I got a TH350 for $399 from Accurate transmissions. It came with a test sheet showing good PSI, etc. So I carefully installed a B&M stage 2 kit. I used a new 2200 stall converter, and Type F fluid.

When I connect the vacuum modulator to manifold vacuum (high at idle), it doesn't even feel like a shift kit is installed, even with half-throttle. I thought this was the correct way to attach the modulator.

But when I connect the modulator to Holley 600CFM vacuum (low at idle, higher with throttle), I get firm shifts, progressively so with throttle. At half throttle, for example, shifts are real hard 1-2, moderate 2-3, just like every normal B&M TH350 kit I've ever driven.

Aside from this, Reverse seems to have slipped on me twice so far. Sometimes I get no gears at all no matter what I do with the shifter. Most of the time, it runs fine. In other words, once I start driving, it never messes up. Could my shifter cable be that bad (it's original from the previous 700R4)??

I also suspect a kinked cooler line (previous owner bent it right as it enters tranny). This I should fix, and I've already purchased a tranny cooler because of the higher stall speed.

Confused on the vacuum source bigtime... Thanks in advance.

 

It should get full manifold vacuum.

Which vacuum modulator is in it? There are 4 kinds; the big black can, and three little irridite-plated cans, with a green, pink, or red stripe.

The one you want is the red stripe. Get that kind. I don't care what some computer says, or what you look it up for; just look in the box, and get one with a red stripe. It fits 350s and 400s, Chevy & BOPC.

Once you get that, adjust it for how you want it to shift. There's a little screw inside the vacuum fitting. Adjust it half a turn for a big step, a quarter turn for a little step; clockwise makes it shift later and harder.

Hopefully you didn't mess anything up while doing the shift kit; it sounds like that's a possibility.

 

Thanks for the reply.

I realize the shift kit mess-up is a possibility, but every care was taken, plus it was upside down out of the car.

Not sure if that explains my "reverse vacuum" situation. The car/tranny loves being hooked up to the wrong vacuum source, it just runs so well it's really weird, it shouldn't.

I'll look again, but I'm pretty sure I got a small/normal modulator that's painted over. I could/would replace it, they're cheap enough, but I doubt they ever made one that "worked with reverse vacuum". Maybe they gave me a bad one, I dunno.

Correct me if I'm wrong, but isn't the modulator supposed to tell the tranny to shift harder with less vacuum (like WOT)?? Mine definately shifts harder with more vacuum.

 

No such thing as a "reverse vacuum" modulator. If you think you have one, get rid of it, and get a regular red stripe one.

If you don't know what you have, get a red stripe one.

Oh, and it's only like $12. So if you have any questions about it, go get a new one, and make sure it's got the red stripe.

Did I mention the color of stripe to look for? Make sure it's Red. Not Pink, not Green, not the big black can.

 

No matter which vacuum source you hook it to, under hard throttle you will lose vacuum. Ported vacuum on the carb has no vacuum at idle, has vacuum at part throttle, and very little/none and WOT. Not what you want to hook it to for any situation--ported vacuum is for the vacuum advance. Make sure it's a good vacuum source too...not a really small line that is tee'ed into other functions.

Hook it to manifold vacuum
Get the red stripe can (like he said above)
Dump the type F and put in dexron(regardless of what the shift kit says).
Make sure the kick down cable is adjusted correctly and working.
fix the kinked line(may be reducing pressure).
Fluid level is perfect (hot running)
See how it shifts....

 

I got the red stripe can, will install and report back. Also got a line to repair the kinked line, in the hopes it is restricting pump pressure. Fluid level has always been perfect running hot.

Kickdown isn't connected, yet. The stock one was getting jammed right at the tranny, so I bought a B&M adjustable, not installed yet. Many say it's not needed, unless you do lots of passing in 3rd which will heat the converter up. Can't get a straight answer on this.

Type F vs Dexron I also can't get a straight answer on. So much controversy. Dumping the Type F isn't really trivial. I mean the pan only holds like 3 quarts. You're suggesting mutliple flushes with Dexron I take it (I have no drain on the converter)?

 

I wouldn't worry about the Type F. For decades, before there was any such thing as a "shift kit" except for the old Fairbanks one, and when "performance" "automatic transmission" was an oxymoron (before converter modification became commonplace), we all referred to Type F as "shift kit in a can". For the years my little bro worked at TCI when they were still in Memphis, they only kept one kind of fluid.... if you bought fluid from TCI, it was Type F from the local refinery.

The kickdown cable won't affect the issue at hand. On a 350, it's not a modulator cable, like on a 700; all it does is yank the trans into a lower gear when you floor it. The trans will work perfectly without it, except that that one function will be absent.

The cooler lines are in the path from the converter to the pan. That is, the pump pumps fluid into the converter, where it gets heated up; as it pumps in, some has to move out; that fluid goes to the cooler, is cooled, and returns to the pan. So all it's doing is making your fluid run hotter. It won't affect line pressure. However, "affect line pressure" is the definition of the vacuum modulator's job; that's exactly all it does.

All in all, the only things that can cause your symptoms, are the modulator; or the shift kit being improperly installed somehow.

"The simplest explanation that fits all the facts is usually the right one."
— Occam, ancient Greek philosopher, from the days when all ATF came in cans not plastic bottles

 

Today when cold, R D 2 1 didn't engage. Revving the motor finally popped it into gear, looks like a bad sign to me.

Well the tranny had a red-stripe modulator. I just replaced it tonight with another new red-stripe. And I have the vacuum properly attached now. When the car is hot, it shifts normal, firm, no slips, all gears work. But it doesn't shift hard, like a stage 2 should, and I can't really feel downshifts, so I suspect low line pressure.

I suspect tomorrow morning when it's cold, it will mess up again, this pretty much would point to the valve body I think right (or the pump, which wouldn't be my fault)? Either I messed up the shift kit, or the tranny was defective at the start. By the way, I followed B&M's instructions to a T, only to find out later that the 18 valvebody bolts are spec'ed to a torque 50% higher in the Haynes Automatic tranny rebuild book. I doubt I can just tighten them now right? The sepator gaskets are probably already soaked.

Stage 2 B&M kit is like $30. A manual valvebody is around $150. Perhaps I should switch out the valvebody. Anyone know a good one that "shifts firm" already. Manual is a plus, but I really want to have an automatic function too. I think Cheetah makes one, but they don't say if it shifts firm.

 

Red modulator is in, no difference, original was red stripe. Fluid is perfect level. Okay, when TH350 is cold, no gear will engage. As it heats up, some slippage occurs (Forward or Reverse gears). At full temp (engine over 170) it never slips and shifts fine (though not as hard as stage 2 should be.

Is it fairly safe to assume I have low line pressure, especially so when cold? Did I not torque the valvebody bolts good enough installing the shift kit (I followed B&M's sheet, but Haynes manual calls for 50% more torque) or was the tranny sick (pump/valvebody) to begin with?? Thanks.