Thoughts on used PWR Brake Booster & Master Cyl

[buening 63]

In regards to using a manual master cylinder as buening said as long as it is disc drum then fine. Mine however was drum drum and had the same size bowls. I opted to change the master cylinder to a disc drum when I went to power brakes. After a quick search on the interwebz apparently the drum brake master cylinder has a residual pressure valve used by drum brakes to keep them from leaking and other important stuff. This valve built in to the master is not suitable for disc brakes.

 

Some M/Cs you can actually remove the residual valve. The main sticking point I came to is the bowl size. There must be a reason why the disc bowl is larger than the drum on the disc/drum master cylinders, which I'm assuming is chosen due to piston size/volume and pad wear. If you consistently check your brake fluid and the fact that these cars don't get the kind of miles that a DD gets, you should be able to use any M/C as long as the residual valve is removed from the drum bowl. There are references online to removing the residual valves from M/Cs.

[buening 63]

My build date is 10/31/1968 is San Jose. Now what does that mean regarding brakes.

 

In regards to bowl size, both bowls are the same.

 

Lately, I've seen or it's just new to me, that you keep the Drum spindels and install (1967 ??) Disc Rotors and get a new 4 piston caliper. Now, do I still need to change my same bowl MC or switch to the MC for disc brakes and how about the Port. Valve?

 

Keep in mind other than appearance, the Bendix and Midland are the same. I'd recommend getting the M/C and booster assembly complete from your local parts store. It should be a bolt in once you cut the hole in the firewall. I'd do a test fit first to make sure it is needed. I don't recall if the hole was only needed for the 70 or for both. With the pushrod offset 1/2" down compared to the 70, I wonder if the 69 didn't need the hole cut further down. Essentially, in 70 the booster mounted in the same location but the pushrod pin hole moved up 1/2" or so.

 

I'm not sure about the drum spindles and 67 disc rotors, but I do know that the drum spindles are used for the 13" Cobra brake swap with conversion brackets. Brackets for disc spindles are also available now.

[LindenBruce 27]

Yes there is a reason for the different bowl sizes. Disc brake calipers have much larger bores than drum brake wheel cylinders and as such more fluid is displaced. The larger bowls are there to accommodate the movement of that extra amount of fluid in and out of the master cylinder.

 

Also, I believe the bore sizes on the master cylinders are also different on manual versus power applications. Bruce

[buening 63]

thanks Bruce, exactly as I was figuring. Regarding bowl sizes on manual and power, it shouldn't differ since the volume to move the caliper bore/cylinders is the same.

[Lemon Owner 11]

And this is exactly the reason why I changed my master cylinder from drum/drum to disc/drum even though my drum M/C was just reco'd. There is just too much going on I do not know about so I just did it the right way. Whenever I try to dodgy things together it just goes wrong. lol

[prayers1 153]

Can someone explain why I have to make the hole in the firewall bigger for the Boosters push rod.

I see that the 1969 boosters rod has a curved end, where as the 1970 is straight.

If making the hole is just for the 1969 Booster rod curve, wouldn't it be best just to use the 1970 and not making a hole at all? Obviously I'm not seeing something here.

 

Also, it looks like I also have to replace the brake pedal. Why is that?

 

If my vehicle came stock w/ manual brakes, it looks like you guy's are saying I'd have to make that hole. How are you guys making that hole, with what equipment, a hole saw, saw sall etc.....

 

Here's a pic of a 1969 & 70 Booster for comparison. Note Bowl size of 1970 MC

 

 

Edited March 6, 2012 by prayers1

[69gmachine 15]

1. The holes don't line up in the same place.

2. I used a grinder to enlarge the hole.

3. A disc brake pedal has the mount higher up to reduce the mechanical leverage as the booster provides enough by itself. If you don't use the correct pedal you will have overly sensitive brakes. Not sure how it will line up as I never tried that combo. Also, make sure the rod is adjusted so that it does not contact the piston when no pressure is applied. That will also cause the brakes to be hyper sensitive.

[prayers1 153]

Thanks 69gmachine!

 

Lemon Owner-Pointed pointed out a good reference point on Mustang Steve's website.

Here is a copy of the template used for drilling the holes.

 

It looks like a lot more holes to drill besides the main center hole.

 

 

It looks like a lot more holes to drill besides the main center hole.

Edited March 6, 2012 by prayers1

[Lemon Owner 11]

You need to elongate the existing holes and add one. But it is not hard and well worth the effort.

 

I used a die grinder to make the centre hole larger. Then just a regular drill to elongate the existing holes etc.

 

The factory brake booster works far better than the CSRP booster I have that mounts to the orignal drum brake holes. In fact in hind sight, I wouldn't even bother with the CSRP kit.

Edited March 7, 2012 by Lemon Owner

[Daves69Coupe 10]

Good leg work there. I do know there was a Midland and a Bendix booster and I don't know the difference. My one is a rebuilt one but is exactly like my original. NJ built M-code front disc.

 

I know over the years I have heard of guys who sent their booster core in and got a booster back with no spacer and they were urgently looking for a spacer. I had to separate my spacer before I returned the core and attached it to the new one, so I wasn't the guy running around looking for a spacer. :)

 

Mine's available cheap, BTW. I eventually went Hydratech's hydroboost. But I had to reuse my power pedal, so you would need to source that.

you still have this spacer available?