Changing master cylinder

[tmorefield]

Well, my pedal is going to the floor! The car still stopped, which was nice. Anyway, I am going to swap out my MC. I have a 1970 Avanti II RQA0406. I have checked Bob Johnstons site to figure out which one I have. My question is: Is this a straight forward job? I have done a master cylinder (helped) but 25 years ago on my 1975 Dodge Charger. Are there any surprises I should expect.

Thanks

Tony

[Charlie Kile]

An easy straight forward job. Be sure if it is a dual unit , it must be bench blead before installing it.

Might be a good time to over haul the vacume booster unit.

Charlie RQB3921

[Gunslinger]

It's a very strait forward job. I'm guessing you have a dual master cylinder like my '70 has.

Cover your fenders and inner fenders to protect the paint from any brake fluid that might spill. Suction out as much of the fluid from the old m/c as you can before removing the lines and unbolt the m/c and remove it.

You should bench bleed the new m/c before installing it to get as much air out if it as you can, then install it. Basically that's it outside of bleeding all four corners of the car, going right rear, left rear, right front then left front.

That's really all there is to it. You need a second person to pump the brakes while bleeding if you don't have a one-man bleeder kit.

One thing to look for...during the '70 model year Avanti Motors started putting silicone brake fluid in the cars as factory fill. After these many years you may not know if the fluid is still silicone (DOT 5), or has been changed to DOT 3. They are not compatible and will cause trouble if mixed...in fact, the way you describe how your brakes are acting is very similar to what happens when DOT 3 and DOT 5 are mixed. Is your current brake fluid cloudy? If so, you might have mixed fluid. Silicone fluid is usually purplish in color.

It would be very prudent to flush out your entire brake system. Use an alcohol solvent and blow it through with compressed air and make sure it's dry. Once your satisfied it's dry, refill with either DOT 3 or DOT 5 and make sure they never get mixed.

[tmorefield]

I made it home safely! I pulled the reservoir cap off and the front chamber was dry! Yikes. I must have a leak in the system. It has to be very recent; I checked the fluids 2 weeks ago. Isn't the front smaller chamber for the rear brakes? Reguardless, it looks like a brake job weekend! Can I bench bleed the MC in the car or do I need to pull it? If I pull it, I may just go a head and replace it.

Thanks ,

Tony

[Gunslinger]

You bench bleed the master cylinder off the car. That's only necessary when replacing the m/c or it's already off the car. You may not have a bad master cylinder but you definitely need to find where the leak is...it could be the master cylinder, a wheel cylinder or a caliper, a hose or a metal line.

Pull the front tires off and you can see if there's a mess of brake fluid on the back of one tire or the caliper and hose. For the rear, if the inside of the tires are dry and not covered in brake fluid, you'll have to pull the drums to check the wheel cylinders. Also check the flexible hose back near the differential.

If any of your brake pads or shoes are covered in brake fluid, you'll need to replace them as well. Brake fluid and brake lining materials are nor compatible and the lining will rapidly deteriorate and not stop well.

[tmorefield]

I checked the back of the tires and the brake lines and no leaks were found. I will pull the wheels off tonight to inspect closer. Will I need a drum puller? The only brakes I have done didn't require one, but I have read that for the Avanti I will. I suppose I can rent one from my local auto parts store. Do I need to go through someone like Studebaker Intl, SASCO or Nostalgic to order wheel cylinders, pads and such or is there an equivalent I can get at NAPA? I know I can get the master cylinder at NAPA.

Thanks everyone for the input and advise, so far. The more the better!

Tony

[Gunslinger]

A '70 Avanti should not need a drum puller...it has flanged axles, not tapered axles like Stude R1 and R2's used. You may have to tap the drums with a hammer to loosen them, but they should simply pull off.

I suspect you'll find a leaking wheel cylinder since you've checked the rest.

When I needed wheel cylinders I got them from Jon Myers. I wouldn't try buying wheel cylinders from NAPA. The problem is in the application charts...the wheel cylinder for your car also fits an older Jeep. While it physically looks right, it's a different bore than an Avanti. It lets too much pressure to the rear brakes and they will lock up before the front brakes bite. Don't ask how I found that out!

It might possibly cost a bit more, but I would recommend buying all your brake parts from the same vendor. Most Stude and Avanti vendor prices pretty much seem to be similar on these parts anyway.

Also...while you have the drums off, check and make sure your rear axle seals aren't leaking. I'm not saying they might be, but while you have the drums off, check everything while you're there. If they're leaking you'll need rear shoes anyway if they're covered in that fluid.

[tmorefield]

I was able to check the rear wheel cylinders, shoes, rear seals, break lines/ hoses, calipers, and brake pads. I did not find any leaks or problems. I did notice some brake fluid under the master cylinder where it attaches to the booster. I ordered a master cylinder from Orielly's but when I went to pick it up; it was not the one I ordered (mis-labeled). I had them re-ordered a master cylinder for a 69 dodge Monaco. I hope to have it in this week.

Tony

[WayneC]

I had them re-ordered a master cylinder for a 69 dodge Monaco. I hope to have it in this week.

Tony

I have a note in my parts manual that says the '65 to '71 Avanti takes an EIS 64874 master cylinder

(EIS is an industry standard, and manufacturers list their M/C's that meet the standard numbers)

Another note says the '71 takes the same master cylinder as a "67-69 full-size Chrysler with disk brakes",

which is what I ordered about 15 years ago, the last time I changed it out on my '71 (I also went to Dot 5

silicone fluid at that time, when I also replaced the wheel cylinders and flex hoses)...

hopefully the 69 Dodge Monaco M/C will do the trick. You could also have the original professionally rebuilt

with a stainless steel or brass bore.

Edited April 22, 2008 by WayneC