Deere Mack Posted April 4, 2014 Share Posted April 4, 2014 Hello everyone! Hope all is well. Started a speedometer repair on the 79 RD today and discovered that the plastic adapter between the speedometer cable and the transmission gear was broke. Anyone know what this is called and is it a Mack only item? Trying to save some run around time and didn't want to go in the parts store asking for a plastic thing-A majigy in the moring.... Thanks...edited: think either my brain or my fingers are not co-operating this evening. 1 Quote Link to comment Share on other sites More sharing options...
j hancock Posted April 4, 2014 Share Posted April 4, 2014 I call it the drive tip but can't say that is the official name.Mack would probably be a good place because you might get a blank stare if you ask at Autozone. Speedo and tach cables sold by Mack come with a bag of various ends so probably there are a few kicking around loose in the mechanics toolboxes. Quote JimIt doesn't cost anything to pay attention. Link to comment Share on other sites More sharing options...
Deere Mack Posted April 4, 2014 Author Share Posted April 4, 2014 Thanks J! Also, my cable spins easily but I didn't see any lubrication, should it have any? Other than it being plastic, wondering why it broke. Quote Link to comment Share on other sites More sharing options...
j hancock Posted April 4, 2014 Share Posted April 4, 2014 It seems the new cables run dry with a spring steel shaft and plastic outer housing. A couple of drops of a 3 in 1 type oil or something really light isn't going to hurt.As far as the tip being broken??? Does it look like it get cut by a little burr in the 90 degree adapter? Make sure everything spins freely. Quote JimIt doesn't cost anything to pay attention. Link to comment Share on other sites More sharing options...
Deere Mack Posted April 4, 2014 Author Share Posted April 4, 2014 It's hard to tell, looks like it could have worn thin and just twisted. I read in another thread where these were replaced with metal but in return would break the cable if a problem occured. Quote Link to comment Share on other sites More sharing options...
Deere Mack Posted April 4, 2014 Author Share Posted April 4, 2014 The correct term would be "tang". I got me a metal tang today so now I should be able to tell how slow I'm going..... 1 Quote Link to comment Share on other sites More sharing options...
j hancock Posted April 4, 2014 Share Posted April 4, 2014 Good deal! Quote JimIt doesn't cost anything to pay attention. Link to comment Share on other sites More sharing options...
Deere Mack Posted April 5, 2014 Author Share Posted April 5, 2014 Almost a good deal.....got it all back together today and no luck, still no speedo. Removed the gear ratio assembly off the trans, put a drill on it and the speedo does work, my drill runs at about 35 MPH. Also, pulled the gear shaft out of the trans yoke and it looks fine and seems to fit snug back in place on the assembly and in the trans. Any clues? Quote Link to comment Share on other sites More sharing options...
Brian Blaylock Posted April 7, 2014 Share Posted April 7, 2014 Is the cable spinning inside of the tang? Quote Link to comment Share on other sites More sharing options...
Deere Mack Posted April 7, 2014 Author Share Posted April 7, 2014 Is the cable spinning inside of the tang?Good Morning Brian, thanks for your thoughts. When I tested it the speedo cable was attached to the gear ratio reducer and the speedo worked, with a drill. I suspect it could be slipping where the spline comes off of the gear ratio reducer and goes into the shaft & gear that slides into the trans. I've got to test it at that point next chance I get. Quote Link to comment Share on other sites More sharing options...
bbigrig Posted April 11, 2014 Share Posted April 11, 2014 I've had many of the 90deg. speedo adapters spread where the tang drive dowel inserts into the adapter. the split end opens up and the tanged dowel spins inside the (female) split of the adapter. I went through a couple of them on 1 truck in a few weeks. It was way worse up here when the temperatures dropped to below freezing. I always went through more of those adapter drives in the winter. Even with that small ring around the split in the adapter drive they have a tendency to spread enough open to allow the tanged dowel to spin within. I got warranty on all of those adapters. Quote Link to comment Share on other sites More sharing options...
Deere Mack Posted April 11, 2014 Author Share Posted April 11, 2014 I've had many of the 90deg. speedo adapters spread where the tang drive dowel inserts into the adapter. the split end opens up and the tanged dowel spins inside the (female) split of the adapter. I went through a couple of them on 1 truck in a few weeks. It was way worse up here when the temperatures dropped to below freezing. I always went through more of those adapter drives in the winter. Even with that small ring around the split in the adapter drive they have a tendency to spread enough open to allow the tanged dowel to spin within. I got warranty on all of those adapters.Good morning! I haven't got back around to investigating this, but I did remove the 90 deg. adapter you mentioned and powered the speedo form the rear of it, just to make sure it wasn't in the adapter. Mine seems to be where the adpater slides into the trans. gear. I'm thinking something might be striped there. Ever have any problems there? Quote Link to comment Share on other sites More sharing options...
Deere Mack Posted April 11, 2014 Author Share Posted April 11, 2014 Here's my problem, #1 is spinning inside #2. It's hard to tell which piece is worn out, if not both. Quote Link to comment Share on other sites More sharing options...
b61mack Posted April 12, 2014 Share Posted April 12, 2014 I just bought a 100 inch speedometer cable, $ 85 at Mack. works like a champ Quote Link to comment Share on other sites More sharing options...
bbigrig Posted April 12, 2014 Share Posted April 12, 2014 I've had the speedo drive gear shaft(#2) in the picture above crack its square drive. (the end where the pin drive connects) I've also had 1 gear shaft drive wear the teeth off. didn't need to replace the gear in the trans that drives that speedo adapter shaft.. Those shaft gear drives were hard to come by a few years ago for my R and MH models with Fuller transmissions and are specific to your specs.(trans gearing, rear ends, tire size etc.) Quote Link to comment Share on other sites More sharing options...
Deere Mack Posted April 12, 2014 Author Share Posted April 12, 2014 I'm in luck! Part #1 & 2 are available and should be here Tues. Yea...... 1 Quote Link to comment Share on other sites More sharing options...
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