I have a '71 f100 custom with a 390 moter and C-6 tranny. The tranny was rebuilt about 13 months ago when I rebuilt the moter. It went back into the truck together with the moter. Now (as my luck would have it, as soon as the warinty expires) I seem to have lost the use of first and second gear. It has third and reverse only. If I start out in first (by manualy shifting the selector into low) the truck starts to drive forward, but only barely, before it drives backwords and then stops alltogether. If I try to downshift while moving at about 25 miles an hour the rear wheels lock and the truck tries to turn around.
Finaly, when backing up if I put the tranny in drive before the truck comes to a COMPLEATE stop, the wheels lock and my head bounces off the back glass. *Ouch* I spent more money rebuilding this unit the first time then i have in the whole truck, I love the truck as it has been a good work horse for me. So this time I am going to do the tranny work myself. (Though I have never done this before) The only thing I have done sofar is drop the filter and oil pan, and rebuilt the valve body. I then reasembled the tranny and tried it out. No differance, thought it does excelerate faster in third from a stand still. However the problems still there. when I droped the pan the first time I looked at the fluid to see if it looked burnt or had any mettal in it. the fluid was red but had a little black stuff mixed with it to. It is somewhat gritty in feel but dosent stick to a magnet. What could be the matter and what do I do to fix it?
Thanks Guys and I hope to get this fixed soon.
Ohh I dont know it this will make any differance or not but when the tranny was rebuilt there was a shift kit installed as well
it is an automatic three speed. (one speed at the moment LOL)
Brad
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It sounds like the direct clutches have welded themselves together.

 

Did you do a air check when you had the valve body out ?

 

stuart1, "It sounds like the direct clutches have welded themselves together." you may be right but that dosent tell me much. Please explane.

Mark a. "Did you do a air check when you had the valve body out ?" I am not shure what you are asking but I will try to answer this question. I used an airhose to check the valve body, to make shure that the valves moved freely. If thats what you ment,
I did not think to put the air onto the tranny itself however.

will this help?

 

The direct cluthes if not lubed correctly will micro weld themselves together from the heat and friction. I am assuming there was some forgien material that lodged itself in the lube holes for the direct clutch housing. There are a million manuals on rebuilding the c6 available. Another thing you can do is contact AAMCO and tell them your symptoms. They'll tell you what it is over the phone and even give you a rough estimate. From there you can price a rebuild kit with all new clutches and steels with the soft parts. I do suggest buying a manual to see if you are able to rebuild it. A lot of people are scared of the automatic and don't want to bother rebuilding them. Truth be told a manual trans is harder to rebuild in my opinion. There will be a few parts that need special tools but you can take them to a shop and they'll do what you need. Remember no task is too hard as long as you give yourself time and patience to understand what your doing.

 

You are absolutly right about one thing. I am verry scared to do this rebuild myself. but for right now it is the only thing that I have to drive and the idea of spending 800 bucks to have it rebuilt again dosent set well with me. I have priced a overhaul kit through Autozone and got a 200 dollar price. is this the way to go? My fear is also with the work that I make this truck do, is this tranny ever going to be strong enuff to handle this moter? should I install an auxillery cooler for the transmission insted of relying on the one in the radeator? I have already replaced the rad once and when I did I doubled the capasity.( Went from a 2 core to a 4 core.) I pull a lot of waight at times and I use the trans to help stop. Maybe I need to look for a differant tranny insted of rebuilding this one? your thoughts?

 

OMGGGGGGGGGGGGGGg.

Run and hide.


The direct clutches are applied in high and reverse gears.

In a forward gear position the forward and direct cluthces are now applied which results in high gear.
When the selector is moved to low or second, that unit is applied plus both clutch pack.
That is the reason for the engine bogging down and stopping.

 

ok Stuart1, I would get in a rebuild kit every thing I would need to fix this? or is there something else part wise I would need?

 

Will give you all the basic parts.
Fibre, steel clutches, some bushings, sealing rings, front/rear seals, modulator.

You will probably need a band and pressure plates but you won't know until it is opened up.
A Transgo stage 2 shift kit would be nice too plus a convertor.

Go for it.
It ain't rocket science. If you run into any problems give me a shout.
I have over 40 years experience as a rebuilder.

 

what should I do with my torque converter? can I reuse the one I got or should I replace it? If so what one would you recomend for a low geared rearend? please keep inmind that I pull a lot of waight behind this truck (8000+ at least). I have pulled on one occasion 15000 and I want to be able to do more, more often.

 

If the clutches are smoked and there is lots of metal floating around get a stock rebuilt.
Get an old a/c condensor, clean it out, use it as a cooler in series with the radiator cooler.
Flush the radiator cooler and lines well.

 

You can put air to the clutch packs through the fluid ports when the valve body is off. If there is a leak you will hear it. I'd do it anyways if your tearing it down, just to see whats going on.

 

I did my C-6 with O.K. results. First, most kits don't include thrust washers, at least mine didn't, and you gotta have'em. Second, I have seen the internal linkage assembled a couple of ways and one will cause some of your problems. Lastly, don't use any kind of rag, cloth or anything else that "may" have lint on any internal part. I did and had to drain, clean both screens, and refill three times to get it working right and most of the rag out.

 

Thank you for pointing that out to me Chiefrider007. I will need to check my parts list to make shure I have them. I seem to have found a "Super rebuild kit" from O'Reilly's that is supposed to have everything in it from filter to bands and plates. But I dont know enuff about what I am going to be putting into this transmission to know what other parts I am going to need.

Stuart1, we you mentioned a "Transgo stage 2 shift kit". Is this something that goes into the valve body of the transmission? I really need some guidence here with the parts. It never seems to fail when I buy something from O'Reilly's, that I get the wrong parts for the job. (Of course I never find this out untill I have my ride toredown and cant go anywhere).

Thanks guys

 

The shift kit is installed in the valve body.

Transgo, no others.

B&M sucks, big time.