jpatfarrell

Before I start taking things apart that really don't need it I thought I would ask here first.

Restoring a '70 cutlass convertible. Been sitting in a shed for 12+ years. Motor starts buit hasn't been driven in at least 12 years.

Got the drums pulled thanks to advice on this board. They actually look really good with lots of brake pad left and no issues with drums or other components.

Now looking at master cylinder & power booster. This is virtually no movement at all when the brake pedal is depressed. The pushrod does not move at all (in or out). Haven't tried with the engine running yet because the fuel system needs work. I am planning on removing the booster and master cylinder but thought I would ask for comments and advice here first.

thanks,

Pat

oldcutlass

I would try to flush with fresh fluid and bleed the system and then get the engine running first before replacing any parts. The brake pedal will be hard without vacuum to the power booster.

scrappie

Sounds possibly like water or moisture got in the master and rusted or corroded the bore enough to seize it? Have you had cover off? Is there fluid? May be time for a new one? The pedal should move still even without running just not as easy as when it is running. When you bleed your brakes its usually without the car running and the pedal moves quite freely. Does it move at all or is it locked?

jpatfarrell

Thanks..

The pushrod will not move at all (in or out), even with a lot of pressure on the brake pedal.

Front brake fluid reservoir was full and looked clean but rear one was nearly empty.

Even without the engine running I would expect to make the pushrod move in or out with heavy pressure to the brake pedal but it is totally locked.

Does this sound like a master cylinder or power booster (or both) problem?

Pat

classicmuscle442

May want to get rebuild kits for master and wheel cylinders, rock auto sells them cheap and then you can move on to getting the car on the road safely. Then could flush all the old brake fluid out like Eric suggested.

scrappie

Sounds like it may be seized. When replacing a master it is usually bench bleed and the plunger will move fairly easily with a screw driver or something similar so to have it not move at all from pedal input seems to me to be locked. I would take it off and put on a bench to see whats up. At this time your gonna want to free up and clean all the bleeders on calipers and wheel cylinders and wherever else because you will need to bleed out any air and flush system with new brake fluid after replacing master. Brakes are kind of important.

jpatfarrell

Good advice....thanks for everyones help.

I see that Amazon has a Wagner MC101254 Premium Master Cylinder Assembly that is suspose to be the right one for $31.

NAPA has some ranging from $39 to $54 that are suspose to fit.

Seems a lot better than trying to rebuild.

Comments on getting this from Amazon or NAPA.

BTW, I'm not building a show car only want it for occasional drives in the country.

scrappie

In that case you just want the correct replacement. I wouldn't rebuild it, just get a new one. They are cheap enough and probably quicker through your local parts store in case you have to return it? I would go to NAPA. Do they want a core for exchange? Might wanna bring yours anyway to match up.

jpatfarrell

Thanks that is what I will do.....didn't see anything about a core charge but I will take it in to make sure it is the same.

Just got it off and the piston is frozen solid. No movement at all.

Is there anyway to tell if the power booster is ok berfore I install a new master cylinder? Or should I plan on replacing it also. I think I saw one onlione at NAPA for ~$85 or so.

Pat

droldsmorland

Bring in the core to match it but hang on to the core if you thinks its the original master. Down the road matching parts might be important to you or the next owner wanting to take it to the next level of restoration. Not worth $20 to give up an original core.
Rebuilding is very basic and easy to do so long as the piston bore isnt pitted.
Replace the round black rubber seal between the master and power booster(if equipped with power brakes)
Buy yourself a power bleeder. You will need to bleed this system at least twice consecutively once its on the road to purge the dirt and water. Run a gallon of fluid through it.
Replace the soft rubber lines while your at it, all 3. Im sure they are brittle/unsafe. Brakes should be bled every couple of years on any car especially one that sits.

jpatfarrell

Replaced the master cylinder and power booster with ones purchaseed at NAPA. Bench bled the master before installing. In process of bleeding the system but not going as expected. Thought this would take an hour then I would be on to the fuel system.

Started with the right rear per the manual. After about 30 minutes of pumping with the hand held bleeding tool still getting a lot of air and not much fluid. Maybe got 2 oz of dirty fluid then starting to get clean fluid (~2 oz) but air bubbles keep coming. Pumped the brake pedal a few times which helped with the volume of fluid but still getting a lot of bubbles. I have kept the master full and did have to add fluid a couple of times.

Decided to switch to the left rear. Cannot get any fluid or even any air here. Acting like a blockage in the line somewhere keeping fluid/air from the bleed valve. Tried pumping the brake pedal but this did not help.

Suggestions?

classicmuscle442

Could be a few problems, the rubber hose by the rear axle could be restricted. The proportion valve could be off center. Try to bleed one of the front brakes and see if you can bleed them normally.

jpatfarrell

Thanks I will go to the front brakes next.

I took out the bled valve and found that it was clogged shut. After I cleared the clog I re-installed it and I was able to get a little fluid out but it seems to be doing the same as the other rear. A lot of air bubbles and just a little fluid even after pulling a vaccum on it for 30 minutes. The is never a solid stream of fluit. Mostiy air with a little fluid. Now I'm wondering if there is a severe restriction preventing good fluid flow and the air is just coming in around the bled valve/bleed tood connections.

Gonna let it sit overnight and see if there is any brake fluid leakage so I could located a problem. The old master cylinder was empty on the rear reservoir and totally locked so maybe there is a bad spot in the line that is sucking air.

I'll do the front tomorrow.

thanks,

Pat