1951 Mack LJ Posted August 1, 2013 Share Posted August 1, 2013 I am going to look at a truck this weekend and wanted to know a few things before I go drive 5 hours each way. From what the owner says it is a 1977 RS685LT. What were the engine options in that model that year? He says it has an engine brake. And a 5 speed trans. He didn't have any idea what the axle ratings were or what the HP and Torque of the engine. He says he thinks it is 300 HP. From the pictures it looks in fair condition for 340,000 miles. I didn't know what the model RS685LT represented. Quote Link to comment https://www.bigmacktrucks.com/topic/32154-1977-rs685lt-questions/ Share on other sites More sharing options...
umodelnut Posted August 1, 2013 Share Posted August 1, 2013 85 in the serial indicates it had a 237 from the factory. Quote Link to comment https://www.bigmacktrucks.com/topic/32154-1977-rs685lt-questions/#findComment-197136 Share on other sites More sharing options...
1951 Mack LJ Posted August 1, 2013 Author Share Posted August 1, 2013 Thanks Vinny. Quote Link to comment https://www.bigmacktrucks.com/topic/32154-1977-rs685lt-questions/#findComment-197147 Share on other sites More sharing options...
Lmackattack Posted August 1, 2013 Share Posted August 1, 2013 It will be a west coast " tall hood" R model later known as a valuliner here in the USA. A 685 should be a 237 maxidyne a 686 would be a 285 tip turbine.Look at the engine. If no side mount charge cooler or front mount intercooler is present, it will likely be a 237. Quote Link to comment https://www.bigmacktrucks.com/topic/32154-1977-rs685lt-questions/#findComment-197148 Share on other sites More sharing options...
umodelnut Posted August 1, 2013 Share Posted August 1, 2013 Yes and there is tags on the passenger side of the motor that tell the specs of the motor. Quote Link to comment https://www.bigmacktrucks.com/topic/32154-1977-rs685lt-questions/#findComment-197151 Share on other sites More sharing options...
1951 Mack LJ Posted August 1, 2013 Author Share Posted August 1, 2013 I will look at the pictures again. I have a feeling it is mostly original. Was there much that could have been done to turn up the motor? He says it is very strong and he mostly runs full size trucks instead of this 5 yard dump. It would be nice if the owner knew more about his truck. The tag on the truck that showed the original torque and HP was worn off. Quote Link to comment https://www.bigmacktrucks.com/topic/32154-1977-rs685lt-questions/#findComment-197158 Share on other sites More sharing options...
Lmackattack Posted August 1, 2013 Share Posted August 1, 2013 If they removed the anti tamper bolts on the govener they likely turned it up. All it takes is a few simple adjustments of the rack stops to get it turned up...if it has a boost gauge you can see what it's pushing and may give a clue. Quote Link to comment https://www.bigmacktrucks.com/topic/32154-1977-rs685lt-questions/#findComment-197179 Share on other sites More sharing options...
thomastractorsvc Posted August 1, 2013 Share Posted August 1, 2013 Pull an oil sample and take it to Speedco or a local place that does on the spot samples, make the 5 hour ride home less of a worry Quote Robert"I reject your reality and substitute my own." Link to comment https://www.bigmacktrucks.com/topic/32154-1977-rs685lt-questions/#findComment-197183 Share on other sites More sharing options...
Vladislav Posted August 1, 2013 Share Posted August 1, 2013 Seems like it would be an interesting truck.Don't forget to post some pics when you be up close.By the word, how does your LJ?Haven't you done much about it? Quote Никогда не бывает слишком много грузовиков! leversole 11.2012 Link to comment https://www.bigmacktrucks.com/topic/32154-1977-rs685lt-questions/#findComment-197269 Share on other sites More sharing options...
1951 Mack LJ Posted August 13, 2013 Author Share Posted August 13, 2013 Found another one a little closer to home and it is a 1980 R685D. What does the D stand for? It is set up with a plow. Same deal with the owner not knowing much about the truck but at least I will not be driving all day just to check it out. Where on the forum here is the number and letter designations of the different models at? Quote Link to comment https://www.bigmacktrucks.com/topic/32154-1977-rs685lt-questions/#findComment-199563 Share on other sites More sharing options...
2stacksuperdog Posted August 13, 2013 Share Posted August 13, 2013 Well i know 685 means 237 unless it was re-powered. Im not sure what D means 1 Quote Matt Link to comment https://www.bigmacktrucks.com/topic/32154-1977-rs685lt-questions/#findComment-199564 Share on other sites More sharing options...
Superdog Posted August 13, 2013 Share Posted August 13, 2013 sure it's not a RD685 ? 1 Quote Link to comment https://www.bigmacktrucks.com/topic/32154-1977-rs685lt-questions/#findComment-199587 Share on other sites More sharing options...
1951 Mack LJ Posted August 16, 2013 Author Share Posted August 16, 2013 Well I end up cutting out of work early Tuesday to go look at the 1980 Mack and after driving almost 4 hours I really didn't want to go home empty handed. Turned out to be an OK truck but needs some work. It came with the plow also. Finally pulled into my driveway at 12:30 at night and got a couple hours of sleep before work that morning. 2 Quote Link to comment https://www.bigmacktrucks.com/topic/32154-1977-rs685lt-questions/#findComment-200042 Share on other sites More sharing options...
2stacksuperdog Posted August 16, 2013 Share Posted August 16, 2013 Looks good. 1 Quote Matt Link to comment https://www.bigmacktrucks.com/topic/32154-1977-rs685lt-questions/#findComment-200047 Share on other sites More sharing options...
thomastractorsvc Posted August 16, 2013 Share Posted August 16, 2013 Congrats!looks like you can make a few bucks to use on fixing the old dog up. Quote Robert"I reject your reality and substitute my own." Link to comment https://www.bigmacktrucks.com/topic/32154-1977-rs685lt-questions/#findComment-200052 Share on other sites More sharing options...
umodelnut Posted August 16, 2013 Share Posted August 16, 2013 Yeah looks pretty solid. Quote Link to comment https://www.bigmacktrucks.com/topic/32154-1977-rs685lt-questions/#findComment-200053 Share on other sites More sharing options...
1951 Mack LJ Posted August 18, 2013 Author Share Posted August 18, 2013 Yeah in all it is a good truck. It made the 170 mile trip home on 5 retread and cracked old tires. The pinion seal started leaking on the way over a 4500 foot tall pass in the mountains. The hydro lines for the plow were leaking at the quick disconnects also. But she never got very hot and even the radiator louvers work. Quote Link to comment https://www.bigmacktrucks.com/topic/32154-1977-rs685lt-questions/#findComment-200335 Share on other sites More sharing options...
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