Lost about which rearend to use.

Edster · Apr 22, 2008

I've got two center chunks, one is a 3.50:1 open diff (now in the car) and I have a later model 3.00:1 limited slip. I love the acceleration the 3.50 gives me but I'm afaid the car will be a dog if I put the limit slip in. I don't have the dough to swap out ring an pinions at this time so it's either one or the other. I realize its up to me in the end but I'm wondering if someone could point out the pros and cons of each. Is it possilble the 3.0:1 could be quicker due to better traction?

SnwMnkys · Apr 22, 2008

Cant you wait a week or 2 until you have $100 a shop swap them out?

Edster · Apr 23, 2008

Its more like 450 dollar job with all new bearings and seals. I reckon I could get by with the old bearings on the trac lok set and just buy seals and it might be 300. Just the set up alone is $250. If I had a new 3.50 gear I would do it my self as the tolerances aren't as critical. See the problem w/ used gears is that they can't be off more than a one thousandth or they will howl or eventually break. Or at least that is what I am told. I'm just not willing (at this point in time) to spend that kind of dough on something like that.

rbohm · Apr 23, 2008

overall the difference between a 3.00 and a 3.50 gear isnt that much. the lower gear feels more responsive off the line because you get the higher torque multiplication, but unless you have a better than stock engine, it will tend to run out of breath where the higher gear is still pulling hard. as i recall car craft did a test, and the difference was less than 1/2 second in the 1/4 between the two gears. if you have each set in a complete pumpkin, i say swap them out and see what happens. you may find things wont be as bad as you fear.

ultrastang · Apr 23, 2008

Edster said:
Its more like 450 dollar job with all new bearings and seals. I reckon I could get by with the old bearings on the trac lok set and just buy seals and it might be 300. Just the set up alone is $250. If I had a new 3.50 gear I would do it my self as the tolerances aren't as critical. See the problem w/ used gears is that they can't be off more than a one thousandth or they will howl or eventually break. Or at least that is what I am told. I'm just not willing (at this point in time) to spend that kind of dough on something like that.

The backlash settings for a NEW ring & pinion are .004"-.008". The tolerances of a used set of gears is .008"-.012" of backlash. You also have to measure case spread and pinion pre-load when assembling the 3rd member. You will also have to setup the tooth contact pattern on the gears. This is not a job for someone that doesn't have the specialty tools or experience in knowing what to do or how to set things up, if you want things to stay together and last.

3.50 is a good all around street/strip gear. If you don't have a real strong engine now, these will at least be a ratio your engine can "grow into".

Another wise choice, if you are going to a lower rear ratio (higher numerically), would be to install an overdrive transmission if you do not currently have one. This will give you the best of both worlds in having all the acceleration on the bottom end without the penalty of high RPMs on the top end.

brianj5600 · Apr 23, 2008

Why not put the trac-loc in the 3.50 chunk? That would not take much. Swap the 3.50 ring gear onto the trac-loc and bolt it into the 3.50 chunk and set backlash. It can be done w/o any special tools. Before I had a dial indicator, I just held the ring gear and checked how much the yoke moved. When I put it back together I tried to get the same feel for the movement of the yoke.

ultrastang · Apr 23, 2008

If these are factory-installed Ford gears, the 3.50 ratio gears will be timed (non-hunting gear set). Do not get them out of time, or you will have problems with either noise and/or accelerated ring and pinion wear. You should see a white paint mark on one of the driving pinion gear teeth and on two of the ring gear's teeth --if these are factory gears.

Obviously the single paint mark on the driving pinion tooth goes between the two marked teeth on the ring gear when they are meshed together upon assembly.

fasttback · Apr 24, 2008

Stick with what ultrastang is saying. It takes speciality tools and skills reading tooth patterns to set up properly. Some may luck out throwing things together and having tollerances close enough, but most times noise and accelerated ware are the outcome. Take your time and do it right the first time.

Edster · Apr 24, 2008

Timing... Yeah that jolted a memory from my high school auto shop class. Ford had donated a 9 inch traction-lok to the school back in the '70s which was the unit we used to learn about rear ends and I remember the timing marks. I also remember using paste and or a strip of news paper to check the tolerence. The strip of newspaper is what gave me the idea that it shouldn't be hard If the paper has nice sharp "folds" and is not cut by the gears after you run it through then you are very close to being on the money.

I'm probably going to leave the 3.50 in and when I get the dough I'm going to put in 4.11s and a gear vendors overdrive. I've been eyeballing that thing for a while and feel it is the way to go. That way if I want to switch back to the toploader I can buy an adapter.

Lost about which rearend to use.

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