Almost at wit's end with my 68....

[Banjo]

I've posted alot about this problem and that, and I'm getting very frustrated (so I've taken to whining like a little girl). My buddy had this truck before me, it was running for many years with no kickdown, and I have not reconnected one when putting in 1990 Lincoln 5.0 with older top end (2 barrel). Here is scenario, which I had thought was voltage dropping into duraspark, but it's not. When I put truck into gear (any) RPM drops about 1000 RPM and it stalls. Sometimes I can get on the gas quick and take off, but after initial takeoff, I'm riding brakes to keep truck slow near the house. As I venture out into neighborhood, it'll continue to gain speed, pulling itself for the most part. IF I apply brakes or try to stop, sometimes I'll idle down low and try to stall. I have plugged vacuum line to power booster to see if it was bad power booster, no change.
Vacuum gauge in park mildly fluctuating from about 17-19 inches vacuum. New distrib/rotor/cap, used duraspark, new plugs/wires. Motor ran fine in Lincoln it was pulled from in junkyard. New metal vacuum line from intake to modulator with new rubber line at each end. Should vacuum be higher in park (can't check in gear alone)? Motor always sounds like slight vacuum leak or miss. Cannot find anything with carb cleaner or propane (around carb base, intake). Here is what really cooks my chicken (I can tolerate mild miss), but cannot tolerate the overly high idle in park (have to have idle screw all way down in 2 barrel motorcraft carb to have enough RPM to not stall when put into drive): put in drive, it won't shift out of first until I manually pull it down into second. Once in 2nd, it won't shift into 3rd. When I move shifter from 2nd to drive, no 3rd gear. Pulling vacuum line off modulator, no trans fluid leaks out. New Trans fluid/filter in C-6 that was rebuilt about 5 years ago.
I'm at my wits' end why rpm drops about 1000 rpm from park to gear (either reverse or forward) and I'm at wits end why transmission won't shift. Are these related problems? What I'm worried about is I jammed transmission bolting together alone (despite installing probably 6 transmissions before this one), by not properly seating torque converter, so I had to remove C-6 and have trans shop go through it, replacing 2 cracked gears, and they installed reman torque converter. I'm worried something else now wrong in transmission causing the vacuum problem (or what I presume is one) when trans put into gear and lack of proper shifting. In fact, there is no 3rd gear. I have considered capping off vacuum to trans and making short run with no modulator, and trying manual shifting to see if I have all 3 forward gears and to see if lack of vacuum connection to transmission stops this 1000 rpm drop from park to gear.
Complicating everything, when I was trying to adjust shift linkage, truck jumped forward in gear upon start and now even with linkage disconnected under truck, column shift hung in park and won't come undone, so I'm taking steering column apart to see what's hanging that up. Please, I need help, I've fought this truck harder than anything before in my life and getting most frustrated and it shouldn't be this hard. Banjo.

[spartman]

Sounds like something funky in your tranny.

Have you tried to put a different tranny on it instead?

Also sounds like you have a vacuum leak somewhere around your intake.

[Banjo]

No, I'm really trying to avoid pulling the transmission. I tried carb cleaner around intake and propane, all the way around, and no idle increase. I've had 2 different 2 barrels on it, with same deal and one was rebuilt by a friend who's pretty good. I can't get over the significant rpm drop between park and gear and why trans doesnt' work properly. Is there a certain amount of vacuum required (in gear) for modulator to function properly?
I have considered taking the 2 barrel intake off and buying a new aluminum intake and popping on it, and I have a functional Edelbrock 600 on my Chevy II that needs a larger carb.

[spartman]

Suppose you could try to clamp off the modulator line and see if that helps.

Sounds like something isn't kosher in that tranny though.

If it were a cheby I would say slide underneath and take the flex plate to converter bolts out and then slide the converter back away from the flex plate and try to run the truck that way.

Since it is a ford i believe it has the studs sticking out of the converter so I don't think you can slide the converter back from the flex plate far enough.

[averagef250]

I got a 70's chevy in my shop a long time ago that did similiar things. The guy just put a cheezball reman 350 in it. That thing baffled me. Tried everything to get it to run right, engine wouldn't run right, turbo 400 wouldn't shift. I finally found out what it was on the 5th test drive when the engine locked up solid. The reman shop didn't install the oil pump driveshaft. I just figured the dash oil light didn't work right. Dropped another 350 in and everything worked perfectly.

I would try to get the engine running perfectly before blaming the transmission. If you disconnect the modulator I'd expect the transmission not to want to shift until redline. Sounds like a big intake leak to me, but 17-19"s at idle doesn't make sense.

[Banjo]

Now, let me clarify, because I did type too much, the 17-19 inches of vacuum were in park. Being alone and not having long enough hose for vacuum gauge to run up to top of cowl and tape to windshield (for example), I don't know what vacuum is dropping to in drive.
Temp runs around 180, oil pressure around 60 cold and drops to around 20 or 25 when warm. I agree it does sound like intake leak, but I'm surprised neither liberal doses of carburator cleaner, nor propane give any indications.
I thought I'd found it when I found bottom gasket below carb plate was blown over some heat riser area, changed that, built metal plate to completely block off this heat riser thing and sealed things with permatex red, which is usually very good stuff. Going around whole carb base with it running with hands and carb cleaner, no idle increase, feel nothing. I do agree the drop of about 1000 rpm from park to gear sounds like massive vacuum leak, but nearly 20 pounds (in park) sounds good, but maybe it's dropping alot lower in gear and not enough vacuum for modulator valve to function properly???

[Freightrain]

The modulator only controls shifting. After accelerating, it reads a high vacuum signal(as load on motor decreases) and tells tranny to shift.

Have you check timing on this motor?

[green68250]

I have a '68 with a 390 2bbl and mine was doing the same thing. I had to have the idle screw all the way down to get it to stay running when i put it into gear. I rebuilt my carb and everythings fine now. I wasnt having the tranny problem but it might not hurt to rebuild the carb for 20 bucks or so and see if that helps.

[REDNECKMOBILE]

I don't know the setup for that motor but I would solve the dying motor before working on the transmission. My bet is you have a vacuum operated emission device acting up and its killing the signal to the carb or you have a carb that needs work. When changing motors I always use pre-1970 carbs and intakes just to get rid of the emission stuff. I don't know if that motor will take the early parts but I would remove anything that works from a vacuum first since the vacuum signal is varying on your motor plus the high reading tells me that the timing will need some adjusting once you get the motor to take gas. Good luck.

[69rangerman]

Didn't have the tranny problem but when I had the small block rebuilt I made the mistake of using universal fit carb gaskets. Had to keep my hand on the throttle at all times to keep it running. Turns out that even thought the gasket looked OK it was a tiny bit not wide enough and was just sucking a huge amount of air.

I switched out to a model specific gasket and it started right up.

Good luck.

[Banjo]

Well, it was a rebuilt 2 barrel (by a friend who's pretty good), and new intake gaskets. I've gotten aggravated and bought an aluminum intake and intend to install that along with a known good 4 barrel of another project of mine that's running (Edelbrock 1406), so I'm eliminating variables. Already tried blocking off line to power booster for brakes, thougth it might have been bad, wasn't.
Hope it's dry this weekend so I can tinker. Banjo.

[Leadfoot]

not knowing what rpm your idle is set at is not helping diagnose

and the trans not shifting is more than likely telling you something.
if its not screwed linkage, or low fluid. its got to be a vacuum problem.

also you got a egr intake? is the egr valve screwed?
t-chain good?

1st the propane/or what ever works at times to help find a vacuum leak but a simple hand over the carb works better if the rpm rises you got problems.

2nd what distributor are you running, dose it have vacuum advance or retard? and dose the pot leak?

3rd are you trying to tune the un-tuneable, check the carbs throttle shaft if there is play, replace the unit. and a compression test would be a good idea also.

also I find then the blind is leading the blind a couple cold beers are in order

[69rangerman]

I wasn't going to mention it, and am not encouraging the expense but I ended up going to a edelbrock 1405. What a difference.
The old 4100 was sucking air around the throttle shafts which kept the idle and power messed up.

I got the 4100 to work with the correct gasket but it was just too worn out.

[Banjo]

Leadfoot, you're right, it's bad of me to ask for diagnostic help with no info to support. I do need to buy a tach, and check my timing and provide numbers, and do need to check vacuum (in gear).
One thing for sure, when I install new intake/carb, I hope to eliminate this. Perhaps I missed a spot on back of intake that is a big vacuum lean that maybe propane/carb cleaner aren't getting to, and I have not tryed hand over carb. Hope to monkey with it some tomorrow if not raining, I can handle cold outside, but not getting rained on while it's cold.
Hope to resolve and post good news one day, I do agree I think it's vacuum creating transmission problems. Banjo.

[fordman]

has anyone mentioned the vacuum modulator on the transmission yet? the hose on it could be bad creating the vacuum leaks. and or the mod could be bad. although to me this doesn't sound like the problem. it could be something to check out.