Excessive engine rpm - 727 tranny

[histoy]

I own 2 Mopars that each have a Sure-Grip with 3.23 gears.   When driving the 4 speed at 62 mph, the tach reads 2,200 rpm.   When driving the 727 at the same speed, the tach reads 3,300 rpm.   This engine is working way too hard!    The 727 was rebuilt and I was told that a new converter was installed with a 1,600 stall, because the engine has a mild Comp Extreme Energy cam.   The trans shifts normally, and the kickdown works fine, but the engine sees to rev high all the time.   My guess is the converter is the problem.  What do you guys think?

[RD]

60 mph should be around 2200-2300 rpm's with a 727 w/a 3.23 gear.  Are you sure you are hitting Drive?  You may still be in 2nd.  Check your linkage setup to make sure it is adjusted appropriately.

[69bananabeast]

any idea what  727 with  3.73 would do at 60 ?

[Chryco Psycho]

I love 4 spds , no slippage

[histoy]

I can feel the transmission shift from 1st to 2nd to 3rd, but the 2nd to 3rd shift happens quickly in most cases.    The transmission kicks down into 2nd gear when I floor it.  I can also manually shift down to 2nd gear.

[deputycrawford]

Histoy, Please let me know if you find the problem. I have a friend of mine with a 74 Challenger that is having the same problem. He has tried a new converter and it hasn't fixed the problem.

[Steve P.]

Are you sure they both have 3:23s?

[histoy]

Each of my cars has a 3.23 Sure Grip.   I jacked them up and rotated the rear wheel one revolution and the drive shaft turned 3 1/4 times on each car.    My friend has a 3.91 Sure Grip and at 62 mph his Sun tach reads 2900 rpm, so that is another reason why I'm concerned that mine reads so high.

[Jon Smith]

my kickdown linkage was incorrectly adjusted when i bought the car and it almost never got out of 2nd gear....

[RECHRGD]

Have you tried the old brake test to try and see where the converter is stalling at?

[Ghoste]

I love 4 spds , no slippage

Oh, I don't know about that.  I have had a few with slippage in my past. 

[histoy]

Rechargd - no I haven't tried the "old brake test".   What do I need to do, and what will this test show me?

[RECHRGD]

Histoy, assuming the tranny rebuild was good and there are no slipping clutches or the like, the "old brake test" will show you (pretty close) what RPM your converter is stalling at.  Just put the car in gear, hold the brake down hard enough so the car will not move and push on the accellerator until 1- the rear tires break loose or 2- the engine will rev no higher.  The RPM at which either of these things occur is where the converter is stalling at.  Converters will stall at different RPM's with different combos, but at highway speed you really should not be having an issue if your converter is anywhere close to a 1600 stall.  Now a 4000 stall would be a whole different story.  Hope you get it sorted out.  Bob

[histoy]

Thanks for the info.  I'll give it a try this week, and report back what happens.

[Steve P.]

Are you hearing a big difference between the 2 cars revs. or just going by the tach.??

[histoy]

There's a big difference in the engine rpm at all speeds, even starting up from a dead stop.

[Steve P.]

There's a big difference in the engine rpm at all speeds, even starting up from a dead stop.

You can't really go buy the first gear sound. Your 4th gear in one car and 3rd in the other are final gears and should be equal. 1 to 1 ratio. that is where to make your comparison. The automatic is going to slip a bit. You will allways lose some with an automatic. That's what Chryco was saying about 4-speeds. You are in or you are NOT.. The only rpm change there is clutch slippage.

Does the automatic car have a sure grip?

[histoy]

Yes, both cars have a Sure Grip with 3.23 gears

[dkn1997]

There's a big difference in the engine rpm at all speeds, even starting up from a dead stop.

I know you said you checked it, but sounds like one of your cars does not have a 3.23 in it.  unless you have a seriousely high stall converter.

I run 3.91's with a very tall tire and I am at about 3k at 60mph.  If your brakes were dragging enough to cause high rpms at cruise, then you woudl certianly smell something very wrong.  just thinking out loud...

[histoy]

I just went out and did the "old brake test" suggested earlier.   I tried it 4 times.   The car started to move at 3200 rpm on the first try, and I held the brake a tighter on the next 3 tests, and the car started to move at 3400 rpm on those 3 tests.   So is that telling me that I have a high stall converter, which will have to be replaced to get down to the 2200 rpm that my Belvedere runs?

[RECHRGD]

As long as evrything in the tranny is good, it would appear that you either have a converter that belongs in a race only car or the converter is bad.  I assume under normal driving when you leave a stop light that the engine revs pretty high just to get you going.  At 60MPH with 3.23's your not anywhere close to what that converter seems to want to stall at.  Unless you've got a large tranny cooler on there, your probably overheating the transmission also.  Does it act the same in reverse?  Bob

[histoy]

The converter is new, but I don't see any identification numbers on it after I pulled the inspection cover.  Obviously it has a higher stall than the 1600 I was told by the rebuilder.  The engine revs high when leaving from the stop light, and I think it's about the same way when backing up, but I don't have to back up too far to leave my drive.  The engine has a little over 500 miles on it since rebuild, so I've been taking it easy on it so far.  This afternoon I got on it a couple of times and ran the tach up to 5000 rpm, but the car's acceleration was disappointing.  Maybe it's because I'm used to driving my Max Wedge Belvedere, but I think the Charger should run better than it is right now, even in stock form.   There's no transmission cooler on it other than the lower tank in the radiator.  The radiator itself is oversized, and we only drive it about an hour and a half at a time, so transmission over-heating hasn't been an issue up until now. 

I guess I'll be pulling the converter out this winter and making a swap.   I don't race the car, so do you have any idea where I can buy a stock replacement converter?  It seems like all the ads I've seen are for ones with a higher stall.

[RECHRGD]

Well it sounds like a bad converter.   I wouldn't drive it anymore until you get a good one in there.  You may have to rebuild the tranny if you do.  Stock and any other replacements are readily available.  I run a converter that was stock on RV's that had 440's.  It stalls around 1500 RPM and works good on my combo.  Your 440 Charger's acceleration shouldn't feel a whole lot less than a stock Max Wedge IMO.    Good Luck, Bob

[deputycrawford]

I would call your local Mopar dealer. They sell the MP converters. I had a 175K. It stalled around 2800. Thats too much for your build. You could step it down to the 144K or the 166K. Just tell your parts man what you want. The 175K is around $249. I believe most of them are about the same price. oh, by the way, your acceleration might be disappointing because the converter burns off too much of the torque. A lower stall speed will bring your lower torque alive. It will be a totally different animal. I over stalled a car once and had the same results.

[histoy]

Problem with excessive rpm finally identified.   I had the rebuilder install a different converter, which improved the performance around town, but RPM remained the same at highway speed.  The rebuilder had put a rigid 7 blade fan on the car when he restored it, and it always made a lot of noise, especially with the smaller sized water pump pulley on my '68.   I had him install a clutch fan, which really quieted down the engine.  After that it didn't seem like it was running 3300 rpm at 62 mph, even though that's what the tach read.   Last night I bought a new Sun tach and temporarily installed it, so I could compare the 2 tachs.  At 62 mph the new tach reads 2450, right where it should be, while the Tic-Toc reads 3300 - 3400.   So... the bum tach & loud fan had sent me down the wrong path.  At least I know what to fix now.  Thanks to everyone for your ideas.

[Ghoste]

Greag Garner at Real Time Performance (I think thats the business name?)can fix the factory tach for you so that it is accurate if you want to use it.