Jizzo17 Posted May 31 Share Posted May 31 (edited) 1985 Mack R600st(?) VIN is 1M1N179YXFA099577 The tach and speedo in this truck is the style with the big clock in it. I am having issues with my speedometer not working at all and the tach bouncing rpms until it catches when I am in the throttle sometimes. I think there is a piece broken inside of the tube that feeds the cable running to the dash because I can turn one end and it won’t move the other any. Is there any way to have that piece rebuilt or can it be replaced? (I will attach a picture of the piece). I am also going to replace the cable. I am replacing the yoke seal coming out of the transmission so I decided to resolve this issue as well Edited May 31 by Jizzo17 Quote Link to comment https://www.bigmacktrucks.com/topic/75597-mack-5-speed-speedometer-and-tach/ Share on other sites More sharing options...
mechohaulic Posted May 31 Share Posted May 31 that piece comes apart. inside will be basically a shaft extension. the 90 degree on end in many cases screws directly to transmission housing. taken apart you have 4 separate sections. 1- drive (piece with gear ) 2- short piece which threads in to transmission case ; 3 -extension having a small shaft inside it ;;4- 90 degree gear box. the cable housing from speedo which threads into 90 degree also has a cable adapter on it. the adapter goes into the 90 . there are a number of ends which can be worn/ broke causing failure . if you are spinning the drive gear and nothing is turning opposite end on the 90 ;; disassemble all parts in the picture. some ends are square others have tabs. Quote Link to comment https://www.bigmacktrucks.com/topic/75597-mack-5-speed-speedometer-and-tach/#findComment-576724 Share on other sites More sharing options...
Joey Mack Posted May 31 Share Posted May 31 Now there's a Man that knows his SH!T !!! Mech, you are a wealth of knowledge... 1 1 Quote Link to comment https://www.bigmacktrucks.com/topic/75597-mack-5-speed-speedometer-and-tach/#findComment-576725 Share on other sites More sharing options...
70mackMB Posted May 31 Share Posted May 31 l was going to mention the key ways being worn also. ......Hippy 1 1 Quote Link to comment https://www.bigmacktrucks.com/topic/75597-mack-5-speed-speedometer-and-tach/#findComment-576726 Share on other sites More sharing options...
mechohaulic Posted May 31 Share Posted May 31 not sure if the '85 was all mechanical or went to electric. in the day of all mechanical; we had roll of inner cable with assortment of ends. inner cable broke we made new ourselves. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/75597-mack-5-speed-speedometer-and-tach/#findComment-576727 Share on other sites More sharing options...
Joey Mack Posted May 31 Share Posted May 31 Mech, i have a roll of it. Just saying. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/75597-mack-5-speed-speedometer-and-tach/#findComment-576728 Share on other sites More sharing options...
70mackMB Posted May 31 Share Posted May 31 When we first bought the MB the 90* was junk. Had a time finding the correct one. .....Hippy Quote Link to comment https://www.bigmacktrucks.com/topic/75597-mack-5-speed-speedometer-and-tach/#findComment-576729 Share on other sites More sharing options...
mechohaulic Posted May 31 Share Posted May 31 correct one defiantly important. some were just 90's other's had gear reduction/ change internally. full mechanical had it's challenges for repair. inner cable broke/ rounded out going into steel adapter, like you mentioned the tabs(tangs) worn /broke. B&R had enough speedo parts to completely make all new; inner/outer housings, large assortment of ends/adapters AND proper crimp tools , another part of mechanics which has changed. whether it be speedo. or hyd lines ; made your own. without need of computer or vin numbers. Quote Link to comment https://www.bigmacktrucks.com/topic/75597-mack-5-speed-speedometer-and-tach/#findComment-576730 Share on other sites More sharing options...
mechohaulic Posted May 31 Share Posted May 31 tach and speedo with big clock inside it ? not talking of the tell tale tachograph ??don't remember tach part of the ole tell tales (as they were called). open door install chart . Quote Link to comment https://www.bigmacktrucks.com/topic/75597-mack-5-speed-speedometer-and-tach/#findComment-576731 Share on other sites More sharing options...
Jizzo17 Posted May 31 Author Share Posted May 31 So the 90 is the problem. Where the rod is supposed to seat inside of a collar that has broken into two pieces and fell out when I took it apart. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/75597-mack-5-speed-speedometer-and-tach/#findComment-576732 Share on other sites More sharing options...
Jizzo17 Posted May 31 Author Share Posted May 31 Here is a picture of my the instrument cluster. The mileage also doesn’t move which is probably because the broke pieces I found inside the 90. Quote Link to comment https://www.bigmacktrucks.com/topic/75597-mack-5-speed-speedometer-and-tach/#findComment-576733 Share on other sites More sharing options...
Geoff Weeks Posted May 31 Share Posted May 31 Checked to see what I have. I have a 777 ratio box and a plain 90 deg but it has 5/8" threads and those look to be 7/8's Quote Link to comment https://www.bigmacktrucks.com/topic/75597-mack-5-speed-speedometer-and-tach/#findComment-576735 Share on other sites More sharing options...
Jizzo17 Posted May 31 Author Share Posted May 31 25 minutes ago, Geoff Weeks said: Checked to see what I have. I have a 777 ratio box and a plain 90 deg but it has 5/8" threads and those look to be 7/8's The ID is 13/16. I’m not sure what ratio it is Quote Link to comment https://www.bigmacktrucks.com/topic/75597-mack-5-speed-speedometer-and-tach/#findComment-576739 Share on other sites More sharing options...
Brocky Posted May 31 Share Posted May 31 That looks like an old Matlack dash!!! They even had 7 day ones for the F model sleeper teams, with a key lock only the home shop had the key to!! 1 Quote Brocky Link to comment https://www.bigmacktrucks.com/topic/75597-mack-5-speed-speedometer-and-tach/#findComment-576744 Share on other sites More sharing options...
Solution 70mackMB Posted June 1 Solution Share Posted June 1 If Geoff can not help you and if Watt's doesn't have it. This is who helped me out, State Line Truck Service 800-286-6531 1005 NH-12, Fitzwilliam, NH 03447 .....Hippy 1 Quote Link to comment https://www.bigmacktrucks.com/topic/75597-mack-5-speed-speedometer-and-tach/#findComment-576746 Share on other sites More sharing options...
Geoff Weeks Posted June 1 Share Posted June 1 My 90 deg is square drive, so that will not be a help, my "777" ratio box is tang drive but I don't know if the parts interchange with the 90 deg, or not, I suspect not. Hippy's place or other speedo shop would likely be a better bet. Quote Link to comment https://www.bigmacktrucks.com/topic/75597-mack-5-speed-speedometer-and-tach/#findComment-576759 Share on other sites More sharing options...
mechohaulic Posted June 1 Share Posted June 1 16 hours ago, Jizzo17 said: Here is a picture of my the instrument cluster. The mileage also doesn’t move which is probably because the broke pieces I found inside the 90. that broken piece is a separate short shaft. the speedo is the ole tattle tell sangamo which take a round paper chart . the 90gear box should have a tag on flat end which will tell ratio. EXTREME CARE is needed when cleaning off the grit. the tag is only thin metal with lightly printed numbers; you will totally wipe off the numbers if cleaning to much. spin the gear box by hand while watching opposite end , one revolution by hand will be 1 complete turn opposite end if it's a 1 to 1 box. ALSO if memory is correct. the shaft with gear which goes into transmission should have a small flex flat washer on it. do you have it ? it acts as a thrust washer for tension also keeps metal shaft from riding on alum transmission case. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/75597-mack-5-speed-speedometer-and-tach/#findComment-576774 Share on other sites More sharing options...
Jizzo17 Posted June 1 Author Share Posted June 1 (edited) @mechohaulic the ratio is 1:1. Tag may be there somewhere but just scraping the dirt off with a pick I couldn’t find it. There also wasn’t a washer in there when I pulled it apart. The only thing that came out were the two broken pieces in the picture. Edited June 2 by Jizzo17 Quote Link to comment https://www.bigmacktrucks.com/topic/75597-mack-5-speed-speedometer-and-tach/#findComment-576781 Share on other sites More sharing options...
Jizzo17 Posted Saturday at 08:19 PM Author Share Posted Saturday at 08:19 PM I found a 90 that I need but it came out of a 75 Mack with a 5 speed. And the owner says it’s more like a .85 to one ratio. Does this sound like it could work for my truck? Quote Link to comment https://www.bigmacktrucks.com/topic/75597-mack-5-speed-speedometer-and-tach/#findComment-578200 Share on other sites More sharing options...
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