904 with very hard 1-2 shift

[604B1duster]

I recently got a 66 dart with a 340, 904, and 3.91s. It has a performance build 904. The 1-2 shift is pretty violent. Doesn’t matter if it shifts automatically or if I manually shift it.
I’m wondering if there is something I can do myself to calm it down. I vaguely remember many years ago maybe removing the servo spring in a 727 to get a hard shift ??? Is this a common thing ? It really bangs 2nd gear, no difference 5mph or 40mph. Hoping for an easy fix.
Happy Thanksgiving

 

[junkyardhero]

have you checked the fluid level and the made sure that the linkage is adjusted correctly?

a lot of aftermarket shift kits can have a pretty aggressive 1-2 shift.

it might just be that the line pressure is cranked up a little too high. easy fix but requires dropping the pan to make the adjustment. but you can check out what else is cooking while you're in there at least?

 

[Ricks70Duster340]

I recently got a 66 dart with a 340, 904, and 3.91s. It has a performance build 904. The 1-2 shift is pretty violent. Doesn’t matter if it shifts automatically or if I manually shift it.
I’m wondering if there is something I can do myself to calm it down. I vaguely remember many years ago maybe removing the servo spring in a 727 to get a hard shift ??? Is this a common thing ? It really bangs 2nd gear, no difference 5mph or 40mph. Hoping for an easy fix.
Happy Thanksgiving

I once mistakenly put a 727 front servo spring into my 904. The 1-2 shifts were bone rattling. It was really difficult to stuff that big spring in there too! I removed the spring after I found out what I did. That resolved the issue. Like junkyardhero said, be sure to check your line pressure to ensure it is not too high. You'll need to pull the valve body to do that, and to access the front servo. Be careful removing the servo cover. If that 727 spring is in there, it will be under a lot of pressure!

 

[MopaR&D]

I agree with the others on checking the servo spring first. One simple mod to firm up the 1-2 shift is to remove the servo spring and install a blocker rod; if that was done in your 904 along with a shift kit like a TransGo TF-2 or TF-3 the shifts will be extremely firm. I installed a TF-2 shift kit in my 904 and did the transfer plate mods (drilled holes) for the firmest shifts but I put the 1-2 servo spring back in when I reinstalled the valve body which is what the TransGo instructions call for. It shifts pretty damn hard even under light throttle at low speed, borderline harsh maybe for some but I like it. I can't imagine how it would be with a servo blocker rod in there, I'd be afraid of breaking something in the driveline.

Another thing to consider, the stall speed and "looseness" of your torque converter in combination with final drive (rear end) gearing will have a noticeable effect on how the impulse from a hard shift is transferred through the driveline and ultimately how it is felt by the driver (and passengers). A loose converter and taller rear gears will reduce the felt impact from a hard shift.

EDIT: Also worth a try checking the line pressure adjustment first, there is a spec either for number of turns of the screw or distance of the "screw nut plate" from the VB, can't remember which.

 

[604B1duster]

Thanks guys. I’m probably now going to wait for spring to work on it and road test as it snowed twice already here in NY and there is salt on the roads. I appreciate the info !

 

[AJ/FormS]

Do you have a functioning KD system?
Do you have a proper 3.91 governor set-up?
cuz if it has 3.91gears with a 2.76 governor, the increased governor pressure, caused by the increased driveshaft rpm, is gonna throw everything outta whack. I always fix this first.
Then;
If that lever down at the trans, is tied back; it will jack the throttle pressure ALL THE TIME, instead of just at large throttle openings. You can untie it, readjust it with a longer tether, then go for a spin, but stay out of the Secondaries. If it shifts better, readjust your KD linkage. Do not drive it without at least some throttle pressure , else it is possible, at WOT to cook the friction materials due to slippage.
If you take the pan off to readjust the line pressure; here's what I did;
I drilled and tapped the case, in line with the adjuster, for a small pipe plug.
When the engine is shut off, the oil level will be high enough to pizz out that hole, so, I only jack the driver's side up. Now I can adjust any time I want and trust me; you'll NEVER get it just right the first time. Out on the road, I just drive up on a curb and skootch in there.

BTW
Line pressure combines with Throttle Pressure, to fight governor pressure, which commands the automatic upshift speeds.
If I have to, and I usually do, I adjust the Governor Pressure FIRST, cuz if it has 3.91s with a 2.76 governor, the increased governor pressure is gonna thro everything outta whack.
In my limited street experience, I prefer LESS line Pressure and MORE throttle Pressure to achieve the same Combined pressure, which I adjust up or down, depending on the engines power level and the load (car weight and rear gear ratio.)
The reason for all that tuning, is to prevent clutch slippage when the Secondaries open, yet have a comfortable driving experience, in auto-shift mode.
And,
after I get all that dialed in, then I fool around with the 1-2 shift valve to get a nice lifted-foot automatic downshift back into first. I like it when I come into a turn, slowing down to not be too hot, and then BAM!, it downshifts all by itself, and I rocket out of the turn. For me, that is just so much fun, when it happens automatically.

A&A has the governor kits, there may be other companies IDK.

 

[MopaR&D]

Do you have a functioning KD system?
Do you have a proper 3.91 governor set-up?
cuz if it has 3.91gears with a 2.76 governor, the increased governor pressure, caused by the increased driveshaft rpm, is gonna throw everything outta whack. I always fix this first.
Then;
If that lever down at the trans, is tied back; it will jack the throttle pressure ALL THE TIME, instead of just at large throttle openings. You can untie it, readjust it with a longer tether, then go for a spin, but stay out of the Secondaries. If it shifts better, readjust your KD linkage. Do not drive it without at least some throttle pressure , else it is possible, at WOT to cook the friction materials due to slippage.
If you take the pan off to readjust the line pressure; here's what I did;
I drilled and tapped the case, in line with the adjuster, for a small pipe plug.
When the engine is shut off, the oil level will be high enough to pizz out that hole, so, I only jack the driver's side up. Now I can adjust any time I want and trust me; you'll NEVER get it just right the first time. Out on the road, I just drive up on a curb and skootch in there.

BTW
Line pressure combines with Throttle Pressure, to fight governor pressure, which commands the automatic upshift speeds.
If I have to, and I usually do, I adjust the Governor Pressure FIRST, cuz if it has 3.91s with a 2.76 governor, the increased governor pressure is gonna thro everything outta whack.
In my limited street experience, I prefer LESS line Pressure and MORE throttle Pressure to achieve the same Combined pressure, which I adjust up or down, depending on the engines power level and the load (car weight and rear gear ratio.)
The reason for all that tuning, is to prevent clutch slippage when the Secondaries open, yet have a comfortable driving experience, in auto-shift mode.
And,
after I get all that dialed in, then I fool around with the 1-2 shift valve to get a nice lifted-foot automatic downshift back into first. I like it when I come into a turn, slowing down to not be too hot, and then BAM!, it downshifts all by itself, and I rocket out of the turn. For me, that is just so much fun, when it happens automatically.

A&A has the governor kits, there may be other companies IDK.

Good catch AJ, @604B1duster at about what road speeds does your Dart tend to upshift to 2nd and then to 3rd under part throttle?

 

[604B1duster]

It has KD linkage. I haven’t checked if it’s adjusted properly, but I will. I’m going to have to drive it and pay closer attention to when it shifts. I believe it all feels pretty normal until it BANGS 2nd gear. After driving it a bunch of times I was able to feather the throttle when I knew it was going to shift to second and I’m able to calm it down a little. If I leave a stop and do a burnout the rpm’s come up so quick with the 3.91s, I shift 2nd pretty quick and BANG, it chirps and it’s so violent I get out of the gas. But it bangs just as much just driving easy, babying it.

 

[Bewy]

You need to drop the pan & investigate before something breaks.....