[wave1957]

I need a new M/C (and booster) for my '70 Impala, with factory power front disc brakes. I am staying with the original set-up/parts.
When I go on Rockauto, there is a good choice, but most of them do not specify if they are for Front disc cars, or if they are for power brakes or not.
How do I know which ones can be correct for me? Or do I have to go for the only one that specifies power front disc brakes (of a brand I have never heard of, by the way, Dynamic Friction)?
Any input is appreciated. Thanks!
At least for the brake booster, there is no such problem there is only 1 available on Rockauto!

 

[curtis73]

It literally tells you under the part number. The one that has only one remaining is for front drums.

 

[wave1957]

That is just it, it does NOT say for each M/C they offer, whether it is front discs or power.. The one you mention for instance does not mention power brakes or not. Only one mentions power brakes and front discs, the Dynamic Friction piece.
So, how can I identify a power front discs M/C?

It literally tells you under the part number. The one that has only one remaining is for front drums.
View attachment 618970

 

[55_327]

See what you can find here: ACDelco Parts

If you google the AC Delco part number, you'll get all kinds of hits. Have to say I've had good service from AC Delco parts over the years. Much better than, for example, Cardone, which is hit and miss.

As for RockAuto, I'll buy from them if I'm 100% sure I'm ordering the right part, but it's hard to beat your local parts stores when you're not exactly sure. On something as heavy as a master cylinder, you could easily spend $15 or more on return shipping.

Just thought of this: Master Power Brakes is a great source for new master cylinders, and they will ask you questions to make sure you get exactly what you need.

 

[curtis73]

Well, you can narrow it down two ways. First, in 1970, GM did not do ANY disc brakes that weren't powered. Disc brakes require far more pressure to operate than drums and there would be no way to stop a disc brake vehicle without power assist. If you see disc brakes, it is for power brakes.

Secondly, look at the specs of one that you're sure is correct, like the Dynamic Friction one. Look at the specs by clicking info and it will tell you the bore size. Now go to the ones that don't have a description and compare bore sizes. GM would have only offered two masters for that car. Any other bias tuning would be done by a proportioning valve difference.

Or.... just order one of the ones that already says "power disc." Easy button.

Another thing you can do is search on Amazon or Ebay (or a GM parts website) and find the part number that would be used on your car. Plug that part number into the search bar at Rock Auto and it will populate a list of interchange parts.

 

[wave1957]

Thanks for the tips, guys! I will do some investigating like you two say.
I like to buy from Rockauto because they have a good choice overall, and because I am in France, and ordering/shipping is really with them, and they are cheap! But I have bought parts from other sites too, so I do not limit myself to Rockauto. Anyway, the local parts store and returning parts are not options for me...

 

[curtis73]

That is just it, it does NOT say for each M/C they offer, whether it is front discs or power.. The one you mention for instance does not mention power brakes or not. Only one mentions power brakes and front discs, the Dynamic Friction piece.
So, how can I identify a power front discs M/C?

It does say. You're misinterpreting how it's being presented. You have to know what they're trying to say. For instance... GM knows that if it's disc, it's power, so if you open a GM shop manual for a 1970 Impala it might give you a bleeding procedure for "w/ front disc" and one for "with front drum." If you open a Haynes manual it might say "w/power brakes" and "w/o power brakes." If you open a Chilton's manual it might say "w/ power disc" and "w/ manual drum."

So when an aftermarket company advertises a part like this, they cover all the bases. Dynamic Friction decided to include them all. But under that Dynamic Friction part number, one of the lines says "Front Disc Power Brakes" That's your huckleberry.

Heck, just take the part number and name and google it and you'll probably find 30 forum posts from all over the web that will answer your question in 15 seconds.

 

[wave1957]

Curtis73, I still disagree with you but it does not matter, really.
I did go on a forum (Hot Rodders, an excellent forum!), I was given ideas on how to search, and I was able to confirm that the AC Delco M/C advertised by Rockauto (which does not show any indication of type) is the one I need: perfect, I like new and Ilike AC Delco over a brand I do not know.
Thanks guys!