I ditched the t56 all together and was gonna go the 4L80e route, but picked up a th400 trans super cheap, and decided to roll with that instead. I've scoured the net looking for ideas on how to fix the issue with the vacuum modulator on these transmissions, and so far the only two ways i've found are a mechanical modulator or the inline check valve. From my understanding the check valve won't handle very much boost pressure, or you may have to run more than one, and that just doesn't interest me at all. The mechanical modulators are no longer made, and finding a used one isn't all that easy.

So my question is, what is a permanent, sure fire fix for this issue? I'm sorry if this has been asked before, but i've spent hours upon hours looking for the fix and still haven't gotten the answer i'm looking for.

Thanks in advance guys, and sorry if this is a common topic, and I just missed it.

 

I should say, i'm trying my best to avoid going to a manual valve body, really don't want to do that. I guess if the best fix is the check valves, i'll just do that and run a couple, but i'm weighing my options here and trying to see if there is something else I can do while the trans is apart.

 

I can still get mechanical modulators.

 

Would a check valve work not work fine? I'm also interested in hearing a solution

 

Check valve usually works fine, but oftentimes you need two in line to bleed off the pressure.

 

Mechanical modulators are $150, you'll also need a 700 TV cable.

Jake

 

The mechanical route definitely sounds more appealing to me. Jake, i'll shoot you a pm, i'm rebuilding a th400 trans right now and already made up my mind about buying parts from you. Maybe you could get me a list together of what all I need to stuff in this thing?