727 gurus: delayed 1-2 shift

[dpstark2]

Guys,

Years ago, I installed a B&M shift kit in my '67 727. As far as I know, the trans is in good shape. It air checked fine and everything works- I just wanted to firm up the shifts. I've spent a lot of time troubleshooting and trying to understand what's going on inside the transmission, and I can't explain why I have a late 1-2 shift. As best I can tell, this problem was created when I installed this kit.

The delay happens in regular driving, as well as manually shifting 1-2. The weirdest part to me is that the delay is, as best I can tell, almost entirely TIME based. No matter what you're doing, when it should shift into second it takes about a second before it actually shifts. Doesn't matter if you're cruising away from a stop, flooring it getting onto the freeway, or anything.

Going from the service manual, the 1-2 shift involves filling the accumulator, then activating the kickdown servo. The B&M kit blocks the accumulator open, so that shouldn't apply. For the life of me I can't explain why the kickdown servo wouldn't essentially instantly activate when the 1-2 shift valve... err... shifts! The B&M kit does swap the inner spring in the kickdown servo. Maybe it's too strong? Maybe one of its seals is leaking?

I just had the valve body apart. It's clean, everything moves freely. The trans doesn't slip. No debris in the pan. It's a pretty annoying problem, but it doesn't keep me from driving the car. Any ideas? Anyone?

 

[Mopar-Charger]

Check the kickdown linkage, and check the fluid. Not enough fluid means not enough pressure! Was this problem prior to the shift kit?

I know my stock 727 has a delayed/mushy shift from 1-2. In an old car I put a transgo SC shift kit and I would chirp the tires 1-2. I'm putting it in my new 727 this upcoming weekend.

Do you have a 727 service manual?

 

[dpstark2]

I have the ATSG manual. Fluid is fine, and it kicks down correctly. It has a deep pan with almost 11 quarts in it, checked hot in neutral. My headers and EFI setup have required a cable operated kickdown, so it's not stock. But I went through a lot of trouble to get the travel at the throttle lever and kickdown lever to be correct. It works, as best I can tell.

I believe this problem originated with the installation of the shift kit. Previously, it worked fine, but I don't remember if I ever tried to shift 1-2 manually and noticed the delay. It's possible there are other issues at work here, but I can't say yet.

From what I can see, all that happens in normal Drive operation when the 1-2 shift occurs is that the 1-2 shift valve moves over under governor pressure (opposed by the 1-2 shift spring), the accumulator is filled up (but it's blocked open by the B&M kit and the restriction is drilled out), and the kickdown servo is pushed out to engage the band (opposed by the springs inside the servo).

So: either the 1-2 spring is too strong (I've tried changing it with no effect on this problem), and this makes no sense with the time-based nature of the problem. Or, the 1-2 shift valve or governor plug are hanging up. Or, the kickdown servo is somehow not actuating correctly or it's leaking.

Any thoughts?

 

[Jackpot50]

Got a gasket on your filter extension? I see you have a deep pan.
Did you put it on at the same time?

 

[dpstark2]

The pan went on after this issue came up. The pan came with an aluminum extension and gasket that goes between the extension and valve body. I have reused this gasket, but since the problem hasn't changed through a couple different efforts to fix it, I don't think the suction side is at fault. At one point, I even put a pressure gauge on the governor port to make sure it was acting normally. Hard to do, but it seemed to track with MPH correctly.

In my efforts to address this, I've tried a different 1-2 shift spring, adjusting line pressure, adjusting kickdown, checking valve body for play, air checking everything, etc. Nothing made a difference. The only thing I haven't done is put new seals on the kickdown servo.

 

[Yatzee]

How coincidental that you should bring this topic up. I am just now in the process of installing a B&M shift kit in a clients shift body for a 68. I would be interested in the number of the kit you're using. I bought the 2 in 1 kit part #10228 and have found the instructions quite concise. I also noticed that there is a trouble shooting section included in the installation instructions. Have you referenced this section. On most of the tranny's I work on, the spring for the accumulator is replace with a solid rod or spool. They really serve no purpose. If they did the 2-3 shift would never experience overlap. I also noticed how much heavier the replacement servo spring is. Perhaps this needs to be installed if it hasn't already. I have found over years that there really isn't much difference between TransGo and B&M as far as performance. I would check to make sure the pressure adjusting screw is set per their instructions because you may actually be a bit low on pressure.

 

[dpstark2]

It's the 10228 kit, set up for "street performance." The instructions are good, and I've cross-referenced the modifications with the ATSG guide and FSM. I believe I understand what the modifications do. The accumulator block off rod is installed. The plate drilling that is done in one location removes a restriction related to the accumulator and the #6 checkball (note that the checkball numbering is different here than in the ATSG- but #6 is the same for both...). The inner spring on the kickdown servo was swapped per the instructions. Line pressure was also set per instructions and checked again last weekend. I haven't measured it, as the port is tough to get to with the headers. I did not make the "off road/race" "1st gear at any speed" modifications. I don't want that.

I have read the troubleshooting guide in the instructions and the only one that got my interest was the kickdown detent sleeve installed backwards, and it's not. I can see where low line pressure might cause a delay. I wish these things were easier to test- it's so messy to pull the valve body. My money is on the inner servo spring at this point. I could be wrong though...

 

[moper]

It's been a while so I went and downloaded the instructions.
Did you install the steel ball inside the 1/2 shift spring?
The kit you mention does not drill the casting at all. That's for the next level kit. Are you sure you got it right? It should be remove a ball, add a ball, add the blocker rod, add the transfer plate, and adjust. No drilling required.

 

[dpstark2]

I had the wrong kit number. See above. It's 10228. Sorry for my confusion.

 

[RT K_line]

You said that you adjusted the second gear band, correct? Did you use the manual for the spec. I have found that 1 1/2 turns out works better than what the manual states. Hope this helps!

 

[dpstark2]

I adjusted the band per the manual for a 4.2 ratio lever, which I installed. I think it says two turns out? I'd have to check. I guess that's easy to try.

So far no luck on this issue. The only other symptom I can throw in the mix is the kickdown. If I'm doing 15 in 2nd, kickdown to 1st is near immediate. Floor it and go. If I'm doing 50 in 3rd, same (but to 2nd of course). If I'm in the range where I should get a 3-1 kickdown, like 20-30 mph, I usually get nothing or a delayed kickdown to 2nd. I can't explain that one. And this is with 3.23 gears since that sort of defines the shift points.

 

[dieseldazzle]

Do any mopar buddies you know of have a stock working valve body they will let you swap in right quick? (Alex maybe??)

 

[mopar 3 B]

I think you need to look at the hydrolics chart again. Is your valve body modification supposed to allow 3-1 down shifts? The factory installed will not unless a complete stop is made. 1-2 shifts are made using components from both end of the 727. 2-3 shifts are made from the front. The delay of the 3-2 shift is often built in to make sure the clutch pack releases before band engagement.

 

[dpstark2]

My factory manual has speed specs for a 3-1 kickdown- specifically 25-33 mph. That would mean to me that the 3-1 kickdown is built into the factory body. It's possible the shift kit messes with this (I'm sure it would at least change the factory speed limits for this function). I'm also fully aware that delays are built into the hydraulics to make sure things release and apply in the correct order and to avoid locking up the trans. However, a .5-1s delay in 1-2 seems wrong and is not the same as other cars I've driven.

Trying another valve body is a good idea. I may be able to get at one. Thanks for the idea.