Master Cylinder Pushrod Retainer Question

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SeattleQQ1Fish

SeattleQQ1Fish

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I have a 67 Barracuda with manual drums all around and a leaky non-original master cylinder. The replacement I chose is a reproduction of the 60’s Bendix drum/drum unit from Mancini Racing MBM Bendix Drum Brake Master Cylinder. The product description doesn't specify power or manual brakes, so I assumed it works for both. I got it yesterday and it looks identical to the manual MC pictured in the service manual.
Here is the problem: the bore in the back of the piston doesn’t have a groove machined in it to catch the rubber retainer on the push rod.
IMG_2834.JPG


The original looks like this:
IMG_2854.JPG

And the new one looks like this:
IMG_2853.JPG


I was under the impression that all manual MCs had this groove in the bore to hold the push rod in. Maybe the unit I got is for power brakes? Is it safe to use without something physically holding the rod in the bore?
Also, the piston retainer on the new unit is just a little tab in one of the screw holes, where the one that came off my car uses both holes, has a rubber boot, and looks like this:
IMG_2850.JPG

Can I use this on the new master cylinder?
 
I ordered a new master cylinder from Rockauto ( same 67 b'cuda manual drums ) and it did have the groove for pedal rod retainer. It is rare to find 2 piston retainers though. I would send that one back. Even if the pedal stop wont allow the rod to fall out, it might make a noise just laying in there.
 
I would plan on returning it, but would first call Mancini Racing to talk through it with them. I would use the boot and plate off your original.
 
The tab is there for transport/shipping. Use the boot and retainer.
 
RedFish said:
I ordered a new master cylinder from Rockauto ( same 67 b'cuda manual drums ) and it did have the groove for pedal rod retainer. It is rare to find 2 piston retainers though. I would send that one back. Even if the pedal stop wont allow the rod to fall out, it might make a noise just laying in there.
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X You suggest that the Boot and Retainer should NOT be used in place of the temporary single bolt retainer tab shipped with the master cylinder. So you would be advocating it's OK for dirt to get in to the piston bore along with condensation and seepage? Not really sure why you would go that route!
 
Right or wrong, I have the MC without the retaining groove. Been working fine for 10 years. I did use the boot and retainer. The pedal stop /stoplight switch keeps it in place.
 
69FBCuda said:
X You suggest that the Boot and Retainer should NOT be used in place of the temporary single bolt retainer tab shipped with the master cylinder. So you would be advocating it's OK for dirt to get in to the piston bore along with condensation and seepage? Not really sure why you would go that route!
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I didn't comment on the boot or it's retainer. The tiny sheet metal retainer isn't to be removed and/or replaced by the boot retainer. That tiny sheet metal retainer is the only thing holding piston and return spring in the bore. I don't know if the boots plate would or not. My 67 has the one sheet metal tab and the boot. That 2 hole plate is not present. Good luck to all.
 
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RedFish said:
I didn't comment on the boot or it's retainer. The tiny sheet metal retainer isn't to be removed and/or replaced by the boot retainer. That tiny sheet metal retainer is the only thing holding piston and return spring in the bore. I don't know if the boots plate would or not. My 67 has the one sheet metal tab and the boot. That 2 hole plate is not present. Good luck to all.
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Look at the photo that shows the small tab piston retainer. Notice that at the 11:00 position a drilled and tapped bolt hole is present. If that drilled and tapped hole is not the bolt hole that matches to the tapped bolt hole that the small tab retainer screw is in and together they are intended to be the bolt holes for the retainer with the boot, what exactly do you think that extra bolt hole is for?
Bottom line is, you are using the shipping retaining tab to keep the MC piston from moving out of the MC bore. The OE design is to use the circular boot mount to do that.
 
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OK so maybe my 67 is missing a part. If the center hole in that plate isn't small enough to capture and retain the master cylinders guts... I dont need one. while I'm thinking about it... I honestly can't recall if the boot is present or not.
I know have the one sheet metal tab in place at the upper hole. I did briefly consider transferring the tab from removed master cylinder to the lower hole of the new master cylinder but had a second thought... a fluid leak would generate rust down there. I might never get that screw out again without a drill. I have brakes. I'll undo my disagree above before yall start shooting. Again, good luck to all.
 
MOPAR4Me said:
I would plan on returning it, but would first call Mancini Racing to talk through it with them. I would use the boot and plate off your original.
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Called Mancini and the person I talked to has never even heard of a groove in the cylinder bore to hold the pushrod in. I returned it and got what I needed from Napa, no problem. Another Mopar lesson learned.
 
The tear drop shaped tab was used on master cylinders intended for power brake applications. The 2 bolt plate with boot was used on manual brake master cylinders.
 
Mine is manual brakes and I used the 2 hole plate and boot. To OP are you staying with the manual brakes?
 
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69FBCuda said:
Mine is manual brakes and I used the 2 hole plate and boot. To OP are you staying with the manual brakes?
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I like the feel of manual brakes, so I'm staying with them. Someday I'll get around to swapping the drums out for disc, but one thing at a time...
 
SeattleQQ1Fish said:
Called Mancini and the person I talked to has never even heard of a groove in the cylinder bore to hold the pushrod in. I returned it and got what I needed from Napa, no problem. Another Mopar lesson learned.
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Unfortunate Mancini's did not have the part/knowledge to serve you, and the wasted time, but glad to hear that NAPA put you back on track.
 
SeattleQQ1Fish said:
Called Mancini and the person I talked to has never even heard of a groove in the cylinder bore to hold the pushrod in. I returned it and got what I needed from Napa, no problem. Another Mopar lesson learned.
Click to expand...
SeattleQQ1Fish said:
Called Mancini and the person I talked to has never even heard of a groove in the cylinder bore to hold the pushrod in. I returned it and got what I needed from Napa, no problem. Another Mopar lesson learned.
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Seattle,

Its now 2024 and I am in the exact same boat as you. I even called Mancini BEFOREHAND advising of your MC missing the retainer groove and the guy said it was probably a manufacturer defect and all the new ones were “fine”. Nope. Mine was exactly like yours. No groove. So Ill be sending it back. My question is can you advise what Napa MC you got instead?

Thanks!!
Thanquol in Wisconsin

IMG_6363.jpeg
 
Thanquol said:
Seattle,

Its now 2024 and I am in the exact same boat as you. I even called Mancini BEFOREHAND advising of your MC missing the retainer groove and the guy said it was probably a manufacturer defect and all the new ones were “fine”. Nope. Mine was exactly like yours. No groove. So Ill be sending it back. My question is can you advise what Napa MC you got instead?

Thanks!!
Thanquol in Wisconsin

View attachment 1716272484
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It was a long time ago, so I don’t remember for sure, but I think I just asked them for a 67 Barracuda drum brake MC.

I now use a Dr. Diff 15/16 MC, which is great. I’m not sure if it works with drum brakes, but it would be worth asking Cass.
 
Ok tx… I ran to NAPA and they showed pics of both the Chinese crap one and the double hump bendix with the snap hoop (which is kinda correct)… the guy understood what I wanted so he ordered a couple from different warehouses and said it looked like they wete dumping the Chicom one and going back to the okd style… hopefully.

Otherwise yes Ill definitely check with Cass… this is all kinda dumb as I have a full working KH set up and will convert anyway - so will need a different MC anyway… sigh. I really like the Mancini one but no way am I not having that locking groove. Mancini is not what it was.

Thanks!!!
 
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