BrickBoard Archives
The files contained in this listing have been automatically archived from the active forums. Because the vast majority of posts are now in one place, this archive is considered legacy. You should use the SEARCH feature OR choose your topic and select date tabs within the forum you choose.
740 OD problem solved...touch wood[ALL/1998] posted by Michael McBroom on
Thursday, 22 May 1997, at 12:02 p.m.
Thanks to everybody who posted responses to my query a couple of weeks back. I thought I'd post this follow-up to pass on what I found out. To recap: the car is an '87 740 with a manual transmission and overdrive. The overdrive was not consistently engaging. It was most likely not to engage if I had wound it out pretty tight in previous gears to 4th, or if I tried to engage it when the revs were greater than 2500 in 4th. Recently, it had begun to pop out of OD, or when I'd hit the button it would pop in and out very quickly, requiring that I hit the button several times.
Fortunately, the fix appears to have been an easy one. I had decided that, before I would tackle anything electrical, I'd replace the fluid in the transmission first. It took me a while to find a local source for Red Line MTL, but I finally found one, and was able to replace the fluid in the transmission/OD yesterday. This alone appears to have done the trick. So far, every time I have tried to engage the OD, it has, and it no longer pops out like it did before. As far as shifting performance goes, I haven't noticed much of a difference. 1st to 2nd had previously been a fairly slow and heavy shift. It seems to be somewhat quicker now than before.
I recently purchased this car, so I have no idea what kind of ATF it was that I drained out. The level was probably not more than a few ounces low (~200ml) -- if that. I did an inexact measurement of the old fluid and came up with something over 2 qts. (My Haynes manual says 2.4 qts.) My guestimate is that there was about 2.25 qts in all. It smelled burnt, though, like brakes or a clutch that had gotten too hot, and was quite cloudy. The overdrive unit (a Type P, btw) looks to be either new or recently remanufactured. I removed the bottom inspection plate from the OD and inspected the screen. It was clean. The magnetic strip on the underside of the plate had a light coating of gray-black residue. I'm curious, does the clutch in the OD have a friction surface similar to those found on regular clutches?
Re: 740 OD problem solved...touch wood[ALL/1998] posted by Mark Klein on
Thursday, 22 May 1997, at 3:23 p.m.
Its very similar to manual clutch plate material. It can wear out but I've never seen one "worn out". The backing which this "clutch material" is glued to can break from abuse (shifting without the clutch)or the o/d can malfunction from fluid pressure loss (internally). I'm a little curious. When your o/d was dropping out of gear, did the indicator also go out? If it was caused by the fluid like you suspect, the indicator would not have gone out when it disengaged. Lets keep our fingers crossed.
Re: 740 OD problem solved...touch wood[ALL/1998] posted by Michael McBroom on
Thursday, 22 May 1997, at 6:08 p.m.
Mark Klein wrote: "I'm a little curious. When your o/d was dropping out of gear, did the indicator also go out? If it was caused by the fluid like you suspect, the indicator would not have gone out when it disengaged."
No, the indicator has always been in-sync with the OD. If the indicator didn't light, the OD didn't engage. If it did, the OD would, too. When it popped out of OD, the light would always go out at the same time.
There's a pressure switch somewhere on the transmission or OD, right? Could it be that, because the fluid may have been a little low, or may have been the wrong type, this condition would have interferred with whatever signal this switch sends?
Re: 740 OD problem solved...touch wood[ALL/1998] posted by abe crombie on
Thursday, 22 May 1997, at 6:24 p.m.
Like Mark was saying if the o.d. goes away without losing the light your fix is probably dead on target. The o ring seals on the o.d. apply pistons will get worn and the o.d. will go away from pressure loss and replacing the oil with thicker oil will make this go away for a while (maybe forever). If the o.d. light goes out and you lose od.then you are looking at 1) od switch wire problems 2) od relay problems 3) 4th gear switch problems
Re: 740 OD problem solved...touch wood[ALL/1998] posted by Michael McBroom on
Friday, 23 May 1997, at 1:21 a.m.
Abe Crombie wrote:
"Like Mark was saying if the o.d. goes away without losing the light your fix is probably dead on target...
If the o.d. light goes out and you lose od.then you are looking at 1) od switch wire problems 2) od relay problems 3) 4th gear switch problems."
Well, like I was saying, "touch wood." I've put over 50 miles on the car since changing the fluid yesterday, and put it through paces that would have guaranteed that the OD wouldn't have engaged before. Not once has it failed to engage, and not once has it popped out.
This OD unit looks like it was installed shortly before I bought the car. No road grime or dirt at all. It's *shiny*. So, I'm hoping that it's in good shape internally as well.
As to why it's not obeying the rules of troubleshooting -- the only thing I can possibly think of is that I disconnected and reconnected the hot wires to the OD solenoid and the 4th gear sensor switch a couple of times. If there had been corrosion or crud buildup on either of these contacts, this may have scraped it off.
Re: 740 OD problem solved...touch wood[ALL/1998] posted by Mark Klein on
Friday, 23 May 1997, at 10:29 p.m.
Funny this happened now. Just this week I had one with a "finicky" 4th gear switch. You could hook a test light up at the relay connector and move the shifter and watch the connection being made and broken. This was manifesting itself as an o/d that would intermittently drop out of 5th. Turns out it was when his hand was resting on the shifter. We'll still keep our fingers crossed for your o/d.
Re: 740 OD problem solved...touch wood[ALL/1998] posted by Michael McBroom on
Tuesday, 27 May 1997, at 1:43 p.m.
Maybe I should have found a piece of solid wood instead of veneer . . .
After 4 days of flawless OD performance, the problem has reared its ugly head once again. I agree that the problem is most likely electrical, probably the the 4th gear selector switch, rather than the solenoid.
I find it puzzling, though, that no amount of jiggling and wiggling of the gearshift lever will cause the light to go out and the OD to disengage once it's lit. Same goes for the opposite condition.
Time to dig out the test light and go through the whole bidness, I guess.
Re: 740 OD problem solved...touch wood[ALL/1998] posted by Mark Klein on
Tuesday, 27 May 1997, at 8:54 p.m.
Let us know if we can be of assistance.