Finally got my 68 F100 SB 390 W/ C6 back from the racing shop. Guys did a wonderful job on my motor and it runs great, however the C6 that I rebuilt and installed seems to change gears way to quickly. I have heard that this is normal of the C6 but wondered if a stall converter might help with this and which one would be best. My rear end is 3.78. Also heard something in one of the postings about a C-6 W/ eo4d upgrade? What is this and is it? Will it give me a 4 spd. auto? If so, is it hard to install? Thanks for any help in this. Scott

 

I think this is pretty common for a C6, especially with higher rear gear ratios (like your 3.78 and my 4.10). When I had mine rebuilt, he got it adjusted where it holds on a little longer to first (it used to shift before I could round the corner pulling out of my driveway). It's much better in first now, but it's in 3rd before 30MPH if I don't have my foot in it. I'm not sure how this is adjusted. Automatic trannies are kinda block boxes to me. I just take it to a tranny shop :-)

As for the E40D upgrade, I think that just changes your gear ratios. It shouldn't give you an overdrive.

 

mine doe's the same thing. some times it feels like I am driving a two speed. I am talking to chevdog on another thread concerning a TCI stall converter he is useing. also am looking at changeing my valvebody to an trans-go kit. look under trans post and B&M shift kit. later fellas.

 

I have noticed that about my C6 too. I was thinking of putting a shift kit in it and having the trans shop do whatever else they needed to do to keep it in gear a while longer. With my 4.56 gears the thing will shift into 2nd at 10mph and into 3rd at 25 if Im just cruising not giving it alot of gas. It shifts so softly now I can barely even feel it if I'm not sticking my foot in it.

I wonder if a 2500-3000rpm stall converter would be about right?

The wide ratio gear kit gives you the same 1st and 2nd gear as the E4OD, that's it. Something like 2.87-vs-2.47 and 1.55-vs-1.43. Third stays the same. You can get it from Summit for about $350.

 

Ok, I just found out the answer to my question about the converter. From what I read at a transmission website, for towing or offroading, a lower stall speed converter is better, but it didn't say what speed...

 

So I guess there is no adjustment for the shift point on the C6 transmissions?

 

the valve body is it. every one here is praiseing the TRANS GO kit as the way to go. I have not done this yet myself but will in the future.

 

I think I will get the TransGo shift kit for mine too, and a modulator.

 

I have installed the modulator along with my TCI pan kit. you can realy feel the differance in the shift, that black stripe modulator did the trick. for the 11.00$ invested it was the best bang for the buck.

 

Thanks, Fordaholic! I'm hearing talk about the green strip modulator as well. Do you know what the differences are between the different colors?

 

I talked with a transmission mechanic the other day and apparently the lack of a modulator valve rod will cause my tranny to stack shift as he called it. He said I could make the rod from a finishing nail just cut the head off it and the point. Start with about 1-1/4" and if the transmission shifts to rough, take it back out and trim it a bit until you get what you want. You can fine tune this with the screw adjustment inside the modulator valve. Will try this out this weekend.

 

Yep! that pesky little rod's gotta be there. I never thought of triming the rod to afect change in the shift, HMMM. sounds like something to play with. as far as the diferent color bands on the modulator go, the best I can tell its the spring pressure inside the valve. thats where the adjustment screw comes in. when you tighten the screw you stiffin the spring just a bit more for a harder shift. the best I can tell any one is to try one and see if you get what you want. if it don't work try another one. for 11.00$ this ain't real high buck.

 

Alright, thanks for explaining that.

 

The stripes on the modulators indicate the range of vacuum needed to overcome the spring pressure inside the diaphragm of the modulator. I don't remember actual levels, but the black stripe modulator is the highest vacuum level version - this winds up giving a firmer shift. The green stripe modulator is the middle of the road version and is probably the most commonly used, but they will all work, just depends on what you want.

You can also change the length of the modulator valve rod as noted, but don't expect miracles. There is a difference you can feel though depending on the length. I've never had to change the length, shift was good with a new modulator and Transgo Sk-6 kit.

I just tried a TCI Sizzler converter in the C6 I just rebuilt - it's a step up from stall - probably somewhere around 2600-2800 rpm and I really like it so far. With the 3.70 gearing on my 79 and the 35's it works really well. It lets the engine spool up up just a bit and I have not felt any loss of torque or power. In all honesty though, I'm comparing a newly rebuilt tranny to one that could no longer move the truck so of course it's going to feel great. I think that the Sizzler series of converters has the vanes set up so that there is very little slip at low rpms (low converter speed).

I'm not slamming the B&M kit - I've used them in the past and they are OK, but I really like the thoroughness of the Transgo kit and it's less than 20 bucks. It changes the valve springs inside the valve body to modify the line pressures (shift firmness) and that's better IMO than deleting check ***** and servo springs. I find the B&M kit is sort of crude in comparison.

You can also change the servo piston and cover (the bore in the cover has to match the piston) for a larger piston. This gives a larger apply area and a harder shift. Don't get too excited about having to have an "R" servo - a tranny in good shape with a good converter and shift kit will give you great shifts. I use the "N" servo, which is actually the smallest size.

 

thank's chevdog that's good info. I have read a lot of good things on the trans go kit's. you got me convinced. that will be my next mod to the trans. along with the converter.