Where's 3rd gear? - Vintage Mustang Forums
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post #1 of 28 (permalink) Old 09-12-2019, 09:21 AM Thread Starter
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Where's 3rd gear?

67/200/c4/PRND21 daily driver (I think that covers everything)

I just drove to the store and everything was great. Fire it up to hit a few more stops and now the car doesn't upshift. I can manually switch between 2nd and 1st, but in the 5 minutes it was stopped 3rd gear has gone completely missing.

In 'D':
I only have 1st gear. Starts off fine, never upshifts. If I'm running in 2nd and switch back to 'D' it will act like it's in neutral above ~25MPH. Less than that and it will re-engage 1st.

In '1':
Runs in first gear like you'd expect. I can manually shift to 2nd just fine.

In '2':
Runs in second gear like you'd expect. I can manually shift to 1st just fine.

Fluid checks out ok.

What the heck just happened? How did parking for 5 minutes somehow kill my upshifting and 3rd gear? I drive this car all the time, so it's not like it's sat and something's gone bad from lack of use.

Do these symptoms sound familiar to anybody? Please tell me it's just the vacuum modulator or something like that. I've got some more running around to do while I let the car cool off and then I'll dig into the shop manual and the car. This just doesn't make any sense that it just stopped shifting out of the blue with no warning or anything.

Thanks
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post #2 of 28 (permalink) Old 09-12-2019, 12:27 PM Thread Starter
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Update:
I pulled the hose off of the vacuum module and no fluid comes out. I don't see any obvious fluid in the line either.

I disconnected the line for it under the hood and put a vacuum pump on it. I can pull a vacuum but it slowly leaks down about 1psi every 2 seconds. Not sure if that's normal or not, but there's never been a hose clamp on the modulator end of the hose so it's not surprising that it might leak a little.

Is there a way to test a modulator? I can't find one in the shop manual but I may just be missing it. Checking the fluid and making sure the module doesn't leak is pretty much the extent of my transmission knowledge so if anyone's got ideas I'd love to hear them.

The only recent work I've done on the car was to install new strut rod bushings yesterday and since it doesn't look like I crushed the cooling lines doing it I don't think those had anything to do with this so I really don't know what's happened here.
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post #3 of 28 (permalink) Old 09-12-2019, 12:41 PM
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Put your vacuum pump on the modulator. It should hold vacuum. If it leaks down, replace it. Make sure you don't lose the rod inside. Make sure the lines you're using for the vacuum line are actual vacuum line, wouldn't be the first time a piece of washer tubing found it's way in there.

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post #4 of 28 (permalink) Old 09-12-2019, 12:42 PM
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replace module with correct one


65 FB 289/3sp Rangoon Red/Red interior
68 Coupe 200/6 T-5 Diamond Blue/Blue interior
68 Coupe 302/C4 Black interior
69 Coupe 250/6 C4, Blue/Black interior
70 Coupe 390/C6 Auto Gold Metallic/Ginger interior
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post #5 of 28 (permalink) Old 09-12-2019, 01:24 PM Thread Starter
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Ok so I put the vacuum pump directly to the modulator and it holds vacuum just fine. So that little bit of a leak down is in the lines.

Does that mean the modulator's good?

If it does, what's next?

Following the 'No shift points' checklist in the manual the next thing is the linkage, so I'm going to go look at that but I'm not sure what to check past that point.


UPDATE:
The linkage is still attached with it's cotter pins still in place at both ends. It can pivot a little in it's joint but the rod and the transmission can't move independently from the shifter. Kinda figured it was still in place since I shifted the whole way home, but the confirmation's nice.

Last edited by Magnus; 09-12-2019 at 01:47 PM.
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post #6 of 28 (permalink) Old 09-12-2019, 01:46 PM
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Check your fluid level. Check the amount of vacuum going to the modulator.
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post #7 of 28 (permalink) Old 09-12-2019, 06:27 PM Thread Starter
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Vacuum at the modulator is 18-19 depending on the rpms and how far the choke is open.

One weird thing though. When I was running the car to check the vacuum I rechecked the fluid level and the dip stick was dry. The fluid was the first thing I checked when I got home and it was over the full level then. Somehow between then and when I was checking the vacuum that fluid disappeared.

I added some more (maybe a pint) and reconnected the modulator and tried driving around the block and it didn't change anything. Now the dip stick looks like it did when I first got home. The fluid is well over the full mark with the car hot and idling.

I don't know what's going on. I don't see any obvious leaking, the lines are still connected, there's no Type-F in the radiator, the modulator holds vacuum and it's getting 18-19inHg. So what am I missing?
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post #8 of 28 (permalink) Old 09-12-2019, 08:26 PM
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Have you run a control pressure check?
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post #9 of 28 (permalink) Old 09-12-2019, 08:29 PM
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By any chance is your kickdown lever stuck? When you pull it towards the rear of the car, it should have a resistance from the spring in the valve body.

Nothing worthwhile is ever quick, cheap or easy, those that can't do, complain

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post #10 of 28 (permalink) Old 09-12-2019, 10:03 PM Thread Starter
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I moved the kickdown lever a little while I was looking at the linkage and it didn't seem stuck to me, but I'll check that again in the morning and make sure it's not binding.

I have not run a control pressure check. I've actually never heard of it before, so I'm learning something new today. If I'm reading the shop manual right it looks like I need to remove a plug near the NSS, thread in an oil pressure gauge that can take up to 268psi, and run through the gears? Is that right? I'm not sure I have a gauge that goes that high, I'm gonna have to look.

Have I got that right? I'm basing that off of the 67 shop manual pages 7-4 - 7-5.
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post #11 of 28 (permalink) Old 09-13-2019, 10:57 AM Thread Starter
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Quick update:

I can pull the kick down lever forward about an inch-ish and then the external spring smoothly moves it back into place. So it doesn't seem stuck. Unless it's really really stuck and is supposed to move more than that.

While I've been typing this, looking at the shop manual and editing pictures to attach I think I've confused myself. Using this grainy pic from the shop manual can somebody tell me which plug is the control pressure take-off hole?
67-c4-control_pressure_port.jpg

I was thinking it was the big square plug, but the more I look at it I think I see that in the illustration so maybe the correct port is the one way off on the left?
67-c4-control_pressure_question2.jpg

So am I checking the pressure behind door number 1 or door number 2?

Thanks
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post #12 of 28 (permalink) Old 09-13-2019, 11:17 AM
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If you have too much fluid in the tranny it will not shift properly. You said it's way above the full line. That's not good. Drain some out.
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post #13 of 28 (permalink) Old 09-13-2019, 01:46 PM
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Fitting #2 is the pressure take-off port. #1 is the intermediate band adjusting screw and lock-nut.
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post #14 of 28 (permalink) Old 09-13-2019, 04:38 PM Thread Starter
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It's a good thing #1 didn't want to come loose then.

So, on to the test results. I've got a vacuum gauge hooked up tee'd off at the modulator end and a mechanical oil pressure gauge plugged into the take-off port. I ran the car for 5 minutes in a 90 garage to make sure the choke kicked down, and it wouldn't go any lower, but the idle might still be a hair high. I don't have a tach so I don't have solid numbers there. I just wanted to mention it to be thorough.

So here's what we've got:
Time | Transmission PSI | Vacuum inHg | Gear
1605 | 65PSI | 19.5" | P * Choke on, fast idle
1607 | 60PSI | 18" | P
1610 | 60PSI | 18" | P
1611 | > 100 | ?? | R * Gauge only goes to 100
1611 | 65PSI | 18" | P
1611 | 65PSI | 18" | N
1611 | 70PSI | 14" | 2
1611 | 95PSI | 14" | 1
1612 | 75PSI | 14" | D
1612 | 65PSI | 18" | P

So it's definitely got pressure in every gear. The vacuum drops when I stick it in gear since the engine's struggling against me standing on the brakes. I missed the vacuum reading in Reverse while I was quickly taking it back out of gear since it had more pressure than my gauge can show.

The only thing that seemed odd to me was that I was getting 60PSI in Park until I tried Reverse and after that I kept getting 65. I don't know if that's significant or if I just broke the gauge, but it's the only thing that jumps out to me.

Do these numbers mean anything to anybody?


Last edited by Magnus; 09-13-2019 at 04:42 PM.
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post #15 of 28 (permalink) Old 09-13-2019, 04:46 PM
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Tranny fluid should be checked only with the engine running and the car in gear. Pull the e-brake and maybe just for a bit of safety block the wheels.


You may need to re-sync your shifter notches with the transmission detents and make sure the shifter is puting the trans lever in the correct positions. Usually checking and adjusting in neutral first then park and 1 will get it lined up.



It is acting however like the valve body needs to be cleaned out which I would take it to a transmission shop for that.


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Last edited by macstang; 09-13-2019 at 04:52 PM.
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