90rd690 Posted December 23, 2018 Share Posted December 23, 2018 Can anyone help me with the rear ratio and weight rating from this picture below? It’s the markings on the top of the rear diff. The tag/label on the side of the diff is un readable. The previous owner told me it has the 300 maxidyne, 7 speed combo thanks Quote Link to comment https://www.bigmacktrucks.com/topic/55111-rear-differential-decode-1990-rd690s/ Share on other sites More sharing options...
j hancock Posted December 23, 2018 Share Posted December 23, 2018 The ratio will be on the right front of the diff and the axle number will be stamped on the back side of the housing. Take a look at the id guide. Quote JimIt doesn't cost anything to pay attention. Link to comment https://www.bigmacktrucks.com/topic/55111-rear-differential-decode-1990-rd690s/#findComment-411802 Share on other sites More sharing options...
90rd690 Posted December 23, 2018 Author Share Posted December 23, 2018 Thank you sir! I’ll get a rag and some cleaner and see if I can find the tags. The previous owner thinks the ratio he ran was .417 and 38k# rear axles Do you think the 1990 model engine was designated a EM7 or just E7 ? And what was the difference ? Jeff Quote Link to comment https://www.bigmacktrucks.com/topic/55111-rear-differential-decode-1990-rd690s/#findComment-411803 Share on other sites More sharing options...
terry Posted December 23, 2018 Share Posted December 23, 2018 7 hours ago, 90rd690 said: Thank you sir! I’ll get a rag and some cleaner and see if I can find the tags. The previous owner thinks the ratio he ran was .417 and 38k# rear axles Do you think the 1990 model engine was designated a EM7 or just E7 ? And what was the difference ? Jeff If it is maxadyne and 7 spd should be around a 5.50 ratio. terry 1 Quote Link to comment https://www.bigmacktrucks.com/topic/55111-rear-differential-decode-1990-rd690s/#findComment-411810 Share on other sites More sharing options...
mackey58 Posted December 24, 2018 Share Posted December 24, 2018 The maxidyne I drive is a 300 7 speed 5.73 rears Quote Link to comment https://www.bigmacktrucks.com/topic/55111-rear-differential-decode-1990-rd690s/#findComment-411869 Share on other sites More sharing options...
mackey58 Posted December 24, 2018 Share Posted December 24, 2018 Also my 90 rd is the em6 300 L Quote Link to comment https://www.bigmacktrucks.com/topic/55111-rear-differential-decode-1990-rd690s/#findComment-411870 Share on other sites More sharing options...
90rd690 Posted December 25, 2018 Author Share Posted December 25, 2018 We got it running today. Runs good but needs 4 new batteries which I expected. Cleaned the tag on the top of the valve cover. It is indeed an E6M. 7 speed transmission with the air shift for low, high and N which I assume is neutral?? Can anyone confirm what the position (N) would be used for??? I need a filter kit. Can anyone copy a post for the filter kit needed for this engine? Looks like it has 2 long oil filters plus one other shorter filter in front of the longer oil filters but it doesn’t look like the slinger filters I’ve seen pictures of?? Looks to only have one fuel filter on the other side of the engine up front on the passenger side. That’s the one I really need as I’m sure it’s needs some attention. Of course the number on it was not visible as I guess it was on the inside. Any help would be greatly appreciated! Quote Link to comment https://www.bigmacktrucks.com/topic/55111-rear-differential-decode-1990-rd690s/#findComment-411902 Share on other sites More sharing options...
90rd690 Posted December 25, 2018 Author Share Posted December 25, 2018 Here’s a few pictures I took of the bulldog today. My plan is to go through it a make a super nice rig out of her! We couldn’t get the door stickers off with the heat gun and they are not representative of the current owner. I’m going to try one of those eraser/buffer wheels. 208” wheelbase Quote Link to comment https://www.bigmacktrucks.com/topic/55111-rear-differential-decode-1990-rd690s/#findComment-411905 Share on other sites More sharing options...
carlotpilot Posted December 25, 2018 Share Posted December 25, 2018 the rubber eraser wheels work great . use a variable speed drill motor and turn it just fast enough to take the decal off . your wheel will last longer and not burn the paint . they don`t work real well on painted letters but they will work Quote Link to comment https://www.bigmacktrucks.com/topic/55111-rear-differential-decode-1990-rd690s/#findComment-411907 Share on other sites More sharing options...
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