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By petew - 13 Years Ago
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My 56 Merc is an original overdrive car and as such has a 4.09 rear end ratio. I would like to drop down to a numerically lower ratio like in the 3.50 to 3.30 range.
Does anyone know of a source for these gears ? I believe these rears are Dana 44's and they still put Dana 44's in Jeeps. Same rear or different animal ?
Pete
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By speedpro56 - 13 Years Ago
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The merc is a different animal. I do have a good 3.15 gear set up for a 56 mercury which is a spare I can sell. The gear selection is small for the mercury unlike a 9" which has a lot to choose from. PH: 828-298-2197 if interested.
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By carl - 13 Years Ago
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Pete I sent you a PM about the gears you need. Carl
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By petew - 13 Years Ago
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Thanks to both of you for the reply. The 3.15's may be a little to low numerically. The car has been converted from the original 3 speed od to a T-5 5 speed which would make those 3.15's about a 2.22 in 5th.
Pete
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By charliemccraney - 13 Years Ago
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Then do you really need a taller gear? I'll be running a 4.something with my overdrive. It's 3.70 now.
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By petew - 13 Years Ago
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First gear is nearly useless with the 4.09's but the car is to heavy to start out in 2nd. Having done this 5 speed conversion in other cars I have learned that a 3.30 - 3.50 rear gear makes better use of the gearing in the tranny and gives you longer legs on top.
Pete
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By lowrider - 13 Years Ago
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I second Petes opinion about 1st gear being useless w/a 4+ rear gear. Your not thru the intersection and the engine is screaming. I dropped mine back down to 3.55 and its much more streetable.
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By charliemccraney - 13 Years Ago
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I was thinking about it on the way to work today. Again, I was jumbling cars and trucks. Cars tend to use smaller diameter tires so taller ratios will work better with them.
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By pegleg - 13 Years Ago
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I would do the math, because we really don't know what your rear tires are. If you can shoot for an over all ratio in low of between 6.5 and roughly 8.0 I think you'll be in the ball park. Racing (drag ) would want more.
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By SkylinerRon - 13 Years Ago
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That overall ratio should be 9 to 12 Example: 3.00 1st gear X 3.50 rear=10.50 With tall ie 29" tires i'd shoot for 12. Goodluck, Ron.
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By petew - 13 Years Ago
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Well you learn something new every day. It makes sense that there would be a formula for optimum gearing I just never knew that one existed.
My tires are 215/75 R15's and a quick measurement shows them to be 27" diameter.
Pete
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By Ted - 13 Years Ago
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And here’s the link to a past thread giving the math formulas for calculating rpm and also the tire diameter based on the metric sizing that’s now prevalent. http://www.y-blocksforever.com/forums/Topic20077-3-1.aspx
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By charliemccraney - 13 Years Ago
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That's about the same diameter as the tires on my truck. You probably have a shorter overdrive ratio. Mine is .63. If yours is a more common .68 ratio, then you can use about 3.43 and cruise at about the same RPM as mine. That will give you about 11.5 in 1st gear and should put you at about 1700rpm @60mph in overdrive with a 2.33 final ratio.
If I'm not mistaken, that car would have had about an 11.41 total 1st gear ratio and about 3.27 overdrive originally. (I'm remembering reading about 2.80 for 1st gear and .8 overdrive)
The best thing you can do is to see where you're at now and then determine the ratio you need to get where you want to be. It eliminates guessing and then you only need to know the final drive ratio. It'll be a trade off for cruising RPM and acceleration.
Edited because I was working with the wrong T5 od ratio. Maybe I was thinking of the GM ratio?
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By petew - 13 Years Ago
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Charlie,
Looks like my OD is .68 making it a a little over a 30% OD as opposed to a 20% like yours. At this point it looks like I need to see what gears I can find and really can't be to picky .
I did the numbers using the ratio calculator and it looks like the 3.15's offered earlier in this thread could work. The t-5 has a pretty deep first gear so it would allow me to travel more that the current 30 feet prior to having to shift to second. Fifth gear ( OD ) would give me a 2000 rpm cruise at 70 mph. Not Bad.
Pete
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By charliemccraney - 13 Years Ago
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I think it will be a 3.35 1st gear. After working out the data, if the engine is relatively stock, and therefore has good low end, the 3.15 will probably work well. If anything, the overdrive may end up being too tall.
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By petew - 13 Years Ago
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I'll take what I can get ( find ) at this point. Also if I change from a 4.09 to a 3. something gear will I be able to use the same carrier for the ring gear or do the carriers change with the ratios ? Another question, it seem to me that the rear in my Merc is the same ( except width and brakes ) as the rear in my 55 Tbird ? Which would allow me to buy a shim and gasket kit as well as bearings if needed from my Tbird parts supplier.
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By petew - 13 Years Ago
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Just wanted to post some of the things that I learned from Carl after he measured the differences between the Merc and the Ford rears
Merc has 20 spline vs ford 19 spline axles
Merc axles measure 1.290 diameter vs 1.230 for ford
Merc axles 2" longer than ford.
Pete
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By charliemccraney - 13 Years Ago
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Can they be swapped easily? The 2' longer axles might prevent that.
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By petew - 13 Years Ago
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More info, turns out that the Merc uses a Dana 45 rear not the Dana 44 like found in Tbirds.
All Dana rears have a "series" number cast in the housing on the 2 o'clock brace ( as view from the back) of the housing center section.
This info told to me by a gentleman from Ratech Which is a place that makes set up parts kits for old rears.
I looked on my bird and found the number 44 in the location described , checked the Merc and found the number 45.
Looks like that series Dana was also used in some Chevy trucks in the mid to late 50's
Pete
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By petew - 13 Years Ago
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Just finished installing the 3.15 gears in my Merc . It is a completely different car , 1st gear is now usable for more than 30 feet and I find myself shifting far less around town.
First Dana rear I have set up but I found a great "how to" online which made it pretty easy to do.
Thanks to Carl for selling me a really clean gear set for a very reasonable price.
Anyone interested in my 4.09's let me know
Pete
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By carl - 13 Years Ago
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Pete
Glad to here the gears worked out for you Carl
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