If you own a Dodge Cummins, your factory transmission lines are living on borrowed time. From the factory these trucks ran rubber hose with crimped steel ends running from the transmission up to the heat exchanger and the cooler. That was fine when the truck was new. Two decades and a few thousand heat cycles later, the rubber goes brittle, it weeps at the crimps, and eventually it lets go. We see it in the shop all the time. A guy loads a trailer, pulls a grade, a line splits, and now he is sitting on the shoulder watching fluid run out onto the road.
The Real Killer: The Factory Heat Exchanger
The factory heat exchanger sits inline with your transmission cooling and uses engine coolant to manage trans temp. There is a thin internal barrier in there keeping the coolant and the transmission fluid apart. On these trucks, that barrier fails. When it does, coolant pushes into your transmission fluid, and coolant inside a transmission is a death sentence. It turns the fluid milky, swells the clutches, and chews up the bearings, usually well before you ever see a temperature gauge move. A lot of the rebuilds that come through our door did not start with a worn out transmission. They started with this.
The Fix: Real Braided Lines, Built for Your Truck
We build direct replacement line kits out of real AN braided hose and proper fittings, not crimped rubber. They hold up to heat, they hold up to pressure, and they are not going to rot out on you in five years. The thing to understand before you buy is that we make these in a bunch of different configurations, because your truck is not the same as the next guy's. You match the kit to four things: your year, whether you want to keep or delete the heat exchanger, your transmission, and whether you run the stock cooler or an upgraded one. Here is how it breaks down.
Stock Replacement vs Heat Exchanger Bypass
This is the first choice. A Stock Replacement or Factory Replacement kit replaces your rotting lines and keeps the factory cooling layout. A Heat Exchanger Bypass kit does that and also routes the heat exchanger out of the loop, so it can never dump coolant into your transmission. If your heat exchanger is suspect or you just want that failure gone for good, get the bypass version.
Find Your Kit by Year
| Year | Stock / Factory Replacement | Heat Exchanger Bypass |
|---|---|---|
| 1994 to 2002 (12V / early 24V) | 94-02 Stock Replacement Kit | 94-07 Stock Replacement w/ HX Bypass |
| 2003 to 2007 (5.9 common rail) | 03-07 Stock Replacement Kit | 94-07 Stock Replacement w/ HX Bypass |
| 2007.5 to 2009 (6.7) | 07.5-09 Stock Replacement Kit | Use the 03-07 bypass routing |
| 2010 to 2012 (6.7) | 10-12 Factory Replacement Kit | - |
2013 to 2018: Pick Your Transmission
The 2013 to 2018 trucks add one more decision, which transmission you are running. These trucks came with the 68RFE, but a lot of guys swap to a 48RE for a stronger build. We make lines for both, in factory replacement and bypass.
| Transmission | Factory Replacement | Heat Exchanger Bypass |
|---|---|---|
| Factory 68RFE | 13-18 68RFE Factory Replacement | 13-18 68RFE Bypass |
| 48RE Swap | 13-18 48RE Swap Factory Replacement | 13-18 48RE Swap Bypass |
Running a 48RE swap in a later truck? The 2007.5-2021 Cummins 48RE Swap Transmission Line Kit covers that build too.
Running an Upgraded Mishimoto Cooler?
If you have already stepped up to a Mishimoto transmission cooler, the fittings and lengths are different, so we make kits cut specifically for it. On the 03-07 trucks that is the 03-07 Line Kit for Mishimoto Cooler, or the 03-07 Mishimoto Cooler Kit with Heat Exchanger Bypass if you want the heat exchanger gone too. On the 07.5-09 trucks it is the 07.5-09 Line Kit for Mishimoto Cooler.
Going to a Remote-Mount or Drop-In Cooler
Building the cooling side up from scratch? Our DIY remote cooler line kits let you plumb a remote mounted cooler the clean way. We make them for the 68RFE and for the 47RH / 47RE / 48RE transmissions. And if you want the whole thing handled in one shot, the 03-09 Elite Drop-In Transmission Cooler Kit bundles the cooler and the lines together.
Just Need One Line or the Bypass?
If only one line let go and the rest are still good, you do not have to buy the whole set. We sell the lines individually, like this 03-07 Replacement Transmission Line, so you can replace just the one that failed. And if all you want is to delete the heat exchanger on a 94-07 truck, the 94-07 Heat Exchanger Bypass Single Line does exactly that on its own.
Who Should Run This
If your truck is bone stock and daily driven, a line kit is cheap insurance against a roadside leak and a five thousand dollar transmission. If you tow or you have added power, it is not optional. More heat and more pressure is exactly what finds the weak point in the factory setup, and the factory setup is rubber hose and a heat exchanger that was a question mark the day it left the line. You can replace these one leak at a time, on the side of the road, for the next ten years. Or you can match the right kit to your truck above and do it once.
Shop FSD Cummins Transmission Line Kits →