Bogging/stalling when braking

[blown240]

Its really easy to find a mechanic that will tell you that everyone on earth would agree with him. Just seems too odd that putting it in neutral solves the issue. That tells me that the trans or the load the trans puts on the engine in drive is the issue.

Have you checked your tire pressure and tailgate latch?

[thelawdoc]

Blown, yes, they agree that it is the load of the tranny that is causing the stall on braking. But they say the solution is to replace the carb -not re-arrange vacuums. I am not convinced...yet. I want to put the vacuums back to the 'incorrect' configuration I had when the truck was perfect and see what results. That will not cost me any money. I am finding it hard to believe that there is any problem with the carb. For one thing, I rebuilt it myself, twice now, and I did it v-e-r-y slowly. The carb is absolutely sanitized. I find it hard to accept that the carb could be bad without a human being able to see what, exactly, is bad. Maybe I am wrong. If the new carb solves the problem, I will happily put on the dunce cap.

[blown240]

I totally agree. Put them back and let us know!

[thelawdoc]

Blown, another longshot that has come to mind concerns the throttle valve disk that is in the carb. This disk mounts its shaft with two small screws. If you think about it, there are four ways to install this disk. Today, I flipped it. No change. The other two ways entail turning it 180 degrees. I do not think that this can be the cause of the braking stall -but I know how sensitive a carb can be to 'changes.' It is just so damn tedious dismantling the carb, mounting the carb, etc. (And yes, I am an idiot for not marking the disk when I rebuilt the carb last month.)

[blown240]

Interesting thought. If that plate has a chamfered edge it would be even more important to have it the right way.

[thelawdoc]

Blown, I checked that. No chamfer. And to the eye, no other variation whatsoever. But flipping the plate did bring a slight rise in rpm's which I corrected via the idle screw. So I told myself, ok, maybe I should now try turning the disk 180 deg.

Clearly, the tranny has to be loaded for the stall to occur. And not merely putting her in drive or reverse, but I have to move at least a few inches.

[blown240]

I'll be curious to see what happens when you put the vacuum lines back the way they were.

[CRGRS 66]

I have been following this mystery, and while I don't have any input as to a solution, there is one thing that made me go... hmmmmmmm. You say that if you are driving and slip it into neutral before braking you don't have the stalling issue... I don't know what this implies, but it seems to imply something...

[thelawdoc]

CRGRS 66, Yep, that is what I am thinking. The load of the tranny and a hard braking at even near 0 mph stalls her. Forward or reverse. I put her in D and give just a drop of gas to move a few inches, I give a hard brake, and she stalls. Soft brake, she does not stall. At the moment, the tranny and dizzy vacuum lines are tee'd for vacuum into the base of the carb. I understand that would be 'ported' vacuum. Tomorrow morning, I plan on giving the tranny private vacuum direct from the manifold. (I have to keep the dizzy at the base of the carb, as I understand it.) I will take the private vacuum for the pcv and have it share with the dizzy. This way, I keep the booster on a private line like everyone says I must, and I get the tranny vacuum back like it was when the truck did not stall on me.

[blown240]

Sounds like a good plan. Keep us posted!

[Jimal]

Originally Posted by thelawdoc

Blown, yes, they agree that it is the load of the tranny that is causing the stall on braking. But they say the solution is to replace the carb -not re-arrange vacuums. I am not convinced...yet. I want to put the vacuums back to the 'incorrect' configuration I had when the truck was perfect and see what results. That will not cost me any money. I am finding it hard to believe that there is any problem with the carb. For one thing, I rebuilt it myself, twice now, and I did it v-e-r-y slowly. The carb is absolutely sanitized. I find it hard to accept that the carb could be bad without a human being able to see what, exactly, is bad. Maybe I am wrong. If the new carb solves the problem, I will happily put on the dunce cap.

I wouldn't put on the dunce cap for not finding an intermittent problem with a carb you've rebuilt; that happens all the time. I'm more concerned with how secure your throttle plates are on the throttle shaft. You usually don't take those off, even during a rebuild. That new carb is sounding better all the time.

[thelawdoc]

Jimal, the two screws that mount the throttle plate are pretty snug. The threads are good. There is only one possible defect about my carb that I can see, and that is the fact that it sits on a gasket on the manifold without any spacer. Here and there I have read that my truck ought to have a 1/2" spacer between carb and manifold. But the truck has run beautifully for so many years without that spacer, I have chosen to ignore the fact for now.

[Jimal]

Originally Posted by thelawdoc

Jimal, the two screws that mount the throttle plate are pretty snug. The threads are good. There is only one possible defect about my carb that I can see, and that is the fact that it sits on a gasket on the manifold without any spacer. Here and there I have read that my truck ought to have a 1/2" spacer between carb and manifold. But the truck has run beautifully for so many years without that spacer, I have chosen to ignore the fact for now.

Those throttle plate screws need to be peened over, and peening them over is a good way to tweak the throttle shaft and cause binding. No amount of snug will guarantee you that they won't back out over time. The spacer's main purpose is to isolate the carburetor from the heat of the manifold. It also slightly lengthens the effective length of the intake runner, but not in any way an old six like this is going to notice.

[thelawdoc]

Jimal, Yes, I am aware that installation of those screws calls for peening them over so as to ensure no backout. I did not do that. I got the truck with the screws unpeened and I found they took a satisfactory 'breaking' when I went to remove them. I do not know whether Loctite was in common use back in the mid-sixties, but I understand that these days no one is peening those screws. Blue Loctite seems to be the preference today. In any event, I feel quite confident that my throttle plate is good. I spent time examining it. And others have examined it. I do not believe that it is deficient in any regard. As for the spacer under the throttle body, here too, the truck did not have it when it ran perfect. Perhaps in the future I will see if she is happy with a spacer, but for the mean time, I think I can go without it. The condition I have simply does not seem to be caused by my lacking this spacer.

[thelawdoc]

Gentlemen, well this morning I put the vacuums back to the arrangement I had when the truck was good. No change. The stall remains. I do not see any other choice now except to throw a carb at her. But for the life of me, I cannot figure what might be bad in my carb. If I could, I would send it down to Virginia and ask the FBI to examine it. Now, my nightmare is that I swap out the carb and still have the stall

[blown240]

I was hoping so bad that you were going to tell us that all is well now!

I guess throw a carb at it. If that doesn't fix it, then its a trans issue...

[thelawdoc]

If it be a tranny issue, I will really drop dead. I just did a rebuild of the tranny a few months ago.

[thelawdoc]

Wouldn't the fact that I plugged the tranny and still had the stall rule out any tranny issue?
And-
Isn't it likely that when a problem goes to six pages here on the forum, it means the engine is haunted?

[blown240]

Not if the trans problem is internal.

I know very little about transmissions, but here is one way to look at it.

When you start the car and haven't moved yet, there is nothing in the transmissions delivering power to the wheels. Once you have moved a bit, there is something moving the wheels. If that something doesn't disengage when you stop, then it boggs the motor. When you give it a bit of gas, the engine is strong enough to overcome the trans not disengaging. when you put it in neutral it doesn't matter if it doesn't disengage, because your in neutral and the motor doesn't bog.

Of course, this all could make no sense at all. Its just a thought...

[CRGRS 66]

Crazy thought here, but maybe worth trying. Maybe there is an issue with one of the vacuum hoses itself...

I had a great uncle tell me a story of when he was driving his car on a vacation (probably in the 60's). When he got up to a certain speed the engine would completely cut out, he would pull over, scratch his head, turn the key, and the car would start right up. He would start driving again, and every time he reached a certain speed the same thing would happen, repeat, repeat, repeat. He stopped at a garage, the mechanic spent some time trying this and that, until he took off the fuel hose. There was a semicircular cut on the inside of the hose, when the fuel flow reached a certain point the "flap" would completely block the fuel flow. The mechanic turned the hose around, and sent him on his way, he kept the car for many years, and never touched the fuel hose again.

Or not... sure is perplexing!!! to say the least.

[thelawdoc]

Well, Blown, then I would suspect that tranny. I recently had the tranny rebuilt, you know. And I 'know' my carb is good. I think I will bring the truck to the tranny shop and see what they say before I throw a carb at her.

[thelawdoc]

CRGRS, Yeah, I know what you mean. We have now been under the hood with this stall issue for like 3 weeks. I know every piece of dust and drop of grime in there. I am going to take the truck to the tranny shop that rebuilt my tranny recently and see what they say.

[blown240]

Hopefully there is some kind of a a warranty with your rebuilt trans.

[chevy_mike]

Not knowing about the trans rebuild, that would have been good to know. Since you kept saying it would run great until moved and you braked, I kept thinking an internal trans issue where something is not releasing after moving but didn't figure it was worth mentioning since nothing was said that anything had been done with the trans recently.

My guess is internal trans issue. Likely a band is not releasing and basically stalling the engine. No different than not pushing the clutch in on a manual trans setup.

It is always helpful to know all the info for troubleshooting a problem. Good luck.

[Jimal]

Originally Posted by chevy_mike

Not knowing about the trans rebuild, that would have been good to know. Since you kept saying it would run great until moved and you braked, I kept thinking an internal trans issue where something is not releasing after moving but didn't figure it was worth mentioning since nothing was said that anything had been done with the trans recently.

My guess is internal trans issue. Likely a band is not releasing and basically stalling the engine. No different than not pushing the clutch in on a manual trans setup.

It is always helpful to know all the info for troubleshooting a problem. Good luck.

I have half a mind to jump on a train down to Brooklyn and fix this thing myself

Unless there is something wrong with the torque converter, I don't see a stuck band leading to stalling under braking. It is also a Powerglide, which isn't a particularly complicated transmission.