Flat Towing

[brute4c]

The drag link was disconnected on the passenger side but still connected on the steering box end...the loose end of the drag link was restrained up and out of the way, to the frame rail.

Brake system:
In 1999, I replaced the stock, but blown, master cylinder and the wheel cylinders...with the stainless steel piston Ford units. ALL the brake lines were replaced, all the brake shoes were new as well. The fluid had been flushed in 2001 and 2004...a total of less than 10,000 miles was put on the truck since 1999. The brakes had been backed off just prior to the tow. When the fire happened, the tow distance was about 60-70 miles from here...not real far, and the speed was 60 mph or less. I felt certain drag all of a sudden on the highway, took the exit that was right there and before arriving at the end of the offramp, as I slowed to about 15 mph, the truck jerked the tow vehicle to a stop as the front bearings locked up at that time. The backing plates were cherry red and brake fluid was flaming from the backing plate as well.

The spring on the brake pedal was strong. Upon teardown, I found the master cylinder piston buried in the bore though the pedal was at relaxed, normal, height...I believe the piston was drawn in by the precipitating incident not that the piston moved and started the chain.

Point: When the truck was first purchased, the drum screws wouldnt budge and were drilled out. No M715 Zone back then...I asked some local mechanics I trust and the consensus was that the drum screws were like the little clips used on the assembly line to hold the drums on before the wheel/tire gets there...a part for the assembly line that isnt needed after. I didn't put them back in. A different edition of the -34 manual from what I had was loaned to me by a member from Michigan, boghog, which included a warning to make sure to keep the drums indexed to the hubs. Barrman has decisively shown that there is a measurable difference in the drum/hub combo runout with the different indexings after meticulous examining and measuring of these parts.

I conclude that the decision to leave out the drum retaining screws was a bad one that I will never repeat and will work to make sure other members know...but...I have driven 14,000 miles on the truck since the drum screws were removed and left out, including driving to LBL, 650 miles in one day, with a single tank of 280 miles, without a single issue with the brakes.

And why was it the front brakes only in a non proportioned brake system with a single reservoir on the master?

I dont know why the fire happened...I wish I did...I hope it never happens to anyone else...certainly not you. If Dave hadnt been stopping anyway, he could very well have been in the same boat...God forbid.

[porkchop]

Was it both front tires or only one? When you replaced the master cylinder was it with another stock one? What was the story about your brake lights being on when you would go out to the truck sometimes?

Dave, which master cylinder do you have in your truck? There has to be a common link between your trucks that caused it.

[brute4c]

The fronts were both locked up hard and there was fire on both sides.
The new master was an exact replacement for the original stock one, single line and all.
I did have an issue with the brake lights coming on after the truck had been sitting...hadnt figured that out. I do know that even when they were on that way, I could push the truck out of the shop by myself...no noticeable increase in drag. It would happen when I was driving too I found out when a buddy of mine was behind me on the highway one day for about 25 miles and told me my brake lights were on the whole way...even after I hit the brake and stopped and then resumed driving...he followed me till he could tell me of the issue...that was actually when I first learned of the issue...

I had forgetten about that...thanks for reminding me!

[porkchop]

I am thinking the brake light thing has a lot to do with the lock up and the fire. I am also trying to see if there is any relation to the aerodynamics of the truck with the windshield up. I know it is a brick, but does driving at higher speed with the windshield up push the front end down? I am no physics major by any means, but it just seems like it would cause more drag.

[amphi]

If for some reason the brake peddle is not returning all the way, the piston cup could block the inlet port. This could allow pressure to build in the system, as there would be no vent to the reservoir.

This is just a guess but entirely possible.

[brute4c]

The truck was operated for a year with the intermittent brake light problem with no incidents. I had driven between 60 and 100 mile trips on several occasions in that time frame, mostly highway, and never had any issues or unusual brake wear or drag...though I dont know why the lights were doing that...I was concerned that the pressure switch was the culprit but the fire got in the way of a diagnosis in that direction...just dont know.

I do know that the pedal spring is strong and returns all the way up...another member, right after the fire, checked it and was surprised how strong the spring was...ruling out a drooping pedal or even a bouncing one from road bumps as the pedal in the tow vehicles isnt that stiff...though I cant rule out a master problem, it does seem somewhat remote after all the miles that were put on the truck since that was installed.

I cant wait to afford batteries for the truck...

[porkchop]

I was thinking of something last night while trying to go to sleep, could the reason the M715 was not to be flat towed according to the manuals is because the t-case is not able to be put in neutral?

[randyscycle]

I was thinking of something last night while trying to go to sleep, could the reason the M715 was not to be flat towed according to the manuals is because the t-case is not able to be put in neutral?

That occurred to me too....The NP200 can find a sort of false neutral, but doesn't have a detent to hold it there.

I think that is wasn't meant to be flat towed also because backdriving the T-98 in neutral wouldn't spin the cluster gear and wouldn't splash around the lube in the transmission. Without that motion to keep the gears wet with 90 weight, there wouldn't be any lubrication for the rear bearing, the needle rollers in the input shaft, or gears on the mainshaft. OK for a short run, but in the long haul, it could fry the bearings in the transmission. Driveshaft removal would eliminate this scenario.

Now before anyone tells me I am wrong, I will say this: I have personally flat-towed vehicles with similar manual transmissions with no ill effects, so maybe it wouldn't happen all the time. Just throwing it out there. However, I also have seen several instances of manual transmissions suffering the fate of no lubrication from being backdriven.

[brute4c]

The NP200 does have a neutral in between Hi and Low range...no detent but it held there in a wheels up tow when my water pump blew 140 miles from home.

During the tow, the front tires were still turning though there was no way to transfer power from the engine/trans, even when it was running, to the tcase.
This puzzled me...Rollie figured it out...the tcase in neutral disconnects from the trans input but the front and rear axles are still both hooked together through the tcase as it is in 4wd already...so the rear wheels turning due to the tow transferred that rotation to the front tires and turned them.

[porkchop]

I have found the neutral myself, but it is not a true neutral like Randy said. One bad road bounce and it is back in gear or the gears start to grind a little.

Which tow are you talking about, Jon. The wheels up tow? Nothing happened to the front end during that did it?