Drum to Disc MC Issues

[Creedmoor]

‘68 Barracuda. Pulled the factory drum/drum MC to replace it with a new drum/disc unit for my front disc conversion. The forum recommends the Raybestos MC36406 as this a non power assist swap and this MC has the desired 15/16” bore. (This thing is huge compared to the original!)

However, the new master has no provision to retain the new dust boot. Suppose I could drill and tap it to transfer the old retainer but that seems like a goofy solution. Any recommendations? Put the boot on the rod, shove it as forward as possible and call it good enough?

Second issue, is there supposed to be a return spring on the rod? Didn’t find one when I took the MC off, but I’ve seen diagrams with and without one.

Lastly, the bolt/nut holding the pedal to the rod is a major pain to get to and remove. Halfway through unthreading it, I was seriously wondering how in the heck I would get it back in there. So, I opted to put some wood between the MC and the firewall and yank on the pedal to separate the rod from the MC. My question is; can I reinstall the rod and boot by just guiding the rod into the back of the MC and just pushing hard while a buddy holds the brake pedal down? Or do I still need to take the rod all the way out and do it on the bench?

Never done this before, so figuring it out as I go. Last tricky bit is going to be replacing the distribution block with a combo one. There is VERY limited room to work in there.

Thanks for any advice and insight!

 

[dadsbee]

Personally I would have just stuck with the original. Front disc reservoir is just bigger to allow owners to be negligent and not bother checking fluid level as pads wear. Pop the residual valve out of the front brake line port and just keep the OE topped with fluid and zero issue..

 

[cudamark]

What year is your car? The '66 and older A-bodies have a spring around the push rod, but, I didn't think the later ones did. I always swapped out the push rods and seals out on the bench.....actually in my vice. I give it it's initial bleed there too.

 

[340sFastback]

Dust boot? I don't ever remember having one on my disc brake master cylinder and I don't think its really needed either.

 

[cudamark]

'66 and earlier models use them.

 

[Divenut]

If I recall, the tube/connection was on the plastic plate between the MC and mounting surface. Dug up this pic, unfortunately can't find a better pic.

 

[Creedmoor]

Oops, sorry guys, violated first rule of help requests! ‘68 Barracuda. I’ll edit my OP. There was no spring but there was a dust boot. I had a brand new in box early 90’s NAPA remanufactured drum/drum master identical to the one I just pulled that came with a new boot AND the little rod retainer rubber thingy which I had just ordered for ridiculous shipping cost.

So, can I just jam the rod into the master from the firewall side? Don’t want to unbolt that damn rod though. Should put a little silicone on it help it slide home?

 

[340sFastback]

Supposed to be little rubber thing on end of rod that goes into master cylinder so rod dont fall out

 

[furyus2]

Look in the bore of the new master cylinder. There should be a groove for the little rubber retainer to lock into. Bench bleed the master cylinder. They sell kits cheap at the auto parts store. Mount the master, line up the push rod, and just step on the pedal to lock the rod into the bore. You don't need the dust boot. And the larger volume of the disc master is needed. It's not just for looks.

 

[cudamark]

Oops, sorry guys, violated first rule of help requests! ‘68 Barracuda. I’ll edit my OP. There was no spring but there was a dust boot. I had a brand new in box early 90’s NAPA remanufactured drum/drum master identical to the one I just pulled that came with a new boot AND the little rod retainer rubber thingy which I had just ordered for ridiculous shipping cost.

So, can I just jam the rod into the master from the firewall side? Don’t want to unbolt that damn rod though. Should put a little silicone on it help it slide home?

The firewall has two sides.....but I assume you mean the interior side. Sure, lube the rubber retainer, start the push rod into the piston, start the master cylinder mounting nuts, tighten them evenly as you draw it up against the engine side of the firewall, and then push the rod into the master cylinder piston until it's fully seated..

 

[ir3333]

Dadsbee is correct. The caliper pistons only move a few thousands of an inch.The extra volume is for pad wear and you'll probably never need it unless it's a daily driven for a few years. The boot is a nice touch, i'd use it. I have drilled
and tapped a master for that very reason. It only takes a few minutes.

 

[Creedmoor]

Dadsbee is correct. The caliper pistons only move a few thousands of an inch.The extra volume is for pad wear and you'll probably never need it unless it's a daily driven for a few years. The boot is a nice touch, i'd use it. I have drilled
and tapped a master for that very reason. It only takes a few minutes.

Thanks! Dadsbee didn’t bother to really read my OP or he would have noticed I already pulled the original MC and bought a new one. His post wasn’t really helpful. Only his opinion - which I respect. Everyone has one.

If I’m sure my drill and tap will be accurate, I may just do that! Thanks.

 

[dadsbee]

I'll disregard your posts in the future and won't offer my 2 cents. Carry on... you could always put the original back seeing the new one is huge compared to the OE.