1994 International 4700 Conversion Begins

[Ozrockrat]

I have seen an extreme case in a complex hydraulic control system that caused a similar symptom to what you are having. But this is a really far out possibility and I am loath to actually mention it as it may lead you down the garden path.

We had a system that the rams would bind on retracting (fine on extension) and then come good. Worse at full speed and could not get it to fail while operating in manual mode. It ended up being a flap of the inner liner of a flexible hose would get caught in the reverse flow when it was strong/fast enough and block the return. If you backed off it would unblock. Operating in manual was configured at reduced pressures so it never got to sufficient flow to trigger the problem. That took months to find and contrary to normal hydraulic testing we eventually found it by doing flow tests not pressure testing.

With this extremely rare possibility in mind I would suggest that when you swap to Dot4 fluid that you drop the hose off the master cylinder (flex hase right at the cylinder on most rigs) and then blow back through from both caliper flex hoses. This should clear any crud that may be causing a blockage. Obviously make sure you don't spray brake fluid everywhere.

If you really want to get technical I do have a set of hydraulic test gauges somewhere in the shop (so rarely needed). You would need to make up a couple of test hoses/T's but you could at least see if you are building up residual pressure.

 

[rlrenz]

Hi Bob, I would not rule out a piston or two hanging up as it is certainly possible. I've rebuilt all 4 and the problem has bounced from side to side. It has not been easy to pin on one particular problem. Eventually, I will get it straightened out. If I had drum brakes I'd be more inclined to tear into it on the weekends. The disc brakes make for a lot of work.

When you switched to DOT 5, what was the reason behind the fluid change?

I had rebuilt a 2 1/2 tom M series truck from the frame up, including everything new on the brake system, from the master cylinder to the air-pac to the wheel cylinders. The new wheel cylinders were Canadian surplus since they had spec'd out cylinders with a larger bore than the US cylinders. The larger cylinders the Canadians selected were to improve braking.

The shop foreman at the area USAR motor pool shop recommended silicone fluid due to it's better temperature capability, plus the US military was converting everything to silicone fluid at that time. I was able to purchase silicone fluid at a collector's show for only $20 per gallon. I used my pressure bleeder to push alcohol through the system, then added the silicone fluid. Solid brakes from day-1.

The shop inspector had cautioned me that DOT-3 and silicone would not mix, but form a layer similar to oil and water. He also said that he thought that if the two were both in the system, they would form bubbles (based on some sophisticated mason jar tests he conducted), so I'd be bleeding the system constantly. I don't know about the bubbles, but filling 3 times with alcohol, draining, and blowing it out each time resulted in a very effective system.

However, after doing s bit of research, I find that it is NOT recommended for ABS systems since it has a higher viscosity than conventional brake fluids. Accordingly, my earlier thought that silicone brake fluid might be a PLAN-B solution should be ignored.

DOT 5

DOT 5 brake fluid is also known as "silicone" brake fluid.

Advantages:

It does not eat paint or skin.

It does not absorb water (BUT!!! See more on this under disadvantages, below.)

It has a higher boiling point than DOT 3 and DOT 4.

It is compatible with all rubber formulations.

It is a good choice for Concours cars which are rarely driven and/or never driven hard.

Disadvantages:

It does NOT mix with DOT3 or DOT 4 or DOT 5.1. Most reported problems with DOT 5 are probably due to some degree of mixing with other fluid types. A residue of the former non-compatible fluid is sufficient to cause serious issues. The best way to convert to DOT 5 is to totally rebuild the hydraulic system. Additionally, the same advice applies if switching from Dot 5 to any of the other fluids.

Since DOT 5 does not absorb water, any moisture in the hydraulic system will "puddle" in one place. This can cause localized corrosion in the hydraulics.

Careful bleeding is required to get all of the air out of the system. It is hard to you without introducing bubbles and thus results in soft pedal feel. These small bubbles will form large bubbles over time. It may be necessary to do a series of bleeds.

DOT 5 is less compressible (often creating a slightly softer pedal). It is not recommended for racing application.
It is hard to pour without introducing bubbles and thus results in soft pedal feel,

It is not recommended by the brake manufacturer, especially for ABS brakes.

It is about twice as expensive as DOT 4 fluid.

It's pretty much incompatible with anti-lock brakes because the silicone fluids tend to be more viscous, which can cause problems with the timing of the pulses that are intended to work with the thinner glycol-base fluid. This sometimes leads to damage of the ABS valving. The rapid pulsing necessary to anti-lock functions tend to cavitate the fluid, as the tiny bubbles collapse and coalesce into larger ones, and then collapse and reform into smaller ones. This tends to counteract the ABS effect and can diminish the actual effective braking. This condition also heats the fluid and can lead to even more sponginess and possible damage to the ABS controller.

 

[scooter421]

Rear end is an N175, if I was to do anything more than changing gears though I think would be getting serious about turning it into a 4X4 and having matched components front and rear. Might as well throw a new trans in the mix too!

 

[scooter421]

Thanks for the update on the DOT 5 fluid. Sounds like a lot of work! If the fluid is the issue causing my problem I think the 4 should solve it. If not, it's got to be calipers or some craziness such as OZ is describing.

 

[scooter421]

Since the beginning of this problem, I've wondered if there was not something acting as a check valve. Someone has replaced the original brake line to the rear which is about 6 feet of it or so. Replacing all the lines is a thought and possibility. Since it was primarily the right rear, I did remove the flex line to inspect it and the "T" fitting that supplies the rear and found nothing wrong in the back. It does seem like it is a problem retracting with the heat build up being a secondary issue. Now that I am thinking about it, I replaced that line when I replaced the rotor/bearings and rebuilt the caliper. At least it eliminates that section of the brake line. When I flushed the reservoir and bled the brakes there was a lot of crap sitting in the reservoir which took a bit of time to clean out. Who knows, there may be a bit of a clogged artery somewhere.

 

[scooter421]

Well; after a variety of car troubles, I finally got back to working on the ambo a little bit. It's surprising what a little break will do to your thoughts! Oz, Ross and I have been discussing different bumper ideas over the past several weeks. The more I thought about it, the more leaving my rear bumper alone made sense for my application. Much of our discussion has been regarding how to mount the spare tire. Since I am sticking with dual set up in the rear (which has it's own pro's and con's) essentially; as Ross said, I have two spares on the truck already. I believe the load rating is about 6600 lbs per tire on mine. The rear of the truck is around 9000; so, even with two I have enough tire/weight capacity. Enough said on that, back to the little bit of work I was able to get done.

With my original intention of having a mounted spare out the window that opened some other options. Underneath my truck in the rear there is a ridiculous hitch frame someone had installed. I had originally wanted to mount my propane tank in front of the right rear tires where I have nice tucked away spot that would work well; however, no longer trying to figure out various possibilities of how or where to mount the spare tire allowed me to come up with a different plan for the propane.

The giant ridiculous hitch bracket will hold two propane tanks side by side and they will be in a steel cage! Amazingly, the hitch bracket from side to side was a perfect fit for the mounting tabs on the propane tank. It will take more tubing to run the propane where I want it, o'well. Now, I have to find another tank! Two tanks opens up opportunities for heat, cooking, hot water.....oh boy!



As for the brakes.....I have yet to tackle that issue......again! I have done more digging on what may be causing the problem with the brakes. I am beginning to agree with the majority that I've got a sticky caliper or possibly an odd master cylinder issue going on. The next time out I am going to be taking temperature readings of the various components to try and get a better understanding of what's happening. I checked the brake pads while I was installing the propane tank and each brake pad was free.

 

[rlrenz]

Holy moly - that hitch bracket assembly looks like it could handle much more than the truck could pull. What is it -- a 4x4" cross tube?

Even though that might be a nice location for the propane tanks, how in the world will you get to them to fill them? Crawl under the truck? And I'll bet that any propane dealer who has to fill them won't crawl under the truck, and the odds also are that they won't let you fill them with their equipment. If you have to unbolt them and remove them for a fill, then hoist a pair of full tanks back into place, you will change the location quickly.

If you could slide them back farther in the framework, and provide an access door for filling, you might be OK.

 

[scooter421]

Holy moly - that hitch bracket assembly looks like it could handle much more than the truck could pull. What is it -- a 4x4" cross tube?

Even though that might be a nice location for the propane tanks, how in the world will you get to them to fill them? Crawl under the truck? And I'll bet that any propane dealer who has to fill them won't crawl under the truck, and the odds also are that they won't let you fill them with their equipment. If you have to unbolt them and remove them for a fill, then hoist a pair of full tanks back into place, you will change the location quickly.

If you could slide them back farther in the framework, and provide an access door for filling, you might be OK.

LOL...it is ridiculous. It's mostly 4x1.5 and 3x1.5 C channel with gussets and welded to the frame, it's not going anywhere easily! They cut a hole through the front and rear sections of the C channel and welded the hitch tube through both sections. They did a good job!

As for the tanks; yep, I will have to get under the truck and remove them for filling. It does not look like it in the photo but there is actually a lot of room under there. I can easily slide them toward the cab, down and out. We don't go through propane very quick. If I plan filling the tanks accordingly, I can remove them and get them filled from the comfort of the shop as needed. I am going to build a header to plumb the propane into. That way I can add a line later if I add heat, refrigeration etc.

 

[rossvtaylor]

It's good to be back working on things after a break, I'm sure! Yes, that doesn't look like very convenient access - but, it looks like a perfect fit and well tucked out of harm's way. I totally understand the "put them where they'll go" planning... I'm with you there! Having two tanks under there will be nice.

 

[scooter421]

Hi Ross, it just so happened when I test fit the tank the air bags were deflated which was a great opportunity for test fitting me and the tank. Even with them deflated, I was able to get under there and use a drill kneeling down. I think you and OZ have a lot more stuff under the rear section than I do. I have the added benefit of being short! Actively looking for a winch and following your lead on the front end mods.

 

[rossvtaylor]

Hi Ross, it just so happened when I test fit the tank the air bags were deflated which was a great opportunity for test fitting me and the tank. Even with them deflated, I was able to get under there and use a drill kneeling down. I think you and OZ have a lot more stuff under the rear section than I do. I have the added benefit of being short! Actively looking for a winch and following your lead on the front end mods.

By the time we get to doing yours, I'll have that all dialed in... I'm happy being the Guinea Pig! Haha!

 

[scooter421]

I appreciate your sacrifice! I am talking to a guy on Craigslist who has a bumper and winch for sale. Unfortunately, he does not know many details about the winch which is a concern. He thinks it's a 15k winch and thinks it's a 12v but it's labelled as a 24v.....sketchy, the red flags are popping up everywhere.

 

[Ozrockrat]

If that is the one that has just been painted I would steer clear of it unless he can show you it working.

 

[scooter421]

If that is the one that has just been painted I would steer clear of it unless he can show you it working.

Yeah, that's the one. He knows far less about it than I would expect. I gotta keep looking!

 

[scooter421]

I finally got around to doing something I should have done a very long time ago. Added cup holders! The original console was a little like swiss cheese from the light controls.



The wiring under there....wow a mess for another day.