Braggs

Fluid will leak out of the vacuum modulator hole... no biggie. Just catch what comes out and put it back in.

The length of the vacuum modulator pin is important. Too long and it will keep the valve open permanently. Too short and it won't open the valve inside the transmission. If you can't find the pin that came out with the previous vacuum modulator, your best bet is to go to a salvage yard and get one from a transmission there, or go to a transmission parts supply store.

You should have also replaced the previous VM with a black stripe VM (if you couldn't tell what the previous one was, like mine that was covered in dirt and oil). The other colors are for cars and provide softer shifts. The spring in the VM should be between 10 and 12 lbs of pressure to compress which means your vacuum line pressure needs to be above that to activate it.

ptharris4990

Good to hear about the fluid. I got the black stripe VM so I should be OK there. I'll try the junk yard. I guess I'll get a vacuum gauge and test the line.

Chris_1

iTrader: (1)

Good plan. Also, a lot of the better versions of the modulator have a screw inside the vacuum port for adjusting the shift.
Of course you need the pin first before the thing does you any good ...

84ordF150

DO NOT put any purged fluid back into the trans (it contains shavings) regardless of the condition of the transmission. Transmission Fluid is detergent based for a reason.
Use new fluid to top off. The original VM had the capability for shift point adjustment.

ptharris4990

OK quick update here.

I got a modulator pin and it has not helped at all. I started with the screw about flush, then backed it out, then screwed it in. No change. I shift it manually and I still have to let off the gas before it engages the next gear.

It also doesn't seem to always want to kick back down to first on its own when I stop.

I'm not so sure about getting the governor off. It looks like I have to remove the transfer case and the 4x4 extension. I just glanced at it but it looks like PITA. Am I wrong on that one? Also if I do embark on that saga will I need to drain everything first? If so, should I be concerned about swapping the fluid after god only knows how long?

I have not measured the inches of vacuum at the tranny but how much do I need to pull to operate the modulator? Braggs, I know you said the spring is 10-12lbs but what does that look like in terms of vacuum? With my previous ignition issues and subsequent advancement is it possible the engine isn't pulling enough vacuum? It runs well enough, I wouldn't take her cross country or to the tractor pull but it hauls wood and manure so far, though it lacks oompf.

I'm very open to suggestions at this point.

Braggs

Yes, it's PITA. Gotta remove rear driveshaft, front driveshaft, transfer case shield, transfer case, and maybe the transfer case adapter. The only fluid you should have to drain is the transfer case. Helps with weight lifting it back into place. A little fluid will drain out of the adapter.

Make sure you have over 12 lbs vacuum before the major repair... Could just be a vacuum leak now that you have the pin.

ptharris4990

Well $10-15 for a gauge to check sounds like a sound investment before I rip the thing apart (again). Just for clarification when you say 12lbs of vacuum is that the same as 12" of vacuum?

Braggs

Again? What did you rip apart before?

Yeah, if you're gonna be doing the work yourself, unfortunately, you'll need a few tools. Might ask at the box store if you can rent one.

You mentioned before that you had "some mean vacuum leaks". How did you test to make sure you had patched them all?

PSI is pounds per square inch. Technically it would be -12" since it's vacuum.

ptharris4990

I never ripped apart the drivetrain but when I was trying to get the vac leaks taken care of I replaced the exhaust manifold, intake/exhaust gasket, EGR pipe (deleted this one actually....I know...lets just not go down the woulda, should, coulda road the job was half done already I just finished it), various other related gaskets etc. What I thought was going to be a 3 hour job turned into a 2 week process involving many stripped and corroded bolts.


So far I have just been using starter fluid with the engine running to check for leaks and going from there. Like I said I replaced the intake gasket where the worst leak was but also have replaced EGR/carb gaksets, plugged unused vac ports, and tightened the pushrod and valve covers. I guess at this point I don't know where else it could be leaking or how to check more precisely than spraying fluid and listening????

Braggs

Sounds like you're on the right path to learning how it works and how crucial vacuum is on these engines.