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Discussion Starter #1
Well, we went through and tuned the new motor up a little bit, and decided to run without the vacuum advance, so I plugged it up. Now it seems like the tranny must be getting a lot fatter vacuum signal, as it has more tendency to hold the gears. Currently, it does not like to shift out of 2nd under slow acceleration until 30mph, while before I plugged the vacuum, it would just shift at 20 or so. The shift quality is still good under moderate acceleration. However, when I open it up all the way and wind it up in the RPM's it has a slower, "ka-chunk" type of shift and does not catch the next gear right away. This is on the 1-2 shift, with the engine wound somewhere about 5000-5200rpm, and the car traveling roughly 50-55 mph. I know the engine can run higher without problems, but it seems like the tranny does not like the high RPMs. Could there be some problem in the tranny that only shows up at high RPMs, while the shift quality is still good at moderate RPMs?

Thanks
Dave
 

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if the tranny were overfilled (check the level while idling in park and warmed up) foaming could affect the shift.

you plugged the vacuum hose to the advance, right? theres no need to plug the can

actually, the vacuum advance BARELY even affects stock engines at wide open (and cammed egines not at all).....all youre doing is hurting your gas milage dude!! /forums/images/icons/smile.gif
 

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If you unhooked the advance and didn't reset the timing, you're not getting as much spark advance at WOT, this would affect power slightly, and alter the shift points slightly...
 

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Discussion Starter #4
We unhooked the advance so that we would not be getting as much timing, as we were pulling into the 50s with the advance hooked up. Now with the advance disconnected and the initial set at about 14-15 we are pulling in about 38 degrees. The fluid level has been holding pretty steady right at the full mark, although occassionally there has been some bubbles on the dipstick when I checked. Not to spite what you have said, but I actually am getting an extra mile per gallon since the disconnection of the vacuum.

Thanks
Dave
 

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Couple things...trans shifts under power sound pretty normal for a stock C4 without a shift kit (or even with one if the frictions are worn or the bands aren't adjusted). Try short-shifting at WOT (down 1K or so) and compare shift quality.

You might have rising vacuum at 5200, causing the throttle pressure, which to a certain degree regulates line pressure, to drop.

Describe the current condition and build state of the trans....also, what is estimated HP level of engine?

Get back to us...
 

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Discussion Starter #6
Pat--

There is a stage one Transgo shift kit in there. I just rebuilt the transmission before we fired over the new motor. All new frictions, steels, bands, seals, springs, gaskets, and whatever else I could get ahold of. Also there is a new 2400 rpm stall converter. The engine is a 331 stroker, and I am estimating very near 400 HP at the flywheel. Shifting a little bit shorter cleans up the shifts some, but is still a little bit clunkier than say a 3000 rpm shift.

Thanks for your help.
Dave
 

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I noted a marked difference between the manual/automatic shift kits I've run in my street cars and the full manual shift kit I run in the race car, with regards to shift firmness......with the W and short shifting (about 4.5K) the race car will bark the slicks good on the 1-2 and barely on the 2-3....no way that would happen with the trans I've run in street cars. I think the line pressure gets boosted up with the manual shift kits, so the actuators move faster and with more force.

Wish I had a better answer for you...
 

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Discussion Starter #8
Alright, thanks for your help Pat. So you don't think that there is anything mechanically wrong with the transmission that could be causing this? I am a little concerned that if it it has this problem at 5200 rpm that it will only be accentuated at say 6000 rpm. I am going to be putting a later valve body in with a bigger shift kit, so hopefully that will help a little bit.

Thanks
Dave
 

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So you don't think that there is anything mechanically wrong with the transmission that could be causing this?

I'd know more if I actually could drive the car but, IMO, I don't think you have a mechanical problem with the trans. Could just be a combination of normal things which, with the HP you're running (essentially the same as the race car), is leaving you with a less than firm shift.
I found that by being especially careful when building the trans, mainly with clutch pak thrust clearances and assembly clearances, that all of the mushiness of the shifts goes away, at least with a full manual valve body (BTW, I'm stilll running the early valve body in the race car, in full manual trim). Also, running a solid wide intermediate band with the old friction material helps IMO....I bought a couple from Ford back when they were still available (don't know if they still are).

Lots of things to think about, but no sure-fire solutions..*G*
 

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Discussion Starter #10
Thanks Pat. Maybe when the tranny has taken all the beating it can handle, I will go back through and try to fine tune it. Where you referring to the frictions in the clutch packs, or on the band itself? The new frictions I got seemed to be of a lesser quality than the original ones, in regards to grip. The bands also seemed to be slightly different, but I gave the outside surface of the drums a light sanding to help those out.

Thanks again for your help.

Dave
 

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Were you referring to the frictions in the clutch packs, or on the band itself?

Both, actually....there are a lot of new high performance clutch/band materials out there now but I'm still running the old asbestos composite materials in the race car trans. Also, I machined the clutch pistons for one extra clutch plate and micro-polished the intermediate drum for maxiumum surface area. The old solid band I'm using covers the entire area of the drum and is very solid.....

There are some tricks to make a stock C4 work with 400HP in a car the weight of yours but nothing too involved....most of the tricks in use now were discovered by experimenters like myself a few decades ago by trial and error...lots of error..*G*

Good luck!
 
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