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Old 11-21-2009, 11:59 AM
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Is this TH350 problem?

Hello guys,

I have strange problem.
If I accelerate steady, about half throttle, somewhere around 100km/h, the car stops accelerating any further and feel like engine stalls.

I am not sure it it shifts into 3rd.
I feel 1-2 shift. The transmission is rebuild with no more than 1000 km on it and this problem just appeared. It was definitely shifting into 3rd before.
The rear axle is 2.29.

Do you think this is transmission related problem?

Thanks for the help.
Ivo

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Old 11-21-2009, 02:06 PM
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Need more info what type car are you talking about Ivo?

Cole
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Old 11-21-2009, 10:33 PM
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Hi Cole,
It is 78' Monte Carlo.

Thanks,
Ivo
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Old 11-22-2009, 03:25 AM
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Hello again,
I made some test and I think I definitely do not get 3rd gear.
I drive the car in D and get stall at about 90 km/h
I drive the car in L2 and again get stall at 80-90 km/h
If I drive in L2 and shift lever to D I do not feel shift, I do this lever shift over 60km/h. Also if I shift the lever form D to L2 I do not feel the shift.
I checked the vacuum at modulator, it is the same as at manifold, 18 in Hg.

What else I need to check in order to point the problem?

Thanks for the help,
Ivo
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Old 11-23-2009, 02:06 PM
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Update and questions

Hello again,
I need some clarifications because it is my first ever automatic transmission I drive.
May be my previous reply is wrong.
It is TH-350 on 78 Monte Carlo with SBC 305, everything stock.

When accelerating, what should I feel when I reach maximum speed possible on a given gear? For example L1 or L2.

With lever positioned on D, around 70 km/h, light throttle, may be 1/3, I shift it manually to L2, there is slide increase in rpm. Does it mean downshift from 3rd to 2nd gear?

Also, what should I feel on the opposite situation, shifting manually from L2 to D?

Thanks for the help,
Ivo
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Old 11-23-2009, 04:48 PM
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You are supposed to put it in(D-for Drive) and it shoul shift through the gears on it's own when you reach certain rpm's or a certain speed.

Cole
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Old 11-24-2009, 06:37 AM
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Hi Cole,
I know this. I am trying to find out if I have transmission problem or engine problem.
The transmission was working, shifting automatically up and down.
Now I have the problems I described in my first post.
That is why I ask strange/stupid questions.

Thanks for the help,
Ivo
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Old 11-26-2009, 11:38 AM
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Couldn't it be the vacuum modulator? Also make sure the kickdown cable is hooked up properly. Or not binding.
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Old 11-26-2009, 11:48 AM
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Quote:
Originally Posted by rack
Hi Cole,
I know this. I am trying to find out if I have transmission problem or engine problem.
The transmission was working, shifting automatically up and down.
Now I have the problems I described in my first post.
That is why I ask strange/stupid questions.

Thanks for the help,
Ivo
There are no stupid questions Ivo. I would check the modulator valve as said in other post make sure the vacuum line is hooked up.

Cole
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Old 11-27-2009, 07:00 AM
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Quote:
Originally Posted by rack
When accelerating, what should I feel when I reach maximum speed possible on a given gear? For example L1 or L2.
Unless modified, the transmission will shift to a higher gear at a predetermined RPM. So if you are in 2nd. gear, throttle wide open, at some speed, the shift will be made automatically into DRIVE. If left in L2 range, upon slowing back down the shift will be automatically made back into 2nd. gear and you would feel the car rapidly decelerate under engine braking.

Quote:
With lever positioned on D, around 70 km/h, light throttle, may be 1/3, I shift it manually to L2, there is slide increase in rpm. Does it mean downshift from 3rd to 2nd gear?
This should give a VERY noticeable change in RPM and the car would rapidly slow due to engine braking, as mentioned above.

Quote:
what should I feel on the opposite situation, shifting manually from L2 to D?
As long as the throttle setting is low enough (not floored) and road speed is fast enough to allow for it (40 or more KPH?), the tranny should upshift into DRIVE. This will cause the RPM to drop noticeably. The downshift from D to L2 would be more noticeable, IMHO.

Often, the adjustments to the kick-down cable or shifter get fouled up during the removal/replacement of the tranny- I would double check them both.

Also, the manual valve into the valve body has an "S" link affair that can be bent accidentally (shown below). This can cause the tranny to be in between gears or not fully into a gear. If readjusting the cable doesn't help, you might have to drop the pan to see if the link is bent.

What was the reason for the tranny rebuild?

The cause of the engine nosing over so bad prolly isn't the tranny. I'd say that you were floating the valves, by the sounds of it.
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Old 11-27-2009, 07:42 AM
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Hello again,
Thank you very much for your answers.

As the problem was going worst and worst, it finally turned out to be loosen fuel filter nut on the carburetor (2bbl Rochester), so the engine was not getting enough fuel at certain point. I tightened it and the problem disappeared
Now it runs fine and shifts very smooth.

Quote:
What was the reason for the tranny rebuild?
It was driven without enough ATF and burned, you can guess the culprit

Besides this, the car is in bad shape and I am restoring it to as much as possible to the original.

Thanks for the help,

Ivo
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Old 11-27-2009, 07:53 AM
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Quote:
Originally Posted by rack
I tightened it and the problem disappeared
Now it runs fine and shifts very smooth. *SNIP* Besides this, the car is in bad shape and I am restoring it to as much as possible to the original.

Thanks for the help,

Ivo
Huh. Whooda thunk it? lol

Send some photos of it, or better yet, start a Project Journal.
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Old 11-27-2009, 08:10 AM
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It is very hard for me with it because it is the only Monte Carlo in the country No parts, no any one with trusted knowledge.
Further more, I am not a mechanic just computer guy doing it for fun

here are some pictures:
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Old 11-27-2009, 08:22 AM
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Well you sure picked a really nice car to work with, I have always liked that style of the Monte Carlo. A neighbor had one when I was growing up and when he decided to restore it he made it into a really nice hotrod along the way.

It went from a tan color to black and gold, I still wish I could find one and build it the same way.
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Old 11-27-2009, 08:38 AM
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Do you mean they are getting rare even in the US?
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