Rob

Does anyone have an electrical and or air plumbing schematics of how the R model trucks are wired? The service manual I have is a little vague due to variations. I've got most electrical functions figgered out, but now need to tackle the plumbing side. Thanks, Rob

I'm going to try this.....

Hi Thad, I'm new to this R model designation and don't know much. My 1978 RL-755L tractor has an aluminum frame, crossmembers, front hubs, differential carriers, and flywheel housing. The hood is no thinner or lighter weight than a standard R model. It is a long extended hood, (almost 64 inches front to back). Trent has a RS-700 series and he could probably fill you in as to what is steel on his tractor. Hope this helps with your quest. Rob

The red "O" with the "X" through the middle is the low air annunciator, and the buzzer accompanies it!! Either you have a problem with an air leak, or the compressor is bad, or a bad switch. If the air is in fact low while driving, the brakes with start to apply at around 40 psi or so. You should have a pressure gauge in the dash, how was it reading? Did you notice the air pressure on either the red, or green needle showing low? You should not be able to get the spring brakes to release until at least 60 psi on the gauges. Rob You are correct as the red annunciator lamp is in fact a circle with three arrows pointing to it, my apologies. I haven't been around this newer stuff much and I did in fact think it had an X through the circle. Oh well, they say the mind is the second thing to go..... Rob

I will have to get a print for the truck to see if I can make it work before pulling the engine. Thanks, Rob

I see no major corrosion anyplace on the frame. I did find that the driver's side front cab support has been welded back together but someone did a nice job. The front spring hanger that has been welded on was for the area that supports the bumper mounting brackets. It is nothing structural. I adjusted the brakes, clutch, took the doors apart and greased the regulators and latches, and replaced about 9 light bulbs in the dash. Amazing difference all in all. The clutch is shot and the engine will run away if accelerated hard. The brakes are great if even down to about 15-20% or so. The power divider is in sound shape as it locks the rears together as it should. This Cat engine sounds just like a Cummins to me, both under slight power, and rapid acceleration (best I can given the clutch situation). At idle, I don't hear anything but fuel ignition/knock as is normal. The turbo sure is loud though. Can't find a tag, but it says "Airesearch" on the turbine side. The rocker boxes on top are leaking oil but it doesn't smoke any blue at all. I really hate to pull this engine but that was the pretense I acquired the truck under. The 1693TA is destined to a good home and the truck it will be installed into is worthy of the engine, (so you know it is NOT a Peterbilt), HA!! I just had to throw that in there. I didn't have a lot of free time today to take pictures but will get that done tomorrow. I had too much getting accustomed to get done. I asked several people at truck parts vendors about this seat, nobody has seen or heard of one like it in this area. I cannot find any tags or identifiers on it either. It sure works well. Rob

The blue is my pick. Pink is for "other" trucks!! Rob

The RL755L showed up on my doorstep today and I must say that I'm quite pleased. It has a very good running Caterpillar 1693TA under the hood with a 12513 transmission, 4.17 rears with an air actuated power divider. The ten tires are all virgin, and are above 75% remaining but mismatched (somewhat). All the aluminum suspension components appear to be in good condition with only the Rt. front spring hanger being welded on. The frame is completely aluminum as are all spring hangers, drop in carriers, crossmembers, cab mounting brackets, fuel tanks, front hubs etc. The cab has a bit of rust but is very repairable. The worst is the back window area as the internal sheet metal that forms the pinchweld is all but gone on the top. I suspect a water leak from the rain gutter caused this. The truck is red in color, and has the embossed bulldog in the door cards, along with diamond pleating, and the headliner is soft cloth material with an appealing design. The driver's seat is air ride but I've never seen on like it. You slide this lever up or down to the height you want the seat to remain at and it stays at that height wether you are sitting in it or not. It works well, but needs to be reupholstered. There is some repair work to be done on the hood, but it is complete. The grille shell is nice with only one nick in the top that I will "tig up" and polish out. All in all, it is a good looking truck. Best of all, it does look as if my Detroit will slip in without a lot of custom fabrication. Hell, even the chrome front bumper is not bent. I'll get some pictures tomorrow in the daylight and post them. Here are some technical questions: There are a couple of gauges in the dash that say something about "brakesaver". One is for temperature, and the other is for pressure. Is this for some kind of retarder that I've heard about in years gone past? Also, there are two air knobs (unlabled) in the dash that when pulled out, air gushes out but they do not appear to do anything. They have nothing to do with the brakes, and both knobs are identical. Again I will post pictures. As far as I can tell, most things do work except the tach, and speedometer. Of course there are some burned lightbulbs but most are just minor things to work with. The truck was driven from Paducah, Ky in one shot so it must have some kind of reliabilty built in, (of course with a bulldog on the hood, that's a given). Rob

Hey Fred, We are going after the RL755 next week; Project R-12 will be underway!! I would be interested in others' opinions as to which ratio I should use in the rears with 11R22.5 tires and a single over 13 speed (I assume). I'm looking for a good balance of power from just off idle to a maximum interstate speed of 75-78 mph @ 1800 rpm. Rob

Edgar, I sure hope I am wrong but your questions sound redundant and the answers do not appear to be what you want to hear. I think you are displaying arrogance with your replies when someone offers their opinion. If there is some sort of handicap involved, (and I do not mean to berate you) let us know as the level of tolerance to your type of questioning will be expanded/enhanced; otherwise please find another board to bother. A good portion of the feedback I've seen from this and other boards is that you are wasting posting space. Regards; Rob

Hi there, I run radials on the steer axle and bias on the drives. I don't like the "hopping" that you get with bias or nylon tires as the radials are much smoother especially after sitting for a spell. I don't disagree with any comments so far but my trucks do for the most part reside inside my shop when not in use so sidewall breakdown is not a pertinent issue. Rob

My 72 has the short handle just like a B model. Rob

Hi Rod, yes there is also a small quadraplex transmission that was offered behind the gas powered trucks. I don't know if the TR72 series was offered behind the smaller gas engines, ie: EN-401, En-464, EN-510 etc... My wife and I are planning a long vacation next year in yours' and Andy's neck of the woods. Will plan to meet if you're for the idea. Don't have any dates yet but still in the planning stages. Rob

Hi Rod, you should be able to install the "C" engine along with a quadraplex trans without much difficulty. You will need to have your driveshaft shortened. I assume that the transmission you now have (Duplex) is the TR72 series, and not the TR67 series. I also assume you will be replacing the transmission with the same type: TR72 series vs. Tr67 series. The mounts for the transmissions are located in the physically same place, the quadraplex is longer in the rear section. Personally, I like the duples for a lot of "pleasure driving". The quadraplex takes a lot of shifting and I'm not saying that is bad, just more work, (or pleasure depending on how you look at it). Rob

I assume you mean the coolant overflow/expansion tank? If you cannot find a new or acceptable used one; If the material is either plastic, or aluminum, I can repair it. Let me know. Rob

Hi Rod. I had a "Maxidyne" series engine in my B model (ENDT-676 with tri-plex) and did not like it very well. Don't get me wrong, it ran and drove perfect but the engine never was in it's proper torque band. It would seem to me that if you are going to use the truck to pull moderate weight, that the 673 engine would be better even though parts are getting a little harder to get (new at least) here in the states. The 237 engine works very well with the wide gear spread of either a 5, or 6 speed to take advantage of the extreme torque ability the engine develops. Just my opinion, hope it is helpful. Did you get the air-o-matic steering installed? Rob

Mine is about 30 psi hot idle, and near 70 psi cold. During a warm pull, 65 is about normal with straight 30 wt. Chevron diesel oil. Rob

Amen to that Fred. Think how the body shop guys feel chasing water leaks, squeaks, rattles, and inoperable electronics and wiring too!! It can be a very difficult way to earn a living!! Rob

The bolt on fender extensions look much better on the white or light colored truck rather than the red or burgundy one shown earlier. Oh yea, shove the girl off to the side so we could have a better look at the hood. Rob

Can't disagree with you on that one Terry. However, I purchased the chassis without an engine. It was "just the ticket" for what I was looking for. The closest thing to heaven my automotive side can think of: A tough Mack chassis, with BIG power. I sure do plan to make Macungie next year Fred, and incidently, I think you've coined the name I'll use; Project "R-12"; I like it. Rob

I've got a few pictures of those in action as mixer trucks pouring the St. Louis Arch footings and foundations. This is along with many, many B models also. I need to find and post them. I had completely forgot they existed. Rob

Hi Mike, thanks for the research. The truck had/has a 1693 Caterpillar in it now, and a 13 speed roadranger. I've never seen a Mack chassis, (this old, 1978) with that powertrain from the factory but I was told the chassis was "as built", and original. Rob

I have purchased a truck/tractor for my Detroit engine and am wondering if anyone here has any knowledge of what powertrain this tractor had when built. I have no knowlege of "R" models, so this will be new to me. If the vin number runs as the B models did, then it would be assumed the truck would have originally been a V-8 engine, tandem axle tractor with aluminum components, but is currently an inline six. Thanks, Rob

Have a good trip there Barry. Be sure to put the word into Volvo that "Some things are best left unchanged". Rob

The bulldog still makes money though. Just has a new profession: