Technical Cadillac 390 power loss when in gear

I have a 1962 Cadillac with the 390ci and the Carter AFB and A/C

When the car is in park or neutral I can rev the hell out of it and it sounds mean

However, whenever it is in gear it is an underpowered chugging beast.

Things performed so far:
Replaced points with pertronix
New coil
New cap
New rotor
New plugs
New wires
New intake gasket
New carb to intake gaskets
Rebuilt carb
Replaced fuel filter
New fuel pump
New water pump
New battery
New ground cables
Timed engine
Tuned air/fuel
Carter does have the metal baffle/shim under it

All cylinders have good compression
Holds 20” vacuum@idle steady
No signs of any vacuum leaks
Fuel pressure steady @ 5.5psi even under load
Car drives fine but lacks power, but can reach and maintain 75+mph
Cannot powerbrake burnout if I tried.

I did find a missing mechanical advance spring, waiting for those to come in.

Side note: FSM recommends 5* initial timing, but mine runs optimally at idle well over 15* (highest vacuum)
Idle in gear is 560rpm

I have checked firing order and all is correct.
The marks on the balancer haven’t shifted and the tdc mark is true (tested with a piston stop)

I thought it may be a exhaust restriction, but when tested with vacuum gauge the overall vacuum drops only 1” (to 19”) and maintains that vacuum at 2k rpm.

I’m out of ideas...thoughts??

 

Compression test?

 

Was just editing my post, all cylinders are between 168 and 180.

 

Dang, you covered all the bases....pondering this. Does it miss? Or just feel anemic?

 

Cant really feel a miss, but the best I can describe it is “chugging” (chug chug chug chug)

Very underpowered.

With the fuel pressure remaining constant under load/in gear I am thinking it isn’t fuel related (though I haven’t blown out the lines or checked the tank pickup screen)

The tranny doesn’t slip when in gear either just acts like you are trying to tow the space shuttle.

I will replace the missing advance spring, but I find it hard to believe that is the cause...

 

Remember a New Part in a New Box doesn't mean it's a good part.
How many miles are on it? Is the timeing chain new? Are the bushings wore out in the distributor?
Have you sprayed anything around the carburator base to see if you have a vacuumed leak? You can check timing Chain by turning the motor back and forth watching the distributor. Float level in the carburator and is the carb. The right size for the motor. That's why quadrojets had small primaries and large secondary's was to stop the bogging down on hard accelerations. Any file line restrictions and it it large enough?
Just some of my ideas

 

Get the spring in, if you are running the vacuum advance at full manifold vacuum instead of ported you may be using all your ignition advance at idle? Dunno, just a thought

 

Well I have 3 carbs and they all behave the same so I have ruled it out.

I had only 3psi fuel pressure before the pump change that got me to 5.5psi. So pretty sure hats good.

All gaskets seem fine (no leaks)

I guess that just leaves the coil/cap/rotor/pertronix?

 

Using ported vacuum and not during initial timing. I am definitely getting that spring in

 

Stuck torque converter?

 

Interesting...

 

Not sure if it helps really but here’s this:



The rattle at the beginning is a loose dash screw.

Also there’s an exhaust leak at the flange you can hear when I rev in gear.

Don’t think this helps all that much :shrug:

 

Just did a high stall test and it passed :shrug:

 

Unless someone has done some sort of upgrade on your transmission, you should have what is referred to as a Hydra-Matic 315 transmission, used in Cadillacs from 1955 to 1964. It was kind of a strange on, as it had TWO torque converters in it, one of which would be drained and filled, depending on how you were driving and the "assumed" gear... What I'm thinking is "does it feel like your gear ratio is waaay to low for your speed?? " .. if so, perhaps one of your torque converters had "locked up" or something..... there is no "lock up" clutch control in the 315. What do you think?... how about a video of you driving ?!?!?!

 

Still has the hydra-matic 315, what you describe sounds about right. I’ll post a video of me driving here in a few (once my wife gets back). I haven’t adjusted the TV Rod yet so my 2-3 shift is a bit long/hard.

 

Foggy memory tells me that they used to be called "Dual Coupling Hydra-Matic" ... There was also a "Single coupling Hydra-Matic" in 1955 Pontiacs that was waaay bad ass.. hard shifts, single torque converter...I had on in my original '49 Ford Coupe.

 

HEY ! ! A fellow Austinite ! ! ! Just noticed...

 

Aka the jetaway 315

 

Let’s get beer!!!

 

I live out near Steiner, below the dam.. going to the Steiner Car Show in the Morning.. never been before.. don't know if it's a BS deal or not.... went to the Twin Peaks South show a couple of months ago.. it was AWWWWFUL ! ! Left in 15 minutes...

 

I went to a show in temple a few weeks back...left when the Ford F-150 from 89 showed up, and the Miata...

 

hahaah.. long drive....

 

PM just sent.

 

Wonder if this adjustment has any bearing on the operation of the dual-range torque converter.

Also, with later, more conventional converters the sprag can fail and cause similar symptoms. If the sprag slips it won't lock the stator and you won't get the desired torque multiplication. The converter then effectively becomes just a really sloppy fluid coupling. Accelerating from a dead stop the car feels like it couldn't pull the hat off your head. But once you get up to a steady 30 or 40 mph everything feels pretty normal. It's not a common failure but it does happen.

 

Here’s a short driving video:

 

I am thinking it must be the tranny, it is almost as if I am starting out in 2nd gear rather than 1st...guess it is time for a rebuild.

And just my luck the ignition switch started going on the fritz...I can kill the engine by jiggling the keys, or just hitting the right bump on the road.

When it rains it pours. Already ordered a replacement ignition switch. I hate new (bad) developments.

 

Rough 2-3 shift is common on this tranny. Are you sure you’re getting 1st gear? You could drop the pan and clean out the valve body, not too intrusive.


Sent from my iPhone using The H.A.M.B. mobile app

 

I am familiar with the 2-3 shift being more ...let’s call it “noticeable”... and it really seems as if I don’t have 1st and it is taking off in 2nd...BUT...it also lacks the power in reverse...but I believe 1st and reverse use the same gear reduction...

 

Hmmm

I’m sure you already have this manual, but here’s what it suggests might be the issue:



I’m guessing tranny here. The only two things you can really service without dropping it are the valve body and governor. The TV rod wouldn’t cause this problem.

According to condition 6, it could be the valve body. It’s worth dropping the pan, cleaning the valve body and making sure nothing is broken.

Don’t read the others, they involve dropping the tranny for a rebuild (too scary).

The governor is more of a pia, but I would try that 2nd.

I am far from a brain surgeon, but I ended up rebuilding the Jetaway on my ‘60 Cad myself. If it comes to that PM me and I’ll give you some pointers.

Good luck!


Sent from my iPhone using The H.A.M.B. mobile app

 

Thanks! And yeah I have the 62 FSM. I’ve been avoiding dropping the pan, but I think the time has come...