OD drop out at lower speeds

[twigworker]

Curiosity here...I have driven, shall we say several, LBCs equipped with both the D and LH OD units over the years and I cannot recall any of them "dropping out" of OD at lower speeds as noted in a thread below. If I squint my eyes and screw up my nose I might be able to make myself believe that certain AH 3000s did but I would probably be making that up based on the throttle position relay out under the hood. In my present B and all of the ones that I have driven lately the OD will work in the top two gears no matter at what road speed the car is moving. I am presently going through a black label LH unit and see nothing that would have any such control, either internally or externally VIA an electrical device. The only thing that I can think of would be a drop in hydraulic pressure when the pump is not working particularly fast in conjunction with the use of a light lubricant such as ATF or 5W or synthetic oil, which of course is a no-no. Perhaps in that case the cone clutch release springs might over ride the available pressure and release the clutch but who knows? If someone can further enlighten me on this I would appreciate it. Jack

 

[BoneIdle]

Jack.

I recently had a problem in 1st and 2nd that appeared to be the opposite of what you describe: Overdrive wasn't releasing fully and the two lower gears would occasionally cease to function momentarily. Serviced the transmission and OD ( drained and cleaned ) and everything seems to work fine now. I'm suspecting the thing hadn't been cleaned in 20 years or so. When I refilled the trans and OD I used 15/40 Rotella T. I have noticed that while I feel no ill effects from the Rotella, that the sizzle in the gearshift knob has quietened down. I'm gonna drain the whole thing again in about 400 miles because I'm curious about how much sludge is still in the system.

As a weird aside, Doc Entropy and I checked the fluid level before I left Tampa and aside from being a little low, the oil was unbelievably clean ( like new ). When I did the service , the oil was black as pitch. I'm wondering now if the stuff up top was never getting into the sump due to sludge.

 

[jlaird]

Cleanlyness is next to Godlyness.

 

[tony barnhill]

OD should drop out in an MGB when your speed goes below 45 (I think that's the cutoff)

 

[BoneIdle]

[ QUOTE ]
Cleanlyness is next to Godlyness.

[/ QUOTE ]

yep! And I found a new one:

The quickest way to a man's doghouse is through his greasy hands! /ubbthreads/images/graemlins/devilgrin.gif

 

[twigworker]

That is strange Tony. Not disputing what you say or if it "by the book" or not, I just haven't ever encountered the drop out on a B. In fact, since I am clumsy and forgetful and drive like a sissy I will often cruise into town in 4th OD and forget to snap the transmission out of OD when I roll up to a stop sign. Then, when I begin to accelerate again when I go into third it is boggy because it is still in OD and I have to very quickly clutch it to make things smooth as I flick back into "normal".

What is it in the OD unit that does the automatic kicking out at 45 or below? I can't see anything other than the spring pressure/hydraulic pressure over ride as noted earlier.

Dear Bone Man,

As far as dirty lube is concerned the stuff that came out of the transmission that I am rehabbing was weird too. Of course there isn't supposed to be much discoloration of the lube simply because there is no combustion process going on that would contaminate it. The only thing that one might expect is perhaps something caused by condensation trickling down the walls of the case and mixing with the oil to cause a light color change but that should be extremely rare. The only other source of "blackness" that I can think of would be the overheating and deterioration of the cone clutch in the OD unit, and that could be caused by extreme use or low fluid level. The one I am into right now had "sort of clean" clean fluid but there was lots gunk in the hydraulic passages traceable to the completely trashed speedo spindle gear and output shaft speedo gear. They simply weren't there any more.

One extra note...I have used gear oil in OD transmission off and on for eons but it struck me the other day that it might not be a good idea to have it in there in cold weather. I was looking at the drain back ports in the bottom of the OD unit and I thought of all of that thick fluid doing it's best to wriggle through the small openings without a pump behind it to get it to move. All I could envision is a sort of damming effect and that the fluid would accumulate where it really shouldn't be and not be where it should, out front and lubing the gears and bearings themselves. After reading and actually thinking about all of this recently I believe that I have talked myself into a strict diet of either a reasonable multigrade engine oil or a straight non-detergent 30 wt.

Jack

 

[Steve_S]

I've never experience an OD dropping out at lower speeds either. I do currently have an issue where I have to hold the gear shift lever to the side to get the OD to stay engaged, but that's a separate issue.

 

[PaulHanley]

I've driven my od engaged at speeds less than 30 mph. It always stays engaged till I flick the switch or downshift to 2nd.