79 F150 400/C6 2wd.

Loss of reverse and it doesn't want to stay in high.

Strange thing happened today. I took my truck on it's longest test drive since rebuilding the transmission. It was about 25 miles. I got to the junk yard just fine and it was running just fine when I left. I went through a drive through to grab a burger and headed home. That's when it started acting funny. It shifted fine 1st to 2nd, then 2nd to 3rd, but it wouldn't stay in 3rd. It would shift into high, but the slightest bit of throttle and it would shift back into 2nd and eventually got so bad that it just stayed in 2nd, so I had to return to the town I was leaving. I drove to an autoparts store nearby. I decided to move where I was parked and when I put it into reverse, nothing was there. It rolled back. I drove it to the new spot and called for a tow truck. Weird thing is that reverse worked just 10 minutes earlier when I left the junk yard. When I got it home 2 hours later, it backed up under it's own power. I let it cool down completely and took it for a test drive and it drove perfectly. I have a few theories or questions:

Kickdown rod: Can it be in such a position that it could take away reverse? I would assume that if the spring wasn't returning it all the way forward that it wouldn't have shifted from 1st to 2nd properly. I ask this because I am not using the Holley spring mount and I'm wondering if the wrong spring set up allows the kickdown to be partially activated.

Fluid: What fluid are you suppose to use after a rebuild and what fluid can't you use. Mercon V says it supercedes earlier fluids, but is that wrong?

Am I wrong to assume that if fluid was the problem that I would have had problems with 1st and 2nd?

Cooling: What are signs of hot fluid other than smelling it. Once again, assuming I would have problems with all gears if fluid was too hot.

My guess is that something is sticking in the valve body, but before I drop the pan and pull out the valve body, I want to make sure all other avenues are exhuasted.

Thanks for any help or advice.

 

No reverse or high is a direct clutch failure.

It will probably have to come out.

 

I'm hoping it doesn't have to come out, especially since it drove fine last night after the embarrasing tow. I think I'm about just switching over to Type F fluid. I would imagine that performance frictions are fine with Type F. Nobody has responded to say if the fluid I'm running is an issue, but I was thinking maybe it was slipping due to the fluid?

 

I agree with stuart1, when you loose reverse and third the problem will be with the direct clutch. The fluid type wont cause it to not engage in reverse or not shift into third, I bet the clutches a toast in the direct drum.

 

You must use a fluid that is compatible with the materials that you used for the rebuild. If you used modern frictions, they are designed to work with MERCON V. If you used old stock material that was designed for TYPE F, then the use of MERCON V has wiped out your direct clutch.

 

I have a similar problem with a fresh rebuild.It will shift fine in all 3 gears until i let off the gas then it goes into 2 and if i give it a little gas it kicks in and out of third and falls back into 2 and if i give it good throttle it"ll kick into 3 and hold until i let off the gas again then it all starts over again.Started acting up after about a hundred miles or so of driving it, worked like a charm before that.Tried different things like changing the torque converter(had a 3500 stall in it/put the stock one back in) changed the modulator valve,and took the valve body back out and rechecked it for sticking valves and it"s still doing it. Could it be I"m using the wrong type fluid? I"m using dexron III which is recommended for my tranny (1980 ford f150 C6) and I think the overhaul kit was for 1967 and up or something like that(Transtec) PS not having any reverse issues works fine.

 

Hi,73 fourxfour

Have you found your problem yet? If so what was it?


Thanks

 

Haven't figured it out yet, but I'm thinking maybe my cooling capacity wasn't enough. It drove for over 20 miles just fine, cooled down while I was at the junk yard, backed out of the parking lot when I left and drove me to the burger joint. There I sat in the drive through for awhile. Then I headed out for my journey home. It was a few minutes after the drive-thru that I started having issues. I would have thought it would have cooled down from air flow if the drive-thru was a problem, but then as I write this I think why haven't I experienced this problem before. It's idled in the driveway longer than at the drive-thru and ran just fine.

It drives just fine now, but I have only taken it down the street and back, so maybe the fluid hasn't gotten as hot, therefore isn't showing any signs of problems?

Another thing I have been thinking about is the inline filter. I have a napa 1622 hydraulic filter on there. Makes me wonder if it could be a problem???

What would the signs of hot transmission fluid be?

 

Oh, 2 other things I wanted to mention or talk about. My kickdown and the valve body.

I keep forgetting to mention that I did disconnect my kickdown after I got it home, but I had already used reverse before doing that. I feel like I'm missing a spring in the kickdown setup and maybe the kickdown lever somehow was in the wrong position? Could the kickdown do anything that would prevent reverse? I guess I can go out there and play with it.

Kind of along the same line as the kickdown, maybe a valve in the valve body being stuck causing a pressure loss? Maybe I didn't do a good enough job on the valve body when I rebuilt it, even though the valves moved freely.????

Thanks for your help!

 

So I've run the truck in the driveway for more than a half hour. I have sat in it with my foot on the brake and in drive for 10 minutes. I still have reverse. Trying to replicate the drive-thru, although it's a little cooler here today. I'm going to take it out for a test drive in a little bit and then I will report back.

To answer a point Mark made, I used modern clutches, not NOS. Raybestos I think is what they were. Do modern performance clutches require a different fluid? Type F? The concensus I got from my research seemed to be that for the 77 and up transmissions when rebuilding you could run modern fluid or Type F if you wanted firmer shifts because Type F is closer to a modern performance fluid. Did I get that wrong?

 

Modern friction material works with MERCON V.

 

Thanks for the confirmation Mark! Now I can take the case of Type F back. Thankfully I didn't use it. It was $80!

So I just drove it around town and it was doing fine for the first few miles. No slipping. It would drop a gear or two when I got on it the way it should and shift up with quick and firm shifts. Even into high. But then it started acting up. It didn't want to stay in high gear again and when I got back home, reverse was gone. I have a vacuum guage installed under my dash to monitor the engine, and it sure seemed like it was low on vacuum when I was coasting downhill in high. I could have sworn the other day it was almost at 30' of mercury coasting down another hill so makes me wonder about that. I wouldn't think if I had a modulator issue of some sort it would take away reverse, but it sure seems that way when I'm driving because I barely touch the throttle and it downshifts. It's brand new, but I also have another brand new one, maybe I'll put it in for grins.

As for the feel of reverse, it doesn't even feel like anything attempts to engage. The rpms don't change going from park to reverse to neutral, but it does drop into gear when I hit drive.

My first thought when this first happened was that reverse-high was fried, but within so few miles, I thought even if I did something wrong I would get 50-100 miles out of it. I am maybe at 30 on a fresh rebuild. But when I left today they were both there and no slippage so I think I have a problem either in my valve body or govenor.

So now that I know this issue wasn't just a fluke my plan of action is to change the modulator even though I don't think it should matter I'm going to do it because it's a 3 day weekend for me and I can't get any other parts such as a temp guage, etc. So just in case I got a bad one that is making this thing run screwy.

Then I'm going to install a temp guage so that I know what the thing is doing, even though I can still touch the cooling lines before and after the cooler. I can't hang on for loner than a second or two, but I would think if it were really overheating I couldn't touch it at all.

If that doesn't tell me what my problem is then I will look into installing a line pressure guage. I could be wrong, but I would think that the pressure goes up to hold it in reverse, so I should be able to see this on the guage.

Then if I have no conclusive information from the pressure guage, I will rebuild the governor and the valve body, or maybe just buy them all ready to go.

If all that doesn't solve the problem then I'm going to give a lot of thought to switching over to a 4 speed since I have everything but the bellhousing and clutch. I won't give up on this transmission, but I'll put it in something else that is easier to install it in.

The fluid is clean and smells just fine by the way, even though I don't have reverse.

 

You must just enjoy tinkering with this. Nothing you are planning to do can cause your problem.

Why would you think that even built wrong you should get 50-100 miles? I would think that if something was wrong you would lose reverse and high in the first mile or two, if that long. It takes a couple seconds of slipping to destroy a clutch.

You have three experts that all have the same opinion. There is only one person with a different opinion

 

When I was getting it towed home I thought for sure the clutches were toast. If this were the case I would think they would be toast whether the trans is hot or cold. But once again after the trans cooled down, I started it up, backed it out the driveway, and took off down the street with it shifting into high and staying there down the street and back up which is a slight grade. It ran just fine and didn't slip at all. I guess I don't know enough to understand why it works cold and not warm/hot.

As to my remark about if I had built it wrong, I guess what I was saying is that I would have expected catastraphic failure almost immedietly, within a few blocks or miles, or it would last awhile but have a greatly reduced lifespan. This just kinda seems in the middle.

I would think that if the clutches were burning up I would have progressively felt the problem get worse instead of it just coming and going. Because the exhaust on this truck make it such a difficult and time consuming task to pull and put the engine and the transmission back in, that I've got to make sure that I've exhausted all possibilities before pulling it out. Working on the transmission once out is not a problem, but I don't have the time or money to pull the trans and redo the exhaust. If the trans really has to come out, the truck will probably just have to sit until after winter. My girlfriends car needs lots of work that has been put off due to my truck. Not your problem I know, but that is why I'm willing to try anything that doesn't involve pulling the trans. The parts for her car start showing up this week.

All of your input has been appreciated!

 

It's been a long road but I think I finally have the problem solved. I actually had two problems. I was using the black stripe modulator and it was wanting shift higher than my truck can rev. A green stripe modulator seems to have resolved that problem. I might need to shorten the modulator pin, but I would think turning the adjustment screw would achieve the same thing. But the big problem was that I was loosing reverse. I knew it was a pressure problem. I purchased a valve body from Broader Performance, but I continued to loose reverse after it was warmed up. I think I need glasses.

This picture is how your pump should look when you pull it out of the box, like mine when you buy a pump instead of rebuilding one. It should not look like this when it comes out of the transmission.
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It should look like this
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I can't believe I missed putting those seals on, but I did. Bone head error cost me a tone of cash.

I was tired of working on my truck, so I threw in the towel and I purchased a rebuilt tranny from a pro that sells rebuilt transmissions on the side. I'm surprised it lasted 5 miles. He forgot to put in the snap ring on the forward clutch. I guess you get what you pay for.
So after his "failed", I took mine back apart to rebuild it again, and right away I noticed the missing seals. Here's was it looks like when your engine reves, shifts, and gives you a loud bang leaving you only with reverse.
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