sodly Posted January 7, 2017 Share Posted January 7, 2017 As usual, I come here seeking an education. Maybe someone can explain something I've never quite understood about Mack trucks. When you think of a tough ol' truck, you think of a Mack R model. At least I do. But I've never understood why the R model frame rails, along side the engine, seem so thin (in profile) compared to most other trucks. When you tip the hood of an R it just doesn't look very substantial up front, frame-wise, compared to say a Peterbilt/KW with their tall, straight frame rails from one end of the truck to the other. Is there just not that much force exerted on the front end of a truck's frame, or what? What do you suppose was the reasoning for not using a straight rail like other manufacturers? Could you get a 20,000 lb front end with those thin frame rails on an R? Or would that necessitate an RD? Does the RD have a more substantial front frame? Or are Mack frames made from a stronger materials and, therefore, don't need to be as tall in profile? I used to have the same thoughts about the early Superliner/Cruiseliner front frames. They tapered down to nearly nothing at the front (I realize to accommodate larger radiators). I found it surprising when the Superliner II came along with its much more substantial (taller) front frame. The total opposite extreme from before! Was this just due to the higher HP engines in the Superliner II and the torque they produced? Or was it because the steering gear was now frame-mounted whereas the old Superliners were axle-mounted? I guess I've just always wondered why Mack frames just generally don't look as substantial as most of their competitors. I realize the heavier models like mixers and dumps have beefier frames but I'm talking primarily about highway trucks here. Any thoughts on this? Please drop some knowledge on me. Thanks! Quote Link to comment Share on other sites More sharing options...
j hancock Posted January 7, 2017 Share Posted January 7, 2017 Mack wanted the engines to sit lower so the frame was designed to accommodate that. If you specified a very heavy front axle, an RD would be the upgrade from an R. As various new power trains were developed, frame rail design were modified. In this thread, there are links to the various frame designs and dimensions. http://www.bigmacktrucks.com/topic/3794-superliner-questions/ Quote JimIt doesn't cost anything to pay attention. Link to comment Share on other sites More sharing options...
Job41 Posted January 7, 2017 Share Posted January 7, 2017 Sodly, I am not an expert on Mack trucks and the various models. However I am an engineer and know something about structures. In the area of the front axle the biggest affects on the frame are shear forces. Cross sectional area of the frame rail is what resists that shear. Also, Mack used a very high strength steel and therefore does not need a lot of steel to resist those shear forces. Frames need to be deep when there is a lot of bending force. ( In engineering terms we call it bending moment.) That would be in the area half way between the front axle and the rear axles. So manufacturers can make frames shallow in the regions of high shear and deeper in the regions of high bending. This understanding allows the truck manufacturer to make decisions in order to lower the height above the ground to the top of the truck frame or lower the region around the engine. Some manufactures keep the same depth of frame rail to make manufacturing easier. I hope this helps. Unfortunately, I don't have the time to write out a better explanation. Best regards, Job41 2 Quote Link to comment Share on other sites More sharing options...
sodly Posted January 8, 2017 Author Share Posted January 8, 2017 Thanks for the help guys. It would be interesting to compare all the specs on a typical 70s/80s Mack frame with their competitors. I've just always found it curious that most trucks back then had straight-rails from end to end whereas Macks tended to have all kinds of odd profiles and changing depths. I always wondered why they looked so unconventional compared to most of the competition. The MH/Superliner frame, in particular, is about the busiest-profile frame rail I think I've ever seen! Quote Link to comment Share on other sites More sharing options...
Popular Post 41chevy Posted January 9, 2017 Popular Post Share Posted January 9, 2017 (edited) 8 hours ago, sodly said: Thanks for the help guys. It would be interesting to compare all the specs on a typical 70s/80s Mack frame with their competitors. I've just always found it curious that most trucks back then had straight-rails from end to end whereas Macks tended to have all kinds of odd profiles and changing depths. I always wondered why they looked so unconventional compared to most of the competition. The MH/Superliner frame, in particular, is about the busiest-profile frame rail I think I've ever seen! My be doubled photos but all the info you might want. Paul htt p:// http:// http:// http:// http:// http:// http:/ Edited January 9, 2017 by 41chevy 7 Quote "OPERTUNITY IS MISSED BY MOST PEOPLE BECAUSE IT IS DRESSED IN OVERALLS AND LOOKS LIKE WORK" Thomas Edison “Life’s journey is not to arrive at the grave safely, in a well preserved body, but rather to skid in sideways, totally worn out, shouting ‘Holy shit, what a ride!’” P.T.CHESHIRE Link to comment Share on other sites More sharing options...
sodly Posted January 15, 2017 Author Share Posted January 15, 2017 I noticed that the Western R model appears to have straight frame rails from stem to stern. You can see it in this video at about the 3:24 mark. Wonder why the Western R is different and doesn't have the traditional thinning frame rails up front. Does the Value Liner? Color me confused. Quote Link to comment Share on other sites More sharing options...
ranchhopper Posted January 15, 2017 Share Posted January 15, 2017 Looks like someone dumped a garbage can in front of the passenger seat. Quote Link to comment Share on other sites More sharing options...
j_martell Posted January 15, 2017 Share Posted January 15, 2017 Here's a few frame pics of the 89 RD before it was redone. First two show the front frame with the E-6, theres a 20,000lbs steer axle under there. The last two show the double frame in the rear. I can't for the life of me remember if the double frame carries all the way to the front, of if it stops under the cab. I'll double check tomorrow when I get to the site its parked at. Quote Lack of planning on your part does not constitute an emergency on my part.... Link to comment Share on other sites More sharing options...
sodly Posted January 16, 2017 Author Share Posted January 16, 2017 Well, I guess you could get a 20,000 lb axle under the "regular" tapered R frame, eh? I thought maybe it would have to be a straight rail frame to handle that. Sorry if this is all basic stuff to some of you. I've still got a lot to learn, lol. There are a ton of nuances when it comes to Macks. Quote Link to comment Share on other sites More sharing options...
Rob Posted January 16, 2017 Share Posted January 16, 2017 Typically the double frames, (inner rail) stop near the front mount of the fuel tanks just before the "splay" outward of the outer rails. I have however seen trucks with full double frames from front to back but they were 800 series. All of the "Valueliner" series of trucks I've seen have been straight rail trucks. Best I know the "Valueliner" series started after the Hayward, CA plant was shut down and this series is a slightly lessened western built truck. These observations could be right, wrong, or indifferent but they are what I've seen. Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment Share on other sites More sharing options...
cstaples Posted January 18, 2017 Share Posted January 18, 2017 RDxxxP had full depth double frame all the way to the front...Mainly for municipal application with plow gear. Quote Link to comment Share on other sites More sharing options...
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