Pete

Glad to here the gears worked out for you Carl

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

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

Can they be swapped easily? The 2' longer axles might prevent that.


Lawrenceville, GA

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

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.     

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.


Lawrenceville, GA

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

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?


Lawrenceville, GA

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 

Lorena, Texas (South of Waco)