Valve bodies and late shifting

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Joined
May 21, 2014
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Location
Rhode Island, USA
My Car
73' Mustang Hardtop- 302 2v V8
Been a while since I posted, it is currently winter here and the mustang has been wrapped up since November, so not much to talk about. However, tax return season is here, and I would love to spend some dough on the mustang.

I rebuilt the transmission and everything went well, but the car shifts late. I did try adjusting the vacuum modulator dozens of times, and made sure the little valve that goes inside was pointing the right direction. No matter what I did I couldn't get the car to shift smoothly.

One thing to mention is that the vacuum modulator is the green stripped one and the one I took out of the car was yellow. However, I can not find a yellow one anywhere.

If that isn't the problem, I have reason to believe the valve body could be.

What do you guys think of the Performance Automatic "Street Strip" valve bodies?

Link Here

 
I have the B&M and it works great. I do not have the kick down hooked up. Shifting in drive is fine. If I shift manually it holds whatever gear long enough that I could blow up my engine. ;)

 
I think that the color indicates the pin length, assuming a C4 here.

There are 4 pin lengths.

1) 1.601-1.611

2) 1.634-1.644

3) 1.650-1.660

4) 1.666-1.677

A typical C4 modulator valve, pin and vacuum modulator. Factory length on modulator pin is 1.620", that may vary 0.010" or 0.015". A longer pin (0.030" - 0.045") will firm up shifts and the shift will be slightly later. A shorter pin does the opposite.

Some modulators are "thread in" design (early trans, pre- 1970). The pin must be there for proper operation of the modulator.

Parts store should be able to tell you what the correct length you need.

 
tightening the band just holds 2nd gear if you find the trans is slipping it is one place to try.

the different modulator colors indicate the size of the diaphragm inside .

now it used to have more meaning because originally the modulators were not adjustable.

green has a larger diaphragm it is a general modulator and should be ok. this assumes nobody messed with the pin and it is still it's original length.

first thing you want to know is how much vacuum is the motor making.

if you have a high performance cam and low vacuum it will mess up the shifts.

make sure your in a good vacuum range at idle over 12HG

CLOCKWISE raises shift point

COUNTER CLOCKWISE lowers shift point.

when you messed with the modulator last season was there a noticeable effect when you turned the adjustment on the modulator.

how much did you move the modulator for adjustment.

i had to move mine something like 8-10 turns to get it in the ball park.

now the valve body does not control the shift points on a C6. that is controlled by the speed Governor which is part of the tail shaft in the rear housing.

if the transmission was rebuilt somebody could of done a poor job in overhauling the governor there are many ways to screw up the governor assuming the trans place even touched it during rebuild. a shift kit changes the pressures in the valve body that makes a shift faster and engage with more pressure,, less slip equals more power to the rear tires. and less wear inside the transmission. this makes the shifts REALLY hard. in the Chevy, GM world the shift kits do change the shift points, in the ford world there really isn't much you can do other then the modulator, there is no aftermarket speed governors really for the C6. you can change the gear ratios but not the manual shift points, you can install a manual valve body that makes the auto act like a manual.. etc.

most trans places are scum and when they say they are overhauling the transmission what that means is we throw some new clutches inside the main body throw it back together and then call you that it is done. this can mean they left the governor all gummed up from 100,000 miles of use, they could of also installed it 180 degrees out on the plate or over torqued the bolts making it stick and not shift right.

since you made sure there is a pin, what i would do next and put a vac gauge on the motor intake vacuum tree and read full manifold vacuum at idle just to make sure your engine is making good vacuum. next just make sure the modulator is actually hooked up to full manifold vacuum.

after that go for a drive and note the approx shift points.

since your shifts are late, run the adjustment counter clockwise like 5 times, and go test drive, was there a noticeable change, if no change at all suspect issue with governor body sticking for a bunch of reasons.

but first things first you have some homework before suspecting something major.

 
How about band adjustment.

Lets say the pin length, valve body and modulator valve are just fine. Would tightening the bands have a major effect on how late or soon the car shifts gears while in drive?
I think that if the gears were slipping then a band adjustment would be needed.

Might also want to check to make sure that your kickdown bar is not hung (it returns freely) up somewhere as the hydraulics would be ported differently and could also affect the shift timing.

The modulator pin will cause the hydraulics to be off too, you may need a shorter pin.

Transmissions are not my strong point but this is what I am thinking the possible causes could be.

 
I'm curious as to what you mean by shifting late ? Are you going by the RPM that it shifts at? Does it shift differently depending on how much foot

you put into it?

Do you still have the kick down installed?

I've always heard more complaints about early shifting.

 
Under normal acceleration, 1-2 upshifts in Drive should happen at 17-30 mph; 2-3 upshifts should occur at 32-50 mph.

During deceleration, 3-2 downshift should happen at 33-37 mph, then 2-1 downshift at 19-21 mph. These are broad speed ranges based on the Ford Shop Manual, along with tire size and axle ratio.

At wide-open throttle, 1-2 upshift should occur at 27-41 mph, then 2-3 upshift at 52-74 mph, again based on the Ford Shop Manual, tire size, and axle ratio.

 
This car doesn't have any type of rpm gauges installed. Its all still the factory dash so I do not know the rpms.

I can tell just from feeling it and hearing it. I can tell it wants to shift but it will hold second gear longer than necessary. It very well may just be the vacuum modulator/pin. It was the yellow version, but I didn't change the pin size when my rebuild kit came with the green one. Or the vacuum isn't strong enough (which would be weird, the car is running an edelbrock 4bbl carb with the matching intake).

Yes, kick down is installed correctly.

I guess I will have to wait to spring to drive it around again before I drop $300+ on a new valve body.

 
If it's just holding second gear to long, check your shift linkage for proper adjustment. I saw one once that you had to push the shifter halfway to neutral to get it to go into drive. After I adjusted the linkage, it worked fine.

Steve

 
The shift adjustment it perfectly fine. I meant when I have my car in drive, and I am riding along the road it holds onto second gear too long before it finally decides to shift into third gear. Ill have to drive the car in spring and maybe add an rpm meter to tell when it is shifting. Iv been wanting to add an rpm gauge to the dash but I can't find something that looks enough like the factory gauges.

 
http://www.rccinnovations.com/index.php?show=menu-tach-all

Skim down the page and you'll see a tach conversion for the clock side of the cluster- by all accounts it is a really nice piece and looks very close to stock.

I'm always impressed at your willingness to jump into repair work on your own car. I am not a transmission expert, so I won't offer much advice except to say I think it is the vacuum modulator based on prior experiences with a FMX many years ago.

 
Thank you so much for that link. That tachometer is absolutely perfect. It is exactly what I have been looking for.

Thanks for the kind words. I love learning about these cars and I am learning a lot from my father. I have been watching him fix cars since I was like seven. He really had no choice but to learn how to fix cars themselves because of finances, and we have save A LOT of money by doing everything ourselves.

We cleaned up the engine last season

Engine%20Original_zps6wazpvpl.jpg


20150503_174237_zpso4fjdjgg.jpg


I think you are right though, I have to look deeper into the modulator. This could be a $40 fix. I may still put a new valve body in though, that can only help.

http://www.rccinnovations.com/index.php?show=menu-tach-all

Skim down the page and you'll see a tach conversion for the clock side of the cluster- by all accounts it is a really nice piece and looks very close to stock.

I'm always impressed at your willingness to jump into repair work on your own car. I am not a transmission expert, so I won't offer much advice except to say I think it is the vacuum modulator based on prior experiences with a FMX many years ago.
 
here are the manual recommended shift points for the fmx and c6

2eztzip.jpg


you don't need a tach just the speedo

all you need additionally is your rear end ratio which you can just ball park.

 
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