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A4ld question

Transit Mk3, 4 & 5(smiley front) Forum. All Transits 1986 - 2000

A4ld question

Postby tltane » Tue Sep 21, 2021 7:09 am

Hello, a question and an introduction at the same time. I have a -71 Ford P7b 17m, equipped with a 2.9 which is converted into carburetor and linked to an A4ld. You might wonder why I'm asking a question in an Transit forum, simply, you seem to have the best knowledge about the certain variant of the A4ld.

Background of my setup
- 2.9 V6 with a carburetor, transmission vacuum from the vacuum plate between carburetor and intake manifold
- Fully overhauled A4ld, new bands, clutch, sprags, servos, vacuum modulator etc
- Transgo shift correction kit
- Early petrol valve body with single solenoid to control the TCC lockup. Not wired, TCC lockup not in use

Now I don't know if there is something wrong with my transmission or if it's working excatly as it should.
- upshifts in "D" (or "3" without OD) work fine and are consistent, no issues
- The issue is when I'm in "D", overdrive engaded, downshift 4->3 with light throttle input works fine up until around 50 mph, light throttle pressure and it downshifts. After 50 mph it will only downshift with the kickdown, newer with the vacuum from light throttle pressure.
- Also sometimes it feels that 4th is hanging when I coast from 60 mph to a stop, engine studders for a moment and then it dowshifts

I remember reading somewhere that with these early single solenoid A4ld you need to manully select and de-select 4th from the shifter, but very little info is available online for these, hopefully there knowledge in this group to either easy my mind or point to a correct direction on what I should do.
tltane
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Re: A4ld question

Postby marcrbarker » Thu Sep 23, 2021 5:22 am

I don't have any direct specific experience this model, but sounds to me the gear selection calculation has too much road-speed-term in the equation. Perhaps the transmission ECU for some reason hadn't taken into account the added overdrive gear.
I guess the road speed sensor outputs a 0V / 5V pulse train from a Hall sensor. Something had been done in the past (to correct a too-high speedometer reading on a different vehicle to this) was fit a CMOS pulse divider circuit, to reduce the roadspeed pulse rate (it deleted every 4th or 5th pulse or something).
Of course if this same pulse signal is also used for the speedometer milecounter, any added pulse divider box would have to be at the transmission ECU end of the harness, not at the sensor end.
This reminds me of about 30+ years ago a vehicle I acquired was on its second replacement engine, that also had something wrong with the road speed calculation but the opposite way round. The engine was late changing up while accelaratung and over revving. I hacked into the ECU circuit a variable parameter I could adjust while driving. After a week or so I found the best all round choice of parameter, a resistor value. When I looked at the circuit board to fit this value, there was already there that exact value I had chosen, which was weird because it wasn't behaving like that value. It turned out the original resistor had the correct markings but was faulty when originally built.
marcrbarker
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Re: A4ld question

Postby tltane » Thu Sep 23, 2021 8:24 am

This version is fully hydraulic operated in all gears 1-2-3-4, only controlled by the governor and vacuum modulator. It doesn't have a solenoid for the 4th gear, only for the TCC lockup which is not in use.

The upshift are ok and at the correct speed / RPM, no issues there. But I was thinking that is this how it should work, that the modulator activated downshifts only happen at quite low speeds and after that it's only kickdown.

3 -> 2: no modulator downshift after 35 mph, only kickdown
4 -> 3: no modulator downshift after 45 mph, only kickdown

I changed to an adjustable modulator and it did it increase the upshift speeds a bit, but very little influence with the downshift
tltane
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Re: A4ld question

Postby marcrbarker » Fri Sep 24, 2021 1:47 am

Ah, it's a mechanical governor, the thing near the prop. That'll be weights and springs then, not electronic like I'm used to dealing with, but still seems to me like too much road speed term in equation ,so something to do with springs weights instead of electrical signals.

Just a thought, do the upshift points happen at the right place because a tweaked-up modulator spring is doing the work? A missing spring on governor would push the shift points downwards on the speedometer dial. A tweaked-up modulator spring I presume pulls these shift points back upwards (only while less vacuum happens, accelerating). Apart from this I don't have any suggestion.
marcrbarker
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Re: A4ld question

Postby tltane » Tue Dec 14, 2021 12:48 pm

Popping this back up with hopes to find someone with experience in these.

Regardless of the valve body (one or two solenoid), if you drive a car with A4ld, does it downshift 4-3 above 60mph without kickdown?
tltane
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