Shifting woes, clutch?

[JohnN-1BADFE]

In my 67 Fairlane GT, when I go to shift at 6K+ rpm's I can not get it to shift into 2nd gear.  It's like it's "locked" into 1st gear.

The engine is a 390/451 stroker that dynoed at 654HP @ 6700 - corrected sea-level.  I am in Colorado at an elevation of 5300 feet, so HP is actually around 500HP. 

I have a Centerforce clutch (I know not the best), but was wondering if I do need a better clutch to accomodate the power I have.  It seems like with the power and rpm I'm shifting at, it's putting such on load on the clutch, it won't disengage to shift into 2nd gear.

Any thoughts or suggestions?  Thanks.

[machoneman]

On a hunch here but.....

-do you have a heavy duty engine limit strap/chain/bar to prevent engine torque from twisting the block over, upsetting the clutch linkage free-play?
-have you had someone depress the clutch while looking at the linkage's movement from underneath car?
-can you check the clutch disc's actual disc-to-flywheel (or disc to clutch face) freeplay when fully depressed (some 'bells allow one to stick a feeler gauge into  the can). This can differ from linkage freeplay btw. 

[My427stang]

In my 67 Fairlane GT, when I go to shift at 6K+ rpm's I can not get it to shift into 2nd gear.  It's like it's "locked" into 1st gear.

The engine is a 390/451 stroker that dynoed at 654HP @ 6700 - corrected sea-level.  I am in Colorado at an elevation of 5300 feet, so HP is actually around 500HP. 

I have a Centerforce clutch (I know not the best), but was wondering if I do need a better clutch to accomodate the power I have.  It seems like with the power and rpm I'm shifting at, it's putting such on load on the clutch, it won't disengage to shift into 2nd gear.

Any thoughts or suggestions?  Thanks.

2 things

1 - Make sure you aren't over-centering the clutch.  A diaphragm clutch will grab again as it goes over center, very often stock linkage has too much throw.

2 - Is the pedal hard?  Remember, the engine wont make a clutch grab harder, only RPM will with a centerforce.  It could just be the counterweights doing what they designed them to do.

I personally would run a better clutch with a setup like that, and although I have really grown to like diaphragms, I'd probably look for a grabby Long style for the power you are putting down

[blykins]

n/m.................

[JohnN-1BADFE]

Wow guys great feedback!  I think I need to upgrade the clutch and pressure plate, so any suggestions to what, is greatly appreciated.

I do have a linkage problem that I was going to address.  It will not shift from 2nd to 3rd smoothly all the time and sometimes it's seems to bind and not go into any gear.  I'm sure the bushings need replaced and causing the linkage to be "sloppy".

The car has a console, which I'd like to use since it's just a street/strip car.  It has the Hurst Competition Plus Shifter and I'd like to upgrade the linkage to straight rods and heim joints, but not sure if that will cause the shifter to need to be "relocated" and have to modify the trans tunnel and still be able to keep the console..... ?

As far as your suggestions......

No -do you have a heavy duty engine limit strap/chain/bar to prevent engine torque from twisting the block over, upsetting the clutch linkage free-play?
No  -have you had someone depress the clutch while looking at the linkage's movement from underneath car?
Have stock bellhousing right now  -can you check the clutch disc's actual disc-to-flywheel (or disc to clutch face) freeplay when fully depressed (some 'bells allow one to stick a feeler gauge into  the can). This can differ from linkage freeplay btw.


Need to check  - 1 - Make sure you aren't over-centering the clutch.  A diaphragm clutch will grab again as it goes over center, very often stock linkage has too much throw.

No, doesn't seem to be   2 - Is the pedal hard?  Remember, the engine wont make a clutch grab harder, only RPM will with a centerforce.  It could just be the counterweights doing what they designed them to do.

Probably should upgrade along with a clutch, suggestions?  - My vote is the pressure plate.

Stock engine/trans mounts that were solid -  1.  How rigid are your engine and trans mounts?  I've seen flexing here cause shifting issues.

Toploader - 2.  If you are running a TKO 500 or 600, sometimes it's the nature of the beast.  These transmissions have production tolerances just like anything else, and sometimes you get one that doesn't have correctly spec'd thrust dimensions, or the finish on the gear cones are not conducive to quick shifting.  I've seen a lot of TKO's that just don't like to be yanked over 6000 rpm.  There are fixes for that, but it involves pulling the trans.

Not really, need to check/do - 3.  Did you dial in the bellhousing?  A side load on the input shaft can cause shifting issues, which could be amplified by the higher rpms.

Again, thanks for the great feedback!!!

[lovehamr]

Unfortunately, I get a lot of calls and emails about problems with Centerforce pressure plates, mainly from the Cobra (or light car) crowd.

I'm one of those idiots (sorry, wrong thread) that Brent is referring to.  I had your exact problem and after talking with Brent I swapped my centercrap out for a McLeod and haven't looked back.

[Monzy]

I switched from a Centerforce II to a Mcleod also but only because I went from a Toploader to a TKO600 which is a different spline.  I had no problems at all with my Centerforce II.  It was recommended that you take out the clutch assist spring if you had one.   This was behind a totally different build fe then yours also.   Pushing maybe 400hp/500tq  shifting at 5200-5400rpm.   


I'd say check some of the basics that have been brought up.   I built some heim joint rods for my toploader and could make that thing shift lightening fast with no effort!  I couldn't do that with the factory linkages but I did have a hurst shifter.   Now I have the TKO600 which is a must for the build I have now but it ain't no toploader when it comes to slamming gears!