Need advice on bad brakes

[Dumpy22]

Hi new M35a2 1966 deuce owner

Recently purchased a bobbed deuce that the previous owner has installed
new master cylinder, air pack, wheel cylinders and hoses from axels to
wheel cylinders. The issue is the truck only slows down gradually when
brakes are applied. Checked the master cylinder for proper free play,
vent and both holes in master cylinder are open. Checked the fluid
presssure at wheel cylinders 500 psi with no air and 1700 psi with air.
checked the adjustment of the brakes with feeler gauge. I even over
adusted the brakes with lots of drag and no change to brakes. With no
air the pedal is high and hard, with air pedal goes down 1.5”to 2”.
When I bleed the air pack and wheel cylinders straight fluid no air. The brakes
do not squeal or moan. Could see plenty of material left on pads
when adjusting. Master cylinder is full and system has no leaks."
Next step going pull the pull the drums. Has anyone else experienced
this and can offer any advice.

 

[gimpyrobb]

What was done with the air lines at the rear of the vehicle? I have seen some shorty deuces with the air lines spliced together, THIS IS VERY BAD!.

They are not to be joined, if they are, separate them and see how the brakes are.

 

[dmetalmiki]

Bobbed is (rather bad!) But..In the name of safety, Check that the air assist pack is working. As, (It seems) It obviously is not, and as a result you have no 'Power assist' braking at all.
Check and Fix that issue ( If inoperative) and you will have full (Old military truck!) braking ability.

 

[fpchief]

He stated he had 500 psi at the cylinders with no air and 1700 psi with air. I have no idea the pressure that should be at the cylinders but isn't that some indication the airpack is working?

Sent from my SM-G955U using Tapatalk

 

[Dumpy22]

The airlines going to the rear of vehicle have been removed and there is a pipe plug
in the air pack for the service trailer port. From what I have read in the forums 1600 psi
is the correct working pressure for the air pack.

 

[doghead]

Inspect your shoes and drums.

 

[73m819]

With grease/oil on the drums/shoes, even one drum/shoe set WILL effect stopping, the truck is made to stop with SIX brake/ shoe sets, with 1 out of 6 set oiled the truck will still stop pretty good, 1 bad out 4 is a different story.

 

[doghead]

What size tires do you have?

 

[Dumpy22]

14-20 tires. Even going 10 miles an hour in my gravel driveway it will just slowly come to a stop.
hopefully I will find something when I remove the drums

 

[doghead]

Your boosted brake pressure is correct.

The master Cylinder creates in the vicinity of 450-500 PSI

The airpack increases this to between 1600-2000 PSI.

I am looking in my resources to see where I found this information and I will post that once I have found it.

Edit:

Commercially available brake pressure testing tools use 2000 PSI gauges.

 

[Dumpy22]

The previous owner said the brakes were not satisfactory even with the original rims and tires.
same issue just gradually slowed down.

 

[dmetalmiki]

oooo,k..Sorry, I should have read more in detail...(But still brain aching over the wrecker fix),
(As) Possibly, the brake shoe anchor point adjustments need correctly setting?

 

[doghead]

It's possible the wheel cylinders are all bad(gummed up/rusted).

Total brake inspection is needed for sure.

remember, NOS parts can be 45 years old and junk inside.

 

[Dumpy22]

Ok, let you know what know I find out

 

[tobyS]

You need to change to 1/1/2" dia wheel cylinders, I believe + new clean brake shoes and drums turned.

When the A3 went to super singles they put 1 1/2" on the front and left the back 1 3/8". Prior to that, the wheel cylinder front and rear were 1 3/8". Your tire size puts a lot more torque on the brake...thus it needs more force against the shoe.

It would be nice to know the ratio of your master cylinder. My A3 is 50/50, so I have equal amounts going each direction, which is great for stopping with 2 axles.

There are some 60/40 split systems too , which could be more closely matched by only using the 1 1/2" on the front. You state the MC is new, I expect dual circuit. Does it have equally sized outlets, front and back?

 

[Dumpy22]

It is a single circuit only one outlet

 

[sandcobra164]

Test pressures seem to be within range. Take the truck for a drive and use lots of brake pedal even while on the throttle. Use an infrared temperature sensing gun to see if you have any brake drums colder by about 50 degrees from the others. I would start on the coldest one as that is where your problem is. I no longer own an M35A2 but mine could lock the rear tandems on pavement in a panic stop situation when unloaded. I only did it once and it took quite a bit of effort on the pedal.

 

[rustystud]

Your pressures are pretty spot on, so I agree with all here that your shoes and drums are the most likely culprits. You really need to take the drums off and check this out.

 

[tobyS]

It is a single circuit only one outlet

"that the previous owner has installed
new master cylinder"
"both holes in master cylinder are open".

Sorry, from these two statements, I thought it had been changed to a dual circuit.

Still, I would want the larger piston on both axles with that large of tires.

 

[frank8003]

Probable advice is to pull all the wheels and drums and clean
and fix all the problems in there that are found.
.
Never know what it is until you do the inspection.