Fronkenstein

Has anyone ever tried separating the gearbox from the differential cavity by plugging the galley? I am awaiting some info back from Swepco and Driven petro products and may do the following:

1. plug the galley between the gearbox and the differential
2. vent the differential cavity
3. use differing fluid formulas for each cavity

If anyone has tried this I would like to hear as to whether it was a fail or something of value was achieved.

In doing some research over the much debated Dextron vs 75w90 subject I have found significant evidence that Dextron was not an alternative. In fact there are manual gears boxes made today that use synthetic ATF.

The RedLine, Swepco and like fluids everyone seems to be using were designed to double as gearbox or diff fluid. These gearboxes are either timed sets or use the Borg Warner conical bronze synchros which are very different from the moly expansion synchros in the 928 box.

The diff wants heavy oil with slippery additives whereas the gearbox wants lighter oil with good cleaning and heat removal characteristics.

Anyway that is my theory and I would like to hear from anyone that has experimented with dual fluids. Saab 900s used 75w90 in the diff and a much lighter oil in the gear box and always shifted flawlessly.

Fronkenstein

GlenL

This is interesting. Sounds like a lot of work to investigate a theory. Do you have a significant problem? You could try running the gearbox fluid in the whole tranny and see if it shifts the way you like.

I've had these out a few times and don't recall that the diff section was separable from the gear section. Seems you'd have to disassemble the tranny to get in a weld (?) a plate in. A seal around the shaft to the diff?

I gotta say, easier to join us on the gear oil trial parade. Swepco? Redline? Mobil-1? Mixes? Additives?

Fronkenstein

Glen,

Why is it any easier to join the parade of empirical guess work than to do what should have been done to begin with. Talking to petroleum techs at Driven and soon to hear from Swepco who I am sure with agree with Driven; confirms that fact that the diff and gearbox really need separate fluids. This is even more important with LSD equipped cars of which my car will soon be; hence my interest.

As far as closing down the galley and sealing the bearing - mere child's play. No welding required just a little time in the machine shop and without removing the transaxle from the vehicle.

They don't call me Fronkenstein for no reason

Fronkenstein

hacker-pschorr

I applaud the effort but it's not like these are new cars and issues are starting to crop up pointing to a problem.

I'm convinced the #1 issue with the early cars is mechanics having no clue how to adjust the double disc clutch and people driving around grinding down the synchros. No fluid is going to help prevent or fix that issue.

The later cars do not have issues with the manual gearboxes, unless they are raced with high torque engines....again...something fluid isn't going to "fix".

Is it ideal? Probably not.
Would the time / money be better spent engineering a good cooling system? Yes.

The fact that these cars never came with a manual transmission cooling system blows my mind.

GlenL

That's interesting. I think you're confusing "empirical" with "anecdotal" and, in any case, are suggesting that you'll have a truly objective way to evaluate shift quality and gear wear. How will you decide if what you've done is good, better or even "the best" way?

Hacker is hitting my real interest in this. After a few hard laps at the track the tranny doesn't like to go into 4th gear. That'd be a down-shift in a corner and it's really inconvenient. A good cooling kit made from off-the-shelf parts would be very much appreciated.

Fronkenstein

Hacker,

So I'm fighting with a grumpy 2nd to 3rd gear transition. I completely released the clutch with a bonnet prop placed between the clutch pedal and front seat mounting bracket. I then crawled under Inga and pushed the "T" adjusters back toward the transaxle as far as the would go as several have suggested be done here on the list. The actual air gap in the "T"'s rivet slot was under 1mm but the pins were right out there. I lubed the "T"s and pins while I was in there with high pressure grease just to be extra sure. I crawled back out and took it for a ride. I experienced marginal difference. The only thing I noticed was that the discs wanted to engage closer together. In other words I was experiencing two engagement points in the pedal travel. One just off the floor about 1-2" what I would call the "slider" that you would use at a light; and the other engagement about another 1" past the first. The second engagement is when both discs are engaging plates on all surfaces before completely releasing the pedal.

Now that I have had this clutch apart 3 times I am comfortable with my understanding of its operation. What I am not comfortable is a grumpy 2nd to 3rd transition. This transmission has been completely refreshed with new bearings, seals and synchros. I've refreshed many Muncie / Borgs over the years but never a Porsche 5 speed with these crazy moly synchro bands. Is there a settling in period for these synchros? As far as I am concerned this transmission shifts hard at low RPM without timing it, but is fine above 2800 RPM. It seems that 1st, 3rd and 5th are the most difficult which are all the "pull gears".

When I dumped the fluid out of the original transaxle, very dirty Dextron fell out. And there was an aluminum tag on it that said "use Dextron III". This and the opinions of race oil producers points significantly that Porsche really did intend them to operate on ATF. Today's ATF like Driven's STF is used in manual gearboxes for racing all the time. However it is not used in transmissions that share gearbox and LSDs.

Anyway I know the following about my clutch:
1) The discs are new
2) The pressure plate is excellent
3) The intermediate plate seems fine, although I am not sure how to test it
4) Throwout bearing is new
5) Pilot bearing is new
6) Throwout tube is new
7) Master cylinder is new
8) Slave cylinder is new (and plunger modified)
9) All clutch lines are new

The only questionable item is the short shaft. There is visible wear if you close. My next step is to buy one of Greg's short shafts to complete the new parts ensemble.

Sorry for the long-winded response but this is starting to irritate me a lot. I am up here on a plane on the way to a product launch and all I can obsess about it this clutch issue

Fronkenstein

Fronkenstein

Glen,

Anecdotal to a point. What I meant by empirical experimentation is creating Dr. Jekyll mixes without any scientific approach or understanding what the mix is really creating. Like I think it was Rob or Randy said 'mixing fluids with additives seldom ends with good results' and was very much against it.

Driven also agreed that creating cocktails, while they may work for a time, may have serious detrimental effects on other components. ATF and LSDs are not compatible.

As far as off the shelf transmission cooler parts? That's not too hard. Get yourself a Saab 95 oil cooler, an electrical oil pump, medium pressure line (doesn't have to be braided just has to be rated for hot oil at 300PSI and some fittings and adapters. I don't know what other guys are doing for their set up but I would put the sump side on the rear dump port with a filter between the pump sump and transaxle and push the oil into the front dump port. The GPM shouldn't be too high as you don't want oil to pile up in the gearbox. So some basic pipe flow math to determine flow through the galley at a temp/viscosity vector that works for your application. The good thing is you can just shut it off when your not tracking the car (if its a street / track car that is)

Fronkenstein

mark kibort

what kind of adjustment of the INT was that?? no no no. just go under the car, no bonnet post needed, and just make sure the gap is 1mm or so. (.75mm).

even if that was the problem, which would show itself mainly at idle and putting the car in 1st and reverse), i dont think that would cause much of an issue between 2nd and 3rd shifts.

there is no need to put different gear oil in the main cavity and separate it from the diff. redline 75-90 NS works great. or for older gear boxes, try swepco... that worked for me when i had the 84.

mark kibort

you absolutely DO NOT WANT TO adjust the H (or "t"s) as you have done. they are designed to stay in place and NOT move. the advice that anyone that gave you or saw about "pushing them all the way back" is totally wrong and i can prove this very easily on a normal 928 dual disc. if you understand how it works, you will see its obvious that that is NOT the way to adjust them and that can cause major drag issues on teh drive line to make shifting very hard. all you need is a 1mm gap and the INT plate retracts from the flywheel but DOESNT GO BACK FAR ENOUGH to have it touch the pressure plate too!!!!!!! KEY POINT!!!! for those that pushed it all the way aback and it worked..... they are very lucky and something is different in their system. (either worn discs, or a lever arm that pull's the pressure plate back further than normal) no reason to do that technique and its more likely to cause a major issue

mark kibort

yes, the early gear boxes need some wear in. I had mine rebuilt many years ago with new synchros and sliders, shift forks, etc.. and it took about 3k miles to be good again. thin oil here is not your friend by the way.
whats up with alunimum label that said use Dextron III. where was that and why do you think it was attached to the stock 78 transmission?

and, after complaining to the shop that did the work long ago, we tried sweptco by advice of Devek and guess what... it worked really really well! i was amazed.

Fronkenstein

Gap between what and what? Under the T or?

And i am using swepco 717 in a 79 transaxle

Fronkenstein

Mark, 1mm gap between what and what? I set this up when I installed it exactly as spec'd. I also referred to that very long and concise clutch post someone put up on the list. When I installed this the INT was equidistant from pressure plate and flywheel. So how could that have been wrong?

mark kibort

1 mm gap bween the H adjuster arms and the center post. read my post on the INT plate adjustment. Its right and you cant go wrong with RIGHT!
how do you know the pressure plate is equidistant? either way, dont do it that way. you adjust it by the H adjusters. their ONLY purpose is to limit how far the INT plate gets pulled back toward the rear when you push the clutch pedal. Thats it!!!! any further than 1mm, and the INT plate will touch the rear disc and that touches the pressure plate. you do his adjustment without pushing the clutch pedal down. i dont know what you were trying to do with the bonnet bar, but i take that is pushing the clutch pedal down, and then going down to the "H"s and pushing them back? thats making the problem much much worse.... then , lubricating them is even more worse!
again, the ONLY function of the H adjusters is to limit rearward travel when you push the clutch to the floor so there is no drag on the drive line. (thus allowing smooth engagement of 1st and R at a stop)

see my pictures on my thread of the topic

DO NOT PUSH THEM BACKWARD toward the transmission to adjust unless there is no gap when the clutch pedal is not being pushed. if so, push them back only to create a 1mm gap

mark kibort

https://rennlist.com/forums/928-foru...ml#post5775273

this is what the Hs look like. the last picture is proper adjstment

Fronkenstein

Mark,

Look at the picture and please answer the question. Your last post seems contradicting so I am now confused.

Here's the pic: