the flyin' scotsman

we're here for you buddy.......man made it, man can fix it

MainePorsche

You're a Good Man Malcolm, thanks.
I was just letting of some steam.
Wanted to check the Operating Pressure to see if it is the regulator valve is OK. This test would've told me a lot.
It's freezing in my garage and I'll do it tomorrow after son's Hockey in AM.
I've done about 15 trans pan drops in my 928 history. I always take care about the pan seating/gasket roll in vicinity of the reservoir, an area that is somewhat obscured to visual. Sure enough, this is where the roll was. For such a little POS thing, draining and the redoing just killed the afternoon test. Plus the fact I hate getting trans fluid all over.

dfrhodes

too curious...any update on this? or have you decided to wait until it warms up?

BC

Any update on this at all MainePorsche? I have SOME of the similar symptoms.

MainePorsche

Guys,
Sorry for not updating sooner. The winter freeze up here, and some profound personal/familial catastrophes had kept me from tending to the car and the List in general.
Enough said.

With full ATF levels at 80', Modulator vacuum disconnected, the Operating Pressure is 120 psi/8k Pa at 1400 rpm in Drive. Not good. Should be 16 kPa +/- 1 .

Is a primary pump change a complete transmission drop ?
I haven't researched this yet.

Edit: Just found the answer on the first line on WSM 38-152

MainePorsche

Guys,
Any recommendations on the way I should proceed ?
Anything I have not considered yet ?
Complete transmission redo vs just the pump components ?
Thanks.
This is a Big One.

MainePorsche

Bump.
Greg, Jim.
Help.

G8RB8

At this stage I think anything short of a rebuild is going to be a gamble. We still aren't sure (at least I'm not) what has failed. Isn't stall speed more like 3500RPM? Have you checked modulating pressure?

3. Check operating pressure. If too low or not available:
a) Disassemble and clean shift valve housing and service
operating pressure control valve.
b) Remove and inspect primary pump, replacing if necessary.

I think this is where we are, but not sure if both these can be remedied with the tranny in the car.
It's probably prudent in any case to have the valve body cleaned.
Good luck

MainePorsche

Hey Jim,
Thanks for the attention.
According to pg. 38-110a in the WSM it is 1400 rpm for a test no longer than 5 secs.
I can only check Operating Pressure - Modulating Pressure measurement requires pressure check while in motion at 140 km/hr.

Correct me if I'm wrong, but the shift valve housing (valve body) can be removed after removing the pan (?) This is where the Controlled Pressure Control Valve and Piston reside. It is also where the Working Pressure Control Valve resides.
I think next step is to get shift valve housing (valve body) off and to Greg.
I will go through the WSM and the 722 transmission pdf's and I hope there is nothing confounding about removing this piece. Are there any specific caveats about the valve housing removal ?

SMTCapeCod

Valve body comes down very easily. If you split the haves, care must be taken due to captured springs and esp metering ***** in the channels, etc.

IIRC one of the publications discusses removal of the operating pressure governor with trans in place...wonder if that could be the issue instead of the pump itself.

Admittedly, I have to go back and review the prior pages for symptoms/etiology.

MainePorsche

Thanks SMT.
I have inspected the linkages to the valve body (some many posts in the past !), but I wasn't sure if there were any attachments/linkages to the ventral surface of the body that were not obvious on inspection. I have read quite a bit on the valve body from two 722 transmission pdf's that were sent to me by Jim (G8RB8).
Craig

GregBBRD

I've gone back and read this entire thread. Very, very strange failure.

I'd still guess something happened in the final drive part of the transmission, if it wasn't for your "lack" of system pressure.

Obviously something failed, suddenly. There could be a pump problem although this is not likely. Could be an internal problem.....like reverse piston exploded and is causing a fluid loss. Could be in the valve body.

I'd agree that best thing to do would be to remove the valve body and take a look. If there is nothing wrong, inside there, then take the transmission apart. Either way, the valve body needs to be "rebuilt".

I've got two of these same transmissions to re-assemble, this week. I'll take some pictures as I install the valve body and separator plate, so it will be esay for you to remove and keep track of the pieces.

Kevin in Atlanta

Didn't one of our vendors get a few crates of new autos trannys last year? Buy a new one?

MainePorsche

Greg,
Thanks for the communication(s).
Isn't the Reverse Shut Off Valve (pistons x 2) and the Working Pressure Control Valve in the valve body ? Would not a fault in these result in the Operating pressure I have ? I think it would be wiser to have a look at the valve body before jumping to transmission at this juncture.
I was thinking of removing the valve body and shipping it of to you. I think I should send it to you for the 'internals'. You would be much better at diagnosing tell tale signs of drive trouble by seeing what is in the valve body. Also, with my lack of experience with this I would hate to have a single metering ball in the wrong place. I'll call you at the shop to get the shipping particulars.
Thanks again,
Craig

GregBBRD

I think this is a good idea. I've done many of these valve bodies and still think they are the hardest part of the entire transmission....they take me hours and hours. I'm not good enough to "throw all the parts in one big bucket" and then be able to put it back together....nor do I think I will ever be able to do this. There's 24 individual springs on one side of the valve body and 14 on the other....not including the ones between the two halves.

I really dislike getting valve bodies that have been apart, by someone else. I did one yesterday that had several springs that were incorrect....and not just in the wrong location. All I can assume is that they "lost" some of the springs and just went over and grabbed whatever looked close to the drawing. Luckily, I'd just had another, of the exact same valve bodies apart, the day before, and it was very "fresh" in my memory....plus I have very detailed pictures of what does where and what it looks like.

The other thing I could do is pull one out of a transmission, go through it, and send it to you, if that would help. I'd send you the entire separator plate assembled, too.