m35 master cylinder compensation port

[7-ton Rolex]

new member here ,question the small hole in my master cylinder stops up about once in a couple of months I clean it out with a ground down rat tail file but it keeps doing it can I remove it and drill it out or would it kill it ,I rebuilt it when I redid my brakes and have put mil spec dot 5 in the system

 

[rustystud]

new member here , question the small hole in my master cylinder stops up about once in a couple of months I clean it out with a ground down rat tail file but it keeps doing it can I remove it and drill it out or would it kill it ,I rebuilt it when I redid my brakes and have put mil spec dot 5 in the system

Which small hole are you talking about ?
Is this one on the bottom of the reservoir ? If so "NO" you cannot plug it. That is your bleed/return hole for the fluid. If your fluid has gunk in it, then you need to totally clean out your brake system. More then likely you have 'O' rings/seals that are bad/worn out and need replacing . Very common problem with our old Deuces. Lack of long term maintenance leads to trouble.
If it was mine I would do a complete brake job on the truck.

 

[cucvmule]

Welcome

How long have you had the truck. Some background information will really help with us knowing how to narrow down what your problem is and how to narrow down on answers to your questions.

Brakes are a very serious issue when not working properly. And what condition your truck is in is very helpful.

A few, many pictures are helpful also as everyone likes picture, and everyone here wants to welcome you and help get you on the trail safe.

Rustystud is trying to be very helpful and understands the problems associated with these systems.

 

[7-ton Rolex]

I didn't want to plug anything I just was wondering if I can drill out the tiny hole inside the master cylinder to a slightly larger size ,I believe it's the compensating port mine may have too small an opening because it takes the 3rd smallest welding tip cleaner to clean it out ,I rebuilt everything on my brakes with new wheel cylinders,lines ,rebuilt short air pack,I just don't think during the casting that the hole was proper size ,it's a 71 35a2 and the brakes work great but when I get a hard pedal I have to take the cap off and clean the port ,now when I say port it's the rear tiny hole inside the master cylinder ,thank's guys

 

[7-ton Rolex]

cucvmule I've owned it 5 years and drive it almost daily in my business

 

[gringeltaube]

.....can I remove it and drill it out.... (?)

Yes, if for some reason that hole (bypass port) was actually too small you can enlarge it a tiny bit, but I would not go over 0.80mm !!

For your reference (and because I was curious too...), I just measured two NOS MC, fresh out of the box: a 0.70mm needle fits trough, loosely. 0.80mm absolutely doesn't; so it's somewhere in between, maybe 0.75mm, at most.

Just keep in mind that with the brake shoes adjusted very tight, then every time- and as soon as- the lip of the piston cup slides past that small orifice, pressure inside the cylinder will quickly build up, so that the soft rubber will try to "squeeze into-" or "escape through" that orifice. So we certainly don't want a hole too big, there. On the other hand, if there is a lot of slack at the brake adjusters, the cup will have travelled past the orifice completely, before any action occurs.

One other thing I'm assuming you have already checked: with the piston completely retracted, the distance from the cup's lip to said orifice is less than 1mm. So it doesn't take that much of any debris to get stuck in between the piston and its stop-snapring to prevent the piston/cup from fully freeing the hole. (Which is absolutely essential for the MC to operate correctly).
Same problem can happen of course, if the rubber had swollen, over time... But that's unlikely when using DOT 5.

Rustystud is trying to be very helpful and understands the problems associated with these systems.

No doubt about it. But it's better to first read - then post: the question here was about "drilling out" (=enlarging) that hole, not plugging it...(!?)

 

[SCSG-G4]

I didn't want to plug anything I just was wondering if I can drill out the tiny hole inside the master cylinder to a slightly larger size ,I believe it's the compensating port mine may have too small an opening because it takes the 3rd smallest welding tip cleaner to clean it out ,I rebuilt everything on my brakes with new wheel cylinders,lines ,rebuilt short air pack,I just don't think during the casting that the hole was proper size ,it's a 71 35a2 and the brakes work great but when I get a hard pedal I have to take the cap off and clean the port ,now when I say port it's the rear tiny hole inside the master cylinder ,thank's guys

The gunk that is plugging the hole is down BELOW the hole. Unless you get all the gunk out, it will continue to plug up even bigger holes until you get a hole too big for the gunk to stop it up, and if you do not cleaned it up then, the gunk will get bigger till it does not work at all. THEN, you will have to either rebuild or replace the master cylinder. Your choice.

 

[7-ton Rolex]

thanks guys !I'm nowhere near .70mm I have a welding tip cleaner set and I can barely fit the 3rd size up from the smallest one through there and I ground down a rat tale file so thin (smaller than a straight pen) that i'm afraid of it breaking off in there ,i'm going to take it off and drill it out today ,thank you all so much!!

 

[SCSG-G4]

thanks guys !I'm nowhere near .70mm I have a welding tip cleaner set and I can barely fit the 3rd size up from the smallest one through there and I ground down a rat tale file so thin (smaller than a straight pen) that i'm afraid of it breaking off in there ,i'm going to take it off and drill it out today ,thank you all so much!!

.7 mm is .0276 inch, .0280 is wire size 70, .0292 is wire size 69, .0310 is wire size 68, .0313 is 1/32, .8 mm is .0315 inch. Drill carefully or you will wind up breaking a drill bit in the hole, making things worse.

 

[7-ton Rolex]

thank you guys when I drill that out tomorrow I'm going to go back into my airpack and try to fix that lip seal in the small piston ,the air side is leaking again and it's forcing brake fluid through the slobber tube I changed over the vent that was originally plumbed with the fuel tank and added the reservoir from Big Mikes is there a trick to those 2 lip seals to keep the first one from leaking ,I have the short air pack and like to have never found a exploded view of it ,the TM only has the long version,thank you all and sorry to be a bother !!

 

[Mullaney]

thank you guys when I drill that out tomorrow I'm going to go back into my airpack and try to fix that lip seal in the small piston ,the air side is leaking again and it's forcing brake fluid through the slobber tube I changed over the vent that was originally plumbed with the fuel tank and added the reservoir from Big Mikes is there a trick to those 2 lip seals to keep the first one from leaking ,I have the short air pack and like to have never found a exploded view of it ,the TM only has the long version,thank you all and sorry to be a bother !!

.
And in all the excitement - we might have forgotten to say Welcome to The Outfit! Safety first. Get your brake problem solved, then welcome, then we need some pictures! You have owned it more than 5 years and it goes to work to earn it's way almost daily... Give the old girl some time in the lime light... Post up a few pictures of your sweetie!

Takes a licking and keeps on ticking

 

[7-ton Rolex]

.
And in all the excitement - we might have forgotten to say Welcome to The Outfit! Safety first. Get your brake problem solved, then welcome, then we need some pictures! You have owned it more than 5 years and it goes to work to earn it's way almost daily... Give the old girl some time in the lime light... Post up a few pictures of your sweetie!

Takes a licking and keeps on ticking
[/Q

 

[7-ton Rolex]

Thank you ,I will send some pics as soon as I can ,my brakes are fine they have always worked fine but little things bug me on my truck that's why my screen name is what it is , a 7 ton Swiss watch !!

 

[7-ton Rolex]

Thank you ,I will send some pics as soon as I can ,my brakes are fine they have always worked fine but little things bug me on my truck that's why my screen name is what it is , a 7 ton Swiss watch !!

.
And in all the excitement - we might have forgotten to say Welcome to The Outfit! Safety first. Get your brake problem solved, then welcome, then we need some pictures! You have owned it more than 5 years and it goes to work to earn it's way almost daily... Give the old girl some time in the lime light... Post up a few pictures of your sweetie!

Takes a licking and keeps on ticking

 

[7-ton Rolex]

View attachment 863688View attachment 863689View attachment 863690

not sure if these went through, first pic is a parade I was asked to attend, and it was an honor!!! this shouldn't have happened guys, but I don't want to get into that and get kicked off my second day

 

[rustystud]

Yes, if for some reason that hole (bypass port) was actually too small you can enlarge it a tiny bit, but I would not go over 0.80mm !!

For your reference (and because I was curious too...), I just measured two NOS MC, fresh out of the box: a 0.70mm needle fits trough, loosely. 0.80mm absolutely doesn't; so it's somewhere in between, maybe 0.75mm, at most.

Just keep in mind that with the brake shoes adjusted very tight, then every time- and as soon as- the lip of the piston cup slides past that small orifice, pressure inside the cylinder will quickly build up, so that the soft rubber will try to "squeeze into-" or "escape through" that orifice. So we certainly don't want a hole too big, there. On the other hand, if there is a lot of slack at the brake adjusters, the cup will have travelled past the orifice completely, before any action occurs.

One other thing I'm assuming you have already checked: with the piston completely retracted, the distance from the cup's lip to said orifice is less than 1mm. So it doesn't take that much of any debris to get stuck in between the piston and its stop-snapring to prevent the piston/cup from fully freeing the hole. (Which is absolutely essential for the MC to operate correctly).
Same problem can happen of course, if the rubber had swollen, over time... But that's unlikely when using DOT 5.

Rustystud is trying to be very helpful and understands the problems associated with these systems.

No doubt about it. But it's better to first read - then post: the question here was about "drilling out" (=enlarging) that hole, not plugging it...(!?)

When I read the part about "removing it" I had assumed he meant eliminating the hole to remove the problem. Now since there is debris in the system it needs to be cleaned out.

 

[Mullaney]

not sure if these went through, first pic is a parade I was asked to attend, and it was an honor!!! this shouldn't have happened guys, but I don't want to get into that and get kicked off my second day

.
The pictures are great!

Sad to see Ryan's face on that banner - but you definitely did a good thing - being there for the parade.

 

[cucvmule]

No doubt about it. But it's better to first read - then post: the question here was about "drilling out" (=enlarging) that hole, not plugging it...(!?)

WWAAATTTT?

Is there something that I replied that was some kind of misdirection?

Was there some editing, gringe? I read nothing about plugging. Where does that come from, and I said nothing of drilling out or can you read.

 

[cucvmule]

And read rusty's response as that having it plugged is not good to keep it clear. To which 7 ton knows it is return orifice.

Wow try and be helpful and this is what happens, turns into what "is is".

 

[cucvmule]

Good Luck 7ton

Take apart and clean out or replace defective parts.