Mikef714

I have a 71` big block with power brakes. The brake master cylinder was leaking from the rear reservoir into the power brake booster so I replaced the master (only). Now the pedal is firm but it takes a lot of foot pressure to stop the car. The replacement master has the following part number 5468309. The master I replaced has a 5460346 part number.

Could I have the wrong brake master cylinder for my car? Any other thoughts on what might be causing hard braking issue I am now experiencing?

Thank you,
Mike

Revi

The correct casting number should be 5460346. http://www.cssbinc.com/delco-master-...-corvette.aspx

Not sure what the difference is with the 5468309? A google search for 5468309 seems to indicate they were used on Chevelles and Camaro's.

https://www.google.com/search?q=corv...bv=2&oq=&gs_l=

63vette427

The correct one should be 5460346. I can't really help you with the hard braking issue but I'm sure someone will be able to help more.

If you had the original one on there before, I would rebuild that one and use it.

Mike Ward

5468309 is not a Corvette part at all. It's for a Camaro, amongst others.

redvetracr

that master might be from a disc drum combination, especially the #309 which I believe is from a `69 Camaro-Chevelle-Gto, look on the front for a two letter stamping

Mikef714

Thanks everyone for the responses. I called the vendor I purchased the master from and was told the part is interchangeable between a Camero and Corvette. However, with the information you guys provided I am somewhat skeptical. The vendor also said that I needed to send an email to someone else in the company for more help; I have yet to hear anything back.

Thanks again guys for all the help.

Mike Ward

Google says otherwise.

https://www.google.ca/search?q=54683...DNOiyAShpYGYDQ

gbvette62

Did you buy the master cylinder from a Corvette vendor, or a regular parts house? I can't imagine a Corvette vendor selling you a "309", even if it is "interchangeable".

Though the "346" was used on 68-74 Corvettes with power 4 wheel disc brakes, I think it was also used on 67 & 68 Camaros, with the power disc/drum combo. When used with a disc/drum system, GM added a check valve (or what I think GM called a residual pressure valve) to the rear reservoir, to reduce the pressure to the rear drums.

I'm hardly an expert on Camaros, but I believe 69 Camaros with the optional JL-8 4 wheel disc brake system, used the same "309" casting MC, that the power disc/drum 69 Camaro used. The only difference to the master cylinder was that the disc/drum's check valve wasn't needed, and was left out.

I don't know that the "309" MC should make that much difference, but if you have one with the check valve (though today's rebuiders often leave them out), could that be the issue?

The "346" has a 1 1/8" bore, when used with power brakes in Corvettes. The "509" casting was used on 68-74 Corvettes with manual brakes, and it has a 1" bore. If I remember correctly, "309" MC's are 1" bore also. The casting number doesn't really mean much, it's the letters stamped on the front of the MC, and what's inside it that counts.

You said that you had brake fluid leaking into the booster. Are you sure your booster's still good, and/or could it still have brake fluid in it?

Mikef714

Thanks again guys for all the help. I did purchase the master from a forum vendor and did receive an email from the vendor saying that the master they sent me should work fine. They also said that if I didn't power bleed the system (which I didn't, but do have a very firm pedal anyway), the problem I am experiencing could be air in the calipers.

I did think about the booster being bad. However, prior to changing the master, the brakes were working fine. The only indication that there was an issue was the low fluid level brake light illuminating.

Mike Ward

There is no such light on any C3 Corvette. The light indicates either a pressure imbalance between the front/rear brake systems, or the parking brake lever not in the 'off' position.

Please let us know which vendor sent you the wrong M/C. I'll make sure not to order from them.

Mikef714

On Monday my plan is to take the car to a local Corvette repair facility (reputable place according to the forum). I will report back whatever they find.

Thanks again

427Hotrod

The issue is the bore size. Get the right one back on there and you'll be OK.

JIM

Mikef714

I just got my car back from the shop and the problem I was having was due to a bad brake booster. So the fact that the casting # on the replacement master was not for a Corvette didn't, al least in this case, cause any issues.

Thanks again everyone for all the help.

rogernison

The 5468309 is the same as my original 69 non power brake car.
It uses a 1" piston whereas PB uses 1-1/8"