Car running bad/stalling in gear help!

[OldCarPilot]

57 Bel 4 dr HT with a aluminum powerglide and 355 engine Holley 750 vac secondaries. Car runs and idles great when not in a gear. If I put it in any gear the RPM drops about 500 and the car threatens to and eventually stalls. This is really bad at an intersection as I need to go into park to get it started again. I can't for the life of me find any vacuum leaks as that is the first thing I looked for. I sprayed carb cleaner around the edge of the carb looking for leaks but that all looked fine.
Any ideas? This is driving me crazy!

[desertratrodder]

Does it have a vacuum booster? Or a modulator on the trans? (Not sure if P/G has one). If so plug each line off to check them.

[porknbeaner]

There is a vacumm port/hole behind the choke assembly on the passenger side. I've had more than one leaking there, never showed up when spraying the stuff around.

This year I found a new one on a 3310. The diaphragm for the secondaries had a tear. That didn't show up when I was spraying stuff around either.

Probably isn't the problem, but it wouldn't hurt to check.

A friend of mine always tells me to check out the line to the vacumm modulator on the tranny and the modulator. I've never found a leak there but he evidently has.

[skipperman]

oldcar...... if the stuff before this post won't fix it then try changing the power valve in that Holley.....'SPECIALLY if had backfired before the problem began...(even a LITTLE backfire)

Jersey Skip

[OldCarPilot]

Did the tuning and still no luck. Replaced the powervalve. Get about 15in of vac at around 800 RPM with the car out of gear. Put it in gear and it goes down to about 9in. Car does its stumbling deal and seems to almost want to quit and sometimes it just cuts out. Can this be transmission related at all? Tq Converter?

[Rocky]

15 in. isn't much vacuum for a stocker motor unless you have .
1.a vacuum leak
2.. plugged exhaust
3. timing retarded
4... lumpy cam
Might see if your timing is a bit slow and you didn't tell us if you had a lumpy cam in the 355. If so, you may wanna go with a stall converter.
Easy test for plugged exhaust is to idle the engine and record the vacuum reading...15 in. in your case...now, bring the rpm's up to about 2000 and watch the vacuum gauge. If everything's ok, it shouldn't drop by more than an inch or 2. If the reading slowly drops as the rpms go up, you gotta plugged system...I've seen plugged cataclysmic converters drop to 1 inch vacuum...
good luck

[OldCarPilot]

The motor does have a mild cam in it. Comp cams xe262. We sort of "covered the problem up". Didn't solve it. It seems like it goes better when we open up the mixture screws beyond where it sounds like they should be, running rich. Turned up the out of gear idle up to about 1000 RPM and it seems MUCH better when we put it in gear. But the problem still exists. We have gone through and plugged up one at a time each vacuum port on either the carb or the intake and still does it.

[Elrusto]

Im ASSuming you have an aluminum intake? What kind of gaskets are your using? This is from Edelbrocks web page:

2. DO NOT use the Fel-Pro Permatorque/Blue intake gaskets. Because of their very hard, non-pliable construction, they don't compress well when used with an aluminum intake manifold. Instead, use a Fel-Pro Printoseal or Mr. Gasket UltraSeal gasket. The factory composition-type embossed gasket also works satisfactorily.

I had the same problem you are. TWICE!! Mine was leaking vacuum from under the intake in the lifter valley. Did what they said and cured the problem.
BTW,the problem on mine started about a month after I got the car on the road, instead of right away.

Mike

[OldCarPilot]

I got the special felpro vortec intake gasket for this intake. Hell The thing may have slipped or something I don't know.

[Deyomatic]

Is there ANY way at all that there is something messed up in the Torque converter that could be causing this? You know how people with a hot motor have to put it in park if they don't have a high stall speed, is THIS our problem? Does it react like you have a vacuum leak and then stall out when your TC's stall speed is too low? I'm sure that with how half assed everything seems to be from the previous owner, this is a stock torque converter, and the motor is theoretically 400+ HP, according to the recipe he followed. It performs perfectly when it is being driven, but it gets sketchy when you stop or idle in gear, but not always.
We can't help but think that if this had a manual tranny, we would not even notice any problems at all.

[Pist-n-Broke]

OK, I'll agree it sounds like a vacuum loss. 15 inch lbs. isn't much to start with. With all you have already done I'd do one more thing. Remove the carb and whatever spacers you have then closly inspect all gaskets. You should have solid imprents all around everything. Sometimes a serious leak is bad enough not to show up with the carb cleaner spray trick. You obviously have a bad one. I've found more than one miss fit between manifold and spacers. You obviously pluged the 3/8 port in the base of your carb.
The Wizzard

[a/fxcomet]

How can this be a torque converter problem??? I have a bigger cam (Comp XE268) in a smaller motor (289) and I ran it for quite a while with the stock converter. No problems- it just didnt jump off of the line as fast as it does now http://www.jalopyjournal.com/ubbthreads/images/graemlins/smile.gif

I'm guessing it just started doing this, right?? Or has it done it since you put the motor together?? I think it might be a vacuum leak too.