mopar_earl Posted November 30, 2015 Report Share Posted November 30, 2015 Hello, I have a lead on a 1998 explorer rear axle for 60 bucks. Don't know the ratio yet. My concern is since pretty much all my driving is in high range (3rd and 4th), will the M6 trans perform OK with say a 3.55? I searched the heck out of this forum but didn't see anything on the semi-auto trans. Currently have 3.90 ratio with 28" tires and the car performs well but would like to lower the rpms for sustained highway speeds. Also it would be great to have modern rear brakes to match my modern front disc brakes. This explorer axle pretty much fell in my lap or I wouldn't be pondering it, well this soon anyways. Lol I'm just concerned dropping from 3.90 might cause the car to be a dog in high range 3rd gear. 4th is 1 to 1 so no worries there. I also have a shift-rite shifter knob button to downshift the M6 at will. Anyone with the semi-autos change their final ratio? Please share your experience. Hoping to find out what ratio the explorer axle is in the next couple days. Thanks, Earl Quote Link to comment Share on other sites More sharing options...
55 Fargo Posted November 30, 2015 Report Share Posted November 30, 2015 Should be just fine considering the M5/6 came with 3.54 gears in Chryslers. It should be no problem.. Quote Link to comment Share on other sites More sharing options...
Dodgeb4ya Posted November 30, 2015 Report Share Posted November 30, 2015 This^^^^^^^^^ Quote Link to comment Share on other sites More sharing options...
mopar_earl Posted November 30, 2015 Author Report Share Posted November 30, 2015 With a flat six? Thought that ratio was used with the hemi and fluid torque on Chryslers? Earl Quote Link to comment Share on other sites More sharing options...
55 Fargo Posted November 30, 2015 Report Share Posted November 30, 2015 no it was used with Chrysler flathead 6s not just later V8s. It will handle it just fine, especially with the fluid drive spinning up from a dead stop... Quote Link to comment Share on other sites More sharing options...
greg g Posted November 30, 2015 Report Share Posted November 30, 2015 how much hill country will you be dealing with? Quote Link to comment Share on other sites More sharing options...
Dodgeb4ya Posted November 30, 2015 Report Share Posted November 30, 2015 Steep long grades might show the 230's power limits. DeSoto's used 3.54, 3.73 and a 3.91 ..engine was a 236 Ci. with Tip-Toe Shift Trans and FD. The 1946-48 chrysler with the M-5 trans and FD coupling used the 3.54 ratio with the 251 engine .. a bit more power and torque but the chrysler is a bit heavier too. In 1950 chrysler's six cylinder cars were offered with a 3.73 ratio with the Prest-Matic trans and std FD coupling.. In 1951-52 chrysler six cylinder cars offered only the 3.9 or 4.11 for 251 (1951) and the 265 (1952) engines with the Fluid-matic trans.. V-8's were equipped with a 3.73 ratio with or W/0 Fluid Torque drive converters. Quote Link to comment Share on other sites More sharing options...
mopar_earl Posted November 30, 2015 Author Report Share Posted November 30, 2015 I live in Pennsylvania, so hills and mountains are plentiful. My 230 is stock other than bored .040 over. My M6 3rd gear ratio is 1.75. 1st 3.75 2nd 2.04 3rd 1.75 4th 1.00 Earl Quote Link to comment Share on other sites More sharing options...
mopar_earl Posted December 5, 2015 Author Report Share Posted December 5, 2015 Any successful ratio changes on the semi-autos? I'm still concerned how the car will perform. Unlike a 3spd car, I can't really shift the same. So I'm pretty much a 2 speed with 1.75 and 1.00 ratios to work with. I have read plenty of successful 3spd and 3spd od ratio changes, but haven't found any semi-auto posts. Earl Quote Link to comment Share on other sites More sharing options...
mopar_earl Posted December 15, 2015 Author Report Share Posted December 15, 2015 Guess I will be the first guy on the forum to change gear ratio on semi-auto car? I will keep an eye out for a 3.55 8.8 Explorer axle to swap inplace of my corp 3.90. Once I do, I will post how the car performs. Earl 2 Quote Link to comment Share on other sites More sharing options...
James_Douglas Posted December 18, 2015 Report Share Posted December 18, 2015 My buddy here in SF drives his '45 Chrysler T&C around here all the time. It was supposed to be an export model going to China and never left the USA. It has the 8 with a fluid coupling and a 3.36 rear-end. All stock from the factory. Drives great. The T&C weight is a lot with all the wood so the HP to Weight ratio is the same as a flathead six in a steel car. Also, as an aside would people stop using the M5 (Gyromatic, Tip Toe Shift, Etc) transmission names when referring to the FLUID COUPLING. It makes for novices scratching their heads when they hit this website. The transmission can take any rear end you put into a car. The issue is how is the acceleration with a FLUID COUPLING. James. Quote Link to comment Share on other sites More sharing options...
mopar_earl Posted December 18, 2015 Author Report Share Posted December 18, 2015 The whole car doesn't care what gear ratio it has. It's the driver that does. Lol the fluid coupling will spin up the same no matter what ratio is used. The transmission ratios is the concern! Pulling out in high range in 3rd with a 3.90 will be different than pulling out with a 3.55 ratio. How much, I have no idea. That's why the post. I know and do call the drivetrain the correct terms. I have a M6 known as a Gyromatic by the Dodge division. It's coupled to the engine with a fluid coupling and dry clutch. The fluid coupler is not a torque converter cause it doesn't multiply torque. At least not on my car. Some cars did have a torque converter. Earl Quote Link to comment Share on other sites More sharing options...
mopar_earl Posted December 18, 2015 Author Report Share Posted December 18, 2015 My buddy here in SF drives his '45 Chrysler T&C around here all the time. It was supposed to be an export model going to China and never left the USA. It has the 8 with a fluid coupling and a 3.36 rear-end. All stock from the factory. Drives great. The T&C weight is a lot with all the wood so the HP to Weight ratio is the same as a flathead six in a steel car. Also, as an aside would people stop using the M5 (Gyromatic, Tip Toe Shift, Etc) transmission names when referring to the FLUID COUPLING. It makes for novices scratching their heads when they hit this website. The transmission can take any rear end you put into a car. The issue is how is the acceleration with a FLUID COUPLING. James. What transmission is in your buddy's car? Semi-auto or 3-speed Earl Quote Link to comment Share on other sites More sharing options...
greg g Posted December 18, 2015 Report Share Posted December 18, 2015 Don't you think, that with Chrysler being renowned for engineering, that the engineers pondered the same questions (albeit for somewhat different driving conditions) and given their thoughtful nature and the needs of different parts and topographical features of the country that they came up with the best ratios for the car when it was sold? So why change it? If your specific target is a slightly more relaxed cruising RPM, put on some taller tires. If your concern is lack of initial acceleration for around town use, put on some shorter tires. A trip to the pick and pull for some extra rims and some used tires for either condition would prove or disprove your query before time and expense invested in changing the rear member only to find it did not address your needs. 1 Quote Link to comment Share on other sites More sharing options...
mopar_earl Posted December 18, 2015 Author Report Share Posted December 18, 2015 (edited) Bottom line, I need to be able to roll at 70 mph without throwing rods. Car wasn't built for that kind of use. Fine for 1952, not for 2016. 3.90 gears are fine if you avoid all highways, which I'm not able to. So it's either change the gear ratio or find the rare od trans to convert the car from semi-auto to 3-speed overdrive. Unlike a 3-speed, the semi-auto is basically a 2-speed with close ratios. I'd rather keep my Gyromatic. I like it. I don't have to shift gears or clutch. Tire sizes only make minor changes to engine rpm. From my research the engine should be kept 3000 rpm or less for during sustained times. That means a 4 hour highway drive is out of the question lol Oh and I have 27" tires and will be replacing them with 28" in the future. Earl Edited December 18, 2015 by mopar_earl Quote Link to comment Share on other sites More sharing options...
55 Fargo Posted December 18, 2015 Report Share Posted December 18, 2015 Bottom line, I need to be able to roll at 70 mph without throwing rods. Car wasn't built for that kind of use. Fine for 1952, not for 2016. 3.90 gears are fine if you avoid all highways, which I'm not able to. So it's either change the gear ratio or find the rare od trans to convert the car from semi-auto to 3-speed overdrive. Unlike a 3-speed, the semi-auto is basically a 2-speed with close ratios. I'd rather keep my Gyromatic. I like it. I don't have to shift gears or clutch. Tire sizes only make minor changes to engine rpm. From my research the engine should be kept 3000 rpm or less for during sustained times. That means a 4 hour highway drive is out of the question lol Oh and I have 27" tires and will be replacing them with 28" in the future. Earl Earl, install a 3.55 modern rearend, say Mopar 8 1/4, or get 3.54 3rd member, which may not be easy to find. The 3.55 diff, 28 inch tires should have you cruising at 70 mph all day long, but your pickup to speed wil be slower... Quote Link to comment Share on other sites More sharing options...
55 Fargo Posted December 18, 2015 Report Share Posted December 18, 2015 3.55 rearend, 28 inch tires = 2900 RPM 3.23 rearend, 28 inch tires = 2740 RPM 1 Quote Link to comment Share on other sites More sharing options...
mopar_earl Posted December 18, 2015 Author Report Share Posted December 18, 2015 Yes, that's why I'm pondering a 3.55 axle ratio. Also I'd like to upgrade to a modern axle and brakes. All I can do is try it. Just concerned climbing hills and mountains. Sure I can do a forced downshift from 4th to 3rd but if 3rd can't handle it I'm screwed. As far as off the line, I'm not concerned. If too slow I will start out in low range and shift into high range. I was hopeful that someone has changed out the final ratio on a actual semi-auto and could comment on its pros and cons. Would love to find the extremely rare M6 with overdrive. That be sweet! Earl Quote Link to comment Share on other sites More sharing options...
55 Fargo Posted December 18, 2015 Report Share Posted December 18, 2015 Yes, that's why I'm pondering a 3.55 axle ratio. Also I'd like to upgrade to a modern axle and brakes. All I can do is try it. Just concerned climbing hills and mountains. Sure I can do a forced downshift from 4th to 3rd but if 3rd can't handle it I'm screwed. As far as off the line, I'm not concerned. If too slow I will start out in low range and shift into high range. I was hopeful that someone has changed out the final ratio on a actual semi-auto and could comment on its pros and cons. Would love to find the extremely rare M6 with overdrive. That be sweet! Earl 3rd should handle it fine. If your rolling along at a good pace, you may even pull those steep grades in high range, with that long stroke engine pulling away Quote Link to comment Share on other sites More sharing options...
james curl Posted December 18, 2015 Report Share Posted December 18, 2015 We had to go down to second before reaching the top of Monarch Pass in Colorado in 2007 in my 48 P 15 with 218 engine. Hit the slope going too slow, am still convinced if we could started at 70 mph at the bottom might have made it all the way in high gear with a 3.55:1 Dakota rear end in the car. These old flat head MoPar engines produce a lot of torque, I took .090 off of the head and .010 off of the top of the block which raised the compression and the car pulls hard in high gear. If you feather the clutch you can start off in high gear if you wish, I am always amazed by the torque they produce. Quote Link to comment Share on other sites More sharing options...
Dodgeb4ya Posted December 18, 2015 Report Share Posted December 18, 2015 (edited) I've never seen or heard of a 1945 T&C eight convertible. I thought they only made the T&C eight convertible from 1946-48 all with the fluid drive coupling and M-5 transmission? The C39 (1946-48 chrysler eight cylinder models) have considerably more torque than the six cylinder cars so they do pull their weight around OK. On the freeway at higher speeds is where the sweet spot is for the chrysler eights. Seventy is nice on the open road. " the M5 (Gyromatic, Tip Etc) transmission" ...... The (Gyromatic, TipToe) are 1949-53 M-6 transmissions.... different and a bit more modern than the 1946 to 1948 DeSoto and Chrysler M-5 transmissions. Edited December 19, 2015 by Dodgeb4ya 1 Quote Link to comment Share on other sites More sharing options...
greg g Posted December 19, 2015 Report Share Posted December 19, 2015 (edited) Well I have put thousands of miles on my car at 3200 RPM or so (60 to 65 mph range) with a 4.11 rear end set over the last 12 years with no mechanical problems. with the 3.90 in your car, your RPM at 70 would probably be in the same zip code. What size tires are you running? my tires are 28.25, Seems if you go to 3.55 and then put shorter tires on you are negating the change. Edited December 19, 2015 by greg g Quote Link to comment Share on other sites More sharing options...
mopar_earl Posted December 19, 2015 Author Report Share Posted December 19, 2015 Well I have put thousands of miles on my car at 3200 RPM or so (60 to 65 mph range) with a 4.11 rear end set over the last 12 years with no mechanical problems. with the 3.90 in your car, your RPM at 70 would probably be in the same zip code. What size tires are you running? my tires are 28.25, Seems if you go to 3.55 and then put shorter tires on you are negating the change. No shorter tires, 28's. 28's with 3.55 would be ideal as far as flat highway at 70. Hills and mountains are my concern. I've done the calculations and found the rpms would be ideal at 70. Earl Quote Link to comment Share on other sites More sharing options...
mopar_earl Posted December 19, 2015 Author Report Share Posted December 19, 2015 Well I have put thousands of miles on my car at 3200 RPM or so (60 to 65 mph range) with a 4.11 rear end set over the last 12 years with no mechanical problems. with the 3.90 in your car, your RPM at 70 would probably be in the same zip code. What size tires are you running? my tires are 28.25, Seems if you go to 3.55 and then put shorter tires on you are negating the change. No shorter tires, 28's. 28's with 3.55 would be ideal as far as flat highway at 70. Hills and mountains are my concern. I've done the calculations and found the rpms would be ideal at 70. I will gamble on 3.55's. Just need to find a fair deal on an axle. Earl Quote Link to comment Share on other sites More sharing options...
James_Douglas Posted December 22, 2015 Report Share Posted December 22, 2015 I've never seen or heard of a 1945 T&C eight convertible. I thought they only made the T&C eight convertible from 1946-48 all with the fluid drive coupling and M-5 transmission? The C39 (1946-48 chrysler eight cylinder models) have considerably more torque than the six cylinder cars so they do pull their weight around OK. On the freeway at higher speeds is where the sweet spot is for the chrysler eights. Seventy is nice on the open road. " the M5 (Gyromatic, Tip Etc) transmission" ...... The (Gyromatic, TipToe) are 1949-53 M-6 transmissions.... different and a bit more modern than the 1946 to 1948 DeSoto and Chrysler M-5 transmissions. Actually, it is a '46. Typo on my part. It is a very early car with '45 CA single rear license plate. Quote Link to comment Share on other sites More sharing options...
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