Blowing Seals...

[Nitekruizer]

I have two FMX transmissions. I have had each one of them professionally rebuilt more than once by supposedly reputable transmission shops. Within anywhere from a couple of days to a few months they always blow an internal seal and start slipping. Usually they don't slip bad enough to burn up completely at least not before the 1 year warranty expires. I take them back as soon as I notice them starting to slip. Someone at the shop always takes them for a test drive and tells me that they are fine. I know my own vehicle and I can tell by the feel of it when the tranny is slipping! Anyway,my question to you guys is do you think the problem is with the quality of the rebuild kits, seals, clutches, bands, etc? Is it a matter of sloppy work on the part of the transmission shop? Is there something inherently wrong with the design of the FMX that it can't keep it's internal seals in place?

[Donnie]

Can you explain just when the tranny is slipping, between 1 & 2 or between 2 & 3.. or when you kick down into passing gear (2nd)...Or in reverse? What year truck & engine size? I will need a lot of info to be able to help you...& no the Cast iron trans is NOT a faulty design .. A lot of opinions will surface..But they were well proven before the c4 & c6 came out.......Donnie

[Nitekruizer]

Both of these trannies came from cars and both donor cars had 351 engines. One was from a 1974 Ford full-size and the other is from a 1978 LTD II. I'm using the trannies behind a bone stock 351W. I don't even drive it hard and I've never used it to pull a heavy load. Just a daily driver. Both trannies slip in all gears including REVERSE. Unless I'm real easy on the gas they slip on acceleration,when going uphill,etc. When that happens I can smell a burnt smell from the clutches and/or bands. When I tried to drive up on to my ramps it wouldn't climb them. I had my foot into the gas and my engine was revving alot higher than it should have been and she still wouldn't move up the ramps. The 1-2 shift seems to be normal,so far. Sometimes the 2-3 shift seems to take place at a slower speed. Both shifts are soft,sometimes barely noticable,especially the 2-3 shift. However sometimes,when I take my foot off the gas and apply the brakes with the tranny in DRIVE,just as shes coming to a complete stop the trans will down shift itself into 1st with a hard bang but again,it's not every time but it is starting to do it more often.

[Donnie]

It sounds to me like you are running low pressure. Inside the pan right at the front of the unit is the pressure regulator. It has a strong clip around it holding the valves (plungers), they do not look like engine valves, but are called valves... into the alum. housing..2 bolts will drop it.
Years ago I recall these valves stroking out too control pressure & getting stuck on one of the passages & not returning, thus allowing the pressure to escape and running on low pressure will burn all friction elements, clutches & bands....ASk your trans man if he could check your main line pressure to see if this is your cause... As I recall we used to put a nut inside the spring to limit the outward travel of the valve so it could not get stuck open..Ford installed a sleeve at some point, not sure when, I think this trans ran thru 1981..Not sure....
Also anytime a trans. fails, it contaminates the cooler & lines to the cooler, these must be replaced or flushed out with liquid..AIR will not clean the lines as they are horizontal and the crap just lies there as the air passes over it, but when the new fluid comes along, with it's new detergents....WHOOSH, out comes all the left overs from the last failure & you are doomed to fail again... A good tranny shop will have a cooler flusher...Not the flush machines that have surfaced in the last few years that every gas & go shop has, one guaranteed to cure all your ills & relieve you of a 100 bux....ALSO, best to use type F in these units .HTH.......donnie

[Nitekruizer]

When I had my trannies rebuilt they installed new torque convertors and flushed the lines and cooler with some type of flushing machine. When I first started having problems I took it back and they test drove it and said everything was OK. I knew it wasn't. I then took it to another shop that I had never dealt with before and paid them to do a pressure test. They too said that it was OK. This was while the problem was still just barely noticeable. Since then it has become a lot worse. When I was driving with the other trans I did drop the pan to see if the metal tubes had vibrated loose but they hadn't. At that time I also pulled out those valves to see if the little "o-rings" were still in place. They were. I didn't know to check if the valves were sticking. When I put everything back it still slipped. I drove it, basically babied it, for about 6 months then replaced it with the one that's in there now. I haven't dropped the pan on the tranny that's in there now. The shop that rebuilt it told me they use the same fluid in ALL of their trannies but wouldn't be any more specific than that.

[Donnie]

Are you saying that the trans that is in it now is doing the same thing as the previous one?
Are you ever getting 2nd gear starts? If you put it in manual low, does it still refuse to climb the ramps? Which converter are you using? the original, or the one that came with the 2nd trans?
Are you dropping the bell housing & installing the conv. into the trans first? or are you short cutting it and dropping the trans with the conv.& bell in place... This can be done , but it requires some careful aligning..It is hard to diagnose on here...if I could see pressure readings, or drive the truck, it would be easy...Hope that you understand.......I'm trying..
You can reply to these queries & I'll give it more thought... I may have more questions.....Donnie

[Nitekruizer]

The convertor was put on the trans then the whole thing, trans and bell, was bolted to the engine. I'm assuming it's a new convertor,the tranny shop installed it when they rebuilt the tranny. No it doesn't want to climb the ramps in manual low either. No second gear starts. In DRIVE it starts in low then upshifts to second and third. The other trans did pretty much the same thing,slipping more and more and a burnt smell until burning itself up.

[Donnie]

Just an after thought.. .........could you have the wrong dipstick..or dipstick tube & be running low oel????????...Run your dipstick down along the outside of the tube as best you can.. or loosen all pan bolts 2 turns===tap the pan loose, hope that the gasket is Duraprene & is glued to the pan & no RTV used anywhere, that way the gasket will stick to the pan & you can tighten it back up.
The pan should be full of fluid, up to at least the case...
If you think the tranny is history, add more fluid, just to see????????????????? Donnie

[Nitekruizer]

Thanks Donnie. The fluid level is okay. It takes 10 litres to fill it. I tried something. I drained some fluid out and poured in 3 bottles of Lucas "Transmission Fix" in it's place. They say to use two bottles. This stuff is really thick so I figured it would bring up the pressure if there is an internal leak somewhere. It also contains what appears to be some kind of powdered friction additive. This actually helped. It didn't solve the problem but at least it's better than it was.

[Donnie]

I just had another thought: there were 2 types of filters used on these units
One filter was a "cloth" type media used by some shops to catch anything that got past the cooler flush process.. these filters were very restrictive & were meant to be changed to the brass screen, which is the correct filter to use... I would also, the next time that you drop the pan, check the "O" ring fit on the filter & make sure that the filter is a tight fit....A lot of extra O rings are included in many kit's as they are meant to fit a lot of diff. applications.. Some o rings are very close in size to each other, & it would be easy for a tech in a hurry to overlook a loose fitting filter... I'd like to see you put this one in the bad..........Donnie