Hi everyone!
I have a 74 Impala with a 400 cid 2 barrel thats had a problem leaving me stumped.A year ago,the car suddenly lost some power,it will barely peel the tires out in gravel when I power brake it.So,I decided a tune up will do it good.Got new plugs,plug wires,distributor cap,rotor,air filter and changed the oil.Car still ran like crap and the tune up didnt make any difference.I checked the timing and timing was good.Did a compression test and I have 140 PSI in all cylinders.Decided to rebuild the carb and cleaned it out of every orifice possible,new fuel filter,choke works,got good fuel pressure,still ran the same(gutless)Decided to borrow a friends 2 barrel as his wasnt as old as mine and in better shape,still ran the same.Did a vacuum test and the vacuum is at 18 kg.Ive checked everywhere for vacuum leaks,even checked around the intake and carb using carb cleaner in thos areas while the engine was running.No change in RPM while spraying these areas for leaks.I did notice the other day I noticed I was leaking transmission fluid and discovered it was coming out of the accumulator(its a TH350) Replaced the o-ring and spring in the accumulator(which was broken) and decided to also change the trans filter and gasket.Did that,filled it with fluid,checked it frequently after it warmed up and going through all gears.Hoping just having a tranny leak and low fluid was my problem,took it for a test drive,nope still ran the same way.Checked to see if all cylinders were firing,they all were.Coil is good also,getting a very healthy spark.The thing is,when I open the accelerator all the way,it barely goes over 30 mph and dosent seem to want to shift.What is wrong?The engine sounds very healthy,no smoke,no overheating.This has stumpted me.Is my compression too low?Is it a transmission problem?The car just feels like something is holding it back.Any help would be appreciated.

 

when you say accumulator, i assume you're talking about the vacuum modulator. pick up a new one, just be sure to look for the color stripe on it and get the same one. also, what is your timing set at at idle, with vacuum advance plugged off? do you have a timing light that will read advance? it could be the vacuum advance unit on distributor. cheap part, just get the OEM numbers off the unit to match it up at parts store.

 

Hi RiceNuker1973,

Welcome to the Chevy Forums.

!974 is a cusp year when they were changing over to HEI for GM ignitions. Do you know if you have HEI? If not, did you change the points AND condenser?

Many people don't realize that on point systems, the condenser keeps the spark release compressed to give the sparkplug it's maximum combustion. If it isn't changed, larger and larger losses of power occur, as well as startup problems.

The shift modulator will leak transmission fluid into the intake if the diaphragm is broken, causing a lousy idle, and a crappy 1-2 shift. If you remove the vacuum tube coming off the modulator and there's tranny fluid, replace the modulator.

 

Thanks for the reply.Its the circular cover that is in between the filler tube and modulator on the TH350.I believe its called the clutch accumulator.Thats what was leaking.I set my timing to stock specs,8 deg BTC @600 RPM with the vacuum advance plugged off.No,i do not have a timing light that reads advance.I will look into that and the vacuum advance.

 

thanks for the welcome
The car does have HEI,the coil is also new.I will check the modulator and vacuum advance today.

 

OK, HEI, check your ECM inside your distributor. The plate on the bottom is lubricated with dielectric silicone grease. If it dries up, you start having trouble. If you can have your ECM tested, do so, but you might just want to replace it, assuming it's original.

 

I didnt get a chance to work on it today.I will mess with it tomorrow.Ill check the ECM,It has been replaced,but that was in 2000(10 years ago)

 

hi,an update.Its been raining all weekend and today was nice enough to work on the Impala.I didnt get the ecm checked,but out of curiousity ,I pulled the vacuum modulator from the transmission I discovered there is fluid going into the vacuum side of the modulator and also when I shake it,it rattles.I bought a new one and it doesnt rattle.Modulator bad?

 

Well,i installed the modulator and it still runs the same. Im really thinking my transmission is on its way out or the torque convertor as the car did sit for awhile with barely any fluid and even before I let it sit,I still couldnt get it past 30 MPH even with the gas all of the way down.The car shifts ok,but is very slow and soft shifting into reverse.I did change the fluid and filter with the same results.
I did notice also Im losing some brake pressure sometimes.I wonder if my master cylinder or brake booster is going bad.Im at my wits end.Gotta love these older cars.

 

OK, so the tranny fluid is going into the engine?