Master Cylinder bore size?

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Big Guy

Big Guy

1970 Dodge Dart Swinger
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I have a 1970 Dart Swinger 340 with front disc brakes and rear drum. i cannot say that the car was original with front disc. The question I have is "can someone tell me what the bore size would be on the existing master cylinder" without having to remove the existing and measuring before ordering a replacement? The existing master cylinder chambers look to be the same size, if that helps.
 
If the two chambers are equal size, it is not a factory disc brake master cylinder, which suggests that the disc brakes were not original. So the bore is kind of irrelevant.

For 1970, the factory disc brake master cylinder bore would have been 1-1/32". The master cylinder would have one large chamber and one small chamber, with a wire bale clamp on the lid.
 
Big Guy said:
I have a 1970 Dart Swinger 340 with front disc brakes and rear drum. i cannot say that the car was original with front disc. The question I have is "can someone tell me what the bore size would be on the existing master cylinder" without having to remove the existing and measuring before ordering a replacement? The existing master cylinder chambers look to be the same size, if that helps.
Click to expand...
Need a little more info.
Are the brakes the year-correct 4 piston Kelsey-Hayes discs with a 4" bolt circle? Or are they the later '73 and up single piston caliper with a 4.5" bolt circle rotor?
Is this a power brake car, or manual brakes?
 
Big Guy said:
I have a 1970 Dart Swinger 340 with front disc brakes and rear drum. i cannot say that the car was original with front disc. The question I have is "can someone tell me what the bore size would be on the existing master cylinder"
Click to expand...

No, because the car is over half a century old and parts get changed (and as has already been stated, a master cylinder with equal-size reservoirs is not correct for a disc brake system—that's for a drum brake system, and using it with disc brakes can make problems).

The original master cylinder on that car had a ø1" bore. The master cylinder with the ø1-1/32" bore mentioned by mvh came in for 1971. However, the '67-'70 ø1" disc brake master cylinder has grown difficult to buy. There is no reason why you can't use the '71-up ø1-1/32" item; that's this one.

While you are paying attention to the brakes, take easy and inexpensive action to permanently fix the rear-lockup problem the disc-brake A-bodies all had from the factory; info here.
 
mvh said:
If the two chambers are equal size, it is not a factory disc brake master cylinder, which suggests that the disc brakes were not original. So the bore is kind of irrelevant.

For 1970, the factory disc brake master cylinder bore would have been 1-1/32". The master cylinder would have one large chamber and one small chamber, with a wire bale clamp on the lid.
Click to expand...
slantsixdan said:
No, because the car is over half a century old and parts get changed (and as has already been stated, a master cylinder with equal-size reservoirs is not correct for a disc brake system—that's for a drum brake system, and using it with disc brakes can make problems).

The original master cylinder on that car had a ø1" bore. The master cylinder with the ø1-1/32" bore mentioned by mvh came in for 1971. However, the '67-'70 ø1" disc brake master cylinder has grown difficult to buy. There is no reason why you can't use the '71-up ø1-1/32" item; that's this one.

While you are paying attention to the brakes, take easy and inexpensive action to permanently fix the rear-lockup problem the disc-brake A-bodies all had from the factory; info here.
Click to expand...
Thank you!
 
mvh said:
If the two chambers are equal size, it is not a factory disc brake master cylinder, which suggests that the disc brakes were not original. So the bore is kind of irrelevant.

For 1970, the factory disc brake master cylinder bore would have been 1-1/32". The master cylinder would have one large chamber and one small chamber, with a wire bale clamp on the lid.
Click to expand...
Thank you!
 
Rick eherenburg has an a body aluminum master cylinder replacement on his eBay store, ricks mopars. He may also have the rear wheel cylinders to apply less pressure 7/8 diameter. He also has an adjustable proportioning valve.
 
Professor Fate said:
Need a little more info.
Are the brakes the year-correct 4 piston Kelsey-Hayes discs with a 4" bolt circle? Or are they the later '73 and up single piston caliper with a 4.5" bolt circle rotor?
Is this a power brake car, or manual brakes?
Click to expand...
This is a manual brake system. They front brakes are the 4 piston Kelsey-Hayes discs with a 4" bolt pattern but looks like they must have come off a donor car. The Master Cylinder has the same size compartments, therefore the car was originally an all drum brake car. From what I can gather, this can cause future brake failure once the front pads wear down and the front system will starve for oil. I will be changing the master cylinder to a newer style with the front disk brake capacity. Thank you!
 
slantsixdan said:
No, because the car is over half a century old and parts get changed (and as has already been stated, a master cylinder with equal-size reservoirs is not correct for a disc brake system—that's for a drum brake system, and using it with disc brakes can make problems).

The original master cylinder on that car had a ø1" bore. The master cylinder with the ø1-1/32" bore mentioned by mvh came in for 1971. However, the '67-'70 ø1" disc brake master cylinder has grown difficult to buy. There is no reason why you can't use the '71-up ø1-1/32" item; that's this one.

While you are paying attention to the brakes, take easy and inexpensive action to permanently fix the rear-lockup problem the disc-brake A-bodies all had from the factory; info here.
Click to expand...
Hey Dan, I was looking at getting some of these smaller wheel cylinders but I noticed Raybestos WC37696 and Wagner WC113704 both look to have a metric brake line inlet.

After some research I found Raybestos WC34876 / Dorman W34876 / Chrysler 3766689 have the 13/16" bore with the 3/8-24 threads for the brake line inlet.
 
Big Guy said:
If I replace the master cylinder with a 1971 vintage with the 1-1/32" bore, will it be necessary to install residual pressure valves for rear drum brakes to insure that seals will not leak or would they be even be necessary?
Click to expand...
For 1973, the residual pressure valve was deleted from the master cylinders across the (Chrysler) board, because drum brake wheel cylinder seals had been improved enough to render the RP valve unnecessary. It is just about 100 per cent certain any pre-1973 car still on the road already has post-1973 wheel cylinders with the improved seals, so you probably needn't worry about it. On the other hand, if you'll sleep better at night, you could put in an RP valve, either in the master cylinder outlet or in line, and it wouldn't hurt anything.
 
autopar3000 said:
Hey Dan, I was looking at getting some of these smaller wheel cylinders but I noticed Raybestos WC37696 and Wagner WC113704 both look to have a metric brake line inlet.
Click to expand...

No, the WC37696 has 3/8"-24 brake line thread, though I do see where RockAuto incorrectly lists it as having 10mm. The WC113704 had 3/8"-24, too, but that no longer matters; it's obsolete/NLA.

(I installed my first set of WC37696s in an A-body almost three decades ago, and the car's original brake lines threaded right on in. That post I linked has been up almost that long, and nobody who's followed it has discovered metric threads on their new cylinders.)
 
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slantsixdan said:
No, the WC37696 has 3/8"-24 brake line thread, though I do see where RockAuto incorrectly lists it as having 10mm. The WC113704 had 3/8"-24, too, but that no longer matters; it's obsolete/NLA.

(I installed my first set of WC37696s in an A-boody almost three decades ago, and the car's original brake lines threaded right on in. That post I linked has been up almost that long, and nobody who's followed it has discovered metric threads on their new cylinders.)
Click to expand...
Got it, thanks for explaining.

I think it might actually be Raybestos providing the bad information to the websites. I saw the incorrect metric sizing listed for the Dorman version of the WC37696 on a different site (PartsAvatar.ca: Canada Online Auto Parts, Body Parts & Accessories), but on Rock Auto the bore sizing for the Raybestos WC37696 wheel cylinder shows as being 0.594" which is... 19/32"??? Seems like a weird size (because it's wrong!).

Some double reverse backwards searching has identified that the 1987 - 1999 Dakotas used the Raybestos WC37696. Looking up that vehicle on Rock Auto shows there are about a dozen options, some for 10" drums and some for 9" drums. They all show that the 10" drums use the 13/16" bore wheel cylinder, and the 9" drums use the 3/4" wheel cylinder. Except for the Raybestos and Dorman options, but again, their parts are probably fine and it's just information that's wrong.

So it looks like the 90s Dakotas are a good reference vehicle to use when the guy at the parts counter gives me that blank stare after I tell him I want a 13/16" bore wheel cylinder for an old Dodge!
 
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