Car won't run past 60mph

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67/6barracuda

67/6barracuda

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Guys,
Here's the deal my 360/727 with a 2.76 rear gear is running 4,000rpm topping out at about 60MPH. It pulls like a freight train getting there. But with the 2.76 I thought for sure id have a high way cruiser. I have 318 heads which I know is choking it out on the big end. But even still I shouldn't be running at such a high rpm at 60mph. I think it may be a trans issue. I do have all three gears shifting fine. This drive train did come out of a RV so I was thinking is there a limiter or something up with the stall converter. I was going to try and do a basic service on it with a new filter and adjust the inner and outer band. Shifts somewhere around 15-20mph to 2nd and around 30-35 for 3rd but then revs out from there.
 
These transmissions don't slip like that without almost instantly frying the fluid, so I would have to say there is a converter problem.
There was never any kind of limiter either.
 
TrailBeast said:
I have 2:73's and ran 120 with basic mods on a 318, so something if definitely up.
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Yeah im a bit confused by it my speedo was off a little. So i used a GPS and even still 71mph was my top speed screaming around 4 grand, something is not right. I do hear a slipping/surging sound if I am around 20-40mph and goose it but besides that no other issues the shifts seem fine. I been trying to baby it until i figure it out. I installed this motor with trans from a junk yard and put it in the car so i have no history really on it other than being told it was from an RV.
 
It gets full throttle. I tried un-hooking my kick down cable to see if that would have any affect. But that didn't prove anything still ran the same.
 
I could get to 70 MPH at 4000 RPM with a 3.91 gear....

Something not right....
 
Have you run the car with another engine/trans combo and it cruised okay?

I would narrow it to the rear gear or transmission issues. You may need to pop the pan and check the band adjustments, then top with new fluid.

Before you do that try and make sure that it is actually engaging third gear. I used to have a gearbox that had a damaged shift link and it did not like shifting properly until I put new links on it.

- boingk
 
I am not 100% on the gears the tag is missing. I also don't recall driving any faster than 70mph when the slant six was in there. I didn't have much seat time before pulling the motor. I guess there's possibility of a steep gear maybe something like 3.91's but in a /6 67' barracuda with a 7.25" rear? I better figure out what gears are in there this weekend. Whats the back yard mechanic way to determine the gears?
 
67/6barracuda said:
I am not 100% on the gears the tag is missing. I also don't recall driving any faster than 70mph when the slant six was in there. I didn't have much seat time before pulling the motor. I guess there's possibility of a steep gear maybe something like 3.91's but in a /6 67' barracuda with a 7.25" rear? I better figure out what gears are in there this weekend. Whats the back yard mechanic way to determine the gears?
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Jack up the rear tires, put the trans in neutral. Spin the tire one full turn and count the turns of the drive shaft...
 
Pedal to the metal should get more than 4k rpm. My best guess... First your original slant 6 throttle cable isn't getting WOT. Second, Wrong throttle pressure linkage and/or adjustment has damaged the trans. You said you disconnected it too which was a bad move. I could go into how a tiny plastic bushing cracked, fell out, made about 1/8 inch lost motion in throttle pressure cable, and killed 1000s of Ford transmissions but I regress.
A torque converter OEM for a much heavier vehicle is wrong for your passenger car too.
Without knowing the cars history ( maybe a previous owner put a different rear under it ) a 67 slant six B'cuda would have a 7.25 rear w/276 gear.
 
I would suspect all of the above, different gear ratio, wrong throttle cable, messed up trans...but then I noticed your running a quickfuel set up

ill admit I know NOTHING about those things BUT it is something different, and therefore...suspect
 
Either you are not getting 3rd gear or something is slipping. Badly.
 
I'm afraid you have a worn out rear clutch set in the trans. If I recall, forward direct drive is through rear clutches.
If they are at their last gasp, you get exactly this symptom. Other things I've personally experienced that do this are internal pressure leaks to the rear clutch, and once I had a torque converter start sucking air and buzzing. When the fluid got foamy enough, the clutches wouldn't engage until I sat on the roadside and waited for the bubbles to come out.
Good lyck.
 
2.93ringgearjpg.jpg
So far I confirmed that I do not have 2.76 gears, I have the 2.93 gears close enough. Says the stamped ring gear. So I added some fresh fluid to the diff and ruled out that its not the gear ratio keeping me from going past 71mph in third gear at 4,000 rpm. It would have been nice to see 3.91's on the ring gear that would have made more sense. So I bought a filter and ATF+4. Next is to drop the trans pan check things out and adjust the band's and see if that makes any difference at all. I also have the common kickdown lever shaft leak. Is it a pain to remove the valve body to change the gaskets on the kickdown shaft?
 
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Are you getting into 3rd gear? Those numbers sure sound like 2nd gear. And it's the front clutch pack that wears out and causes no 2-3 upshift.
 
C130 Chief said:
Are you getting into 3rd gear? Those numbers sure sound like 2nd gear. And it's the front clutch pack that wears out and causes no 2-3 upshift.
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Yes i get all three gears but it feels like something is holding the trans back. I also don't think its totally slipping either. I can from a dead stop gas it and it runs right through the gears but at 60-70mph the motor just seems its trying to hard to move the car. I also notice while backing in reverse it seems to take an unusual high rpm maybe 2000-2500 rpm before its grabs likes that when it stalls and grabs. But in drive it grabs around 1200-1500. Its trial and error, these are the things you deal with when buying a unknown motor and trans from the junkyard and just take a chance on it performing. So far the motor runs great I just got to get it tune a little better. I keep playing with the timing to see if it makes a difference so far no luck. Right now im at 10BTC all in at 2500 total 34degrees but i just tried hooking up to the manifold vaccum to see by chance it would run better. I honestly think im pulling to much fuel pressure for my carb so I got to check that out as well.
 
C130 Chief said:
Are you getting into 3rd gear? Those numbers sure sound like 2nd gear. And it's the front clutch pack that wears out and causes no 2-3 upshift.
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I worked out the RPM's for 27" tall tires, 71 MPH, 2.93 gears, and the trans being in 2nd gear, and it comes out to 3800 RPM. Sure sounds like it is stuck in 2nd.......Is there a definite drop in RPM's of over 30% when it makes what you think is the 2-3 shift? Have a tach?
 
nm9stheham said:
I worked out the RPM's for 27" tall tires, 71 MPH, 2.93 gears, and the trans being in 2nd gear, and it comes out to 3800 RPM. Sure sounds like it is stuck in 2nd.......Is there a definite drop in RPM's of over 30% when it makes what you think is the 2-3 shift? Have a tach?
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Your calculations lead me to believe that its not getting third. I have a 215/70/14 tire which is about 25.85" but i don't think that would change the equation much. However, it definitely makes the transition or feels like its shifting to third. But maybe its just kicking it back down to second as it makes the transitions. I probably should have made a video. Its now on jack stands so i can spend more time on my back rolling around on concrete. Ill see what the trans shows me when i drop the pan and make some adjustments.
 
mbaird said:
make sure you are getting full throttle....
Really !
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x2. I saw this exact problem on a TV show a while back. The car (70 Vette if I remember) was falling on its face at about 60. As it turned out, with the pedal to the floor, there was a good 1/2 inch more carb linkage travel needed to be at full throttle. Sounds like good advice.
 
67/6barracuda said:
I also notice while backing in reverse it seems to take an unusual high rpm maybe 2000-2500 rpm before its grabs likes that when it stalls and grabs. But in drive it grabs around 1200-1500. Its trial and error, these are the things you deal with when buying a unknown motor and trans from the junkyard and just take a chance on it performing.
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Reverse needing more RPM's may be an indication of something wrong; those high reverse RPM's are quite abnormal. Reverse typically needs higher fluid use and will drop the internal pressures if something is wrong with fluid delivery or leaking.

BTW, what do you have for a kickdown linkage? Is it in place, connected, and properly adjusted?
 
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