[71firebird400]

Hi; I have a 1971 Firebird w/ manual brakes (disc/drums). At this point the car will barely stop; the tires won't lock up at all. I replaced the old master cylinder with a replacement from Napa. This is what the current Master Cylinder looks like:


Now; this does not appear to be right since every other system I've seen with discs/drums has a larger "bowl" in the front than the rear. I've tried numerous parts websites and they always come up with this master cylinder for a '71 Firebird. But; if I search for a 1975 Firebird with manual brakes I get this Master Cylinder:


The bottom one looks better to me than the top; would there be any issues if I were to put the '75 Master Cylinder into my '71 car? Any thoughts/opinions would be helpful; thanks!

[scottk]

There should be no issues as long as the cylinder matches your pushrod.

But the top cylinder is the correct casting style for 70-74 manual disc/drum.
They used the dual bail oval cap like the 67-69 disc cars. part# 5455517.

[BDHABT]

I have the master cylinder in the top picture on our `70 Firebird.The car has been in my possesion for 19 years,and I`ve never changed the m/c.My parents bought the car new,and I could not find any reciept for the m/c being changed.They could have lost the paperwork though.Mine stops ok,though it does sink a little.Time to replace.

[Ken K]

When you buy a replacement master cylinder, they sell you one that is pretty much standard. There are too many different style master cylinders to get one that looks the same. I went to a few parts stores and had them open up the boxes to look at the master cylinders, they were all the same. They have it in the computer to ask if it's a deep or shallow piston. The deep piston is for manual brakes. The prices are all over the place on the master cylinders, it depends who is selling it. Ask who the remanufacturer is. Most places use Cardone. Carquest charges about $19.00 with a core.

[71firebird400]

Shoot; I was hoping I had the wrong one. I guess my next step is the proportioning valve since its the only part I haven't replaced.

I don't believe its the brake lines because the car stops straight and if it were say the rear line then wouldn't the fronts lock up still? Since it seems like the system is not achieving full power I believe the restriction has to be something that controls the entire system (master cylinder or proportioning valve) Of course I could be wrong; but at this point I'm getting fed up.

[screamingchief]

Sorry I did'nt reply to your PM right away,had some stuff to do today,but better late than never,right?

Anyhow here you go,same deal as you got from NAPA,and that is the correct style master for the car,all the manual disc F-bodies of this vintage that I've seen use the same style master.

Likely the problem your dealing with lies elsewhere,but never just dismiss anything out of hand as being a possibility,as surely that will be your downfall.

Good luck with this.

[Karch]

Check the piston diameter, as the manuals have smaller diameter pistons so there is more travel to displace the same amount of fluid (which makes it easier to push).

[71firebird400]

Karch- I also thought this could be the problem and checked it.
ScreamingChief- thanks for the picture!

Well I think I'm going to replace the proportioning valve which brings me to my next question; what part number?

I found "25509418" on another forum; but it was for a '78 Firebird w/ power brakes; I'm not sure if it matters though.

Thanks.

[scottk]

The GM dealer might list one for your car.

1978 had larger rear cylinders and a different valve than your car.

The PY parts master lists 5472359 for 71-75 Firebird and Ventura.
It's no longer being reprouced.

the 1257177 is listed online by Delco (172-1350) for 1974 but check with the dealer. The delco online catalog isn't 100% reliable. they start listing a disc/disc valve for the firebird after 1975.
http://www.oewarehouse.com/Merchant2/merchant.mv (ac-direct.com)

[Razorhorn]

Originally Posted by 71firebird400

Karch- I also thought this could be the problem and checked it.
ScreamingChief- thanks for the picture!

Well I think I'm going to replace the proportioning valve which brings me to my next question; what part number?

I found "25509418" on another forum; but it was for a '78 Firebird w/ power brakes; I'm not sure if it matters though.

Thanks.

Keep us posted if replacing the proportioning valve addresses your problem. There's at least one other person on this forum with similar symptoms.

[Karch]

Did this get resolved?

[71firebird400]

nope The car still stops like a barge. Hard pedal, no leaks, no clue whats wrong. It stops straight.

Here's a list of what I've done:

new wheel cylinders in rear
new rear brake shoes
new front calipers
new front pads
rotors turned
new master cylinder

I thought it could be the rubber hoses but they don't flex at all when I hit the brakes; I thought it could be the lines but all the brakes bleed with the same rate of flow (which looks normal to me). I left it at replacing the proportioning valve next, but I have not done this yet as I've been preoccupoed with other projects. I'll let you all know when something happens!

[screamingchief]

I thought it could be the rubber hoses but they don't flex at all when I hit the brakes

There is absolutely no way you'll be able to "see" if the hoses are bad beyond some extremely obvious external hose damage or leakage.

The only way to know if they're bad is to install new hoses and see if the condition improves any.

I cant tell you how many good "looking" brake hoses I've had to replace as a brake tech,too many to remember for sure!

I'd replace all the hoses before I'd bother with the combination valve.

JMO.

[71firebird400]

Would you recommend stock rubber hoses, or the braided type? I added up the costs and they both come out to be close to the same price.

[screamingchief]

Either or,kinda depends or what you like,if in fact they are the problem the improvement with either type of hose will be like night and day.

The braided deals should expand a bit less than the stock type will,and generally should give a firmer pedal feel,but in some cases the difference is'nt always that noticable on all cars.

It's kinda a draw IMO,as long as appearance is'nt a factor,most would say use the braided hoses.

[71firebird400]

Well I took the easy way out and ordered some rubber hoses from the local Napa; they come in tomorrow and I plan to get them installed by tomorrow evening. I really hope this helps (since I'm running out of things to replace!) but if it doesn't thats no big deal.

Oh and I've got a cool story to share- today I was cruisin with my little brother and we spotted a split bumper 70-73 camaro parked behind a mini storage. We decided to stop and see if it was possibly for sale, after talking to the guy who owned the place for a while he mentions there's another car under a cover thats a "heavy duty" firebird. I asked him if we could check it out and sure enough its a '73 SD455! First one I've ever seen in real life. The car looked pretty rust free but it would need a lot of work (interior was shot, as was paint). Anyways I thought it was cool finding one of those in town.

[Razorhorn]

I FINALLY solved the brake problem on my kids 78. It had similar symptoms as yours - stopped like a barge. One difference is the 78 has vacuum assist.

Anyway - long story short, the problem was cheap wheel cylinders on the rear. The bad ones were actually new cylinders so I never suspected they were the problem. I stumbled across a thread in this forum about a similar problem and I figured for a few bucks it was worth the try. I replaced them and the car stops very well.

One other side-note. I even had a problem with one of the new replacement cylinders on the passenger rear. I couldn't get all of the air out of the system on that side only when I was bleeding. There weren't any visible brake fluid leaks, but darned if air wasn't getting in from somewhere. Returned that wheel cylinder, got a replacement and voila - problem solved.

[71firebird400]

Hey I installed new front hoses (didnt get the rear) and it made no difference. I was experimenting with my brother in the rain and I can barely get the front tires to lock up on wet pavement the rears will only lock up after the fronts. Maybe its bad wheel cylinders, like Razor suggested- I buy all my parts from Napa if it makes a difference.