Too slow to low

Raider L

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@75gmck25,

Yep, yep.
What I did many years ago was I never did change out the kick down bracket from the one that was on there when I had the stock 2 bbl. on it. Why? I don't know. The only thing I can think why I didn't change it was I didn't believe I was going to use the kick down all that much. I thought I wasn't going to use it, and instead if I wanted to go through the gears would be if I was at a stand still and would have it in 1st and just floor it as in racing. I have the Auto Meter shift light set up where it has a 5.6 "pill" in the front of the light so the light comes on at 5,600 rpm telling me it's time to shift to the next gear.

I can only remember actually using the kick down one time when I found myself jammed in between two tractor trailers out on interstate and they were looking like they were trying to pen me in. So I gunned it and zipped out from between them. I do remember having to floor board it to get it to work then. Considering that, it wasn't working right then, when it should only take 3/4 throttle to get it to down shift. With the new kick down brackets I just got in I will try to get it to do just that. Then if it's still shifting to soon into 3rd in Drive, the governor needs to be re-done, maybe it's just a spring change it'll need to work like I remembering it working. Before I could floor it in Drive and it would whind out each gear. Now it doesn't matter how much gas I give it it goes right through all the gears and when it reaches 21 it's in 3rd.

When I built the truck I do remember we put a 2,000 stall converter in it, but that wouldn't make it shift sooner than the governor was getting it to do anyway, I don't believe, because I remember how it was when it was stock and I could whind each gear out in Drive, and it wouldn't shift to 3rd at low street speed but at a later, 26-28 mph. So I know it wasn't due to the higher stall we put in when we rebuilt the truck. It did the same thing it used to do. The stall converter was doing things I couldn't detect by the governor doing what it was supposed to do anyway.
 

78C10BigTen

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@AKguy, @Matt69olds,

I went to that site, AK. It was okay. But I typed into my computer, "What shift point change is there with governor spring change, TH350" And it took me to the B & M site where they have a governor recalibration kit that has several weights for outer and inner flyweights, and several colored springs. It also had a whole instruction sheet and explained what the governor was for and how it worked. What your site AK, said was that if rear end ratio has been changed then the governor is out of calibration. Well, I didn't know that!! Also it said the calibration process is trial and error, I figured that. The B & M site also interated that if rear end ratio has been changed the governor is out of calibration. It said that I need lighter weights for later shifts, or a spring change can also affect the shift point.

I have no idea what was done to the governor other than the trans was overhauled.
The problem is my physical condition has gotten so bad what with crawling under and out from under the truck that I just can't be doing it more than one or two times and I'm finished!

So I'm just going to try to get my son to help me get the truck up and I'll try to mess with the modulator valve first and maybe that will get the trans where I need it to be. But that thing about the rear end ratio change worries me. I drove it for many years and even raced it a little right after the truck was rebuilt and the trans shifted what seemed right on. It wasn't early or to late at WOT. So If the trans shop did anything at all to the governor it should be the same. But the other day I got on it with moderately heavy acceleration and it still shifted to 3rd at 20-21 MPH. Now I don't know if that's the modulator valve or the governor or both!

Now, there was some mention about the down shift cable in my TH350 that needed to be adjusted. I may look at that later. I can mess with it, but at least I know it's been overhauled and not in the terrible shape it was in. So whatever I do won't cause it to do what it was doing before. At least I hope it won't. If I do mess something up I know that I've got the time and money to get in the shop and get the dang thing right.
Good thing you mention rear end gear change... my truck has been through 3 engines, 4 trans (all th350's) and 3 rears just in the 5 years ive owned it. I did go from 3.08 gears ( whole rear swap) to 3.42 without ever changing trans governor. I personally never noticed any differance in shifts...
 

59840Surfer

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FWIW - I grow tired of all the misinformation about transmissions - especially the older one - which were my income for many years.

As a retired builder of transmissions, you need the Throttle Cable (it's not really just a 'kickdown' cable) and the modulator to work in conjunction with each other.

One affects the fluid pressure (firmness) of the shift, the other affects the timing (the modulator works with the governor to also use the driveshaft RPM).

Ultimately they ALL affect the shift timing.

At WOT - if you are really getting to WOT and there's not some carpet pad keeping the pedal off the floor ... you will then get kickdown if everything's adjusted correctly.

Are you sure it's really a THM350 and not a THM250? They look pretty much alike - same-o pan and basically the same case - but one has no Intermediate Clutch and instead uses a band to apply 2nd gear.
√ There will be a band adjustment screw and locknut on one and not the other.

The 250 usually came attached to the 307ci corporate engines, but I've found them in trucks when guys bought a used transmission from a junkyard and never realized it was the wrong unit.

Remember that they outwardly look alike and will bolt up the same.

........ unless you know the difference.

So --- the governor is basically letting the transmission drop into 1st gear as you come to a stop ... but it also affects upshifts/downshifts, coupled with what the governor says (driveshaft RPM/roadspeed) as to how far it will drop --- eg: from 3rd to 2nd or from 3rd all the way to 1st.


Recap ---> it needs both the cable and the modulator working with the governor to make it all work correctly <ahem!>

...............and your change in rear end ratios isn't big enough to really count much.

BTW: a nicely built and correctly tuned THM350 can perform and can fool an experienced builder. If they just ride in the vehicle they won't be able to tell the THM350 from a good THM400.
 

85 Squarebody76

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@Matt69olds,

And whoever else who is well experienced in TH350's. I just had my trans rebuilt. I can't give you any details whatsoever about what they did or what parts they put in. But they came highly recommended because of all the race trucks, cars old and new, and hot rods, custom purpose built vehicles they deal with those trans all the time. I felt they knew what they were doing especially since my truck is far from stock even though the trans is stock.

So here's my question, it's shifting too early from 2nd to 3rd, like at pulling away from a stop under light acceleration it's in 3rd gear at 20 mph. I've driven this truck since '81 and I have paid close attention to how the trans works and I like it going into 3rd at about 24 maybe 26 mph, and with a bit more acceleration maybe 28 but NO later. Now I know that it also would shift to 3rd if I was going real slow like as if you were looking for an address and were just slipping down the street it would shift to 3rd at 22 mph. I know the trans is set up to do that as well. That function is okay. I wouldn't want to still be in 2nd driving slow at 30 mph because I'm not far enough into part throttle yet. It decelerates okay, like it should.

And under moderate acceleration, like from a stop, you are pulling out into traffic that is at street speeds of 35 to 45 it would shift to 3rd at I think...28 mph, maybe 30 but it would take moderate acceleration part throttle to make it do that, you know? The way it's set now even under moderate acceleration it shifts to 3rd at 20 to 21 mph, no matter.
I know from hearing people on this site and from what I've read in magazines the TH350 are these soft and easy shifting transmissions and they are made that way, and a lot of people don't like that about the 350's. It's just what I've gotten used to and it's alright with me. You know everyone is different like that. I don't care for a hard shifting trans when I'm going down my neighborhood street at 25 mph, you know? I don't ever drive down them at 25 I always drive at 30 or maybe even 33. Never the less, I called the trans shop that rebuilt it and the guy said turn that screw in the modulator valve, "...a couple of turns." I made some comment and that was the end of the call. I knew to do that to the modulator valve but just to make sure that was all, that's why I called in case I needed to bring it back over there.

My other question. How much will "a couple of turns" produce in mph? And which way, in or out, I think "in"? What will a quarter turn, a half a turn, three quarter, etc. produce in mph change? When you all were helping me last year, the trans was to messed up for any changes to be working right, that's why I never fooled with it in that way. And that's why I told you all I've never messed with transmissions at all.

And I have read about the different springs that can go inside the thing, and damn it my memory, it's got the domed cover with the wire clip on it, and it's on the left side near the back kinda, that has the fly weights inside of it, I can't remember what it's called. Can't some gear shift timing be changed there as well? Help me out here, What's it called and would I need to fool with that?

Or playing with that little screw in the back of the mod. valve will be all I need to do?? And also, will changing the screw setting change all shifting, 1st, 2nd, and 3rd or just 2nd to 3rd?
Turn the screw clockwise to raise the shift points and counter clockwise to lower shift points. no more than 1 turn at a time and test drive than adjust more if not where you wand it. Raising the shift point will also raise the pressure during the shift.. so it will have a firmer shift too..
 

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