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Old 03-15-2010, 07:17 PM
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A couple problems - TH400 trans and power brakes

The vehicle in question is a 79 C-10. I recently installed the TH400 and a 454 engine. After having this truck for 3 1/2 years I finally got to drive it again. Ive only driven it once, and that was when it had a 350 and a 3 on the tree manual trans.

I installed a TH400 out of a 78 suburbanI used to have. Trans worked fine when it was pulled, however thats been about 4 years maybe 4 1/2. Now I cant get it to shift out of first. It COULD be related to the brake problem i'm having but i dont really think so, but I dont know thats why Im asking here.

The brake problem: I step on the brake, the engine stumbles and dies. Leaky brake booster perhaps? I dont know. It was fine when it was parked 3 years ago....

I did have the brake booster off so i could swap out the brake pedals and steering column. I forgot exactly why it had to come off, but for some reason it did. I dont know if this has anything to do with it or not. I also had to replace the master cylinder. I noticed some rust around the inside portion of the booster, behind the master cylinder. So maybe its bad, but my question is, is there something i may have messed up or put together wrong when i did all my disassembly and reassembly? Or is it simply time for a new booster?

If the booster is leaking too much would that cause my trans shifting problem?

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Old 03-15-2010, 07:26 PM
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Oh, I also have crap for power brakes to. Its like i get a split second of power assistance and then its gone. Gotta really romp on the pedal to get it to stop. Ugh!
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Old 03-15-2010, 07:32 PM
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Quote:
Originally Posted by Torque454
If the booster is leaking too much would that cause my trans shifting problem?
Could- if the modulator is plumbed off of a "T" shared w/the booster. Possibly even by the booster leaking vacuum enough to lower the vacuum at the port where the modulator is supplied from, but it would have to be leaking very bad- and this would make the engine run terrible, if at all- at idle, especially.

Disconnect the booster and plug the hose to see if that cures the stumble. Just remember the brakes will not be up to par. So be careful, and only do this in a safe area. But I'm betting the booster is toast and needs replaced in any event.

It could be a bad governor gear, as well. Bad gear = no shift out of first.

If it's a bad modulator, or the hose to the modulator is split or off, there will still be a shift w/enough RPM. IIRC, there will not be any shift at any RPM w/a worn out gov. gear.
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Old 03-15-2010, 07:39 PM
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The booster gets its vacuum from the throttle plate at the back of the carb. It IS unported manifold vacuum tho. The trans is getting vacuum from a port on the back of the manifold.

The brakes are not very well assisted as it is so unplugging it wouldnt hurt much. I'm pretty sure that its got to be related to that tho, or else its just coincidence that the engine stumbles and dies when i apply the brakes - even when sitting still.


Could the trans modulator go bad from getting wet? I power washed the trans with hot water to clean it up some before i installed it, im sure the modulator got pretty wet but I didn't get any water in the trans itself.
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Old 03-16-2010, 12:25 AM
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Yup, sounds like the booster is bad. Just replaced mine because of no power assist. It was also causing a vacuum leak throwing off my air/fuel ratio at idle.

As far as the no shift, check the hose connecting to the modulator and see if any trans fluid comes out. Sure sign the mod. is cooked.

Another guy just last week had a no shift problem after sitting for a few months but it turned out the hose was disconnected when he got it back from the shoddy shop he took it to.
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Old 03-16-2010, 06:27 AM
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Like Cobalt said, the trans problem is probably either lack of vacuum to the modulator or a stripped governor gear, and as he said, with no modulator, it WILL shift, but you'd have to wind it up pretty good to make that happen. Sound like your brake booster is toast.
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Old 03-16-2010, 09:39 AM
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No Shift

Governor or modulator one of the two is probably the culprit. I would replace the modulator first as it is cheaper and easier to change. Verify that the vacuum hose is in good shape at both ends.

The Governor nylon gear could have gone bad after sitting for so long. They get old and brittle and sometimes crack and break off. You can get a new one from the part's store, on line, or from the U-pull-it yard. Just make sure that the gear is in good shape and there's no wear on the shaft. There is a bushing in the TH400 that if it moves, it will wear the shaft 1" to 1 1/2" on so watch for it. If you replace the governor, don't forget the rubber O-ring gasket on the cover. Be prepared for a blast of fluid when you take the cover off. Sometimes there is, and sometimes there isn't. Better to be safe than sorry (don't tast good at all!).

I could have posted this on my first post but getting home from work at midnight, I suffer from brain fade! Sorry.
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Old 03-16-2010, 10:05 AM
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Quote:
Originally Posted by Torque454
I'm pretty sure that its got to be related to that tho, or else its just coincidence that the engine stumbles and dies when i apply the brakes - even when sitting still.
It needs fixing in any event, but the stalling out is because of the huge vacuum leak caused by the defective booster. As for whether that is also affecting the modulator vacuum, I tend to think not. If it lowered the manifold vacuum THAT severely- the engine would be running VERY poorly due to the lack of vacuum. I would think.

Quote:
Could the trans modulator go bad from getting wet?
No.
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Old 03-16-2010, 11:57 AM
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Guess my next step is to replace the booster and maybe the modulator. The vac hose is new and hooked up on both ends. I just did it the other day when I was reinstalling the engine and all.
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Old 03-16-2010, 12:18 PM
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Quote:
Originally Posted by Torque454
Guess my next step is to replace the booster and maybe the modulator. The vac hose is new and hooked up on both ends. I just did it the other day when I was reinstalling the engine and all.
Yeah, I agree. Booster first, you need it anyway. But if you want to work on the tranny problem first, just block off the hose going to the booster so there's no vacuum leak when you hit the brakes.

Then see if by chance that changes the no-shift condition.

If it doesn't, you can pull the modulator from the tranny, and using a piece of vacuum tubing hooked to a vacuum source on the engine (engine running, obviously- you are using the engine as a "vacuum pump"), hook the modulator up to the tubing and see if it retracts. You can also do this by mouth.

And if it does retract, see then if it will hold a vacuum by bending the tubing like a garden hose when you shut the water off, or by putting your tongue over the end of the tubing in your mouth.

It should hold a vacuum as long as YOU do- there should be zero leak-down. And as mentioned before- there should be no ATF in the line or the port of the modulator.

If that all checks out, the next move is to pop the wire bail off the governor cover and pry it off to get a look at the governor. It will just pull straight out.

If the gear's damaged- you will see it. Keep it CLEAN- no dirt or dust, etc.
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Old 03-16-2010, 07:11 PM
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I plugged the line to the booster and it runs fine. It even shifted. However it was hard to tell that it shifted. Its got open headers right now so its loud as can be and now with the 4.10 gears the rpms are still high-ish when it shifts. So I dont know if i just didnt hear it shift or if the shifting problem was solved by plugging the booster, but either way the transmission is now shifting.

I am careful not to get into the throttle very much because it is very, very loud and im in a residential neighborhood full of elderly people and parents with kids. I'm surprised people dont complain about it sitting there idling its so loud. I've got magnaflow mufflers for it but i can only get one side on with a strait pipe due to crossmember clearance issues on the other side. I'll unfortunately have to go to a muffler shop and have them bend a pipe to go under or over the crossmember. The main reason ive got headers was mainly so I WOULDNT have to go to a muffler shop. The performance gain is just an added benefit

Just my luck.
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Old 03-16-2010, 07:29 PM
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Quote:
Originally Posted by Torque454
I plugged the line to the booster and it runs fine. It even shifted. However it was hard to tell that it shifted. Its got open headers right now so its loud as can be and now with the 4.10 gears the rpms are still high-ish when it shifts. So I dont know if i just didnt hear it shift or if the shifting problem was solved by plugging the booster, but either way the transmission is now shifting.

I am careful not to get into the throttle very much because it is very, very loud and im in a residential neighborhood full of elderly people and parents with kids. I'm surprised people dont complain about it sitting there idling its so loud. I've got magnaflow mufflers for it but i can only get one side on with a strait pipe due to crossmember clearance issues on the other side. I'll unfortunately have to go to a muffler shop and have them bend a pipe to go under or over the crossmember. The main reason ive got headers was mainly so I WOULDNT have to go to a muffler shop. The performance gain is just an added benefit

Just my luck.
Cool! Progress is a GOOD thing!

What I next tell you is sadly, from experience.

Hearing loss is cumulative. By that (as it was explained to me by my Dr.) I mean that every time that your are exposed to loud noise, there is permanent damage done. You do NOT even have to hear that 'ringing' like after a concert for the damage to be done- but if you DO have a ringing in your ears after a show, etc.- you can BET there's been significant, irreversible damage to your hearing!

Over a lifetime (or MUCH shorter, if the exposure is severe/repetitious) this will cause you to get a constant ringing/noise in your ears called "tinnitus".

Once this begins, there's no going back, it's basically permanent. Even when you sit in a quiet room, you'll hear it. Not fun.

If I had a dime for every, "HUH?" I've used in the last twenty years, my house would be paid off.

Bottom line- use hearing protection. It's cheap insurance you won't be deaf in your later years!
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Old 03-16-2010, 07:34 PM
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Might be too late, I have ringing in my ears all the time anyways. I have for years tho. Thanks for the heads up tho. I do need to be more careful about my ears and my eyes.
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Old 03-17-2010, 12:25 AM
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Tinnitus

HUH? What he say? After vietnam and a couple of yrs bracket racing I now work in a factory and I have to wear ear plugs! Now I am deaf.
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Old 03-17-2010, 07:08 AM
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Quote:
Originally Posted by Torque454
...I've got magnaflow mufflers for it but i can only get one side on with a strait pipe due to crossmember clearance issues on the other side. I'll unfortunately have to go to a muffler shop and have them bend a pipe to go under or over the crossmember....
I generally build a new crossmember, or modify the stock one,
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