M35A2C master cylinder failure?

oifvet · Jun 14, 2012

I believe the master cylinder on my 1989 M35A2C failed. Whatever happened, happened at the end of a test drive following fluid changes and spin-on conversions. It was one of the classic :deadhorse:

stories associated with brakes going out and the potential for disaster only a breath away.

Aside from the "what could have happened" part of the story, when am beneath the truck and I am pulling down on the pedal arm there is a "washing machine" (or) "plunger-in-the-toilet" sound of the fluid bypassing inside the master cylinder. There is no "pedal" and there is NOT a brake fluid leak anywhere underneath the truck or near any wheels. Air pressure is good. The system was and still is full of DOT 5 silicon brake fluid. The brakes were operating well, and the pedal just went to the floor as I arrived at my driveway.

My question(s) will be...
What has happened?
Is this a rebuild or a replace?
Is there a core for the old master cylinder, or is it a throw-away item?

The many threads on brakes do not necessarily answer these specific questions. Any helpful advice or direction would be much appreciated.

Thank you (all) in advance.

Flyingvan911 · Jun 14, 2012

I'm glad you are safe. If the fluid level in the master cylinder is still at the right level, I would say you've lost a seal and the fluid is bypassing like you suspect. I'm no expert, but that's my guess. I say rebuild it.

WillWagner · Jun 14, 2012

It can be rebuilt, try to stay away from the likes of Saturn, AVTE, etc. They sell Chinese stuff and the do fail rapidly. Go to NAPA and get a kit from them.

oifvet · Jun 14, 2012

O.K., now I must ask if this is an easy "bench" job, or will I need specific brake tools?

It REALLY sounds like the fluid is just pure blow-by! The system only causes a little movement in the r/f brake (that I can hear easily), but the hand-brake holds the truck on level ground.

The seal that failed (hoping and assuming that is all that happened), sure seems like an achilles heel!

If I go to NAPA, what am I asking for?

I wish I could post the video I took (with sound). Amazing, the amount of fluid sloshing inside the master cylinder and no braking!

This truck is an '89 and only has 9955 miles.

I know things fail, but... :shock:

gringeltaube · Jun 14, 2012

oifvet said:
...............Is this a rebuild or a replace?....

..... its probably time for a rebuild. But first pull the guts out; then you will know what happened...

Rebuild kits are available, relatively cheap; not sure about their quality, though. NOS replacement MC are out there and not overly expensive, either.

The fun part of removing the MC comes when you get to the last one of 4 bolts...

G.

73m819 · Jun 14, 2012

gringeltaube said:
..... its probably time for a rebuild. But first pull the guts out; then you will know what happened...

Rebuild kits are available, relatively cheap; not sure about their quality, though. NOS replacement MC are out there and not overly expensive, either.

The fun part of removing the MC comes when you get to the last one of 4 bolts...

G.

Is this why sometimes only THREE bolts are found ???

oifvet · Jun 14, 2012

The fun part of removing the MC comes when you get to the last one of 4 bolts...G.

This is true of any number of bolts associated with just about anything I do! aua

I count two (2) air packs. The MC only has one filler cap, though. Do these dual-circuit systems usually have just one cap? I thought I was seeing two caps on some reserviors in the many threads I have studied.

Regardless, I will need a day to spin down from the thought(s) of what could have occurred on Dead Man's Curve. I was tempted to post under the Chaplains' Corner! (All due respect intended!)

73m819 · Jun 14, 2012

oifvet said:
This is true of any number of bolts associated with just about anything I do!

I count two (2) air packs. The MC only has one filler cap, though. Do these dual-circuit systems usually have just one cap? I thought I was seeing two caps on some reserviors in the many threads I have studied.

Regardless, I will need a day to spin down from the thought(s) of what could have occurred on Dead Man's Curve. I was tempted to post under the Chaplains' Corner! (All due respect intended!)

Now think about bumping your speed up to 65 +

gringeltaube · Jun 14, 2012

73m819 said:
Is this why sometimes only THREE bolts are found ???

LOL... soldier X- logic: that missing #4 won't give a fight, next time.....

G.

DeucesWild11 · Jun 14, 2012

Sure sounds like an internal seal issue to me. I rebuilt both my MC and Airpack. Do you have any brake fluid coming out the slobber tube on the side of the engine? That could also suggest an internal seal issue.

oifvet · Jun 14, 2012

73m819 said:
Now think about bumping your speed up to 65 +

...Or, driving in a parade behind the band when they suddenly have to do a, "Mark-time... March!"

My last truck split a brake-line at a flare/fitting after I cleared an intersection! I had enough pedal to get off the road and into a truck-stop parking lot before there was none! Very bizarre!

You can inspect and inspect... There are some things that just happen without much warning. It's like nearly every disaster. "If (someone) would have only known."

gringeltaube · Jun 14, 2012

oifvet said:
.....
I count two (2) air packs. The MC only has one filler cap, though. Do these dual-circuit systems usually have just one cap? I thought I was seeing two caps on some reserviors in the many threads I have studied.
................

No personal experience here, with the dual circuit system trucks...
But you should have access to this TM at least: SMARPI 9-2320-209-14&P (attached, below...)

Admin: I just checked our Deuce TM-section; could we have this one listed, please?

G.

clinto · Jun 15, 2012

WillWagner said:
It can be rebuilt, try to stay away from the likes of Saturn, AVTE, etc. They sell Chinese stuff and the do fail rapidly. Go to NAPA and get a kit from them.

I have not seen rebuild kits (or a NAPA crossover #) for the 1987-1989 dual circuit master cylinders.

If it's out there, it needs to be in this thread

G-Force · Jun 15, 2012

Check the level in the plastic reservoir. On some plastic reservoirs I've seen on cars and some trucks with one cap the reservoir is partitioned inside and you can lose half of the fluid but not the other half. Just an idea....

oifvet · Jun 15, 2012

News!

I studied the situation under better (day) light and saw fluid inside the engine compartment! BRAKE FLUID! :shock:

DOT 5 started pouring down on me as I pulled on the brake pedal arm from underneath the truck.

I opened the engine hood and driver's side inspection panel and had my wife press the pedal as I watched for the leak. I almost got a facefull of DOT 5 as it shot out of the white nylon vent line that is routed from the top of the reservior to the engine compartment firewall!

What in the world?

Again, this is a USAF (contract) M35A2C with dual circuit brakes as if an M35A3, but the reservior is NOT remote mounted. It is attached to the top of the master cylinder. Possible Bendix P/N 2232693 (obsolete). Casting on outside of master cylinder indicates "1.75 BORE".

Has anyone ever seen such an event?

G-Force · Jun 15, 2012

Does this do it with the truck aired up???
If so try pressing the pedal with no air, You could have an airpack problem.

nk14zp · Jun 15, 2012

WillWagner said:
It can be rebuilt, try to stay away from the likes of Saturn, AVTE, etc. They sell Chinese stuff and the do fail rapidly. Go to NAPA and get a kit from them.

Any one know the NAPA PN for the single MC kit?

doghead · Jun 15, 2012

Isn't that what it looks like in the TM?

Air blowing out the vent is classic bad air pack. (which one?, you'll need to remove the vent lines and see which one).

I'd rebuild both, and the master cylinder.

oifvet · Jun 15, 2012

G-Force said:
Does this do it with the truck aired up???
If so try pressing the pedal with no air, You could have an airpack problem.

This happened with NO air. Pedal to floor... fluid pushed out through top of master cylinder reservior vent line.

The truck has two air packs obviously, but this white nylon vent line is just a thin diameter tubing that is attached to the plastic reservior that is attached to the MC and accessed through the driver's side floor of the truck. This MC is well before the air packs. I don't think the air side of the system is introduced at this segment.

Kipman suggested that the ports of the MC might be plugged. I think that might have some credibility.

I spoke (at length) to a Bendix tech rep as well as their customer service department.

Bendix P/N 22333867 is available, but is for the M35A2C and has a remote reservior. Apparently not the same MC.

Bendix P/N 2232693 appears the same, (has reservior on top of MC), but is discontinued/obsolete. 2.742 - 2.747 bore diameter indicated.

Neither have a rebuild kit through Bendix (who are trying to distance themselves from hydraulic brakes and focus on air only).

TNJ Murray shows a master cylinder for M35A2C for close to $500.00. No reservior, and cannot tell if it is the same application.

Suggestion from Bendix... "Remove MC and inspect... take to NAPA and try to locate fitting parts the same size and application."

I'm looking at this MC... Only problem is the lack of screw-on/off filler cap.

http://www.steelsoldiers.com/attach...ing/150688d1257181395-split-brakes-mc-web.jpg

DHennon · Jun 15, 2012

On Mr. G. That 4th bolt can be a real heartbreaker!

M35A2C master cylinder failure?

Active member

Well-known member

The Person You Were Warned About As A Child

Active member

Staff Member

Rock = older than dirt , GA. MAFIA , Dirty

Active member

Rock = older than dirt , GA. MAFIA , Dirty

Staff Member

Active member

Active member

Staff Member

Attachments

Moderator, wonderful human being & practicing Deuc

Member

Active member

Attachments

Member

Active member

4 Star General /Moderator

Active member

Member