S4/GTS tranny conversion

diverdan · diverdan's Garage

My 1992 GTS Euro (S4, 28/42 engine) (2.75? or 2.?? rear axle ratio) automatic has sprung a leak from the front seal perhaps via the seal between the torque converter and the transmission. So this may be the time to convert to a manual trans. I have an 83 Euro donor car (G28/07/12 transmission) or for a few hundred bucks and my old automatic I could get an S4 Euro box. I am quite happy with the dual disk clutch from the donor car, but wonder about the advantages of the Borgwarner syncros. I also wonder what you guys think about the 2.20 US ratio verses the Euro ratios on the S4. I guess my GTS has little value except to me as a hot rod and in addition wonder how all these changes may affect its importability to the US when I have to come back. Anyhow, I enjoy these projects.

Diverdan

928sg · 04-08-2008, 05:55 AM

If you are going to convert your GTS auto to manual don't use any transmission older than 1985. The newer synchro's are much better. You could use the dual clutch from the older car just make sure the intermediately plate isn't warped or out of spec. The transmssion final drive ratio shouldn't effect importing to the US. Also make sure that you get LSD in the manual trans that you get.

One thing to keep in mind is that the GTS came factory with PSD instead of LSD and by going with a non PSD trans you potentially devalue the GTS. You will also need to remove the PSD pump and assembly if you go with LSD. In addition you will need to create a plug that will make the PSD computer think that the PSD is still present otherwise the computer will shut off, and disable the ABS as well. BTDT.....

I did this on my 90 model S4 which also came with PSD & now has LSD.

I used the trans from an 85 euro which is 2.73 I would have rather found a 2.20

RyanPerrella · 10:03 AM

I would get a later transaxle as has been mentioned above.

I am however going to try the dual disc setup in my GT so if you already have that then i would keep it. The stock GT and GTS 5 speed flywheel and PP weights 50lbs. Far too much for me, Ive been told the DD setup weights about 35 as is. I am trying to reduce rotating mass to gain responsiveness in the engine, so again i would stick with the DD setup that you already have. Seems like a great option to me, but get a newer gearbox.

Sterling,

I just bought an LSD from an 85 and was debating on switching the PSD diff and throwing this in. However i think it was you that mentioned putting a bolt through the transaxle where the slave cylinder goes to engage the diff so that it would act like a 40% LSD.

Do you know anything about this?

I dont know if my PSD is functioning correctly, the dash says its deactivated and i had tried to bleed it a couple years ago but couldn't get anything out of the bleed valve.

I can either buy a new pump for $1100
try and have the original pump rebuilt unknown cost and unknown source
try the PSD bolt trick and call it a day (easiest solution)
or try and swap in the 85 diff and pull the PSD.

I dont like that the PSD only works up to what is it 20-30mph, i find that annoying. But there was talk about making a chip to engage or activate the PSD at speeds over the factory setting which would make the system much more attractive.

Just curious what options there are I will be pulling the transaxle to reseal it and clean it up and thought i would come to a solution for the diff before pulling the thing. Having done this before, would you do the same thing again, or what would you do?

928sg · 04-08-2008, 10:40 AM

LSD is more work.... Mark Anderson had the bolt setup on his race car for a while. He would be the best resource for that. I would bet that there will be a degree of adjustement to get it just right.....

Danglerb · 04-08-2008, 10:52 AM

Borg vs ZF 5 spd preference is about $1000 USD, there is little or no market for older non LSD 5 spds and Borg's sell immediately, even faster with a LSD.

Diverdan if you are going to pull your auto and the PSD, maybe somebody in the states would be interested in buying the PSD parts? Can the PSD be used the Euro S4?

RyanPerrella · 04-08-2008, 10:54 AM

i may be interested in the PSD pump assembly assuming it works

SeanR · 04-08-2008, 04:48 PM

Quote:

Originally Posted by RyanPerrella

i may be interested in the PSD pump assembly assuming it works

Ryan, I'll be willing to take the non working one you have if you want to get rid of it. I've been wanting to take one apart so I can see what it takes to rebuild them. Besides, Ang's has it in her '90 and I like spare, non working parts.

RyanPerrella · 04-08-2008, 05:05 PM

Sean,

Still not sure if thats the cause for my PSD not being activated, but if it is and i do replace the pump with a new one, i have to be honest, I would want to take it apart or try and find a source for a rebuild myself. I think we do need to find someone to donate one, and we need to decide on someone to give it to in the 928 world and see if they can find a common fault with these. I think its a fairly common thingso it would be great to know what the issues is. I wouldnt be surprised to find that the failing part is common, and it could also be a cheap fix, but who knows, we need to find one and dissect it for sure.

I guess if i did buy a new one i could donate mine for research, but i would want it back.... preferably fixed (wink wink)

928sg · 04-08-2008, 06:23 PM

Dangler,
I have an 85 euro with lsd and the later synchro's.... it has the 2.73 ratio.... know of a buyer? I would like to have a 2.20 with lsd instead... I've heard the 2.73's have a higher resale than the 2.20's.

RyanPerrella · 10:10 PM

probably, i would prefer it was useable over a wider mph range though. (Speed restriction)

Apparently it can be cured via software. If that can be done then the locking can probably be mapped and tuned and make the PSD a really cutting edge system again. Currently it has some limitations, pumps that aren't so robust is one of them.

RyanPerrella · 10:09 PM

Your not again comparing a 928 and a big rig? Uhhhhhh, you will never get it.....

No Mr Wizard, Actually i was thinking more along the lines of Ferrari's E-Diff, or BMW's M Diff, or any number of other ELECTRONIC Diff's that are used as a TRACTION AID, not a lock or non lock only. These help with high speed handling and traction which becomes an issue when your making lots of HP. These are far more advanced then the difs you use to turn open and locked to climb up rocks and tow cows around and haul manure around with.

I dont know how Ferrari or BMW actuates its diff, but i assume its not far off what porsche did 15 years earlier with PSD which uses hydraulics. So what i am saying is that the hardware is there, the software is probably lacking and the computing hardware maybe insufficent as well. But the PSD uses yaw sensors and accelerometers (I believe) to make its adjustments. So the basic framework is there. I think it can be improved upon if someone could hack into the coding and see what kind of information it collects and if you can alter its parameters then you could possibly get a much better, more complete system.

Your standard LSD is DEAD in modern sports cars from the likes of Ferrari and Lamborghini. Even Mitsubishi and Subaru use this kind of stuff on various EVO and STI cars.

diverdan · diverdan's Garage

Great information. Thank you! Devaluation of the GTS is not a concern of mine as this car is not pristine and it already has an S4 engine. It has value to me as a cool hot rod. Mechanical and electrical complexity with their higher costs are not something that I care to have. ( My 83 Euro S is drop dead gorgeous and pretty simple, but I dig the GTS flares and the S4 engine really has better efficiency and more grunt, besides this thing was so cheap, less than I have invested in my golf in the last month.) I had to do it. Where is the PSD pump located? Even ABS is something that I can live without. I realize that in some cases it is very beneficial, however, if I'm in a skid and I need to go straight I can do that or release the brake long enough to make the thing change direction and then go back to the four wheel skid if need be. Yeah, the automatic stuff is better than I am, but I want to be the brains behind the control.

OK. I'll go with borg syncros, that is decided. Limited slip or PSD? I guess that would come down to maintainence costs and reliability. What is involved?

Thanks again.

Diverdan

RyanPerrella · 04-09-2008, 10:40 PM

unless you buy a 90 + GT or GTS gearbox you will have to ditch PSD. Buy an earlier box 85-89 and you can add a traditional clutch type LSD to it.

Sell your PSD pump to me, it is behind the left side rear wheel behind a small plastic cover. You can't miss it! Its got a bunch of hydraulic lines going to and from and has a small reservoir on top of it.

Assuming it works I want it. PM sent

Also i have a late model LSD as well, that may or may not work for me. (Probably not) but i maybe selling that.

928sg · 04-10-2008, 08:13 AM

Dan,
Its pretty easy to fake out the computer into thinking the PSD is still there. You have to completely unplug all the electrical connections to the pump assembly. There is a round 2 wire plug. make a plug that shorts those 2 wires together.... and no more warnings on the dash. If it's disconnected there are only 3 mounts if I remember correctly and it comes out.... I took out the line that went to the diff as well.