datsun 160J SSS Posted May 30, 2015 Report Share Posted May 30, 2015 Hello all . I have a question someone may know? I pulled a 5 speed trans from a 720 pickup I think it was a 85 2 wheel drive I liked it because it had a short tail trans that would fit my 73 620 pickup and it would work with the stock bench seat . Anyway I need a new speedo pinion the one that was in the trans is trashed . I ordered a new pinion from Nissan but it's to short and cant be returned :confused: the pinion itself is a long body total length is 3.50'' inches, black body, pinion is mounted on the driver side tail housing gear was red in color anyone know a part number ? when I ordered the first part it supersedes to a new part number witch is to short :sneaky: 1 Quote Link to comment
DanielC Posted May 30, 2015 Report Share Posted May 30, 2015 The speedometer pinion is matched to the rear axle of the truck. If the pinion from your old 1973 620 transmission can be made to work, that will keep your speedometer accurate. 1 Quote Link to comment
datzenmike Posted May 30, 2015 Report Share Posted May 30, 2015 First of all is your speedometer completely accurate? This is the time to correct any problems with reading too fast or slow. It's unlikely the 720 had the same differential gears and tire size as your 620. Your '73 has a totally different transmission and different speedo pinion design in it and should have a 16 tooth pinion but the later 620 with the 71B 4 and 5 speeds (with same speedometer gauge in dash and gearing and tires) this changed to a Red 20 tooth. If your 720 5 speed transplant has a 20 tooth or a Red plastic pinion gear then this is likely the closest. If however when fixed you find that you are traveling faster than the speedo says (needle too low) you can change to a 19 tooth to speed the speedometer cable up about 5% or 2.5MPH at 50 MPH. If too fast a reading a 21 tooth can be used to slow the speedometer cable by about 5%. Be sure to order the pinion for a later 720 transmission. A 20 tooth Red is 32702-58S20 for the sleeve with the 20 tooth gear, for just the plastic 20 toothed gear (cheaper) 32703-78104. It was also used on the '84 and up S12 (200sx if they can't find it under the 720) To the best of my knowledge this 20 tooth will be correct if your 620 has the same tire size. 1 Quote Link to comment
DanielC Posted May 30, 2015 Report Share Posted May 30, 2015 When setting up speedometer pinion gears, you must first get the distance traveled correct. The odometer has a geared relationship all the way to the rear tires. This is a constant, that does not change, nom matter how old the vehicle is. At least vehiciles with mechanical odometers, like our Datsuns. The speedometer is not mechanically connected to the transmission. The speedometer needle is attached to an alumnium cup, that a spring holds at zero. The speedometercable spins a magnet inside the aluminium cup, and induces a electrical current in the aluminium, and this makes the aluminium cup how far the needmlemove in the same direction the magnet is spinning. How high the needle reads, in relationship to the speed of the magnet spinning can be adjusted. The odometer cannot be adjusted in the speedometer. That is why you have to correct the odometer first, with the speedometer pinion gear, then adjust the speedometer reading. 1 Quote Link to comment
datzenmike Posted May 30, 2015 Report Share Posted May 30, 2015 Absolutely true. I'm assuming everything is working correctly. Currently I'm having a problem with slowing the speedometer down to read the true speed after a differential gear change. I can not only tell I'm going to slow at 30MPH but confirmed 34 MPH at 50KPH (31MPH) Yes I have a MPH speedo in a KPH country. I currently have a 20 tooth pinion and would really like a 22 but NLA at Nissan. I'm not that worried if the odometer is out or not just don't want the po po stopping me. Quote Link to comment
datsun 160J SSS Posted May 31, 2015 Author Report Share Posted May 31, 2015 Thanks guy's the question is part numbers the pinions I have ordered are to short for the pinion body am looking for 19 tooth .total length 3.50 the aluminum body pinion will not make contact with the gear inside the tail shaft . so do I have the right pinion ratio I don't know? I don't have anything to try I know the rear gears were swap to 3.88 works great for a lowered mini .Thanks Quote Link to comment
datsun 160J SSS Posted May 31, 2015 Author Report Share Posted May 31, 2015 32702-58S20 is what I ordered from Nissan it's to short .my pinion is fitted on the driver LH side the old part numbers superseds to the short body .I may have to try and press off a gear or make the new short gear fit the long body and make a short extension to contact the speedo cable . Quote Link to comment
datzenmike Posted May 31, 2015 Report Share Posted May 31, 2015 Thanks guy's the question is part numbers the pinions I have ordered are to short for the pinion body am looking for 19 tooth .total length 3.50 the aluminum body pinion will not make contact with the gear inside the tail shaft . so do I have the right pinion ratio I don't know? I don't have anything to try I know the rear gears were swap to 3.88 works great for a lowered mini .Thanks Try turning the pinion 180 degrees. Cut a new notch for the hold down key. I just nicked it with an angle grinder. Sleave now sits upside down to reach the mainshaft speedo drive worm gear. Quote Link to comment
datzenmike Posted May 31, 2015 Report Share Posted May 31, 2015 32702-58S20 is what I ordered from Nissan it's to short .my pinion is fitted on the driver LH side the old part numbers superseds to the short body .I may have to try and press off a gear or make the new short gear fit the long body and make a short extension to contact the speedo cable . Just read this post. I have one of those short 5 speeds but it's from a 4x4 and doesn't have the pinion sleeve in it. I don't know what they use. Quote Link to comment
datsun 160J SSS Posted May 31, 2015 Author Report Share Posted May 31, 2015 Thanks mike . if I put the one you have in the photo it will fall in to the trans .too short . this could be a no fix :confused: Quote Link to comment
uberkevin Posted June 2, 2015 Report Share Posted June 2, 2015 I'm pretty sure I just need a cable. But I hope you get this fixed up so your speedo is working g right. I use a gps. Quote Link to comment
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