79 f150 supercab LB, 351m, c6 AT, 72,000 original miles. The problem started with second gear not engaging and trans would eventually shift to third. This happend occasionally at the beginning and then it became more frequent. I would feel the trans halfway shift to second but not fully engage, and as I accelerated it would engage to third gear at about 35mph. I changed the fluid and trans filter, and added a bottle of Lucas trans stop slip. This fixed the symptom completely and truck seemed fine for a couple months. Then the same thing started happening but got progressively worse, including a whining noise and thump after if and when second would engage. Often the truck would start out in third gear and I would creep along untill the truck got up to speed, then it would drive normal. Reverse worked fine too. I adjusted the intermediate band as specified with no change. I then changed out the modulater with a green stripe (I thought this was the correct one) this made the problem worse so I put the old one back in. I have since learned from the ford book that my truck calls for a purple stripe modulater which i picked up todsy but havnt tried yet. Now the part that baffles me. I took the vacuum line off the modulater (the original one) and capped it off, then test drove truck. Its starts out strong infirst gear and I can switch manually to second and it shifts perfect. No third gear. Reverse works fine too. Also like this the noises and thumps are gone. It essentially drives normal with exception of not having third gear. Im assuming this means i have a vacuum problem? I have checked lines and cant find any problems. I did rebuild the carb a couple months ago and have had a little trouble getting it tuned just right but trans worked fine right after carb rebuild and for a while after. I should also mention that when i shift into drive there is a two second delay before it engages unlike reverse which is immediate. Taking the vacuum line off modulater corrected this problem as well. I appreciate greatly any suggestions anyone has. Thanks for reading

 

Didn't you post this a couple days ago in another thread?

I still think a re-build is called for, including a torque converter

If you're up to trying it yourself, get the bad shoe video off ebay and the rebuild kit.

Ps...unless you're the original owner, its more likely 172,000 miles on it

 

Yes I posted about trans trouble several days back but my description of symptoms had gotton so confused I thought it best to start over now that issues were clearer. The 72k are documented well. I bought from original owner who is passed now but was a surgeon and used the truck very little over many years and took it for maintenance often. He kept everything. How long would you say a rebuild would take for someone new to transmission work but can follow detailed instructions well like I did with carb rebuild? Thanks

 

Having never done it myself, I can't say. However, LaserMike just rebuilt his and could probably give you some pointers.

I think the hardest part is getting the transmission out of, and back in to, the truck. Experienced guys rebuild them in under a day. If you get the parts and video ahead of time, and study the video repeatedly, you could probably do the rebuild in a long weekend.

Anyway, I'd plan on a week, or three weekends. But again, I have no experience with it, and am only going by what others here have said.

 

Yeah I hear ya. Im a planner, I would definately study up and be confident before I tackle domething like this. I think I'm starting to realize that a rebuild is gonna have to happen one way or another. Question is is unusual for fluid level in trans to be much highet on dipstick with truck cold? This is the case with mine and I hate not understanding why. The stick is hard to read when hot, i have to rely on the little holes because fluid gets on it up higher but third (highest) hole will be clear. Just strange to me, never had a vehicle where I couldnt see a definitive level on stick.

 

Yes, the fluid reads high when cold, just like when you initially change the oil and the filter has not filled, you get a false high reading on the engine dipstick. I have only owned a few automatics but as a seat-of-the-pants rule assume that what looks like a quart over cold will be about right when hot.

 

I wouldn't worry too much about the cold reading. The dipstick itself says "check when hot, idling in park". So get it hot (driving for an hour?), pull over, pull the dipstick out, wipe it, put it back in, pull it back out and check it. Fluid should be between the holes, as I recall.

 

I'd try the proper modulator, but it sounds like the transmission might be due for a rebuild.
What about your kick-down linkage?

I had a '68 Cougar with a C4, and one time the vacuum line to the trans got disconnected, and it acted very much like yours when you disconnected the modulator, but mine felt soft and like it was slipping. I was sure relieved when I found the problem and my transmission went back to normal.
72,000 sounds low, but if that doctor was towing big boats or lots of horses, then I guess it could be worn out.

 

So I put in the new modulator (book called for a purple stripe). No change which really sux. I'm guessing that the way it acted with vacuum line removed ( shifting good manually, no noise or slipping) is really irrelevant ? Is it still possible that low vacuum pressure is the reason first and second are acting screwy and third and reverse operate good? Really wa nt to be sure before I pull the transmission that a rebuild and probably a shift kit are going to correct the problem (any recommendations on shift kits welcomed too). Thanks for input

 

Btw the kickdowm wasnt working right and right now i have it and am driving with it removed. Also not sure if i mentioned but with modulator on when I put the gear selector in D theres a 2 second hesitation in engagement (reverse is strong and quick). If i remove vacuum it corrects the long delay when I put it in drive.

 

In the 79, I once forgot to hook up the vacuum hose to the modulator, and the transmission wouldn't automatically upshift from first to second.

My 78, however, wasn't as easy. When cold, it'd take a long time to engage forward gears. Reverse was good. Then the problem became worse, to where it took a while to engage the forward gears when warm. It's now in the shop for a rebuild.

 

I've decided that even with the low mileage I'm gonna have to go for the rebuild. A good point was made about not knowing if the PO towed alot. It does have a HD hitch on it and it looks like it was added. I cant afford it until jthe first of next month but Lucas stop slip is helping me get around as this is my only running vehicle at the moment. Any suggestions on rebuild appreciated. Also should I put in a shift kit and which one? I will replace torque converter to, any suggestions on that appreciated too. Thanks for all the input

 

The best way would be to get one of your other vehicles on the road, and tackle the rebuild yourself. Although you could probably do the job in a few days. I don't like not having at least two running, driving, vehicles.

 

Yeah, I recently sold my 86 Suburban cause i really needed cash and there was no way I would sell my ford even though it wasnt running as good. Its stressful only having one vehicle. Do you think I could tackle a rebuild in two days? I really can't miss work and do not want to attempt if two days is not realistic.

 

no offense, but guys that CAN do it in two days KNOW they can do it in two days. For the rest of us...no way