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Discussion Starter #1
hey guys, im thinkin about swappin my gears, and NO this isnt a question on which ratio i should get!

i was wondering how difficult the process is, as i have never done this before. should i try to do it on my own? or should i break down and take it to a speed shop.

also, im pretty suer im going to 3.73s, but was wondering if this would put too much stress on my motor? its got about 128000 miles on it, but it runs really strong. just lookin for some opinions or experienced insight.
 

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systronic said:
hey guys, im thinkin about swappin my gears, and NO this isnt a question on which ratio i should get!

i was wondering how difficult the process is, as i have never done this before. should i try to do it on my own? or should i break down and take it to a speed shop.

also, im pretty suer im going to 3.73s, but was wondering if this would put too much stress on my motor? its got about 128000 miles on it, but it runs really strong. just lookin for some opinions or experienced insight.
i said i wanted to do the same thing and the response i got was i should leave it to the pros. he told my driveshaft would need to be rebalanced and the tools alone would costmore than the install.
 

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systronic and reese77, if you really want to know whats involved in swapping gears, check it out.

http://www.angelfire.com/theforce/5ohcpa/cpa5ohtech001.htm

You can then decide which option is best. As you will see it's not a "Remove, Replace & Torque" process, there are specifications that require the use of special measuring equipment. If any is not done as a shortcut, the noise the gears could end up with is a "whine X2" (one from the gears and one from the driver), and it becomes "permanent" after a 200-500 miles drive.....BTSTDT.... GL
 

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I've been going back and forth on this myself the whole summer. I'm probably going to do it myself pretty soon. I put new ABS sensors in last weekend in preparation for pulling the axles. Didn't notice what year you had but if you have ABS I'd plan on replacing the sensors - they'll probably break. My car is by no means rusty but those suckers were stuck!

The angelfire site lok like it has a pretty good write up on gear installation.

I have a used set of 3.55 and 3.73 Ford gear sets. I have read both good and bad concerning used. Over the past 15+ years I've read multiple times used are quiter. I've heard otherwise online lately, but in the past in printed publications, I've read that used are quieter......

Regarding installation I'm wondering if there really is too much hype about gear installations so that's why I'm going to try it. I may screw up...... but I'm gonna try it.

My 3.08s are running fine so the current pinion is obviously set up ok. I'm planning on measuring the current pinion head, the new pinion head, and shimming accordingly to get the same total as the original. The 3.73 I have measures 1.89" and had a .032 shim and the 3.55s measured 1.88 and had a .033 shim. The length of the tooth on a ring gear is between 1.25 to 1.50 inches long. When you set these things up a lot of emphasis is put on measuring but at the end of the day, every article tells you to go by the wear pattern on the teeth. The "wear pattern" on a tooth is pretty darn subjective. Seems like if you have a 1.25 to 1.50 distance to work with for the wear pattern you could be off by a whole .10 inch or so and still be in the ballpark! So I question what's all the hype on pinion depth measurements in the .001 accuracy range? If you look at a lot of the "professional" measuring practices and "tools" they recommend it's hard to see how they can actually get measurents more accurate than the .01 range.

Backlash and bearing preloads, yes I can see where that needs to be accurate. But the whole pinion depth thing seems way too over emphasized. Can any professional installers out there explain to us why .001 accuracy is so important?

As far as 3.55s vs 3.73 I keep going back and forth. 3.73s will give a better 2nd gear but will also make 1st wind up real fast and require fast shifting to 2nd everytime you leave the stoplight - seems like it could get old on the street. Leaning towards 3.55s right now........
 

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Pinion depth is the amount of space perpindicular to the ring gear, very crucial to the life of your rear end and bearings for that matter. It would pre-maturely wear on the pinion splines in a manner that would be "eating" the gear...hope that kinda paints a picture.:shrug
 

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Joel5.0 said:
systronic and reese77, if you really want to know whats involved in swapping gears, check it out.

http://www.angelfire.com/theforce/5ohcpa/cpa5ohtech001.htm

You can then decide which option is best. As you will see it's not a "Remove, Replace & Torque" process, there are specifications that require the use of special measuring equipment. If any is not done as a shortcut, the noise the gears could end up with is a "whine X2" (one from the gears and one from the driver), and it becomes "permanent" after a 200-500 miles drive.....BTSTDT.... GL
sweet:wavey
 

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Just seems like all the worrying about the pinion depth to a .001 accuracy isn't really possible. The measurement is taken to the head of the pinion. The head is not a machined surface but a forging. In other words, it's not a truely flat machined surface. You cannot get and exact .001 measurement.

This is why they talk about getting the average head length when you do the pinion depth set-up by way of measuring the old head versus the new. Even when you use Fords method with the tube and jig and slide the shims in, which part of the head to you consider correct? My 3.55 Ford pinion head (of which Ford is supposed to have the tightest manufacturing tolerances of them all) measures 1.889, 1.887, 1.885, and 1.890. That's a maximum variation of .005 so how can we hold to a .001 spec? This would imply to me that the shim you use could be either a .030 or a .035 and be "within specs". So why all this worry of .001 accuracy? In the end it seems like all the measuring eventually goes out the window anyhow and it comes down to the very subjective "pattern" you see . A "visual" setup is going to allow for way more variation in pinion depth than even a .005 accuracy factor.

Kind of like when you multiply 2.0 x 2.00000000. It's only as accurate as 4.0 not 4.00000000.

Just seems like the pinion depth thing is over blown.
 

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Discussion Starter #8
i figure if im gonna go with the swap, ill let a pro handle it. itll be cheaper to have it done right, than for me to screw it up and need a new rearend. plus i could get them to do a rebuild while theyre at it. thanks for that link, and input!
 

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yeah it is over blown, honestly at the time i didnt have a pinion depth gauge when i installed my gears. I used the shim off of the original pinion. My only way of determining that it was ok, was to use a paste to visually see the driveline and coastlinne impression on the ring gear. of couse, now you can get a depth gauge from summit from 89-179$ we are all perfectionists....arent we??:laughlitt
 

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KK95GT said:
Seems like if you have a 1.25 to 1.50 distance to work with for the wear pattern you could be off by a whole .10 inch or so and still be in the ballpark! So I question what's all the hype on pinion depth measurements in the .001 accuracy range? If you look at a lot of the "professional" measuring practices and "tools" they recommend it's hard to see how they can actually get measurents more accurate than the .01 range.
well. when i set up rear ends i use the ford tools which do not rely on tooth pattern. its actually a couple of specially designed tools which fit in with the pinion bearings and sticks up to the point where the pinion would sit. then you take a huge pipe that is the size of the diffential and is bolted down with the main caps. then you slide shims into the gap between the two and until one doesnt fit you use the previous one. (i'm not very good at creating a mental image of what this looks like until you see what im talking about) the shims are .010-.019 and a .030 (or at least in the last one i did it may very per car) (you stack 2 together to get a bigger number as in a .011+.014=.023 which is acurate to the .001)

ford only have us check the gear pattern to verify that it is set up correctly not to measure with

and btw, why all this measuring may not be 100% acurate but its a hell of a lot more acurate then just throwing it together and trying to make the gear pattern look good. whatever your reading that says to only use the gear pattern is wrong and was written for someone who doesnt want to take the extra effort to do it right
 

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I used Boss Mustangs and Corral.net articles and information for my installation guidance on the '95 gear change I just did, but for "written literature" regarding tooth patterns, my original 1966 Ford OEM factory shop manual goes into great detail regarding tooth patterns. In the final step it specifically states "If the patterns are not correct, make the changes as indicated". Ref part 4-1, page 4-5.

Just about every article I've ever read has mentioned a final tooth pattern as the final check no matter what the "measurements" say.

And yes I would now have to say the whole installation process is way overblown!! I finally put the 3.55s in and they're working great! I used the original .032 shim from the 3.08 pinion and re-used the original .256 and .291 carrier shims. Unded up with a .014 backlash (exactly the same backlash the 3.08s had before I pulled it apart) which is within the .008-.015 acceptable range. Tooth pattern looked great and they're perfectly quiet!

Guess this is a good example of Fords high manufacturing tolerance controls!

Yes it was time consuming but it sure wasn't the rocket science everyone plays it up to require! Plus, isn't it always more gratifying to be able to say "Yeah I did it myself" !
 

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Discussion Starter #12
SURE IS! unless of course you did it wrong.... haha
 

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Yeah but isn't most every "first time" in life a learning lesson? I always figure all you can do is plan ahead and research things to the best of your abilities and then just go for it. Sometimes you win, sometimes you loose. Most of the time, if you take your time and you're careful, you'll come out on the win side!
 
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