Raybestos or Doctor Diff master cylinder for 1969 Dart with 9" manual drums?

[cb474]

I finally have time to replace some brake parts on my 1969 Dart Swinger (with the 225 inline 6). The current master cylinder is more than a decade old, although it has only a few thousand miles on it. But one of the reservoirs seems to have some rust in it. It looks like it's a Raybestos master cylinder or one in that style.

I'm trying to decide whether to just replace it with another Raybestos master cylinder, that would be simple, because it's an exact match for what's there. Plus, for this sort of basic after market part Raybestos seems like it's probably the best quality (compared to Dorman, Centric, etc.). Or to go with the Dr. Diff master cylinder that people seem to like.

Any thoughts?

I'm not sure what the bore size is on my current master cylinder. The Raybestos says in online specs that it's 1". That article that floats around by Brad Schroeder says that in 1969 it would have had a 1" bore. My Haynes manual says it was 15/16". Dr. Diff does not offer a 1" option. I did notice that after the current master cylinder was installed, the brake pedal was a lot harder than I ever remember it being (but the old master cylinder was so shot at that time, who knows). In any case, that's a difference between a new Raybestos (1") and Dr. Diff (15/16").

I'm also a little surprised that people say in threads here that they've had issues with the caps on the Dr. Diff master cylinders leaking, even when new. People have so much respect for him. I'd think he would try to resolve the issue.

Another difference is I can get the Raybestos master cylinder for about $60. The Dr. Diff costs $125 (plus shipping). I'm not made of money. I'm perfectly happy with the current Raybestos style master cylinder, accept that it's rusting. But I can see how the Dr. Diff has some advantages.

Anyway, I'm curious what people would suggest. What their experiences are with these master cylinders.

 

[junkyardhero]

put the raybestos (stock) style one on it.

you can get a replacement at autozone, napa, rock, etc.

no need to go hi-zoot for your set up.

 

[cb474]

put the raybestos (stock) style one on it.

you can get a replacement at autozone, napa, rock, etc.

no need to go hi-zoot for your set up.

Thanks the the thoughts. I guess there is also this one:

MOPAR 2660809 BENDIX DRUM MASTER CYLINDER (Reproduction)

MOPAR BENDIX 2660809 DRUM MASTER CYLINDER (Reproduction) by TRM Inc. FREE SHIPPING (USA ONLY) FOR INTERNATIONAL SHIPPING, PLEASE CALL +1 817-429-0105 TO ORDER

therammaninc.com

The other Bendix reproduction ones, like from MBM, seem like they have issues, from what I read here. But that one looks like it may be better made. Although I'm seeing some not great comments about Ram Man in threads here.

 

[junkyardhero]

don't buy ANYTHING from the ram man unless you're holding it in your hands and you're okay with zero-point-zero after sales support.

seriously, look at his online ratings in forums and the BBB.

 

[4mulas]

Everything is pretty much made in China, Korea, or Vietnam. Get the one you want and eluded to in your first post which is Raybestos. Don’t over think it. If it gives undesireable results return it and try another one! Good luck

 

[cb474]

Well, I ordered the Raybestos master cylinder (from Amazon) got it and the way Raybestos packages it is terrible (in a box and plastic bag that can't handle the weight without breaking). It had little spots of corrosion on the outside and in the reservoirs. So I sent it back, since my current master cylinder works fine, but has corrosion in one of the reservoirs that is discoloring the brake fluid (which is the reason why I want to replace it). I ordered another one, hoping it would be better, but I have my doubts.

Why do they make these out of cast iron anyway? Isn't that just begging for them to rust?

 

[Bewy]

Different m/c bore sizes are sometimes different between manual & power brakes. Manual will have the smaller one.

 

[72bluNblu]

I'm also a little surprised that people say in threads here that they've had issues with the caps on the Dr. Diff master cylinders leaking, even when new. People have so much respect for him. I'd think he would try to resolve the issue.

Another difference is I can get the Raybestos master cylinder for about $60. The Dr. Diff costs $125 (plus shipping). I'm not made of money. I'm perfectly happy with the current Raybestos style master cylinder, accept that it's rusting. But I can see how the Dr. Diff has some advantages.

Anyway, I'm curious what people would suggest. What their experiences are with these master cylinders.

I run the 15/16" Doctor Diff MC on my Duster. I did have to replace the gaskets on the caps after I did the initial install and bleeding. Seems to me like the gaskets that come with those master cylinders are only good for a certain number of openings/closings before they start to seep. The position of the vent in the cap is also important though, you want it facing toward the back of the car.

Now, that being said, pretty much all of the factory style master cylinder gaskets will seep too. Occasionally you might find a good one, but realistically a small seep is pretty common.

These are the replacement caps and gaskets for the DoctorDiff MC's (also, he doesn't make them, he just changes the bore diameter for the 15/16"). I haven't had any issues with mine after replacing the gaskets after the initial install and bleeding process, but they've only been off and on a couple times since then. I suspect that occasional gasket changes are just part of the deal of you want zero seepage.

These are the vents, you don't want them pointing forward

Here's how NOT to face the caps... (vents/arrows should be pointing at the firewall).

Why do they make these out of cast iron anyway? Isn't that just begging for them to rust?

yeah, all the factory MC's are going to rust, it's just the nature of the cast iron. The rust in the fluid is actually less of an issue than the moisture that causes it, the brake fluid is hygroscopic and it absorbs moisture over time. Which is why you should flush your brake system every few years, or even more frequently in a high humidity area. If the brake fluid has taken on a cloudy/rusty appearance, well, it's time to flush it. You can go to a synthetic brake fluid to avoid that particular issue, but that has its own pros/cons. And of course if you have standard steel brake lines those will rust too!

And "they" make them out of cast iron because it's a fairly cheap material that works with the other requirements. If you don't want cast iron, the more modern style that's aluminum/plastic is about your only option.

Different m/c bore sizes are sometimes different between manual & power brakes. Manual will have the smaller one.

A-bodies are actually backward when it comes to manual and power disk master cylinder bore sizing. That's because the power booster linkage for the A-body changes the pedal ratio. So the power disk cars actually got a smaller bore master cylinder than the manual disk cars.

This is from the '73 manual, for drums and the later single piston calipers with the manual/power differences listed. A-bodies (V&L) have a larger MC bore for manual and smaller for power, while the B/J/R/W follow the usual pattern of having a smaller bore MC for manual brakes and a larger one for power brakes.

From the '70 manual for the KH disks, only one bore size listed

 

[Bewy]

Didn't know that about the A bodies. I stand corrected.

 

[RustyRatRod]

Read post #5 and memorize it. You seem to be searching for good American made products. Here's a clue. There ain't any. Everything, no matter the brand box it's in comes from overseas now. If you want good, American made, then rebuild the factory Chrysler parts you have and try to find older NOS kits from Chrysler, Napa, Echlin, EIS, Wagner, or any of the other older American brands. Because any rebuild kits you buy anywhere new will be the same chinkiseum crap you get anywhere else.

 

[4mulas]

These are the vents, you don't want them pointing forward
View attachment 1716436790

Here's how NOT to face the caps... (vents/arrows should be pointing at the firewall).
View attachment 1716436791

Why?

 

[junkyardhero]

Why?

because the fluid slops out and gets all over the place when they're faced forward. more and more frequent G's from braking v accel.

 

[cb474]

I run the 15/16" Doctor Diff MC on my Duster. I did have to replace the gaskets on the caps after I did the initial install and bleeding. Seems to me like the gaskets that come with those master cylinders are only good for a certain number of openings/closings before they start to seep. The position of the vent in the cap is also important though, you want it facing toward the back of the car.

Now, that being said, pretty much all of the factory style master cylinder gaskets will seep too. Occasionally you might find a good one, but realistically a small seep is pretty common.

These are the replacement caps and gaskets for the DoctorDiff MC's (also, he doesn't make them, he just changes the bore diameter for the 15/16"). I haven't had any issues with mine after replacing the gaskets after the initial install and bleeding process, but they've only been off and on a couple times since then. I suspect that occasional gasket changes are just part of the deal of you want zero seepage.

View attachment 1716436789

These are the vents, you don't want them pointing forward
View attachment 1716436790

Here's how NOT to face the caps... (vents/arrows should be pointing at the firewall).
View attachment 1716436791


yeah, all the factory MC's are going to rust, it's just the nature of the cast iron. The rust in the fluid is actually less of an issue than the moisture that causes it, the brake fluid is hygroscopic and it absorbs moisture over time. Which is why you should flush your brake system every few years, or even more frequently in a high humidity area. If the brake fluid has taken on a cloudy/rusty appearance, well, it's time to flush it. You can go to a synthetic brake fluid to avoid that particular issue, but that has its own pros/cons. And of course if you have standard steel brake lines those will rust too!

And "they" make them out of cast iron because it's a fairly cheap material that works with the other requirements. If you don't want cast iron, the more modern style that's aluminum/plastic is about your only option.



A-bodies are actually backward when it comes to manual and power disk master cylinder bore sizing. That's because the power booster linkage for the A-body changes the pedal ratio. So the power disk cars actually got a smaller bore master cylinder than the manual disk cars.

This is from the '73 manual, for drums and the later single piston calipers with the manual/power differences listed. A-bodies (V&L) have a larger MC bore for manual and smaller for power, while the B/J/R/W follow the usual pattern of having a smaller bore MC for manual brakes and a larger one for power brakes.
View attachment 1716436788

From the '70 manual for the KH disks, only one bore size listed
View attachment 1716436792

Thanks for all the detailed information. I'm waiting on my second "Raybestos" master cylinder. Hopefully this one won't come pre-corroded.

I suppose I could just not worry about the small amount of corrosion in my current master cylinder. It's only in the reservoir for the front brakes, which are working fine. Although I find that after I bleed it and the car sits for a few months (it's not driven often), the fluid in the reservoir gets discolored just sitting there.

I am wondering, with the DoctorDiff master cylinders, if they have vents in the caps, doesn't that let moisture in and contaminate the brake fluid? And then wouldn't this accelerate the deterioration of the brake lines and other brake parts, even if the master cylinder itself is aluminum/plastic?

 

[72bluNblu]

Thanks for all the detailed information. I'm waiting on my second "Raybestos" master cylinder. Hopefully this one won't come pre-corroded.

I suppose I could just not worry about the small amount of corrosion in my current master cylinder. It's only in the reservoir for the front brakes, which are working fine. Although I find that after I bleed it and the car sits for a few months (it's not driven often), the fluid in the reservoir gets discolored just sitting there.

I am wondering, with the DoctorDiff master cylinders, if they have vents in the caps, doesn't that let moisture in and contaminate the brake fluid? And then wouldn't this accelerate the deterioration of the brake lines and other brake parts, even if the master cylinder itself is aluminum/plastic?

None of the braking systems are airtight. The stock master cylinder allows the brake fluid to pull moisture from the air as well. If it didn’t, you wouldn’t have rust in there.

I’ve been running the DoctorDiff MC on my Duster for over a decade now. I think I’ve changed the seals in the caps once or maybe twice in that time, and the fluid lasts just as long as it did in my Challenger which has a stock cast iron MC for most of the time I was driving it. If anything the fluid lasts longer now.

 

[cb474]

None of the braking systems are airtight. The stock master cylinder allows the brake fluid to pull moisture from the air as well. If it didn’t, you wouldn’t have rust in there.

I’ve been running the DoctorDiff MC on my Duster for over a decade now. I think I’ve changed the seals in the caps once or maybe twice in that time, and the fluid lasts just as long as it did in my Challenger which has a stock cast iron MC for most of the time I was driving it. If anything the fluid lasts longer now.

Yeah, I'm wondering if I should have gone with DoctorDiff. I received my second "Raybestos" master cylinder today. This one does not have corrosion on it, like the first one. But the box was even more beaten up, with all kinds of packing tape holding it together, and the plastic bag that presumably is supposed to protect the master cylinder from moisture had many tears and holes in it.

It really makes no sense how Raybestos packages these. They take a very heavy cast iron part, put it in a plastic bag, then shove it loose in a box with nothing holding it in place. So in shipping the very heavy object shifts around in a box that can't take the abuse, and everything, box, plastic bag, tear apart. I'm very underwhelmed.

But, I've got one in reasonable condition. I guess I'll put it in the car. But if there's a next time, I'll probably go DoctorDiff. My one hesitation is that DoctorDiff does not do a 1" bore, which is what's specified for my year Dart.

 

[4mulas]

Yeah, I'm wondering if I should have gone with DoctorDiff. I received my second "Raybestos" master cylinder today. This one does not have corrosion on it, like the first one. But the box was even more beaten up, with all kinds of packing tape holding it together, and the plastic bag that presumably is supposed to protect the master cylinder from moisture had many tears and holes in it.

It really makes no sense how Raybestos packages these. They take a very heavy cast iron part, put it in a plastic bag, then shove it loose in a box with nothing holding it in place. So in shipping the very heavy object shifts around in a box that can't take the abuse, and everything, box, plastic bag, tear apart. I'm very underwhelmed.

But, I've got one in reasonable condition. I guess I'll put it in the car. But if there's a next time, I'll probably go DoctorDiff. My one hesitation is that DoctorDiff does not do a 1" bore, which is what's specified for my year Dart.

You’re over thinking it. Just get the 15/16 bore. You need the 2 post adapter too. He sells the thing as a whole kit which save a couple dollars.