I got my tranny rebuilt around a month ago and I installed a vacuum modulator. Shifts were amazing but on my last trip to the track, the tranny hits the rev limiter instead of shifting to 3rd I check my fluid and it's very liquid, looks like water or cooking oil instead of tranny fluid... I can barely see the color of the fluid. I let it cool for a few hours and when I try it again it shifted perfectly.

This was last weekend. Today I checked my fluid and felt a burnt smell on the oil. I called the guy that built it for me (he's on vacation) and he told me the vacuum modulator could've made too much pressure, causing the tranny to start burning up. He called his helper and he installed some kind of sticker that is going to tell him if the tranny is overheating...

I know there has been discussion about this, but is he right?

 

If you run "too much" line pressure, it will not burn up the transmission, it will make the shifts too hard, wear out the front pump a little sooner, and in general be a little harder on parts, that's it. The sticker he is telling you about, tells him how hot the fluid has gotten. It is usually on the side of the pan. If you have "overheated" the fluid this will tell you and you can "fix" the problem by adding an external cooler, or whatever you need to do to solve this, if in fact if this is the problem. Most 3-4 clutch problems are due to capacity (not enough clutches), not enough volume of oil going to the clutches, not enough line pressure, too much clutch clearance, etc. What did he do as far as the type of clutches and how many did he use? This would be a good start. I use the vacuum modulation on all of my performance buildups, and have never had them cause any problems.

 

I've never seen a vacuum modulated 4L60E that lasted very long. Vacuum modulators are VERY bad ideas, unless you want to keep replacing transmissions. Do yourself a favor and find someone who actually knows about the 4L60E and have them take it back out, and put the EPC back in.

You might want to get someone else to work on it. If he was misinformed enough to install a vacuum modulator in the first place, he's not a very wise choice for a transmission builder.

Frank
CPT

 

I have a vacumm modulated 4l60e built by Dana at Pro-Built for well over a year. Granted no track runs, but hard as hell on the car. 35k miles later no problems. I went through 2 stock trannys in less time than that. I'm no tranny pro but the trannys seems good to me.

Satisfied Pro-Built customer

 

i was always under the impression vacuum modulators increase the life????

im looking for transmissions at the moment, 4l60Es, im looking into probuilt, any suggestions???

 

I have built many 4L60E's using the vacuum modulator, and they are doing quite well. I'm sure that there are some builders "that" have not been able to install the vacuum modulator with success, (lack of understanding vacuum modulation, and how it works) but that does not mean that other successful builders, have had problems using them. I'm sure if you look around, you will find "others" beside me, that build and use the vacuum modulator successfully, in their performance 4L60E's.

 

No track runs, and your car is stock??? Let us know how long the vacuum modulated trans last if you ever start making more HP.

Frank
CPT

 

I've understood vacuum modulation for many years. You need to understand it when you build a TH350 or TH400, which is the only place a modulator belongs (or works).

It's not just my 4L60E units that haven't worked with modulators. The fact is, I've never seen ANY that did. Well, any that are in serious performance cars.

Frank
CPT

 

Looks like I've brought up a touchy subject :ugh: