Mack 5 speed speedometer and tach

[Jizzo17]

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 Saturday at 09:21 PM by Jizzo17

[mechohaulic]

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. 

[Joey Mack]

Now there's a Man that knows his SH!T !!! Mech,  you are a wealth of knowledge... 

[70mackMB]

l was going to mention the key ways being worn also.    ......Hippy

 

[mechohaulic]

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.

[Joey Mack]

Mech, i have a roll of it.  Just saying.  

[70mackMB]

When we first bought the MB the 90* was junk. Had a time finding the correct one.    .....Hippy

[mechohaulic]

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.

[mechohaulic]

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 . 

[Jizzo17]

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. 

[Jizzo17]

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. 

[Geoff Weeks]

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

[Jizzo17]

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

[Brocky]

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!!

[70mackMB]

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

 

[Geoff Weeks]

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.

[mechohaulic]

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.

[Jizzo17]

@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 32 minutes ago by Jizzo17