That sure took a long time for those parts to come in. Took forever for those drums to finally come in. Installed drums, bearings and seals. Bled system as before and now she stops as it should. I've had times on other units where the drums being out of round would cause self adjusters to over tighten but never when clean would fail to stop a truck especially with such a hard pedal. Lesson learned.

I ordered new drums. Should be in this week. At this point I am just throwing parts
on this piece.

I read all post is it possible that the drums are like mirrors and need to be cut also some times aftermarket shoes don't have the same material on them and can take a lot of braking before they seat to the drums. check drums noise maybe new shoes on glazed drums.

Not sure if this will help. I dont have access to Mitsi manuals but I think the TCM FD70 is pretty much the same and this is all it says about hard to stop. it also brakes down the operation of what they are calling a hydromaster which im guessing is the booster.

Trouble Shooting

Pedal travel is normal, but braking effect is poor

Inside of power cylinder is poorly lubricated or air leaks from power piston or power cylinder due to damaged packing = Replace packing or lubricate power cylinder.

Air leaks between power piston shaft and piston = Retighten

Poor contact of vacuum valve = replace vacuum valve and atmospheric valve as a set and calk them to 17mm

Hydraulic air cleaner is clogged = disassembly and clean.


5·2·5. TEST METHOD OF "HYDROMASTER"
(1) Performance Test
Remove the plug at the back of the "Hydromaster" and install a vacuum gauge. Start the engine and idle at approximately 450 rpm. Keep the engine in this condition for more than 130 seconds with the revolutionary speed of the
vacuum pump at 700 rpm. The vacuum gauge should read more than 600 mmHg.
Next press the accelerator pedal to increase engine rpm to about 1800 rpm.
The revolutionary speed of the vacuum pump is approximately 2500 rpm. Keep
this condition for about 80 seconds. The vacuum gauge should read 700 mmHg
or higher.

(2) Vacuum Tighteness Test
Gain a negative pressure of 500 mmHg by the same procedure as for the performance test and shut down the engine. lt is normal if the gauge shows a decrease of less than 25 mmHg per every 15 seconds. If a decrease of more than the specified is observed on the gauge it is an indication that the check valve does not have sufficient vacuum tighteness or there occurs vacuum leakage from the joint of the negative pressure pipe. (As a substitute procedure for vacuum tighteness test, remove the plug,send a compressed air of 1 kg/cm2 into the "Hydromaster" and immerse it in water. )

(3) Capacity Test of Power Cylinder

(a) Produce negative pressure of about 600 mmHg inside the power cylinder.
(b) Shut down the engine. Fully press the brake pedal and release it at once.
When the pedal is pressed, air suction sound is produced by the "Hydro master" air cleaner. The power cylinder is considered normal if this sound is
heard once out of every 3 to 4 times the brake pedal is pressed.

If I find anything else ill let you know. the manual has diagrams I cant post so idk how much this will help if at all.

Everything inside the brakes are new. No oil and drums are clean and no grooves.
Backing plates looked good and I didn't see any unusual contact points.

i have a couple questions
1) what did the backing plates look like where the shoes rub/contact at the plate?
there should be small pad areas where the edges of the shoes rub on the plate, reason i ask is they will wear at those points and get grooves worn in them, these grooves can cause the shoes to hang up and not apply correctly. This is a common problem especially in these trucks that seems to get overlooked quite a bit.
2) what did the shoes look like? were they clean and dry? no grease or brake fluid embedded in them? If they had gotten any grease or fluid in them at any point in the past they should be discarded and new shoes installed. Once they get contaminated it is impossible to get all of the grease/fluid out of them and it will seep back out when they get hot and cause them to not grab properly.
3) also the drums, is the contact area good? no wear/grooves?

I know you don't want to take the hubs back off to inspect this but you may have to.

Let me try to answer these questions. We are not sure if the brakes worked before it was sent to us from Florida to be going to another one of our other sites. I found that the booster vacuum resouvoir was not connected so we thought that was the problem. I removed the resouvoir and pulled a vacuum with our A/C pump. Pulled and held vacuum so we reconnected. Nothing changed. This is when I suspected the unit had a problem before it got to us since the resouvoir was disconnected.
As far as the pedal, everything is free and connecting rod has just about an 1/8" play before contacting the booster so not to actuate prematurely.
I did not check booster to see if it not leaking because the old booster and new booster are acting the same.
Parking brake is connected to the drive shaft and not associated with the wheel brakes.
As far as the grinding inside the drum that has me scratching my head. The sound we hear sounds like the springs inside the drum are over stretching but the shoes are sitting fairly tight in the drum. I have adjusted multiple times without any change.
Tomorrow I am going to check to see if the breather tube from booster to filter is clear. I assumed it was and I didn't blow thru it when replacing booster so I cannot be 100% certain.
Not sure if I posted this earlier but today I had it running wide open and shifted to neutral then shut down motor and while drifting I applied brakes and it seemed just as bad as when I had vacuum from the pump. I really do not want to have to break these drives down again just to inspect the shoes and associated hardware. BTW the brake lines are steel and it has 2 lines coming from M/C (one to each wheel) and they are in good shape.
Again thanks. Ed

You mentioned testing vacuum going to the booster, but have you checked the new booster itself for proper operation and vacuum leaks?

Pedal assembly in good shape not binding at all?

Not trying to be a jerk just cant think of much else that you havnt replaced yet

Another question would be was the truck stopping properly before the brake replacement or was this the initial issue to begin with?

Is the parking brake working well?

Not sure what the grinding noise would be unless somthing isnt right inside the drums binding maybe, or was it a problem before the brake replacement or is it coming from somewhere else possibly drivetrain. But I wouldnt know with out hearing it myself just guessing

Sorry for all the re edits. Was re reading your initial post and had missed a few items youve checked/replaced. I hope you figure it out cause im pretty much out of ideas already myself

Installed a new master cylinder today as well as tested vacuum resouvoir. Same results. Hard pedal but not so great stopping. Only thing not replaced are the steel brake lines and they look good. If I turn hard left or right so only 1 wheel is turning I have the same results. I drove it to max speed and put in neutral and shut down motor then applied brakes. Same results.

I was thinking the same however I don't ever remember this due to a m/c. I have seen them bypass when depressed slowly but hard when fast pressed but never not having enough power is something I haven't seen. Thanks for reply. I will order a new MC tomorrow and let you know what I find out.

Based on what you described, you really need a.new master cylinder.