Redneck Coronet Posted July 5, 2015 Report Share Posted July 5, 2015 (edited) What should the "cruising" rpm be? At 50mph Im turning about 5,000 and that is in 4th gear. Gyromatic 50 Dodge 6 banger. Thanks Dan Edited July 5, 2015 by Redneck Coronet Quote Link to comment Share on other sites More sharing options...
Barabbas Posted July 5, 2015 Report Share Posted July 5, 2015 I expect you've got a problem with your Tach---at 50 you should probably be turning closer to 2500 but I don't know your 4th gear ratio, your rear end ratio or your tire size Quote Link to comment Share on other sites More sharing options...
TodFitch Posted July 5, 2015 Report Share Posted July 5, 2015 I am a little surprised that any American passenger car was equipped with a four speed back in 1950. . . As Barrabas noted, it would be surprising if you are turing 5000 at 50 MPH. If I could get my 1933 up to 5000 RPM in high it would be going 96 MPH and I doubt that your car is geared lower than mine. If you have your mounted tire diameter, final drive ratio and high gear transmission ratio, then you can plug those into one of the many RPM calculators lurking on the web. Quote Link to comment Share on other sites More sharing options...
greg g Posted July 5, 2015 Report Share Posted July 5, 2015 Well if his car is a Coronet it might be a gyromatic and there for could be considered to be in 4th in high gear. My suspicion would be that his transmission might not be shifting into its upper range and what is being Identified as 4th might be considered 3rd, and therefor not at one to one of top gear. Seems to me with that set up in high, 60 mphshould be in the 2900 to 3300 RPM area depending on tire diameter. if it is a gyromatic, merely selecting the high range shifter position does not assure a gear change into top gear. I do not know the gear ratio for thelower gear of the higher range but if it is in the neighborhood of second gear in a three speed, it might be above 4000 at 50. Quote Link to comment Share on other sites More sharing options...
William Davey Posted July 5, 2015 Report Share Posted July 5, 2015 OP states that he has a Gyromatic in his first post. Back calculating using assumed 28-29 inch tire diameters yields a final drive ratio of 8.6 to 1. The calculator used assumes top gear in the transmission is 1:1. So if my thinking is right 3rd gear in his gyromatic would be 2.09 to 1 if the differential has 4.10 gears. Anybody know the actual 3rd gear ratio? Quote Link to comment Share on other sites More sharing options...
B-Watson Posted July 6, 2015 Report Share Posted July 6, 2015 Actually, two American manufacturers offered a 4-speed in the 1940's and early 1950's - GM and Chrysler. GM's was Hydramatic, a fluid coupling with two, two speed planetary gearsets, giving four forward gears. And Chrysler's, of course, was its 4-speed semi-automatic, that in 1950 was the M-6 and called Presto-matic on Chryslers, Tip-Toe Shift on DeSotos and Gyro-matic on Dodges. 4th gear is direct drive. Rear axle ratio was 3.9 in 1950 with 3.73 optional. Standard tire was 6.70x15, 7.10x15 optional. Gear ratios - 1st - 3.57:1 2nd - 2.04:1 3rd - 1.75:1 4th - 1.00:1 Quote Link to comment Share on other sites More sharing options...
TodFitch Posted July 6, 2015 Report Share Posted July 6, 2015 Actually, two American manufacturers offered a 4-speed in the 1940's and early 1950's - GM and Chrysler. Interesting. I did not know that. For what it is worth, with typical tire aspect ratio for that era, the standard sized tires with a 3.73 rear gives about the following RPMs at 50 MPH: 1st - 7800 RPM 2nd - 4500 RPM 3rd - 3850 RPM 4th - 2250 RPM Quote Link to comment Share on other sites More sharing options...
greg g Posted July 6, 2015 Report Share Posted July 6, 2015 the 3.9 with 28 inch tires would be running 4500 at 55, so I stand by my assumption that he is not shifting into high gear in high range. Quote Link to comment Share on other sites More sharing options...
Redneck Coronet Posted July 7, 2015 Author Report Share Posted July 7, 2015 It is a gyromatic and it is going into 4th gear. I have both shifts in low range and high range. I am using a Mac tools et 390 tach unit. It has 3.90 gears with 215/75 15 tires. will try another tach unit. Quote Link to comment Share on other sites More sharing options...
greg g Posted July 7, 2015 Report Share Posted July 7, 2015 (edited) That set up should be in the neighborhood of 3000 rpm at 60mph. Edited July 7, 2015 by greg g Quote Link to comment Share on other sites More sharing options...
Niel Hoback Posted July 7, 2015 Report Share Posted July 7, 2015 Is your fluid coupling full? Quote Link to comment Share on other sites More sharing options...
Redneck Coronet Posted July 7, 2015 Author Report Share Posted July 7, 2015 (edited) Is your fluid coupling full? is that fed from trans oil? Also the rpms are constant no apparent signs of slipping while driving. Edited July 7, 2015 by Redneck Coronet Quote Link to comment Share on other sites More sharing options...
Don Coatney Posted July 7, 2015 Report Share Posted July 7, 2015 No. Do you have a manual? If not suggest you buy one. Quote Link to comment Share on other sites More sharing options...
greg g Posted July 7, 2015 Report Share Posted July 7, 2015 (edited) Nope. Seperate fluid, check and fill access on trans hump under carpet on pass side DO NOT drop fill plug. Most common replacement fluid is universal tractor hydraulic fluid. Available at Places like Tractor supply etc. Stuff is for powering tractor accessories like bucket lifts. raising three point hitches etc. You position the plug, remove it and stick in a finger. If it comes out wet yer good to go, like a standard trans of diffy. The fluid drive while providing no torque multiplication till 53 was 95 to 98% efficient. So in good nick should only add 100 or 200 RPM to any speed per RPM equation. About the same as current lock up torque converters when compared to unlocked, in comparison to a dry clutch set up. Edited July 7, 2015 by greg g 1 Quote Link to comment Share on other sites More sharing options...
Redneck Coronet Posted July 7, 2015 Author Report Share Posted July 7, 2015 No. Do you have a manual? If not suggest you buy one. Its on the list but I am layed off and already spent close to 1700.00 getting it roadable I inherited it last month. Quote Link to comment Share on other sites More sharing options...
Don Coatney Posted July 7, 2015 Report Share Posted July 7, 2015 Its on the list but I am layed off and already spent close to 1700.00 getting it roadable I inherited it last month. Have you read everything there is to read in the resources section of this web page? Located on the tool bar at the top of this page. Also use the search function as you can learn a lot by reading there. Quote Link to comment Share on other sites More sharing options...
Plymouthy Adams Posted July 7, 2015 Report Share Posted July 7, 2015 (edited) is that fed from trans oil? Also the rpms are constant no apparent signs of slipping while driving. only the Hy-Drive (53-54) was fed by engine oil and that is a true torque converter and not a coupler....sort of a go between till the first true automatic for Plymouth appeared on the scene mid production. Follow Gregs advice on checking the coupler fluid level.... Edited July 7, 2015 by Plymouthy Adams Quote Link to comment Share on other sites More sharing options...
Redneck Coronet Posted July 7, 2015 Author Report Share Posted July 7, 2015 is that fed from trans oil? Also the rpms are constant no apparent signs of slipping while driving. After i get the carb back on ill get under it andlocate the plug. somebody pop riveted a repair panel across the floor access. Quote Link to comment Share on other sites More sharing options...
Redneck Coronet Posted July 7, 2015 Author Report Share Posted July 7, 2015 Have you read everything there is to read in the resources section of this web page? Located on the tool bar at the top of this page. Also use the search function as you can learn a lot by reading there. nothing showed uo search for running rpms. Have been reading lots from chrysler page. Quote Link to comment Share on other sites More sharing options...
_shel_ny Posted July 7, 2015 Report Share Posted July 7, 2015 (edited) I would be looking for a substitute tach to try. The sound of the engine on my 48 with 3.73, and 235/75s on the back if pulling 5000 rpm/s would have scared the bejesus out of me. I would envisioned pistons and rods appearing through holes in the water jacket. EDIT: if your car is moving OK, ie. starts out and drives, goes up hills and such, your fluid coupling level is probably fine Edited July 7, 2015 by shel_ny Quote Link to comment Share on other sites More sharing options...
_shel_ny Posted July 7, 2015 Report Share Posted July 7, 2015 (edited) nothing showed uo search for running rpms. Have been reading lots from chrysler page. Did you use "advanced search" ? Edit: that takes you off this page for a more extensive search. Edited July 7, 2015 by shel_ny Quote Link to comment Share on other sites More sharing options...
TodFitch Posted July 7, 2015 Report Share Posted July 7, 2015 nothing showed uo search for running rpms. Have been reading lots from chrysler page. My calculator is at http://www.ply33.com/Misc/speed#calc But there are others http://lmgtfy.com/?q=road+speed+rpm+calculator 1 Quote Link to comment Share on other sites More sharing options...
greg g Posted July 7, 2015 Report Share Posted July 7, 2015 you can not access the fluid plug from under the the car. Quote Link to comment Share on other sites More sharing options...
Plymouthy Adams Posted July 7, 2015 Report Share Posted July 7, 2015 so you are going by a tachometer that may or may not be reading correctly and thinking FD coupler as a suspect when if fact you could also have a slipping clutch..the coupler is only one part of the drive..you still have a clutch disc in the setup... I would first test the tach against another one, say a hand held tach/dwell meter that is so commonly used on tuning these older engines...set your baselines first as a true KNOWN figure... Quote Link to comment Share on other sites More sharing options...
Dave72dt Posted July 7, 2015 Report Share Posted July 7, 2015 The ET390 is a hand held. I don't want to insult the OP, but was the tester set on 6 cyl? Setting on 4 or 8 will give you higher or lower RPM than actual. Quote Link to comment Share on other sites More sharing options...
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