Red Horse Posted April 14, 2017 Share Posted April 14, 2017 Well guys the speedometer in my B 61 never worked since I bought it. The seller did include a rebuilt speedo so I thought I would put it in today. Pulled the old one out and to be sure, put it in a drill chuck and it worked!. So then I disconnected the cable at the trans. When I pulled it out, I ended up with a short fitting about 2" long that went into the trans and it had liked a crimped end that the cable popped out of. I got to thinking, is this my problem? Speedo is okay but could the cable not be making contact with this fitting? stripped out? I did not put the speedo back into the dash so I will be driving th truck tomorrow and will see if the cable is turning. Appreciate any thoughts. Quote Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/ Share on other sites More sharing options...
Red Horse Posted April 15, 2017 Author Share Posted April 15, 2017 On 4/13/2017 at 8:52 PM, Red Horse said: Well guys the speedometer in my B 61 never worked since I bought it. The seller did include a rebuilt speedo so I thought I would put it in today. Pulled the old one out and to be sure, put it in a drill chuck and it worked!. So then I disconnected the cable at the trans. When I pulled it out, I ended up with a short fitting about 2" long that went into the trans and it had liked a crimped end that the cable popped out of. I got to thinking, is this my problem? Speedo is okay but could the cable not be making contact with this fitting? stripped out? I did not put the speedo back into the dash so I will be driving th truck tomorrow and will see if the cable is turning. Appreciate any thoughts. Well for sure cable not turning. Also talked to a few guys who said common cure was pulling cable from trans end and reseating the cable in that 2" piece by resetting with a hammer. Anyone have this experience? Quote Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367425 Share on other sites More sharing options...
HarryS Posted April 16, 2017 Share Posted April 16, 2017 The two inch piece in the trans should have the driven gear on the other end. Does that turn as it should? If so then the square connection for the speedo cable has to be the problem. I've heard of the hammer fix but never tried it. Quote Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367540 Share on other sites More sharing options...
70mackMB Posted April 16, 2017 Share Posted April 16, 2017 Bob, Rick and l were thinking of you using JB Wield where the cable pulled out of the drive pin. l need to get into the MB's because it stopped working also.......... Hippy Quote Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367553 Share on other sites More sharing options...
Bobby j Posted April 16, 2017 Share Posted April 16, 2017 45 minutes ago, 70mackMB said: Bob, Rick and l were thinking of you using JB Wield where the cable pulled out of the drive pin. l need to get into the MB's because it stopped working also.......... Hippy Hippy. Does that truck still have the sangamo speedometer clock in it.....also Mack had two different round ends with key way on it that slid into pencil gear it's best to have the metal ends as the newer plastic ends will round out.....Bobby j. Quote Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367554 Share on other sites More sharing options...
70mackMB Posted April 16, 2017 Share Posted April 16, 2017 1 hour ago, Bobby j said: Hippy. Does that truck still have the sangamo speedometer clock in it.....also Mack had two different round ends with key way on it that slid into pencil gear it's best to have the metal ends as the newer plastic ends will round out.....Bobby j. No tattle tail speedo in it now. lt did have one but someone cut the mount for it off. The hole for the cable is still there by the shifters. We are looking for one to replace it...... Hippy Quote Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367557 Share on other sites More sharing options...
Red Horse Posted April 17, 2017 Author Share Posted April 17, 2017 Guys- thx for responses. I guess your idea Hippy on the JB weld sounds like a shot. And Harry- the cable end that goes into the 2" adapter is like a "half square"-or should I say, half round with a flat face-so in essence half circle. I was by myself this afternoon and I jammed the two inch adapter onto the cable and it feel like it had enough resistance to be spinning the cable. I'l see if I can get another pair of eyes in the driver's seat to see if the speedo end turns. Quote Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367577 Share on other sites More sharing options...
Freightrain Posted April 17, 2017 Share Posted April 17, 2017 Sounds like the pencil gear in the trans bushing is lobbed out(not square anymore). I had a couple of those gears, but they got stripped out about 10 yrs ago. I kept trying to keep mine working, but I worked with Rob and I put an electronic speedo in it. Today you can get GPS stuff, but back then I machined the parts and Rob did the electrical testing. It has worked flawless for years. That bushing unscrews from the transmission, like mentioned, it holds the gear inside the transmission that rides on the gear on the output shaft. Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367592 Share on other sites More sharing options...
mattb73lt Posted April 17, 2017 Share Posted April 17, 2017 If the cable checks Ok, sometimes there's an adapter to interface with the "pencil" gear drive. Check that and make sure that everything locks and drives together. If all that is good, I would suspect the pencil gear and the spiral drive on the tail shaft of the transmission. The pencil gear is pretty easy to get at. Back off the bushing where the speedometer cable attaches, the small shaft should lift out with a little effort. I've had those eaten up by the spiral drive. If it's the spiral drive, that's going to be a little tougher to get at if it's bad. I have several pencil gears and spiral drives I've collected up to fix issues I've had. If that pencil shaft is bad, the gear can be pressed off and put on a good shaft to keep the speedometer accurate or at least working. Let me know if you need one and I'll get it to you. I'll take some pics of them tonight. Quote Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367614 Share on other sites More sharing options...
Red Horse Posted April 18, 2017 Author Share Posted April 18, 2017 12 hours ago, mattb73lt said: If the cable checks Ok, sometimes there's an adapter to interface with the "pencil" gear drive. Check that and make sure that everything locks and drives together. If all that is good, I would suspect the pencil gear and the spiral drive on the tail shaft of the transmission. The pencil gear is pretty easy to get at. Back off the bushing where the speedometer cable attaches, the small shaft should lift out with a little effort. I've had those eaten up by the spiral drive. If it's the spiral drive, that's going to be a little tougher to get at if it's bad. I have several pencil gears and spiral drives I've collected up to fix issues I've had. If that pencil shaft is bad, the gear can be pressed off and put on a good shaft to keep the speedometer accurate or at least working. Let me know if you need one and I'll get it to you. I'll take some pics of them tonight. Thx Matt. I did not get to it today but I'm going to pull the 2"adapter, engage the cable, then spin the cable (from the adapter end) while I have an observer in the driver's seat to see if cable is turning. If it does, I guess case is made that problem is in the tailshaft-correct? Quote Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367669 Share on other sites More sharing options...
mattb73lt Posted April 18, 2017 Share Posted April 18, 2017 1 hour ago, Red Horse said: Thx Matt. I did not get to it today but I'm going to pull the 2"adapter, engage the cable, then spin the cable (from the adapter end) while I have an observer in the driver's seat to see if cable is turning. If it does, I guess case is made that problem is in the tailshaft-correct? It may be. If the cable, speedometer head and connections all check, then I would suspect the pencil gear or spiral drive. The pencil gear is really easy to pull and check. Quote Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367680 Share on other sites More sharing options...
HarryS Posted April 18, 2017 Share Posted April 18, 2017 When I changed from TRD 72 to TRD 720 by speedo was off about 10%. I tried changing just the pencil gear and found out the pencil and spiral drive have to a match. Changed the spiral (that took some effort) and now it's synched. Quote Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367718 Share on other sites More sharing options...
mattb73lt Posted April 18, 2017 Share Posted April 18, 2017 They do. There's a number on the shaft and I also count the teeth. Some of these pencil gears are trashed because of that. They can be slightly off, but the mesh is important. I believe that spiral gear I have was done in because of that, Along with the pencil gear. Quote Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367722 Share on other sites More sharing options...
Freightrain Posted April 18, 2017 Share Posted April 18, 2017 (edited) After I started putting some miles on my truck it ate up the pencil gear. Next one lasted even shorter. Pulling the tailhousing isn't a big deal(once you've done it a few times LOL). My drive gear had some chips in it and likely why it ate up the pencil gear. I just had it apart again this winter as the seal started to drip on the yoke. Once you get the hang of getting the cotter pin out of the 2 1/4" castle nut on in the yoke, then get the nut off, it is downhill from there. Blasted and painted again: Edited April 18, 2017 by Freightrain Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367725 Share on other sites More sharing options...
mattb73lt Posted April 18, 2017 Share Posted April 18, 2017 Now there's a fix. So that pick-up (sensor) needs to be 90 degrees from target? Did you do the machine work or send it out? Quote Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367729 Share on other sites More sharing options...
Freightrain Posted April 18, 2017 Share Posted April 18, 2017 Yes, I did all the machine work(I work at machine shop). I made the reluctor wheel to mimic the gear width and diameter. The tooth count was figured by Rob after he did some testing. The tailhousing I machined for the sensor. Yes, the pickup needs to be perpendicular to the reluctor wheel. I'm sure there is some kind of specification, but I made it 90*. 1 Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367734 Share on other sites More sharing options...
mattb73lt Posted April 18, 2017 Share Posted April 18, 2017 Wow, that's awesome. Some really good info for the future if I need to go that way. The reluctor would be a challenge. Very similar to the RPM sensors that Bell Helicopter uses and calls Mono-pole Pick-ups, measuring the magnetic fields of gear teeth as they pass. Quote Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367740 Share on other sites More sharing options...
Red Horse Posted April 19, 2017 Author Share Posted April 19, 2017 Larry, Matt and Harry S. You guys have convinced me I should do the math and post a chart on my dash-"1500 RPM in X gear= Y MPH"! Well I got underneath it again this afternoon and pulled that two inch connector off the cable-which by the way has no gear on it. I stuck it back into the transmission thinking if gear in trans is okay I would not be able to turn it. spun freely-that says the issue is in the trans??? I should probably post a picture of this "connector as it does not look like anything Matt you have posted. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367763 Share on other sites More sharing options...
mattb73lt Posted April 19, 2017 Share Posted April 19, 2017 That should help get us in the ballpark of the issue. Those gears I posted reside within the housing that Freightrain posted and the pencil gear is about 4" long. His modification is nice as there are no moving parts for the "drive" and will probably outlast all of us. The thin collar is against the bushing the cable connects to. On my B-42 there is a small plastic adapter that connects the replacement cable to the pencil gear. On the pencil gear there will be a small series if numbers for that gear. The mesh is important as you will wear out the gears quickly if there's a significant mismatch. As for the chart, I made one for mine for every gear using all the ratios/final drive/tire diameter (RPM=Gear#=MPH). Helped a lot as my speedo was inop when I first had it on the road. Quote Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367772 Share on other sites More sharing options...
HarryS Posted April 19, 2017 Share Posted April 19, 2017 I used a plug in GPS until I got mine fixed. I would probably still be using it but there was a leak at the rear seal so that had to be replaced along with the in/out bearing and race. I had to invest in a Harbor Freight 1" drive socket set for the job. Quote Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367778 Share on other sites More sharing options...
fxfymn Posted April 19, 2017 Share Posted April 19, 2017 GPS or even a cell phone app seems like the way to go if it starts heading down the road of complicated repairs. I use a GPS on mine since the speedo bounces around so much. 1 Quote Money, sex, and fire; everybody thinks everyone else is getting more than they are! Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367810 Share on other sites More sharing options...
mattb73lt Posted April 19, 2017 Share Posted April 19, 2017 4 hours ago, fxfymn said: GPS or even a cell phone app seems like the way to go if it starts heading down the road of complicated repairs. I use a GPS on mine since the speedo bounces around so much. I have one now, too. I use it to check all my cars as one has no speedometer ( Model T) and 6V so it eats battery life while in use. Very useful for determining speedo accuracy. Quote Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367836 Share on other sites More sharing options...
Freightrain Posted April 19, 2017 Share Posted April 19, 2017 Yes, I've used a phone app for speedo before. I have found that the electronic speedo I have seems to skew out of calibration the faster you go(it reads faster then you are going). Just a few MPH, so I don't worry about it. Seems real accurate in town, around 30-40 mph. 65-70 mph it reads faster then you are going. 18 hours ago, Red Horse said: Well I got underneath it again this afternoon and pulled that two inch connector off the cable-which by the way has no gear on it. Hmm, I wonder if it is a speed reducer/adapter? I've seen those before and I originally was going to use one til my gear finally gave up. Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367839 Share on other sites More sharing options...
Red Horse Posted April 19, 2017 Author Share Posted April 19, 2017 3 hours ago, Freightrain said: Yes, I've used a phone app for speedo before. I have found that the electronic speedo I have seems to skew out of calibration the faster you go(it reads faster then you are going). Just a few MPH, so I don't worry about it. Seems real accurate in town, around 30-40 mph. 65-70 mph it reads faster then you are going. Hmm, I wonder if it is a speed reducer/adapter? I've seen those before and I originally was going to use one til my gear finally gave up. Larry- I am reaching up under truck and the only thin g I feel is the threaded mail end sticking up from trans. Maybe I should raise the body and see if I can see anything else looking in from in back of cab . By the way, in addition to the two inch piece, there is what I would call a thick washer with a beveled top- when it fell out I was not expecting this but I'm guessing the beveled edge goes up against the attaching collar and the flat side goes against the trans. Quote Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367868 Share on other sites More sharing options...
Freightrain Posted April 20, 2017 Share Posted April 20, 2017 Yes, raise the body, that will give you easy access to see what is up there. Maybe a picture? It should just be an insert threaded into the transmission, maybe an inch tall, threads for the speedo cable, wrench flats to be able to unscrew it. Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment https://www.bigmacktrucks.com/topic/49539-trd-720-speedometer-drive/#findComment-367900 Share on other sites More sharing options...
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