrake%2FRAYBESTOS%2FMC39195-ANG-P01.jpg&imageIndex=&displayThumbNails=true&langId=-1#

On this particular factory '78 Cadillac Eldordo MC, it is front port = front brakes / rear port = rear brakes.

When in doubt, look it up online at any competent auto parts website or www.raybestos.com as getting the lines at the MC accidentally hooked up backwards will create overly aggressive rear brake actions along with under powered front brake actions. The master cylinders do not produce equal output out of the ports as some believe, as the locations of the compensation ports in the fluid wells and the internal piston setups are specially tuned to provide different front / rear volumes and output characteristics.

[67 455 Bird ragtop]

Thanks for the clarification. Your response was my first impression of my MC.