HK Trucking

How about this one ... it was on Ebay last year. I pesonally like it better.

Thanks, Josh.

A lot of engineering went into that black one, with that air over hydraulic brake system etc.

And... it has a manual transmission. Most builders of that kind of stuff take the easy way out and use an automatic.

Hi Dan, a "Dynatard" does essentially the same thing as a "Jacob's Engine Brake" but operates different. "Dynatard" uses a modified camshaft profile and electric solenoids over the exhaust rockers to force the cam followers to ride this profile when engaged. There should be a switch on the dash to turn it on or off. Most of the "Dynatard" equipt engines have a single wire attached to the governor section of the injection pump. This wire attaches to a foil strip on the underside of the cover that contacts the fulcrum of the pump rack to force a ground to the system engaging the solenoids. If someone has been into the governor, or taken the cover off and bent the strip it could be making contact at idle which could cause the problems you mention. Herb helped me with one of mine that was doing exactly that.

I'll get you a copy of the adjustment procedure if you like. It is quite simple to adjust but for starters, remove the wire if present and see if the problem persists.

Rob

Hi Rob.

Based on what Dan was describing I was also thinking that one of the Dynatard solenoids could actually be mechanically sticking in the applied position even when no actuation current is present, causing 3 cylinders to be braking while the other 3 are running normally.

Back then, if I remember correctly, Mack was using the Dynatard type cams in all their engines,whether equipped with a Dynatard or not, and a special valve adjustment procedure was necessary with these.

If the engine is not Dynatard equipped and this is happening, it's possible the valves have not been adjusted correctly, causing the exhaust valve lifters to ride on the Dynatard portion of the cam profile.

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Suicide doors on an R model? WTF.

I commend the builder for the effort & skill needed to build it, but that narrowed nose ruins the end result.

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From the stories I've heard, the new DPF equipped MP's never actually run long enough to get the oil dirty, so a centrifugal filter is no longer necessary.

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I owned 2 of em back in the 70's, a 1955 and a 1941 weapons carrier type, sure wish I wouldn't have sold them.

They're just like a mini B model, complete with unsynchronized transmission.

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I had the exact same thing happen on a 96 CL a few years ago.

The speedo sensor had a physical encounter with the trans output shaft, sensor was wiped out, and the E7 427 then derated because of no speedo signal.

The 427 felt like a END 673 170 HP motor at that point.

Replaced the sensor, and all was well again, until the range shift setup exploded a while after that.

Yes, it was a Mack T2130 trans, those transmissions have a genetic predisposition to range shift failure.

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Well i finally broke down and called my mechanic. The injector pump checks out okay, He says I have low compression and need a engine overhaul...

I call B.S.

If it was worn out to the point of not having enough compression to start at normal ambient temperatures (70*), you'd have massive amounts of blow by coming out the crankcase breather,along with massive oil consumption, and you did not mention either of those problems.

I've seen (and owned) a lot of worn out Mack engines, and they all would start without ether at 70* or so.

I agree with FJH, there's a leak somwhere on the suction side of the fuel system, and a drainback problem when it is not running.

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a little smoke from a mack...sounds normal to me!

I'll second that.

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Hi Guys,

I have to choose between two tractors: a DM688S and a R688ST. The R688ST is a 1988 model and the DM688S is a 1991 model. Can you please advise me on the advantages/disadvantages of either model, and what the difference between the two is? Thanks in advance!!

In general, if you're going to use the tractor for heavy hauling, such as moving equipment on a lowboy or pulling a dump trailer, then the DM688s will be what you want because it's heavy spec'd.

For normal on road trailer truckin', then the R688st would be more appropriate.

This is just a broad generalization, as it depends on the exact specs of each unit.

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Sounds like maybe the diaphragm is ruptured in the LDA, and the rack cant ever go to full fuel.

Yes, the engine is very tired. When started it yesterday, it ran for a short while then started bucking, popping and shaking the truck, throwing a lot of white smoke out the pipes. I've never heard anything like it myself other than to say it almost acted like an old mechanical engine with the jake on at idle. When it was running, it seemed like there was a noisy valve or rod, but these old Mack engines are hard to tell which knock is normal and which is not.

Looks like it's a Dynatard equipped motor?

If so, it sounds like one of the Dynatard solenoids is stuck on.

Can you hear the engine fan coming on when it's hot?

If not, the viscous fan drive could be shot, causing the fan to be inoperative, resulting in overheating.

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Trent, are you guys running that at the Mackville Nationals this year?

Even if you're not, then you oughtta swing up this way & attend this show:

http://www.mackvillenationals.com/

The company I work for is a major sponsor of the pulls, and this year, instead of crushing cars with a monster truck, my boss is gonna take the D8N Cat dozer out on the track & demolish the cars!

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You too have a blow up doll????????

Rob

Now we know why he needed that air hose connection on his truck. It ain't for inflating tires!!!!

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Most of the Ford L8000 & 9000's that I've seen have the Sheppard P/S box. You should find "F.L. Sheppard" or something like that cast in the housing. The only adjustments on those is the relief valve screw, but that has no effect on free play, it just relieves the hyd pressure when the box is at it's extreme right or left motion.

As James said, be sure the box is in the middle of it's travel with the wheels straight ahead.

Otherwise get a factory rebuilt steering box. I've never had much luck with non factory rebuilt Sheppard steering boxes.

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Mornin' Rob.

What pump shop in WI did you suggest to him? Valley Diesel in Neenah?

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Actually, just disconnecting the air line from the puff limiter cylinder will make a night & day difference in throttle response & costs nothing.

It will create black smoke on acceleration though, I suppose maybe that won't fly in CA.

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Well, allow me to preface my remarks by stating that I have an innate dislike of automatic transmissions.

That said, there were lots of Mack fire trucks factory equipped with Mack diesel engines and Allison automatics.

The ones I remember sounded like they had either a 237 Maxidyne or a ENDT673C 250 H.P. thermodyne in them. Never actually popped the engine cover on one to see for sure. Maybe some of our fire truck friends on here can shed some light on this.

You stated earlier that your H model currently has a triplex, so as Superdog said earlier, you're gonna have to do some calculations of trans high gear ratios vs your rear axle ratio if considering a transmission swap. For example, if you have a TRT7220 triplex now and you replace it with a TRL107, 1076 or 1078 5 speed, the high gear in the 5 speed is 1:1, same ratio as your triplex has in 4th direct, therefore your truck would be very slow with the 5 speed unless you change the rear axle ratio to a faster one. This is just one example of what could happen, there are many variables depending on the particular transmission being considered for the swap. Just wanted to give a heads up, so you don't get any surprises, all things must be carefully considered & calculated.

no Randy,thank you for thanking me for thanking Rob and thanking Barry.

Great post! Thanks Tom!

May have burned contacts in the series parallel switch. Perhaps it makes a poor connection on the initial attempt, then when you try it a 2nd time it connects.

Check with Rob, he likes rebuilding those switches.

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A TRQ77 series "baby quad box" would work well too.

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I believe they'll fit the housings, but if the 74 R model was on springs then those carriers will not have the attaching points for the transverse torque rods needed with air suspension.

In 74 they would also have the tapered stud type mounting for the fore & aft torque rods, rather than the 2 bolt mounting found on the air ride, and later model spring ride carriers.

I should also add that I'm assuming the rears you have are CRD92 and CRD 93 type, which is what that air ride would have.

Embossed with a hand stamp.

Rob

Rob, is that similar to a "Tramp Stamp?

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Littlerig, When did it start? Did you change any tires on the rear's? Does it make more noise when your pullin or when you let off it? BULLHUSK

You know, maybe this is another one of those power divider clunking threads.

I wasn't thinking along those lines with my previous response because the title of the thread is "howling rear end"

We need more clarification from the original poster.

Worn ring & pinion, worn bull gears, or clearances set wrong will cause Mack rears to be noisy.

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