Bogging/stalling when braking

[ls60apache]

drive the truck to a hill where it will get to rolling on its own in neutral.with engine running hit the brakes and see what happens. if it still stalls its not the trans.

[blown240]

That's a great idea!

[thelawdoc]

Guys,
I do not know of any hills here in Brooklyn. I know the truck will not stall in neutral on a level street. That is what I do at the lights and stop signs as I go from point A to point B. I do not see why a hill would matter. But I think I will just bring her back to the tranny shop and see what they say about it. If I replace the carb and the stall remains, then I would be sure that there is some tranny problem. There are simply no other suspects.

[TJ's Chevy]

I'm no smart geek when it comes to auto trannys, but..with my experiences..like I said in an earlier post...my 496/ 400 turbo trans combo...sometimes it will stall when I come to a stop..and I have to give it a little fuel to keep the rpms higher...no its not a carb issue...it seems to have been that way since new..I don't remember any more cause I never paid attention...Have you checked for intake manifold vacuum leaks? By spraying some carb cleaner around the intake ports you'll find out if there's a leak because the engine will stall...Replace the carb...and if that fails...then it is something tranny related...with auto transmissions it seems that sometimes there is to much strain on the engine when coming to a stop and that seems to cause the bogging and stalling...Like something is out of adjustment. Like said..I'm no auto tranny geek. In neutral if you slam on the breaks nothing happens...which means there is now vacuum leaks....but in drive when yer moving and your coming to a stop it starts to stall and bog tells me that something in the tranny isn't right...something is cause strain on the engine causing more rpm needed...Whats your idle in park? When you drop it into drive what does your idle fall down to?

[thelawdoc]

TJ, She idles at about 550-600. When I put her in drive, I think she goes down to like 450. She gives 16" of vacuum. And she stalls only with a hard brake, not soft and easy.

I also think it is something in the tranny. Because I have rebuilt this simple carb twice, cleaned her like four times, and examined it above and beyond. And because I recently had the tranny job.

I am going over to the tranny shop this week to see what they think.

[TJ's Chevy]

When in drive have you tried cranking the idle up? 450 is awfully low for an in gear idle...I think that may be your issue cause...if you think of the amount of strain in the engine from vacuum and tranny...450 is a low rpm...try adjust your in gear idle to 650 and it might make a difference...did on my 496.

[thelawdoc]

TJ, over the course of the last few weeks, I have set the idle at various points up to 900. No change in idle has really made any difference. Maybe when the idle was 200 higher, I could brake a bit less gently and avoid the stall. But no real change. The idle I have set right now seems where she is happy. Perhaps it is a little higher than I quoted, but it is pretty much as I said. Believe me, we are not talking about any idle adjustment here. Two guys have been adjusting the carb for hours in the last few weeks. Plus, a third guy also had his hands on her for an hour. They said my carb is bad. And when I mention maybe something in the tranny, they scoff at the thought.

[TJ's Chevy]

Originally Posted by thelawdoc

TJ, over the course of the last few weeks, I have set the idle at various points up to 900. No change in idle has really made any difference. Maybe when the idle was 200 higher, I could brake a bit less gently and avoid the stall. But no real change. The idle I have set right now seems where she is happy. Perhaps it is a little higher than I quoted, but it is pretty much as I said. Believe me, we are not talking about any idle adjustment here. Two guys have been adjusting the carb for hours in the last few weeks. Plus, a third guy also had his hands on her for an hour. They said my carb is bad. And when I mention maybe something in the tranny, they scoff at the thought.

Well I'd try a new carb then....3 people saying the carb is bad...something must be wrong then. The mono jet version would be a better choice then the model b imop...cheaper to. I don't recall the price but auto zone sells them for a fair price. If tranny shop fails I'd try a new carb...they only last so long...ever since I converted to a new carb on my 292 never had issues thus far. 600 cfm worth of fuel is going in there...no bogging or stalling here. lol

[Jimal]

Originally Posted by TJ's Chevy

When in drive have you tried cranking the idle up? 450 is awfully low for an in gear idle...I think that may be your issue cause...if you think of the amount of strain in the engine from vacuum and tranny...450 is a low rpm...try adjust your in gear idle to 650 and it might make a difference...did on my 496.

It seemed low to me too, but 450-500 is the number out of the shop manual.

[thelawdoc]

TJ, If putting on another carb will solve the issue, I will be overjoyed. But I find it so odd that a bunch of people can look at a simple Rochester B, dismantled to core components, find it to be in fine condition, and yet then say 'it is the carb.' If it is the carb, why can't anyone say what it is about the carb that is bad? At the same time, I find it overwhelmingly suspicious that I just did a tranny rebuild, and this stall comes about. I forget the precise idle that I have right now (I tried so many), I am pretty sure it is around 600, but I know it is the idle she always had. Anyway, no other idle has helped. As well, though I am by no means a mechanic, and I have but rudimentary knowledge about how a carb works, and even less knowledge about the intricacies of a tranny, my intuition is telling me that I have a tranny issue here. I just cannot see a carb going bad overnight. In my mind, when a symptom appears overnight, one should see what was done overnight. Here, I got a tranny job and I did a tune-up. Three guys cannot tune the carb and rid me of the stall? I am no gambler, but I am putting my money on the tranny.

If the tranny guys tell me it ain't the tranny (as I think they will likely do) I will get a carb. Then, if the stall remains, I will tell them to go back into the tranny. If the carb does solve my issue, I am going to keep the core and somehow find out what is wrong with it. I don't feel comfortable running the truck with a carb that can go bad and not show evidence of the bad part.

You mention a mono jet version. What is its advantage over the Roch B? Do you have a particular model number or vendor of this mono jet? Is it a simple, easy to adjust carb for a novice such as myself? What about maintenance and rebuilding?

Thanks, guys.

[caddyhack]

I've read through most of everyone's post but didn't see if all of the tuneup parts that you replaced on your truck were ever swapped back to the stock part (parts that were on it before the problems started)???? Is your truck 12 volt or 6 volt because most parts guys might assume it's a 6 volt system, or you may have already converted it to 12volt and the parts guy grabbed 6 volt parts.
One of my first thoughts goes to your new parts like cap, rotor, plugs, coil, etc . Did you possibly get any 12 volt parts instead of 6 volt parts? The 12 volt parts might be working good enough for you 6 volt system and causing these phantom problems! Because the kid at the part store might have grabbed the wrong part even experienced parts guys get confused on the older vehicles. or it could have even been a returned part that was put in the wrong box??? Just a thought

[thelawdoc]

Caddyhack, I am on 12v. I am pretty confident all of the parts are perfectly fine. I tested the condenser, coil, etc. And she starts up so nicely, and runs so nicely, that I cannot see any of those parts being suspects. Of course, if the tranny and carb get ruled out, I will have a real migraine on my hands.

[caddyhack]

Sometimes wrong parts ( like 6 volt parts on a 12 volt system) might work for a while but cause phantom problems. Did you check if you possibly have any 6 volt parts on your truck? It might start and run fine until it gets that one little thing to over power it's system and make the truck shut down
Most parts guys might assume that your old straight 6 motor is running a 6 volt system

[thelawdoc]

Caddyhack, Nah, there are no 6v parts on her. That is for sure. So many parts have been checked and double checked on this truck in the last few weeks, that if there be a bad part I would accuse my buddies of a conspiracy.

[caddyhack]

Do you have a list of all the parts that were done to the truck. All the parts done during the recent tuneup and even parts that were replaced within the last 2-3 months prior to the failure. Because parts go bad... Even brand new parts

[caddyhack]

Something like the starter that could have been replaced months ago could be back feeding to the ignition and causing a draw. So list all the parts that were done to see if it was something that was done during and/or prior to the tuneup

[chevy_mike]

caddyhack - 1960+ trucks are all 12 volt. No conversion would be done. The engine series (194,230,250,292) were never 6 volt setups either.

Now that we have more info (trans rebuild) and that fact it doesn't stall when in neutral and hit the brakes, I am almost 100% sure the problem is in the trans. That said, idle in gear should be approx. 700-750 RPM's for an automatic. Manuals should be 650 range.

[thelawdoc]

Chevy, I will raise the idle to 750 when in drive. Also, I just found a broken motor mount on the driver side. Could that have any influence on this weird stall?

[caddyhack]

Yea sorry. I just read through almost all of the posts. I still think a wrong part could have been installed. Thelawdoc said he isn't the most mechanicly inclined so it's possible that a wrong part could have been installed or rebuilt incorrectly. Its possible that he or all of the people that are working on the truck didn't notice a little plastic spacer or little washer is missing when the carb was apart. Thelawdoc could have tossed a little part that was needed or his kids or dog could have knocked it off the kitchen table when he had it apart for a few days like he said.

[blown240]

a broken mount may allow the motor to move just enough that it pinches a wire or a fuel line, but I doubt it. May as well change it though, since its broken.

[caddyhack]

Have you tried borrowing a carb from a buddy's car or a guy at the local weekend car shows that has the same motor? Is that possible? Rather than blowing apart your tranny. I say carb or faulty new parts

[blown240]

I wonder if a broken mount could cause the motor to move enough to bind the torque converter?

[thelawdoc]

Blown, well the motor does jump a bit when I give hard acceleration, but it does not stall in Park nor on the highway when I do that. Still, I wonder...

[blown240]

If you have somewhere local to get that mount, I would but it on before you take it to the tranny shop and they blame the broken mount.....

[thelawdoc]

Blown, I will order a mount right now. But I am trying to figure out which mounts- when I go to Summit, they have mounts for a few dollars each and they have for over a hundred dollars, and they look the same. http://www.summitracing.com/search/p...-size/4-1l-250