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I’m gathering parts to do a mild upgrade on mine now..

One of the things I’ve noticed after talking to two trans shops is that they both pushed me towards a stock rebuild with a shift kit and didn’t want to talk about anything else. “It’s a waste of money, you don’t want that” was what I heard about billet input shafts, upgrading the strut, lever, servos, clutches, etc. Even when I pointed out what I wanted to do HP wise (450-500 is my goal) they just tuned out and said something about warranty and never having problems with the 48re. My take away was that I hadn’t found the right place yet.

That’s a long way to say be sure you find the right guy!
This is because the local "transmission shop" only knows how to do a stock build with a shift kit. You start talking about a 500 hp diesel transmission and they are immediately out of their comfort zone. If you're looking at running that power level (and why wouldn't you?), you're going to need a well built transmission. A stock one with a shift kit won't get you there.
 

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IF you are a DIY sort, read the info from BAXY.
Followed that along with input from Cereb.
Been pulling heavy RV for 9 years on the rebuild /NO problems
Best of luck to you.
 
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I’m gathering parts to do a mild upgrade on mine now..

One of the things I’ve noticed after talking to two trans shops is that they both pushed me towards a stock rebuild with a shift kit and didn’t want to talk about anything else. “It’s a waste of money, you don’t want that” was what I heard about billet input shafts, upgrading the strut, lever, servos, clutches, etc. Even when I pointed out what I wanted to do HP wise (450-500 is my goal) they just tuned out and said something about warranty and never having problems with the 48re. My take away was that I hadn’t found the right place yet.

That’s a long way to say be sure you find the right guy!
From what I have learned at 450-500HP stock clutch counts with upgraded clutches and a high pressure valve body with good converter will absolutely handle that power level. But what many places call a high pressure valve body just are not high enough pressure and the 2nd gear band apply lever/servo springs does need to be set up to take the pressure change into account or you will have shift timing problems on the 2-3 shift. This is the only “timed” shift in a 47/48RE, it just part of the original 727 design.

I somewhat agree with what was said here accept in the 2nd gear apply setup.

Dynamic transmission is worth the drive from anywhere in my opinion. Doesn’t mean there’s not other good shops, I just think John is a great guy and seems to have been able to make these as good as they can get. I would at least call him.


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Gravel, ya a lot shops don’t think you NEED a full billet built tranny. Let me tell you, it makes a big difference putting the power down and not worrying about it.


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At 450-500HP? Billet input at most for peace of mind but your not going to break the other shafts at 500HP?

VB and TC is where the money should not be saved!

This is just my opinion.


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This is because the local "transmission shop" only knows how to do a stock build with a shift kit. You start talking about a 500 hp diesel transmission and they are immediately out of their comfort zone. If you're looking at running that power level (and why wouldn't you?), you're going to need a well built transmission. A stock one with a shift kit won't get you there.
The guy that wrote this is the guy to talk to.


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At 450-500HP? Billet input at most for peace of mind but your not going to break the other shafts at 500HP?

VB and TC is where the money should not be saved!

This is just my opinion.


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Billet input is all I’m planning, and agree that it’s mostly for peace of mind. I’ll likely end up at 500hp max, on 35s, towing 10k or so for weekend camping trips.

Plan is to do mine in stages to see how comfortable I get taking on the next step. First is a fluid change, band adjustment, install the billet small parts, and see how much I can tell about the overall condition. Next two steps, and I haven’t decided what order, is a good single disc TC and the apply lever, or install the Transgo 48re-hd2 shift kit. When all that is done, I’ll start gathering tools and parts to do a full rebuild with the input shaft and new clutches. Since this is a first auto trans job for me, I don’t want to just dive in and do everything at once, if there is a glitch I’ll have no idea where to start looking.

If it goes sideways at any point, I’ll backdate to the last known good combo and seek pro help to finish it up. I’ve done a lot of technical projects in the past, using this method has been very successful.

I’ll do my best taking pictures and doing a write up of the whole thing.
 

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At 500 hp, a billet input shaft is more than just peace of mind. You'll need it. I would also not run a single disc converter at that power level (or any power level, for that matter). I HIGHLY recommend a triple, and with the correct stall speed. I see many guys ruin an otherwise decent setup with the wrong stall speed.

You'll also want to run billet servos (both of them), accumulator piston, band lever/anchor/strut, and a custom valve body. A "shift kit" will only get you so far. You're going to need more pressure, especially in the lower gears where the OEM valve body doesn't activate the boost valve. Good clutches are a MUST as well. I would definitely increase the clutch count in the direct while you're at it.
 

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Dynamic, what do you suggest for stall speed? How much lower than stock? It’s hard to even get an idea what stock is when my converter just lets the motor spin up to 2500+ with any load, even with a completely stock tune in it.
 

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With a stock turbo, I would recommend about 250 rpm under stock. I like to use the Goerend 15SS triple (or its DPC equivalent) when retaining the stock turbo, or an aftermarket turbo up to about 60mm. Larger than that on the turbo size, and I would jump up to the 17SS (or DPC equivalent), especially if running 37" tires on stock gearing.
 

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I’m not planning on changing the turbo beyond (maybe) a bigger exhaust housing on the stocker and maybe a boost fooler. 90% of my power increases will be from tuning. And as soon as the 37s are worn out I’ll go to 34-35s. BTW, I’ve got 3.73s.

So the 15SS or the DPC equal is it.

Appreciate your help!
 

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So the 15SS or the DPC equal is it.
Yes, either would be a great choice. Upgrade your flex plate while you're in there as well.

Yes, 3.73's will work well with a 34" or 35" tire. If you were going to stay with a 37" tire, I would re-gear it.
 

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I keep reading about how a triple disc TC has to have a billet input shaft. Am I ok running a triple on a stock input for a while? Will keeping a milder tune (60-90 HP) be enough to keep a stock input alive for a few months? The stock input shaft was why I was thinking of going single disc, and then when/if a single had problems holding I’d upgrade to a triple down the road a ways.

So will a triple disc kill a stock input shaft quickly? Can I compensate in the VB to help the input shaft survive?

A HD flex plate is planned for sure!
 

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Another internet myth... Granted, in the hands of someone who doesn't know what's up, you can definitely have trouble. But I run triples on stock input shafts all the time. I run nothing but triple disc converters, in fact. I haven't run a single disc converter behind a Cummins in decades...literally. Lockup calibrations in the valve body are what makes it safe and reliable. With good valve body calibrations, you're more worried about your power level with a stock input shaft.
 

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I drove a 2006 3500 mega cab 5.9 for 10 years and had no trouble pulling whatever I wanted with the 48RE. I sold it at 157,000 miles and went to a 2007 3500 mega cab 6.7 with the 68rfe. I just finished stretching my frame and am putting the finishing touches on my allison transmission conversion. Dave at CAConversions helped me make it happen. I couldn't afford to buy one of his built transmissions at the time, so I bought a rebuilt Allison 1000 and he sent me a triple disc converter. After driving almost 4000 miles now, I can say without a doubt that this is the best setup i've ever driven and will never look back. Yes, it's expensive. I believe that you pay for what you get, and I have an outstanding drivetrain right now. I have a hard time believing that they weren't built this way from the very beginning. I pull my 14,000 5th wheel on a weekly basis and my truck has never felt this solid before, ever. Every shift is firm and on the money. I know that there are a lot of folks out there that run 48's and 68's for a lot of miles and don't have any problems, but in my book that is just asking too much. I believe that i'm asking very little of my allison 1000 and I believe that is why there are so many motorhomes and medium duty trucks out there with allison transmissions. I wasn't willing to put my faith in a transmission rebuilder when the allison is built from the start to handle the weight. If you do nothing else, give Dave a call and talk with him for a few minutes. The phone call probably won't even cost you a dime. If you do, tell him C.W. in Denton, Texas, is loving his transmission conversion!
 

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Yes, the Allison is far better than the 48 or 68 ever thought of being. They still have their weaknesses, but they're definitely a step up.
 

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I drove a 2006 3500 mega cab 5.9 for 10 years and had no trouble pulling whatever I wanted with the 48RE. I sold it at 157,000 miles and went to a 2007 3500 mega cab 6.7 with the 68rfe. I just finished stretching my frame and am putting the finishing touches on my allison transmission conversion. Dave at CAConversions helped me make it happen. I couldn't afford to buy one of his built transmissions at the time, so I bought a rebuilt Allison 1000 and he sent me a triple disc converter. After driving almost 4000 miles now, I can say without a doubt that this is the best setup i've ever driven and will never look back. Yes, it's expensive. I believe that you pay for what you get, and I have an outstanding drivetrain right now. I have a hard time believing that they weren't built this way from the very beginning. I pull my 14,000 5th wheel on a weekly basis and my truck has never felt this solid before, ever. Every shift is firm and on the money. I know that there are a lot of folks out there that run 48's and 68's for a lot of miles and don't have any problems, but in my book that is just asking too much. I believe that i'm asking very little of my allison 1000 and I believe that is why there are so many motorhomes and medium duty trucks out there with allison transmissions. I wasn't willing to put my faith in a transmission rebuilder when the allison is built from the start to handle the weight. If you do nothing else, give Dave a call and talk with him for a few minutes. The phone call probably won't even cost you a dime. If you do, tell him C.W. in Denton, Texas, is loving his transmission conversion!
I seriously looked into this option. I was in communication with CA Conversions for over a year. The problem for me was the overall cost if your trying to get the Alison to hold 500+HP. That combined with not having to tow heavy much at all lately. It was going to cost me more than double a built 48.

But I am still envious of your setup!

I do however think a 48 is much more “fun” on the street than an Allison. But it’s not a heavy duty transmission and the gear ratios are less than ideal.


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With a stock turbo, I would recommend about 250 rpm under stock. I like to use the Goerend 15SS triple (or its DPC equivalent) when retaining the stock turbo, or an aftermarket turbo up to about 60mm. Larger than that on the turbo size, and I would jump up to the 17SS (or DPC equivalent), especially if running 37" tires on stock gearing.
I went with the 15SS and I believe what is said here about a larger turbo and stall speed. I just swapped the stock 2003 SO Holset 341 (the one with 56mm compressor wheel) for a 351 with the 60. This is a stock turbo for all 04.5 and up 5.9’s. There is now a noticeable turbo lag, nothing to complain about but I will be curious when I order a 62 or 63 here in a month or so what it will be like.

Stock tire size now but I have 35’s sitting in the garage next to 4:10 axles.

FYI if you pay for goerend’s lifetime warranty you get at least one free re-stall within a year.

For now the 15SS is fantastic. What a difference! When everyone says they can’t believe they waited so long... there’s a reason for it!


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