SpreadingLime Posted November 10, 2023 Share Posted November 10, 2023 Hello all. I've recently acquired a '75 R685 for a parts truck/ fixer upper ( not sure yet ). As the title says the rear diff housings have round axle tubes instead of the square that I am used to. The carriers are Cr 92 & 93 , same as my other rigs. My question is are there any differences in round vs square housings. Are they just an old design? Thanks all. Quote Link to comment https://www.bigmacktrucks.com/topic/73523-rear-diff-housing-round-tube-not-square/ Share on other sites More sharing options...
Geoff Weeks Posted November 10, 2023 Share Posted November 10, 2023 I think it comes down to the vendor that made them. I know that is the way it is on other makes. Being Mack rears are Mack only, I can't be sure. I've had IHC's with both types, and in the book, it stated it was who supplied the housing to IHC, other than that there is no difference Quote Link to comment https://www.bigmacktrucks.com/topic/73523-rear-diff-housing-round-tube-not-square/#findComment-541723 Share on other sites More sharing options...
doubleclutchinweasel Posted November 10, 2023 Share Posted November 10, 2023 I know that "Mack" rears HAVE been made by other people than Mack. Not sure what years, though. A few years ago, we were in a Meritor (formerly Rockwell) plant, and they had "Mack" rears, which Meritor had made there, stacked to the ceiling. Contract work, I suppose. Again, not sure if that happened that long ago. 1 Quote "Eagles may soar, but weasels don't get sucked into jet engines." Link to comment https://www.bigmacktrucks.com/topic/73523-rear-diff-housing-round-tube-not-square/#findComment-541724 Share on other sites More sharing options...
mechohaulic Posted November 10, 2023 Share Posted November 10, 2023 rackin my brain on this one ; should remember . question I have is the rating on the rears 34k /44k and so on. can't remember a round tube in 55k class. 34's with lighter spring set up and rubber bushings ?? I know as stated other vendors made "mack" parts. 92/93 carriers ; going with the R 685 is an R685st . are both units same gvw rating ? Quote Link to comment https://www.bigmacktrucks.com/topic/73523-rear-diff-housing-round-tube-not-square/#findComment-541725 Share on other sites More sharing options...
Geoff Weeks Posted November 10, 2023 Share Posted November 10, 2023 Rockwell made their own "top losding double reduction rears, are you sure they were not those models? Quote Link to comment https://www.bigmacktrucks.com/topic/73523-rear-diff-housing-round-tube-not-square/#findComment-541726 Share on other sites More sharing options...
JoeH Posted November 10, 2023 Share Posted November 10, 2023 The heavier 55k rears are cast iron square; lighter ones were stamped I believe. Post pictures! 1 Quote Link to comment https://www.bigmacktrucks.com/topic/73523-rear-diff-housing-round-tube-not-square/#findComment-541728 Share on other sites More sharing options...
mechohaulic Posted November 10, 2023 Share Posted November 10, 2023 noticed location (AK) and spreading lime. could be the closer model number is a RS/RL western, making things like rockwell rears more do able . Quote Link to comment https://www.bigmacktrucks.com/topic/73523-rear-diff-housing-round-tube-not-square/#findComment-541729 Share on other sites More sharing options...
mechohaulic Posted November 10, 2023 Share Posted November 10, 2023 also seeing his truck is an '88 R690 vs a '75 R685; that type of yr spread anything possible. for original question == it's all ok run it . Quote Link to comment https://www.bigmacktrucks.com/topic/73523-rear-diff-housing-round-tube-not-square/#findComment-541732 Share on other sites More sharing options...
Solution terry Posted November 10, 2023 Solution Share Posted November 10, 2023 Round ones were early housings, don't know the exact year they went with the square housings. terry 1 Quote Link to comment https://www.bigmacktrucks.com/topic/73523-rear-diff-housing-round-tube-not-square/#findComment-541736 Share on other sites More sharing options...
doubleclutchinweasel Posted November 10, 2023 Share Posted November 10, 2023 3 hours ago, Geoff Weeks said: Rockwell made their own "top losding double reduction rears, are you sure they were not those models? According to the folks in the plant, these were made for Mack. Not sure if that was a 1-time thing, an ongoing order, or what. 1 Quote "Eagles may soar, but weasels don't get sucked into jet engines." Link to comment https://www.bigmacktrucks.com/topic/73523-rear-diff-housing-round-tube-not-square/#findComment-541739 Share on other sites More sharing options...
SpreadingLime Posted November 12, 2023 Author Share Posted November 12, 2023 Thanks all of you for the info. The history that all of you have stored away is always impressive. "Mech" you are correct on the truck being a 685ST. Build sheet from Mack says that the rears are 38K. I kind of suspected that the round tubes were just an older design like Terry had stated. Everyone have a good weekend. Quote Link to comment https://www.bigmacktrucks.com/topic/73523-rear-diff-housing-round-tube-not-square/#findComment-541827 Share on other sites More sharing options...
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