C4 not upshifting

Dmgctrl88 · Jul 10, 2016

Hello all. I recently completed my ranger v8 swap. Thread is in my signature.

The motor I built runs great and is tuned in, however when I drive, the truck will not leave 1st gear. I have solid reverse and forward gears. I can put it into 2nd manually after going, but when I put it into drive, it drops back down to first. I had a valve body with a transgo shift kit installed, and tried swapping it with a stock one from another C4, but that didn't change anything. What am I missing?

Specs:
I have a fuel injected 5.0 from the late 80's Speed Density. I have a 1979 C4 with an H servo. Linkages are connected and correct. I am not using a kick down cable. I have a long vacuum hose running up to one of the metal tongs on the plenum vacuum tree. Yellow Modulator, adjusted one turn counter clockwise and almost flush with the modulator/hose tip. I do not have the original steel vacuum line.

Tedybear · Jul 10, 2016

Dmgctrl88 said:
Hello all. I recently completed my ranger v8 swap. Thread is in my signature.

The motor I built runs great and is tuned in, however when I drive, the truck will not leave 1st gear. I have solid reverse and forward gears. I can put it into 2nd manually after going, but when I put it into drive, it drops back down to first. I had a valve body with a transgo shift kit installed, and tried swapping it with a stock one from another C4, but that didn't change anything. What am I missing?

Specs:
I have a fuel injected 5.0 from the late 80's Speed Density. I have a 1979 C4 with an H servo. Linkages are connected and correct. I am not using a kick down cable. I have a long vacuum hose running up to one of the metal tongs on the plenum vacuum tree. Yellow Modulator, adjusted one turn counter clockwise and almost flush with the modulator/hose tip. I do not have the original steel vacuum line.

Some silly questions, but ones that have tripped people up in the past:

Is the push rod present in the valve body to move the spool valve? I've seen them drop out while people work on stuff and not notice.

Can you put a vacuum gauge on the line going to the modulator and verify solid vacuum reading. Long rubber hoses are not really recommended as they can pinch and twist cutting off the vacuum.

Hook up a vacuum pump to the modulator and see if it holds vacuum. Some are setup with a small 'vent' in some applications. I'm not sure if yours has it or not. (thinking probably not) Could be a tear internally. Normally you'll start to see blue smoke as it will draw ATF into the intake. So this likely won't be your issue, but sense basic checks to be done...

Had something like you've described happen on a G20 Chevy. Line rotted off the modulator. Wouldn't shift until it hit 40+MPH. Really severe.

G/L with it!

S-

Angie · Jul 10, 2016

"Normally you'll start to see blue smoke as it will draw ATF into the intake. "

Blue or White smoke? Reason I ask is, used to suck trans oil into the intake after a blown modulator and the smoke was white, not blue.

Dmgctrl88 · Jul 10, 2016

I verified that the valve was present and in the right direction (small side inwards)

The pin is present as well. The modulator is a new yellow stripe I ordered from Rock Auto. There is no transmission fluid present in the vacuum line.

I'm beginning to think it's vacuum related though. At first I ran the vacuum to a tree on the firewall. I moved it to the metal tree on one of the smaller metal stems on the plenum, but with no change so far.

So far I adjusted the modulator counter clock wise one full turn. It is now less than 1/8" from being flush with the modulator stem.

I'm seeing many other cars run a steel line for 90% of the way, while I have a long rubber hose (which is new).

A friend mentioned he had the same issue but with a lopey cam on 351.

I'm running a very mild crown vic standard roller cam, but with an HO upper and lower intake manifold and throttle body.

How do I check vacuum? I don't even know what kind of gauge/pump setup to get. Do I check at the top near the manifold or do I check down near the modulator?

alwaysFlOoReD · Jul 10, 2016

I'd check at both ends, that way if you see a difference you can find out why. Vacuum gauge is basic to all mechanical work and is cheap. Any auto parts place should have one.

Sent from my XT1032 using Tapatalk

Tedybear · Jul 11, 2016

Angie said:
"Normally you'll start to see blue smoke as it will draw ATF into the intake. "

Blue or White smoke? Reason I ask is, used to suck trans oil into the intake after a blown modulator and the smoke was white, not blue.

Might have been light bluish in color.

White smoke=water/steam in exhaust.

Blue tint to smoke=Oil in exhaust.

http://www.harborfreight.com/fuel-pump-and-vacuum-tester-62637.html

http://www.harborfreight.com/brake-bleeder-and-vacuum-pump-kit-69328.html

Handy tools to have in the box. You can actually cap off your vacuum line to the modulator and then attach the vacuum pump to it. I'd jack-stand the truck up so the drive wheels are off the ground and give it about 18 inches of vacuum to the modulator. Put in drive (CAREFULLY) and with a solid 18 inches of vacuum direct to the modulator it should shift though all gears normally. You'll have to gently accelerate and you'll feel it shift. Do NOT allow the speedo to climb to high. Normally taking it to 20-30MPH on the gauge should be sufficient, as if you have an open diff in the rear end (not posi-trac) you can double the speedo' to get exactly how fast the wheels are spinning. Clearly if anyone is reading this with a 4wd? You'll want all 4 wheels off the ground on jack stands for safety.

If everything else with the vacuum modulator appears to be working fine?

I'd consider the chance of the governor being stuck as possible. That is on the output shaft of the transmission. While it's not a common fault, you've already changed out the valve body where the spool valve for the modulator sits. If the governor valve is stuck and not moving, there's a chance it could always "Think" the car isn't traveling forward fast enough to shift on it's own.

It's a bit messy of a repair. Last time I had one apart was a long time ago. Had a bit of grit causing the valve to bind up.

http://auto.howstuffworks.com/automatic-transmission12.htm

For those playing at home....

S-

Angie · Jul 11, 2016

I'd jack-stand the truck up so the drive wheels are off the ground and give it about 18 inches of vacuum to the modulator. Put in drive (CAREFULLY) and with a solid 18 inches of vacuum direct to the modulator it should shift though all gears normally.

Easier way is to get a vaccuum gauge and run the hose from a open end on the "T" from intake, run the hose throu firewall and have the gauge in cab as you drive on the streets. If you take off the vac line and try driving a truck the shifting will be extremely hard (as in banging into) gears as it shifts hard.

Dmgctrl88 · Jul 11, 2016

I will try this out this week and report in. I appreciate it. Probably going to try the driving method since it is a 4x4.

85_Ranger4x4 · Jul 21, 2016

Any luck?

Dmgctrl88 · Jul 26, 2016

I ran a full steel line that mates to both the intake vacuum and the modulator with a rubber hose holding both together. It still will not upshift.

I'm waiting to get the ranger back to my house since I'm no longer able to use my buddies shop.

So far I've tried a 1974 car valve body, cleaned up. No change in getting it to shift.

I'm going to do the associated checks via a vacuum gauge as outlined in the C5 diagnosis page (Thanks!!!)

Worst case I'll have to drop the transfer case and check the governor.

Add in an intermittent fuel pump issue (I believe its the in tank fuel pump). Which causes the ranger to go out after reaching warm operating temperature. I plan on re doing the whole fuel system, with new lines and pumps and filters. I still have the original I think. It's probably about time.

Will report when I get the truck back and get some work done on it.

Dmgctrl88 · Aug 18, 2016

Finally got a chance to do some vacuum testing. I bought both of the above items at harbor freight, the vacuum pump and the gauge.

I applied 18 vacuum to the modulator directly, and tucked the pump up in the truck and drove it. No change whatsoever.

I ran the vacuum gauge to where I had the modulator line running from the vacuum tree and got the following at idle.

Any ideas?

I'm beginning to think I will need to drop the transfer case and check the governor. After that, I think its time to take it to a transmission shop, which will hopefully be an easy fix.

Dmgctrl88 · Sep 17, 2016

So I rebuilt my entire fuel system because the ranger kept stalling. After re doing the fuel system I drove the truck around town and it finally shifted into 3rd gear! Someone give me the rbv v8 user badge!!!!!

Tedybear · Sep 23, 2016

It's ALIVE! Jolly well done!

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C4 not upshifting

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