Will a Generic Dorman check valve work in my Midland-Ross booster?

Have you ever repaired a Midland Ross single diaphragm booster?

  • yes

    Votes: 0 0.0%
  • no

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  • just replaced

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    2

Gerald Morris

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Felicitations to You Moparians!

Now that I'm getting some control over the engine temperature, I'm starting to look at other systems in states of egregious neglect. ONE of these is the vacuum brake booster! We generally don't like any such thing in our vehicles, but for the sake of expediency and preserving this car's original state as much as possible, I'm willing to consider leaving the Midland-Ross booster in, IFF it WORKS properly! For the present, the booster is on the chopping block.

Hissing brakes when my foot is applied, and they work none too well at that. I see signs that the flipper attempted to rebuild the master and wheel cylinders, but he didn't touch the brake booster, for which, I'm grateful.

Looking in the FSM, one probable source of malfunction might be the check valve. I'm willing to spend ~$10 on a replacement, but NOT $100! Yes, there are highway robbers out in Cyberland jacking folk with prices like $115 for an NOS check valve!

I see that entire, working brake boosters seem rare as boar teats, including even the bottom of the barrel, Cardon't. I'm not subsidizing THOSE criminals again.

So, Dorman makes a generic check valve which looks like it MIGHT fit in place of what's on that Midland Ross booster. Do any of you Mopar Mechanical Sages know if this thing is worth the effort of trying? It runs about $7 at VatoZone.

If that would be money tossed into the gutter, then can the check valve be rehabilitated, say, by spraying a shot of penetrant into it? Or would that aggravate things? I might try that on the morrow.

No question of ONE thing: that brake booster LEAKS VACUUM, and I now suspect THIS is THE MAJOR VACUUM LEAK WHICH HAS DRIVEN MY ENGINE TO OVERHEAT THESE LAST 3 WEEKS!

Note: when I first began driving Gertrude, around the start of October, we got a couple weeks of service from her, and got her through emissions with a remarkably LOW hydrocarbon count in the exhaust, suggesting a VERY LEAN fuel system. She wasn't overheating YET, BUT....

My initial surprise that the miserable power brakes worked at all pleased me at first, but now, that feature has markedly deteriorated. I'm not the least surprised about this: a car which has spent several decades in a barn will be apt to have dry membranes and such. BUT, IFF this is a CHECK VALVE matter, then something might be done without too much effort.

I suspect I'm most likely going to REMOVE that booster this coming weekend. I looked, and see holes which look just right for bolting a Bendix (or any other Mopar type) master cylinder straight to the firewall. These have never been used, but they exist all the same. I expect my 1966 pushrod WILL work in the Bendix master cylinder just fine here, so long as I install the MC properly, sans booster.

If any of you have ideas on this notion, do post them! Again, I'm ALWAYS grateful for responses, even if I occasionally get peeved by a few of them. I freely admit my practical ignorance in many, MANY mechanical matters, as I'm just a blackballed junky engineer, who has done a lot more time as a junky than my papered profession. Thus I try to show some Humility to folks, and admit my faults....
 

Davea Lux

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If you are getting hissing when the brakes are applied, that usually means the diaphragm is leaking and the booster needs to be rebuilt. Booster Dewey exchange in Portland does quality restoration work on boosters, and his boosters are all shipped with new check valves as part of the repair process. Usually runs about $200 for a Midland unit plus shipping.

The mounting plate and the brake pedal for manual brakes is different than the ones for power brakes. If you try to mount a manual master cylinder on the power brake pedal and mount, you will have very poor braking because the leverage supplied by the pedal is different. The manual brake system has the master cylinder mounted higher up on the mounting plate, this has the effect of increasing the leverage to stop the car without a power assist. The manual pedal will have the hole for the linkage pin in a higher position as well.

If the Dorman catalogue shows the generic part as compatible with your application, the check valve should fit, but I doubt that is causing the hissing.

Dave
 

Trace 300 Hurst

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Dave is right, and it's not your check valve (although the generic Dorman would very likely work). Whilst looking for a tiny rattle under the dash, I stomped on the brake pedal a few times (with the engine off). Prior to this unthinking action, the booster was perfect. But the result of my stomping? An immediate hissssssssssssssss....... the next time I drove the car. And it quickly got progressively worse as the diaphragm failed worser until I got only one shot at slowing down before having to let the booster build up more vacuum.

So, I just went through this process, described here:
Pics of "Booster Steve" rebuilt 69-70 8.5 inch dual-diaphragm unit.
 

Gerald Morris

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If you are getting hissing when the brakes are applied, that usually means the diaphragm is leaking and the booster needs to be rebuilt. Booster Dewey exchange in Portland does quality restoration work on boosters, and his boosters are all shipped with new check valves as part of the repair process. Usually runs about $200 for a Midland unit plus shipping.

The mounting plate and the brake pedal for manual brakes is different than the ones for power brakes. If you try to mount a manual master cylinder on the power brake pedal and mount, you will have very poor braking because the leverage supplied by the pedal is different. The manual brake system has the master cylinder mounted higher up on the mounting plate, this has the effect of increasing the leverage to stop the car without a power assist. The manual pedal will have the hole for the linkage pin in a higher position as well.

If the Dorman catalogue shows the generic part as compatible with your application, the check valve should fit, but I doubt that is causing the hissing.

Dave

THANK YOU DAVE, for confirming my suspicions regarding this booster. Sitting in a HOT Arizona barn for several decades probably would dry out and crack even a brand new diaphragm, so my surprise that the thing works at ALL is all that remains. It's not working terribly well now. I'm sure the crack has worsened.

I'll try looking up Dewey again. I did so last night but the URL came back dead. OK, he's alive and BUSY! 4-5 week turnaround. Looks like I need to get another core somewhere if I go with letting Dewey do the rebuild. Price is reasonable though. I'm NOT going to muck about with rebuilding that booster myself! Lives beside mine depend on that.

I WILL get out some measuring devices and measure the brake pedal setup in the '68, and compare that to what's in our '66. It occurs to me that I MIGHT be able to transfer the brake pedal, and firewall plate too (if there is one, not sure, looks like the MC went straight onto the firewall in the '66) and just transfer the manual works from Mathilda to Gertrude.

Reckon I'll be standing on my head a bit today, and maybe more this weekend. I thak the Lord I CAN still DO stuff like that, but I DON'T look forward to such self-torture, oh NO Precioussss NO!

You're one of the Best Lights shining on this Forum Dave. Again,

Gratias Magnum.
 

Gerald Morris

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I actually had a check valve split apart on me. There is just a thin wafer of material in there. I don't believe that spraying any kind of lubricant in there is going to assist anything.

Agreed. Desperation oft spawns half-arsed notions.
 

Gerald Morris

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The mounting plate and the brake pedal for manual brakes is different than the ones for power brakes. If you try to mount a manual master cylinder on the power brake pedal and mount, you will have very poor braking because the leverage supplied by the pedal is different. The manual brake system has the master cylinder mounted higher up on the mounting plate, this has the effect of increasing the leverage to stop the car without a power assist. The manual pedal will have the hole for the linkage pin in a higher position as well.

Dave

I've measured the length of the moment arm from the piston rod to the top of each brake pedal for my 2 specimens. The 1966 pedal measures 10" from the center of the piston rod bolt to the top of the brake pedal. The 1968 pedal measures 9.75" for the same.

Yes, the booster assembly appears a little lower on the plate than the master cylinder on the 1966 manual setup, but the plates themselves clearly bolt onto the firewall the same, so I should have no difficulty swapping over the manual plate from Mathilda to Gertrude, while keeping the pedals. I WILL measure the total length of each pedal arm and how it mounts to be sure, but I now suspect I can do this swap without TOO much pain. At worst, I'll have to swap the pedals also.

I also probably should take the newer Bendix clone master cylinder for Gertrude. While I LOATHE using sino-copies of original American products, I've found that master cylinder to be excellent in the 14 months I drove with it. The old MC in Gertrude has new rubber in it, but is FILTHY with CONTAMINATED FLUID, which I shall purge entirely, and probably the wheel cylinder rubber as well ASAP. That Texas redneck trucker-flipper-YAHOO did stereotypical grade work. Such as he abound yet in that State, though there also are many better Folk too. The man isn't malicious, particularly, but simply comes from a certain socio-economic-ethnic milieu which he couldn't escape. I did narrowly, by the Grace of God only....

I'll post you when I do this operation. Your advice always rings the BEST tone!
 

Gerald Morris

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Thx Alan. Got the Dewey link. I'm going to pull that booster for good. I MIGHT send it off for re-working, or NOT. I've been measuring the dimensions of how the master cylinder aligns, the length of the pedal's moment arm with the booster or direct connection to the piston rod, and found only a difference of 1/4" greater length for the direct connection. The master cylinders actually align in the exact same place! So apparently, the difference between a 1966 master cylinder on a direct connection and a 1968 MC on a booster is VERY small. I measured the distance from the top of the MC to the top of the firewall, and found but 1/8" difference, which can easily be from the way the plates are bolted to the firewall.

To wit: I expect I can delete the booster with minimal trouble, now that I have the piston rod for manual brakes, and the retainer. The boot and adapter plate i can re-use or get off my newer MC. In truth, I likely will use the new one. That reman MC on Gertrude looks like a sloppy job. The flipper got it at NAPA, but it smells like a Cardon't job.....
 
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