did the 3.73 to 4.30 swap yesterday - Ford Powerstroke Diesel Forum
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Old 06-10-2013, 04:41 AM
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did the 3.73 to 4.30 swap yesterday

guys with larger tires: do it. i have been having 3.73s in my truck since i bought it about 3 years ago. since then it has had a 37" tire. never paid any mind to the gears because the truck was running good and all vitals were good. just recently i swapped injectors and turbo and noticed i had a significant increase in egt (about 100 degrees) while cruising. in my quest to figure out why someone brought up putting the truck in o/d and see what the egts did. well they dropped significantly, about 70 degrees.
so i started my search for 4.30s. to have my local shop do it would have run about 1500 for the rear and 1200 for the front using yukon parts. this is not a project i was willing to tackle myself. i have seen a bunch of post lately about guys wanting better mileage so i figured id see if anybody wanted to swap rears, cheap for both parties. found a guy about 3.5 hours from me who wanted 3.73 and he had 4.30. drove out yesterday and swapped complete rear ends. now i have a factory ford built rear end with 4.30s for about $100 in diesel. cant beat that.
the results: so much easier to drive. power seems like it is just sitting there waiting to be used. the first 50 miles back were hilly, never once did it down shift or feel like it was struggling. egt dropped about 70 degrees cruising at 70 (ambient temp was the same coming and going). about a 200 rpm increase at 70, right at 2k now. boost and ebp are much closer now, used to be close to 2 to 1 now they are about 1.5 to 1. vgt % dropped about 10%. no increase in exhaust tone that i could tell. havent refueled yet so i dont know about mileage but it looks to be very close. the only thing that it didnt help was my eot, raised about 4 degrees (running BPD oil cooler). the temp is still well withing spec so im not saying anything bad just giving results. temp going was max 187, coming home was max 191. like i said not bad at all just a little change. i guess with the rpm increase the oil doesnt sit in the cooler as long so it cant cool as much.
overall i am very happy with the decision and would suggest it to anyone who is running larger tires, your engine and trans will thank you. hopefully city mpg will have a slight increase due to it being easier to get going, if not oh well. hopefully the member i swapped with has the results he is looking for. i cant foresee any negative side affects for him, he is running factory tires and was looking for a decrease in rpm at interstate speeds

Last edited by 94slowbra; 06-10-2013 at 04:45 AM.
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Old 06-10-2013, 04:45 AM
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so are you gonna pay to have the front end done?
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Old 06-10-2013, 04:49 AM
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very good question, forgot to mention that in my original post. yes the front will be done soon. not sure on what parts im going to use because i rarely us 4x4, probably used it 3-4 times in 3 years. may just go with a US standard gear instead of the top of the line gears. but yes it will be done soon
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Old 06-10-2013, 04:53 AM
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i wouldnt cheap out cause yes you dont use it often but when you do use it you need it.
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Old 06-10-2013, 05:02 AM
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I'm going to weigh my options and see.
Also I'd like to add that some people mention that a mod is the single best mod they have done. I can't say that this is the single best mod but it has made some of my other mods come together and all work together. So in that sense it was definitely a good mod
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Old 06-10-2013, 05:48 AM
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You should try a ride in a truck with 4.56/37s! Serious usable power! Cobra just wanted to note the higher RPMs move the oil through the cooler faster, less dwell/cool time. I will not be an issue - but if you want BPD does advertise the HD coolers for the lower gear ratios due to the flow rate. I just put me on one this weekend.

Last edited by jetjock15; 06-10-2013 at 05:52 AM.
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Old 06-10-2013, 05:56 AM
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If you only used it off road when you really need it I wouldn't even worry about changing it. It just makes it a ***** to get in and out of 4wd. But if your trying to drag race or do pull offs your sling that front drive shaft so fast.
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Old 06-10-2013, 06:15 AM
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I have 4.30s in my F450 4x4 from factory and if I'm not mistaken, we have the same front end so maybe you could find a set from the wreckers for much cheaper than what are being quoted from a shop. Just a thought.
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Old 06-10-2013, 07:00 AM
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Quote:
Originally Posted by jetjock15 View Post
You should try a ride in a truck with 4.56/37s! Serious usable power! Cobra just wanted to note the higher RPMs move the oil through the cooler faster, less dwell/cool time. I will not be an issue - but if you want BPD does advertise the HD coolers for the lower gear ratios due to the flow rate. I just put me on one this weekend.
well there was no easy route for 4.56s. if i towed often or very heavy like you i would have considered but i dont. im not concerned about the oil temps. just stating the difference. trucks with stock oil coolers cant even dream about 191. pm sent.

Quote:
Originally Posted by risco View Post
If you only used it off road when you really need it I wouldn't even worry about changing it. It just makes it a ***** to get in and out of 4wd. But if your trying to drag race or do pull offs your sling that front drive shaft so fast.
i thought running two different gear ratios was a big no no? i dont race or pull with it, just use it to get out of sticky situations

Quote:
Originally Posted by harrisford View Post
I have 4.30s in my F450 4x4 from factory and if I'm not mistaken, we have the same front end so maybe you could find a set from the wreckers for much cheaper than what are being quoted from a shop. Just a thought.
450s have a wider front track width so that wouldnt work. good thought though. im going to do some research and find the best solution for the front.
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Old 06-10-2013, 08:26 AM
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Isnt the front track width just because of the wheel spacers? When I bought the f450 I looked at doing a 4.10 swap and I was going to use a center section from a F350
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