I saw that BD Performance sells a bypass tube deleter kit which is just two pieces of tubing to replace the bypass tube, it's fairly cheap to buy the two pieces (about $25 shipped) I have heard of issues where the valve to the tube has become faulty and has restricted the flow to the cooler and only allowed flow through the bypass tube. Or where the cooler has plugged and the bypass is the only route where the fluid flows, I have been trying to figure out where the bypass valve is located and it looks that it is a little ball (check valve) in the rear bolt where the rear line connects to (believe it's called the 'cooler line case fitting') Can I just knock that little 'BB' out and just leave the bypass tube connected, so it would just always flow through that and the cooler at all times. Or would I be better off just buying the bypass tube elinator kit (also will the kit increase pressure or not change anything?) It seems like even with the bypass eliminator kit the little ball is just left in the line. Any input would be gladly appreciated. I am trying to address the 4R100 issues to prevent tranny issues down the road.

 

I've also considered doing this. When I do it, I'm just going to buy the kit and remove the bypass entirely.

If I lived in a place where it got REAL cold, however, I wouldn't do it at all.

In Los Angeles it isn't going to be a factor....

Pop

 

So this bypass is sort of like the thermostat right?

 

so i need to get informed here, what's this bypass?

 

From what I understand it keeps the trans fluid from going to the cooler and just circulates it back to the trans until it reaches a certain temp. Am I correct here or way off?

 

You're way off.

The bypass is a pressure relief valve. There is no thermostat in the bypass. If the cooler plugs the bypass opens and keeps fluid flowing to the rear of the trans where it is used for lube. If you remove the bypass and the cooler plugs you don't have any lube to the rear of the trans. You'll be replacing the trans after that because there won't be enough usable parts left to rebuild it.

If you remove the ball in the check valve all the fluid will flow through the bypass all the time and almost nothing will go to the coolers. The bypass does not help the trans warm up, it is only there to insure that there is always lube to the rear of the trans.

It's rare for the bypass to fail. It's not rare for a cooler to get restricted, and then the bypass opens. When that happens the trans runs hot and a lot of people replace the bypass. That's not the problem, the restricted cooler is the problem.

 

Interesting Mark... I'm failing to see why would anyone want to replace the bypass?

 

These guys think different from what you said! Ford Super Duty 4R100 Transmission - Four Wheeler Magazine

 

The way Mark explained it makes more sence to me than the paragraph Wood said in the mag.

From mag article.

Ford Super Duty 4R100 Transmission - The Wood Way
2. The first thing Wood explains to customers is where Ford went wrong when they designed the transmission in the first place. Notice the small "bypass" line on the workbench. This line was designed to allow transmission fluid to reach operating temperature quickly after start-up. Basically, it involves an inline check valve that opens up, allowing ATF to bypass the cooling circuit when restrictions are above a specific value, e.g., cold temperatures, or with the addition of extra transmission coolers and/or increased line pressure. This is bad for those of us who like to improve things over stock. Without proper cooling, ATF quickly degrades, causing internal components to wear prematurely.

 

So why is woods welding the bypass line?

 

Maybe he thinks he knows what the bypass line does but in reality he does not.

The way Mark tells it the bypass is mainly for lubricating purposes in the rear parts in the trans and really has little to nothing to do with cooling.

 

It can affect cooling, but only if the coolers are restricted. It can bypass when it's cold out, but it's going to have to be REALLY cold, well below 0F. And if it does bypass then it probably won't close again until it warms up outside. A cooler that's getting a blast of very cold air while driving down the road doesn't ever heat up. But how much cooling do you need at -30F?

 

Mark is right, it's a PRESSURE bypass, not a thermostat.

However, I do recall a few people having issues with it opening up and staying open especially when it's very cold out.

If it is determined to be a problem, flush the coolers or just replace them.

A good tranny shop will/should replace them on a rebuild.

 

Yeah, it sounds like Wood is thinking that Ford intended to use the higher pressure of cold fluid to trigger a pressure relief valve that would in turn act as a temperature sensitive bypass valve. That would be a pretty hokey way to do something.

And if you're right Mark, and I assume you are, being the expert here, Wood is building "hardened", "heavy duty" transmissions that have a fatal flaw - i.e. a blocked cooler (or a cooler line that gets crimped by road trash?) would cause transmission failure.

Sounds like someone should send Wood a link to this thread!

 

Quote from woods 9. Each and every transmission Wood rebuilds also receives a brand-new factory Ford radiator. This is always necessary because, once contaminated with clutch material, it's almost impossible to get the same efficiency from the built-in transmission cooler. In the case of '99 trucks, Ford didn't include a built-in transmission cooler with the radiator. This is part of the reason why they had that silly bypass circuit with the check valve shown earlier. In '00-and-later trucks, they improved this design and included a separate circuit for ATF temperature regulation at the bottom of each radiator. This design helps bring the ATF up to normal operating temperature at initial start-up. It also helps cool the ATF under extreme conditions.