I have a 1966 mustang with a automatic transmision and v8 engine. my question is: why does my car only shift once from standing still. I am only able to go about 40 mph at high rpm and the car wont shift? I want to go faster but the trans wont shift and the engine is in high rpm.its like that's the top speed of the car. I want to know if anybody knows why?
2006-11-02 06:20:06 · 10 answers · asked by gmv20002000 1 in Cars & Transportation ➔ Car Makes ➔ Ford
90%+++ odds it's one of 3 things
Vacuum Modulator is bad.
they cost 10~15$,,you can replace it yourself in minutes with no special skills or tools.
Vacuum SUPPLY is bad.
Broke hose,,COLLAPSED hose,,,a Different hose broken on same vacuum source,,,
a Plugged vaccuum port.
Downshift/Kickdown/"passing gear" Linkage stuck in actuated position.
the kickdown Lever on the trans is VERY loose & light,,,feels like its connected to Nothing.
The ROD from the Carb is plenty More than heavy enough to operate the thing on WIEGHT Alone.
It has a "return spring",,,,the spring actually SUPPORTS the rod's weight.
without the spring the trans gets stuck in Kickdown mode.
Which makes trans shift on Governor Control Alone.
MAX RPM,,,way above 40mph in 2nd,,,50~60mph
Even 50mph is 25% more RPM than 40mph.
Same effect as holding gas pedal on the floor till it shifts.
C4's been around a while,,probably well over a Billion miles worth.
What they do,how they work,how they fail ,etc hasn't been any mystery for about last 30~40 years
If it's SHIFTING from 1>2,,and back down to 1,,
It's functional.
maybe wore out,,maybe weak.
but it's working.
No matter how "Broke" it seems.
Because of the car's age,,and the engine's condition being an Unknown,,,
I cannot reccomend you trying a full throttle Governor Shift to hi-gear.
Those cars DOWNSHIFT at HIWAY SPEEDS,,programmed to do so in the era of 70mph Legal Speeds
Assuming avg size 14" tires 13.5" radius???
a common 3:1 rear axle
40MPH is ONLY about 2200 RPM in 2nd gear
2200 RPM in HI is about 60mph
3500 Rpm in Hi,,is about 90~95mph
In 2nd gear,,thats about 65mph
4100 RPM is about 75mph in 2nd gear
and 110 in HiGear
If You'd run a typical C4 Trans in a Early Stang w/ 3:00 Axle and 14"tires....
You'd have to run it OVER 70MPH to produce a Full Throttle,Governor Controlled UPSHIFT to 3rd
3500 to 4000 RPM at least
That's "up there" on an old motor,,,roughly 100MPH equivalent in Hi Gear.
But not really all THAT hi an rpm with engine "unloaded" by being in 2nd gear
But if You did run it "stuck in 2nd" up to 65~70~75,,,You'd probably find it would shift into 3rd all by itself
3500~4000 would shift to HI,,and rpm would fall back to 2200~2500 rpm @ 65~70mph.
It MIGHT downshift itself AGAIN though,,if Kickdown is stuck down.
It would "Think" You floored the gas pedal" again
But in any case,,,40mph in 2nd is nowhere NEAR fast enough to see if it will shift itself into Hi Gear,,,
when You have probs with Modulator or Kickdown lever
ASSUMING the tire size and axle ratios I guesstimated are Close,,
Your car needs to go about 65 in 2nd gear before a upshift will occur...thats about 3500 rpm
It oughta do 4000~4200 Safely--that's between 75~80 in SECOND GEAR,,just to put things into perspective
Which is inline with what i said ealier,,
1966 Cars were made to downshift at Hiway Speeds in the era of 70mph speed limits
A "NEW" '66 Ford 289 would do 5000~5500 RPM reliably and safely,,,over 95 MPH in 2nd Gear
Point is,,Cruising along at 70,75MPH ,,
A Driver could floorboard the gas pedal,,
Forcing Downshift to 2nd gear at 75,,,
and ACELLERATE from 75 to near 100mph in 2nd gear before engine redlined.
I'm sure your trans is fine and shifts to 3rd EVENTUALLY.
But at even just 40mph,,it sounds & feels like engine is fixing to fly out the car.
But,,Not even CLOSE
2006-11-02 12:38:59 · answer #1 · answered by Anonymous · 0⤊ 0⤋
try a trans. conditioner fluid from local parts store most of the stuff you pore in when the trans is hot drive 20 miles let sit over night then try it again most have seal ex panders it worked on my 66 sedan de ville good luck
2006-11-02 06:27:21 · answer #2 · answered by great white fisherman 4 · 0⤊ 0⤋
First thing to check is the shift modulator ( if it doesn't shift into third ) and the vacuum line that feeds it
2006-11-02 06:23:03 · answer #3 · answered by Anonymous · 0⤊ 0⤋
The vacuum modulator on the transmission may be bad or the vacuum line may be off.
2006-11-02 14:20:07 · answer #4 · answered by Josh S 7 · 0⤊ 0⤋
You have probably got a valve stuck in your valve block its not allowing any upshifts.Also your govenor might be stuck changing your transmission fluid may help Mick UK
2006-11-02 06:24:38 · answer #5 · answered by mick 6 · 0⤊ 0⤋
go to trany shop. may be modulator.... my ranger needed one. 75 bucks fixed it did u check fluid...of course u did.
2006-11-02 06:25:36 · answer #6 · answered by Anonymous · 0⤊ 0⤋
Transmission is slipping. (going out)
2006-11-02 06:22:48 · answer #7 · answered by The Hit Man 6 · 0⤊ 0⤋
your tranny is going out, third gear is either gone, or vavles are stuck
2006-11-02 06:22:41 · answer #8 · answered by Anonymous · 0⤊ 0⤋
your right, thats top speed. learn to live with it.
2006-11-02 08:46:11 · answer #9 · answered by eastcoastrockerdude 3 · 0⤊ 1⤋
You need a new tranny.
2006-11-05 10:16:47 · answer #10 · answered by George K 6 · 0⤊ 0⤋