at what speed does your TH400 shift

[JointTech]

im still worried about really romping on this motor so i'm basically 1/8 to 1/4 throttle max.
i feel like it shifts from 1rst to 2nd at about 5mph. 2nd to 3rd at about 15 or 20. Once its in third it just keeps getting louder to go faster It does feel like it coasts ok once up to 45 or 50. ie I can let off the gas and it doesn't slow way down like if i held a car in gear to low.

[da-burb]

Your transmission shift points are determined by the vacuum modulator. If the vacuum hose is off or if the diaphragm inside is ruptured it will shift very fast. If you have a new modulator some are adjustable. A small straight screwdriver into the hose end of the vacuum modulator, clockwise turns, and it will raise the shift point. One of those will probably fix your problem.

[JOJABOY]

Welcome to owning a TH400 with 4.10 gears. My truck runs exactly the same way (shifts at same speeds and slows dramatically if I let off the throttle at cruise speed). I bought a new vacuum modulator for $10 or so and it was bad. Sucked tranny fluid straight into the intake and smoked like a chimney. I am saving for a 700r4 upgrade to get that overdrive gear.

[WadmalawJoe]

It's crazy, whenever I'm over 40 mph and let off it slows down quick almost like lightly applying the brakes. I'm anxious to get a overdrive transmission as well, plus gas mileage is horrible, but I didn't buy it for good mileage!!!

[JointTech]

i need to check mine. I think its a 3.7x but this thing had a 5th wheel hitch in it at some point so I wonder... Its a 14 bolt rear end so its not stock. im debating between the 200 and 700 for an overdrive. although that gear vendor over drive looks cool in theory.

[JOJABOY]

700r4 1st is lower too. Good grip and rip. Finding 700 is easy. Can install yourself. Will just need drive shaft work done by a shop.
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[JointTech]

I remember that. Ill have to check my notes (google) on why i liked the 200. I think the overdrive is taller? closer spacing between 1 and 2? Im not drag racing. I had a 700 in a 77 blazer and after finally getting it adjusted it ran pretty good.

Long dumb story here but I'm bored..
Was going to drive the blazer from Oregon coast to north carolina. Had to go up to seattle first to pickup my brother.
I had a 14ft camper trailer I was towing packed with all my worldly belongings. Plan was to mainly camp on the way back.

Well somewhere between portland and seattle the tranny started overheating. blowing fluid all over. bad scene. Expired tags and no insurance. yea dumb kid.

So I pull into a casino that has RV parking to check it out.
Decide theres no way im going to be able to fix it. It just couldnt handle the load of the trailer.
So I did what any idiot kid would do. I got all the important stuff out of the trailer and put it in the blazer. Unhooked the trailer and drove away.

Made it all the way to NC by way of seattle with only the exhaust falling off once

Never did here anything else about the camper. somebody scored. It was packed with stuff and the camper was mint.

anyway sorry for the ramble. But i think maybe thats why subconciously i have something against 700s. heheh

[JointTech]

found it. dang i didnt even make it to portland. lol.

https://maps.google.com/maps?q=Spiri...gl=US&t=h&z=18

[TBONE1964]

Maybe this will help.

There are two things on a TH400 that control shift points. The vacuum modulator and the governor. The governor is behind the plate with 4 bolts holding it on the side off the trans.

The springs in the governor control shift points primarily at light throttle. Changes to the springs affect shift points more up to 35 mph area depending on gear ratio - tires ,etc.

The weights affect higher speed shift points more than the springs do.

Later WOT shift = higher RPM will happen by lightening the weights ( inner) on the governor.

The vacuum modulator affects mostly the light throttle shift points. At WOT the vacuum will be near zero and the modulator will be ineffective.

A good trans guy can tweak shift points in without to much trouble.

[SS Tim]

THe stock shift points are in the factory chassis service manual around 7-35. There is alot of information here. In your case determining what ratio you have and equivalent tire size will give a starting place to match up to.

[JOJABOY]

There's a 200-4r in Riverside looking for a home. Guy wants $250 for it. He'll probably take $200 though. The 200 is the length of the TH400. All you have to do is move the brace back and drill two new holes. Drive shaft would work. All you would have to do is get a TH350 or 200-4r slip yoke and a conversion u-joint. Then it's the same hook up as the 700. (lock up wiring and TV cable)

[JOJABOY]

My problem isn't the shift points. Mine is the 4.10:1 rearend. My motor puts out plety of power to get the ol girl up and going. My kickdown switch is connected to the trans but there is nothing on the carb linkage to depress the plunger. Haven't felt a need to fix it. 3rd gear from 35 mph to 65 mph with plety of power.....just wishing I had a 4th gear so I can cruise at 75. LOL

[TBONE1964]

Jojaboy,

If you have a 400 trans, you should have a switch by the gas peddle that controls power to the kickdown switch on the trans.

It should be attached to the bracket that holds the gas peddle to the firewall.

[JOJABOY]

no....mine is a 69 and the kickdown swich is bolted to back of intake and is depressed when throttle linkage is at wide open throttle.

[JointTech]

Originally Posted by JOJABOY

There's a 200-4r in Riverside looking for a home. Guy wants $250 for it. He'll probably take $200 though. The 200 is the length of the TH400. All you have to do is move the brace back and drill two new holes. Drive shaft would work. All you would have to do is get a TH350 or 200-4r slip yoke and a conversion u-joint. Then it's the same hook up as the 700. (lock up wiring and TV cable)

is it on CL?

[JOJABOY]

No. Some guy from down at Pendleton had 231 and 200-4r from a mid-80s Oldsmobile or Buick or something has it. It's at a mechanics shop in Riverside. he pulled motor and tranny to install V-8 and different tranny. Sold the motor but the trans is still sitting in Riverside. He offered it to me, but I'm not in a position to start tranny swap. Just had foot surgery and don't have garage space right now. I can go find his number if you want to text him.

[TBONE1964]

Originally Posted by JOJABOY

no....mine is a 69 and the kickdown swich is bolted to back of intake and is depressed when throttle linkage is at wide open throttle.

OK, I have had 72's with 400's. I was not aware the 69's had the switch on the carb. learn something new everyday.

[JOJABOY]

Originally Posted by TBONE1964

OK, I have had 72's with 400's. I was not aware the 69's had the switch on the carb. learn something new everyday.

Yup. I have been debating on installing 71-72 accelerator pedal in my 69 so that I can go to throttle cable vice rod linkage. Think I may make that upgrade when I go to an overdrive trans.

[TBONE1964]

FYI,

Buick, Olds and Pontiac had different bolt patterns for mounting to the engine than a Chevy. Unless it has the dual pattern, it will not work for you.

[JointTech]

i better do my brakes and suspension before I get all hot and bothered on a tranny swap

[jocko]

Originally Posted by JointTech

i need to check mine. I think its a 3.7x but this thing had a 5th wheel hitch in it at some point so I wonder... Its a 14 bolt rear end so its not stock. im debating between the 200 and 700 for an overdrive. although that gear vendor over drive looks cool in theory.

if your truck was originally a sbc, then your rear end gearing would be 4.10 unless RPO'ed to an even deeper gear. If your truck was originally a 402, then it would have come with the 3.54 gearing in your 14 bolt.

My preference is for 2004R since it's roughly same length as TH350, what it would be replacing. However, if you're EVER gonna use that 5th wheel, a couple hundred dollar 2004R that was yanked from behind a 231 will definitely not hold up. Personally, I would not run a bone stock 2004R or 700R4 behind a C20 sbc or bbc. But a strengthened one - yes, I would, and that is my plan actually. But, like you, AFTER I finish the brakes... Ha. First things first.

[JointTech]

5th wheel hitch is gone. removed by po. I didnt think 14bolts were oem in 72. hmm. when i jack it up to do the brakes Ill do the count the spins trick to find the ratio.
it was a 402 originally.