71 demon master cylinder

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roadripper

roadripper

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Bought a rebuilt master cylinder for a demon we are working on , it
Has drum on rear and disk on front. The replacement master cylinder
The reservoir size is the same ? :wack:the original master cylinder has
Two different size reservoirs larger one for the disks , my question is did
My auto pets supplier give me the wrong master cylinder or does this mater?
:banghead: Thanks Mike
 
Your Demon prob has Kelsey Hayes 4 piston caliper disc , drum .The large master cylinder is for Bendix brakes 73 and newer disc and drum , think they will bolt up to booster but might be a problem with bore size, and length of rod, and also line fittings for master cyl . But some one here prob knows for sure . Good luck .
 
That's what I thought large reservoir for disk I gonna take back to part supplier and see if he has given me the correct master cyl :( thanks for your input. Mike
 
So I went to the auto parts store and he checked
The numbers on the invoice and he said that this is
A master cylinder of a 71 demon with front disk brakes
:banghead: I always thought reservoir size was different
When using disks , so here is a pic of the new master cyl
Maybe I'm wrong but I don't want to plumb it and put fluid
in this thing and have it not work right !! So any help on this
Would be great. Thanks mike
 

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The factory ones did have a larger reservoir for the discs. Various aftermarket one's did have castings that look like yours & will work with discs. I would definitely check the bore size & verify it's right, believe it should be 1-1/32" for yours. Also check the connection dimensions, you don't want to have to bend new lines. I had one that was intended for discs where they put in the drum check valve- when you put in fluid make sure it flows out of the disc part but not the drum. Definitely bench bleed it.

Unfortunately all the replacements I know of are from China with spotty quality control. Even the rebuild kits are China sourced. The rebuilt ones seem worse, they seem to throw anything in the box whether right or not. If you ever find a vintage USA-built one, buy it. There are some guys that make a living out of selling old rebuilt MC's that actually work but pretty pricey. The best of all worlds is to have an original stainless sleeved & rebuild it with quality parts.
 
So I measured the bore diameter and its around
1.07 dia , so plumb the front disks to the back resevoir?
Thanks. Mike
 
No, they probably gave you a drum/drum MC. Every time I have gone to a parts store they have done the same thing. For some reason the brake parts lists are all #%$@ed up for the years 67-72, wherever disk brakes are involved. Try asking for a MC for a 72 340 Dart. The correct ones do exist, the book just lists the wrong references.
 
Again that looks like an aftermarket disc brake MC to me. If you want factory correct or correct-looking then that's a different ballgame. Also 67-70 & 71-forward are different. Early has a smaller 1" bore. I used one that looked like yours for an early app & it now works fine after I rebuilt it, it started leaking shortly after install, again the spotty quality thing. Front brakes go to rear of M/C. Drums require a check valve that holds a few PSI pressure whereas discs do not. For mopars this amounts to a little spring & stopper under the brass fitting in the port. You must make sure the disc portion does not have this, short of taking it apart you can check the flow with the ports open, if it has the check valve then fluid should not pour out. If your discs have this check valve installed they will drag.

Not to scare you, but my experience with replacement M/C's has been piss poor. I have a disc brake C-body & 2 of NAPA's finest quality failed not long after I put them in. I took one apart & it had a lengthwise score in the cylinder that looked to be just crappy machine work. The original made by Bendix lasted 25 years. NAPA M/C's are made in the aforementioned communist-bloc country so there's really no advantage to buying from them anymore. I gave up & sleeved/ rebuilt the Bendix to be safe. It's not a pleasant feeling to be stopped on a hill with your pedal slowly dropping to the floor & a car 2 feet from your bumper.

It is true that the parts store part number references that come up for these early M/C's are pretty screwed up, you have to double check everything.
 
So I went back to the parts store again today and told them to look up a master cylinder for a 73 dart 340 with power disk brakes !! turns out its a different part number :banghead: picture on website shows master cylinder with the large resevoir :cheers: so that tells me that the part supplier numbers are all screwed up as stated, cause this is the same master cylinder that came with the demon in the first place ! lol so master cylinder is four days away :wack:

thanks again for all that helped in this mater Mike
 
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