Need your opinion

[Seth_O]

I pulled my airpack today for an R&R and it leads me to a couple of questions.

• should I pull the master cylinder as long as I am down there and have the airpack out of the way? attached are pic's of the MC. It looks pretty clean to be honest, it's in much better shape than the airpack, but since I already have the fluid drained, and the airpack out of the way it would certainly be a more convenient time to do it, and I can't tell if it's leaking from the bottom, or there is fluid spray up from the airpack below it.

• since I already have the system pretty well drained, should I switch to DOT 3? It's obviously considerably cheaper and more available. In the research I did (before asking this question ) I couldn't find any real functional reason to stick with the DOT 5 (presuming I do an adequate job flushing the system and completely removing the DOT 5.) I am capable of making up my own mind, but part of that process is getting the opinions & thoughts from folks that are real subject matter experts.

I appreciate your thoughts and opinions.

 

[gimpyrobb]

That looks like crap that has been dripping from in front of your MC. It doesn't hurt to go ahead and pull it to inspect since you have to bleed the system anyway. Might catch something wrong, might have some crud in there, or it might not. But you will know for sure if you do.

 

[Seth_O]

Tks Gimp. Also, I found a really good thread discussing DOT 3 vs DOT 5, not sure why it didn't come up in my search before. I think I have the answer I need on that.

 

[gimpyrobb]

I wasn't going to comment on that but, I like the 5 better. I have seen too many corroded brake components in systems that use 3.

 

[rlwm211]

If the airpack needs to be rebuilt, you can bet that the
master is the same. I say this because moisture
and crud are the enemies of both
and if it is in the airpack, it got there from the master cylinder.
This is all in terms of the brake fluid side.​

Airpacks also suffer the same problem any air operated device
does in regards to moisture accumulation. That might be a reason
for the air pack to have issues before the Master, but this is conjecture on my part.​

Based on the pictures, your secondary seal on your master is leaking.
If the bore of the master is badly corroded, you will have to hone it
until it is suitable for use, and if it is bad enough, that will be out of
spec in terms of diameter. I know this because my master was bad
enough that when cleaned up the secondary weeped as it was not big
enough to seal the bore and keep the brake fluid inside.
Master cylinders are fairly inexpensive.​

As to the DOT3 versus DOT5 discussion I prefer the 5 also as it
eliminates some of the worry of trapped moisture rotting my lines
and components from within the fluid system. Most folks do not
realize that DOT brake fluids other than 5 should be flushed every
couple of years to remove the absorbed moisture. DOT5 or BFS repels
moisture while the others absorb it.​

Just my two cents​

RL​

 

[gimpyrobb]

Some times the air pack can be in bad shape and not the MC because of a lack of draining the air tanks. Moisture in the air lines would have no effect on the MC.

 

[rlwm211]

Agreed Gimpy on the water in the airpack from the air system.
I would point out that the entire air portion of the air pack
is aluminum and very resitent to corrosion and it is
sludge that is the buildup problem from moist air.

I would be concerned for the leak from the boot of the MC
as being an indication of a bad seal minimum,
and that requires a rebuild to repair the MC.

With the amount of time a lot of these trucks sat at National Guard
depots before being sold, there is a high possibility,
and probability for that matter, of moisture getting
into the brake systems and affecting the corrosion prone portions.
For what little it costs for a master rebuild kit, and the
fact that the entire system is already drained,
I would rebuild the MC if only for peace of mind.

Just my two cents.

RL​

 

[glcaines]

I would go ahead and replace the MC since they can be picked up for a reasonable price and there is very little additional labor involved. Then you will know you are 100% on this part of the brake system. I would also never consider using anything but DOT 5.

 

[Seth_O]

Tks guys, appreciate the responses. I will pull the MC today, and rebuild it at the same time as the airpack.

Better to have the peace of mind.

 

[AGE|kshaufl]

+1. DOT-5 or BFS is a little easier on the rubber seals in brake parts.
+2. It can also take a little more heat than DOT-3.

The only downfall that I can think of is that DOT-5 has a little more compressability than DOT-3. It can give you the impression that the brakes are a little spongey.