Honing a master cylinder

[jsd245]

So I’ve got this master cylinder out- can see some discoloration  in the bores- can see it but can’t really feel it. There was no “rust” so to speak of , except at the very end opening where the piston doesn’t ride. The rubber washer in the very end the sits behind the spring cup was also folded over- the air inlet in the plug was totally blocked with rust so the master cylinder was essentially sealed. I guess a combination of all, these things led to it not working.
 

I’ve honed it a bit, hone I got is 240 grit ,  but still see the discoloration, which clearly means those are pits even though I can’t feel them. So I guess I need to hone until they are gone. With a hone that fine I know I’m not removing much material. My only experience honing is opening up shotgun chokes. I ream them  and then hone the last .001.002” . It takes forever to hone out that last bit, so again I know I’m not removing much material. I’ve honed for about 5-6 minutes and the picture is what I have. 
 

Tough to see in the photo but of course the worst pitting was at the opening , but in the bore you can see what I’m talking about. If you run your finger over it it feels smooth.  I figure I’m just gonna hone until it’s gone where the cups ride. The rebuild kit came with the tru k so I don’t have much to lose. 

How much luck has everyone had honing a master cylinder and having good function after? I’ve always just bought a new one since for most cars they are cheap- yet a replacement on this 1 1/2 bore one seems to be $250.00

 

[kencombs]

If you can't feel it, it will be fine.   Haven't done one in a long time but it used to be at least a weekly job on masters or wheel cylinders.  Never had a failure of my work

[jsd245]

So this worked out fine. Honed it bench tested it and it held pressure fine. Hopefully even though the rest of the brake system was replaced  the “ new” wheel cylinders that sat for 5 years aren’t now bad. Will find out this weekend. 

Edited January 21, 2022 by jsd245
Edit

[Dodgeb4ya]

The real leakage test is checking for slight leakage into the rubber boot after three months or more of use.

The leakage can be more when there is no pressure on the piston cups on a honed cylinder.

The rubber cup lips are flared out  against the cylinder bore when the brakes are applied causing a good cup to cylinder bore seal.

When the brakes are sitting released and no extra cup to cylinder pressure...there can be very slight leakage depending on cylinder bore finish and condition.

[jsd245]

Well I guess, but my main concern concern right now  is will the master hold pressure when I’m trying to stop. I need to drive the truck so I can get a VIN Check for registration. With my jury rigged gear puller set up in the vise to test, I got it up to 300 psi. And it held there for 5 min without dropping.  I’m not really sure what the mechanical advantage is on the brake pedal, but with a 1.5” cylinder I’m sure there can’t be more than 500# or so pressure in the master. Probably less. If it’s a 6 -1 ratio on the pedal, max I’m probably getting is 350 psi. 
 

At some point I will probably be dismantling this truck to do a light restoration, and at that point perhaps I’ll just send it out to get sleeved so I have no long term issues. 

[Dodgeb4ya]

I think you have done good and the MC will work just fine.

[kencombs]

15 hours ago, Dodgeb4ya said:

The real leakage test is checking for slight leakage into the rubber boot after three months or more of use.

The leakage can be more when there is no pressure on the piston cups on a honed cylinder.

The rubber cup lips are flared out  against the cylinder bore when the brakes are applied causing a good cup to cylinder bore seal.

When the brakes are sitting released and no extra cup to cylinder pressure...there can be very slight leakage depending on cylinder bore finish and condition.

S otrue.   I've read that is the reason for the metal cup expander and spring used in some cylinders.  I wonder why, (other than cost) that wasn't used by more manufacturers? Higher residual pressure valves also help, at least 10psi for drum brakes.

[jsd245]

2 minutes ago, kencombs said:

S otrue.   I've read that is the reason for the metal cup expander and spring used in some cylinders.  I wonder why, (other than cost) that wasn't used by more manufacturers? Higher residual pressure valves also help, at least 10psi for drum brakes.

I don't see that this truck holds any residual pressure in the brake based on what's in the master cylinder. Unless the booster somehow provides it, but the booster was an option anyway.  I don't think it would matter anyway, that rear cup seal would never see pressure. Neither would the front one with the brakes not applied. 

[kencombs]

55 minutes ago, jsd245 said:

I don't see that this truck holds any residual pressure in the brake based on what's in the master cylinder. Unless the booster somehow provides it, but the booster was an option anyway.  I don't think it would matter anyway, that rear cup seal would never see pressure. Neither would the front one with the brakes not applied. 

there should be a residual pressure valve in the master, right before the exit fitting.  that provided the pressure for wheel cylinders, the cup expanders/spring was used in a lot of masters.  Residual and/or expander/spring for wheels, expander/spring in master.  I didn't make it clear that the residual was not for the master, just wheel cylinders.

[Tooljunkie]

You can clearly see the brass fitting in the bottom of the master. No residual valve. If its holding fluid with no pressure on pedal, you should be good to go. 

[jsd245]

Master cylinder was fine-but the front left cylinder let go and started leaking on my first short drive. Not enough to kill the brakes but was dripping pretty good when I took a look after. So it looks like while all the brake lines were replaced, only the rear Cylinders were either rebuilt or replaced. And it looks to me like one of the rear cylinders that were replaced may be the wrong one- the bleed screw in one side is so close to the brake line fitting you can barely get a wrench on it.

[Brent B3B]

On 1/22/2022 at 7:44 PM, jsd245 said:

 the bleed screw in one side is so close to the brake line fitting you can barely get a wrench on it.

Yeah that doesn’t sound right… so it doesn’t look like this? 

 

Edited January 24, 2022 by Brent B3B
Photo removed

[jsd245]

8 hours ago, Brent B3B said:

Yeah that doesn’t sound right… so it doesn’t look like this? 

 

No- you can see one side where the fittings are very close- this is the new cylinder - you can see the fresh bolts. The other one looks to be unchanged and I assume original. Further- in the box of parts that came with the truck there was an old cylinder - which I assume came off the truck in the rear, my best attempt at measuring f(pistons are stuck solid)  seems to be a 1 3/8 cylinder. The pistons are red in it.  So I'm thinking even this one is not original. but it has Has the wider spacing between the fittings. The brand new one appears to match the one on the truck with narrower spacer between fittings and has a 1.25" piston.

 

 So I'm thinking I've got mismatched cylinders on the back . I think I just want to send them all out to be sleeved or replace them but want to make sure I'm working with the correct rears.  
 

does anyone with a 1.5 ton know what size the rear wheel cylinders should be? 

[Brent B3B]

The B4GA should be 1-3/8” straight bore front and rear

 

[RobertKB]

This is why I like getting old cylinders, which were usually made in the US or Canada, sleeved. The new ones made elsewhere are often just not quite right. 
 

I’m think the ones with the more space between fittings are right. I agree having matching cylinders is best. Others with more knowledge will likely chime in. 

Edited January 23, 2022 by RobertKB

[jsd245]

4 hours ago, Brent B3B said:

The B4GA should be 1-3/8” straight bore front and rear

 

So the replacement is not right- but the old one I have is. That’s good. I can just send it out to get sleeved along with the one that is still on there. 

[jsd245]

So I got the front off- they are step bore on this truck, 1.25 to 1.3875. This matches up with the parts book- my serial number matches up with the series that has two different part numbers on the front so that indicates a step bore. Good news is it looks like DCM has new ones to fit both front and rear on this truck for $58. I called white post- $150 each to sleeve and rebuild so much cheaper just to buy new. 

[Brent B3B]

Sweet! Sounds like your set. ?

just so you don’t think I was trying to mislead you, I was only telling my experience on my B4GA and what the shop manual says

http://dodgepilothouseclub.org/know/B4_manual/B4_brakes.pdf

 

 

I really need to not respond, I just seem to confuse things.

 

keep on truckin ?

[jsd245]

5 minutes ago, Brent B3B said:

Sweet! Sounds like your set. ?

just so you don’t think I was trying to mislead you, I was only telling my experience on my B4GA and what the shop manual says

http://dodgepilothouseclub.org/know/B4_manual/B4_brakes.pdf

 

 

I really need to not respond, I just seem to confuse things.

 

keep on truckin ?

Hah no I really appreciate the help and advice- don’t stop! You can see in the parts book it changes in 53 depending on serial number. Why? No idea. I bet prior to that it was the same front and rear. Part of the fun on these trucks seems to be the forensic parts investigation when trying to work in them. It’s not easy! 

[jsd245]

So - the brake saga continues.  I guess the PO didn’t do as much work as I thought! All the lines got replaced but both front wheels cylinders were shot. Clearly were  original. Front wheels and drums are off, one wheel seal was leaking anyway and for some reason the grease in that wheel was very thin and sticky- so it had leaked into the drum and soaked the shoes, which is too bad because they had quite a bit left. 
 

at this point everything is off, including the backing plates  I am de- rusting and painting. I got the shoes relined at a local place who really seems to know what they are doing, they arced them appropriately to the drum size. Pretty lucky I have a shop close by that relines friction materials. 
 

so I have all the parts I need, new wheel cylinders from DCM, I found some NOS front wheel seals from vics. Bearings and races look perfect and the drums are very  good- their ID is just about exactly 14 1/8. Further reinforcing that this truck may in fact have only 24,000ish original miles.  Once the fronts are done I will move to the rear since I know I have one incorrect wheel cylinder back there. 

[wallytoo]

good progress.  you'll be driving it in no time.

 

i sourced 4 oem wheel cylinders for mine, although one is from a later non-stepped bore 1.5-ton (right rear).  i kept the originals, and if i ever need to replace a wheel cylinder again, i'll send out the appropriate one for a sleeve.  i have kept all of the old parts that are rebuildable, as they are generally better than anything aftermarket.  i've got two spare oil pumps, a generator, distributor, and a starter, too.

 

i am lucky, too.  a local place that relines shoes was able to reline my parking brake band correctly.

Edited February 7, 2022 by wallytoo

[jsd245]

Slowly but surely getting through this. Fronts are done. I was hoping the rears would be OK. I have the new wheel cylinders but was hoping to wait until it warms to switch them. Nope. After a few stops with markedly improved brakes (Now that I had front brakes) the drivers rear cylinder let go. I suspected it might because I could lock the passenger rear up on gravel- but the drivers rear seems to be providing no braking. It is also the one with the wrong wheel cylinder. So I guess I gotta get right into the rears. 

Edited February 21, 2022 by jsd245
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[RobertKB]

Yup, might as well do it all at once. Then you know exactly what you have. 

[jsd245]

Finally- brakes are all done. Pretty much everything replaced front and rear, drums turned, new shoes, wheel cylinders. Luckily the rear drums had plenty of thickness left because they were heavily rusted and grooved. Brakes are excellent in this truck. I was surprised. The booster is clearly working.

Edited April 17, 2022 by jsd245
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