Rob Posted March 13, 2012 Share Posted March 13, 2012 I'm installing a T2090 trans into a 1988 R690 truck with 4.17 Mack rears. This is a mechanical speedometer equipt truck. The former and deceased owner had the original five speed Mack trans replaced with a T2100 series transmission, (used). Utilizing the original to the replacement transmission speedometer gearing, the indicated speed was very low compared to actual road speed. I'm looking for the correct pencil gear to drive the speedometer at the correct indication of road speed. Again the new drivetrain combination is a Mack T2090 transmission with Mack 4.17 rear gearing on 11RX22.5 tires. Can anybody break this down and guide me on the correct speedometer drive gear?Thanks,Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/23816-having-a-rough-time-with-speedo-gear/ Share on other sites More sharing options...
lucerne tractor Posted March 13, 2012 Share Posted March 13, 2012 I thought there was going to be pictures of you in a speedo that didn't fit, I had to see this!!! Quote Link to comment https://www.bigmacktrucks.com/topic/23816-having-a-rough-time-with-speedo-gear/#findComment-106997 Share on other sites More sharing options...
Rob Posted March 13, 2012 Author Share Posted March 13, 2012 I thought there was going to be pictures of you in a speedo that didn't fit, I had to see this!!!All my "Speedo's" fit as they should, (according to me). Other peoples don't tend to agree. I have to wear a "cup" to prevent chaffing however.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/23816-having-a-rough-time-with-speedo-gear/#findComment-106999 Share on other sites More sharing options...
b61fred Posted March 13, 2012 Share Posted March 13, 2012 Rob, I am thinking that you will need to install a speedometer gear adapter inline, You know the little boxes that are usually stripped out and causing the speedo not to work on the old stuff. I think the "pencil gear" in the truck trans has very little tolerence unlike automobile aplications. b 61 fred Quote 15 gears...no waiting! Link to comment https://www.bigmacktrucks.com/topic/23816-having-a-rough-time-with-speedo-gear/#findComment-107052 Share on other sites More sharing options...
Rob Posted March 13, 2012 Author Share Posted March 13, 2012 Rob, I am thinking that you will need to install a speedometer gear adapter inline, You know the little boxes that are usually stripped out and causing the speedo not to work on the old stuff. I think the "pencil gear" in the truck trans has very little tolerence unlike automobile aplications. b 61 fredHi Morgan, this ratio box works well without any flutter to the indication on the indicator. There are five separate pencil gears available for this transmission. Everything is present including the drive gear, the driven gear, (pencil gear), the length adapter, the ratio matching box, and cable with jacket. It just read much too slow for the road speed you were traveling. When running 65, the speedometer indicated about 51-53mph.I'm thinking this T2100 transmission probably came from a donor truck with a high 3.XX ratio rear axle before being installed into this R model.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/23816-having-a-rough-time-with-speedo-gear/#findComment-107054 Share on other sites More sharing options...
Freightrain Posted March 13, 2012 Share Posted March 13, 2012 Hmmmmm, sounds like you need someone to make you onna them thar elektrunik speed o meterisms. I gots one in my truck. Maybe I can hook you up with the guy that helped me??? Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment https://www.bigmacktrucks.com/topic/23816-having-a-rough-time-with-speedo-gear/#findComment-107055 Share on other sites More sharing options...
Rob Posted March 13, 2012 Author Share Posted March 13, 2012 I B toyin wit dat opchun two... This 2090 trans is already set up for the electronic speedo including the pickup and reluctor wheel; plus I have an electronic variant already that is factory Mack but I want to use it in my "Project R-12" truck. If this isn't settled acceptably I may go the electronic route.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/23816-having-a-rough-time-with-speedo-gear/#findComment-107056 Share on other sites More sharing options...
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