"Screw" The PSD - How do you defeat it?
#1
"Screw" The PSD - How do you defeat it?
My PSD motor is toast and I’m giving my checkbook a break until this Fall to buy a rebuilt from Roger. Until then, I see in post 3 of the thread below that a bolt can be used to manually set the lock-up. How do you do that? Is it the PSD adjustment screw that he's refering to?
Thank you / Bruce
https://rennlist.com/forums/928-foru...e-rebuild.html
Post #3:
Thank you / Bruce
https://rennlist.com/forums/928-foru...e-rebuild.html
Post #3:
Last edited by NoVector; 03-02-2012 at 07:30 AM. Reason: Added url
#2
Get one of those level brake pumps, a shutoff valve and a quick disconnect so you apply pressure to the system and make it behave like a LSD?
http://www.pacificcustoms.com/hand-operated-brakes.html
http://www.pacificcustoms.com/hand-operated-brakes.html
Last edited by Andre Hedrick; 03-01-2012 at 06:56 PM. Reason: Link for hand brake pumps.
#3
Get one of those level brake pumps, a shutoff valve and a quick disconnect so you apply pressure to the system and make it behave like a LSD?
http://www.pacificcustoms.com/hand-operated-brakes.html
http://www.pacificcustoms.com/hand-operated-brakes.html
Last edited by NoVector; 03-02-2012 at 07:32 AM.
#4
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Someone suggested a hand-brake lever idea in thread a while back--I think it was Greg Brown who was kind of dig'n the idea and how it could be used in a track car. I was hoping for something easier and less expensive, like "Remove the slave cylinder, cover the holle with a plate and then adjust the PSD bolt..."
I know Time Murphy tried this on one of his cars. Put a GTS trans into it and it ended up throwing him into a ditch. Granted he's got close to 600WHP on this particular car. He blamed the PSD bolt trick. Decided to get an LSD and retrofit it. He said it worked much better after that.
If your purpose id to just street the car and you're at sub-400 WHP levels, I think the bolt trick might be okay. But I have no personal experience with it.
#6
I know Time Murphy tried this on one of his cars. Put a GTS trans into it and it ended up throwing him into a ditch. Granted he's got close to 600WHP on this particular car. He blamed the PSD bolt trick. Decided to get an LSD and retrofit it. He said it worked much better after that.
We went from WOT to full throttle closed and the car snapped sideways without warning.
Lucky for Tim he was able to keep it from going *** over tea-kettle.
My 79 diff was setup by Todd and I'm not 100% sure what he did but it's tighter than any other 928 I've driven. First time I drove it at speed into turn 5 at 120mph I simply let off the gas and I felt the ***-end stepping out. Taught me to heel / toe damn fast in that car.
#7
I think Mark A had issues with the slip amount changing as the tranny heated up (using the bolt method). I also wonder about running all the time with the PSD arm locked in place... I am guessing here, but suspect the PSD runs open diff most of the time..and then adds pressure as needed..and then releases.
Porken gave me the idea of using a hydraulic rally brake lever in conjunction with the rear slave....but I have yet to add this to my track car...
Porken gave me the idea of using a hydraulic rally brake lever in conjunction with the rear slave....but I have yet to add this to my track car...
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#8
Thanks everyone. You convinced me, I'll leave it as is. If the regulator, slave cylinder and lines need replaced too, I could easily see this project going north of $2,500. Guess I need to look into making that calendar after all
#10
If it's just the motor, you may be able to get by on the cheap. Lincoln MKvii from '86- 81 used ATE
brakes with the electric/ hydraulic motor.
Dimensions of the motor are:
housing= 4 5/8" to mounting flange (long)
flange=2 1/2" od - mounting "step" = 1 7/8" od
motor drives pump with a "tang"
electrical connection into motor=1 red & 1 brown
wire
mounting is probably not the same, but could be worked around if it physically fits.
These are in the self service junkyards for around $ 10.00 or so
Pic shows a Lincoln ap.
http://www.google.com/imgres?q=linco...75&tx=27&ty=71
brakes with the electric/ hydraulic motor.
Dimensions of the motor are:
housing= 4 5/8" to mounting flange (long)
flange=2 1/2" od - mounting "step" = 1 7/8" od
motor drives pump with a "tang"
electrical connection into motor=1 red & 1 brown
wire
mounting is probably not the same, but could be worked around if it physically fits.
These are in the self service junkyards for around $ 10.00 or so
Pic shows a Lincoln ap.
http://www.google.com/imgres?q=linco...75&tx=27&ty=71
Last edited by Jim Devine; 03-03-2012 at 12:59 PM. Reason: add
#11
SAAB 900/9000 models in the early '90s had MkII ABS pumps manufactured by ATE. These pumps build extreme pressure and there is no need for a brake booster, which leads me to believe it may function in a similar way to the 928 PSD system. The accumulator in this system looks identical to the 928 PSD one. It is also the same as the accumulator in a Buick Reatta (). It may be possible to use parts from the SAAB assembly in the 928 PSD system. You can find used pumps in self-pull salvage yards for $30.
Dan
'91 928GT S/C 475hp/460lb.ft
Dan
'91 928GT S/C 475hp/460lb.ft
#12
Probably like the Lincolns. The pressure is controlled by the big switch that screws into the casting. As long as you use the Porsche switch, the rest of the assy doesn't know if the pump motor has been changed or not.
Looks like there might be some options to save a buck.
Worth looking into.
Looks like there might be some options to save a buck.
Worth looking into.
#13
The price for rebuilt PSDs are pretty incredible; in the ballpark of 10-15% of the total value of the car. Man, I wish I knew the PO had disconnected it AND pretty pissed it wasn't caught during the PPI. But like the Army, I need to build a bridge and get over it. Thanks again / Bruce
#14
Buy a Rebuilt PSD - you know it makes sense 8>)
__________________
Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission? George Layton March 2014
928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission? George Layton March 2014
928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
#15
Running it as an open diff is no big deal really. Many 928s are open diff, many of those with factory slips are worn to the point they act like an open diff. The PSD is designed to do some neat stuff in turns but how often are they driven at the limit anyway ?? Fix it when you get tired of the warnings or plan to sell the car, until then just drive it and enjoy.