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Someone is a little hazy on the pressure switch function
The '87-up pressure switch signals the EZK to retard timing during up-shifts AND downshifts, 1-2-3, and 3-2-1. (Downshift retard is shorter duration.)
I think anyone who cares understands what he meant, we all know this is a very binary system, no fancy code in a transmission computer that we all know doesn't exist with Porsche's intent to reduce torque to components during high load transitions when the trans is in a vulnerable state. I played around in this area for a while, but no longer do..but did end up with a modified/stronger clutch assy in my rebuild.
I don't think the gulf between what was said and what Porsche actually DID was lwas large enough to get up in a wad over it just to claim a high ground.
Look, Greg doesn't write code, you don't build transmissions..and neither of you are English majors, it's not what either of your customers pay ya for
I don't think the gulf between what was said and what Porsche actually DID was lwas large enough to get up in a wad over it just to claim a high ground.
Apparently, it was enough for you to spin the goofball's misunderstanding of the system.
The guy may have lots of experience but is completely worthless on theory. Valiant that he keeps trying, and trying, and trying...
First gear starts (or second gear takeoff with immediate downshift) are not the problem. If you let the transmission shift at low rpm, part throttle, low load (which my gizmo does) then it is just a normal gear change like the '83 to early-'87 transmissions do.
Constant full throttle, high rpm shifts, are going to accelerate wear. I suppose you could spin that to be what the guy is saying.
The last 928 I have is a strong 84 USA, into which we swapped 89 S4 trans. Single best mod I've made, albeit it was necessary due to broken 84 case. (83/4/5/6 autos cases are similar ...i just had access to the spare S4 drivetrain, I inch bigger diameter TC case, hence went that route). Second gear start, which can be defeated a couple ways. But real key to this swap, besides robustness, is the lower-than-typical transaxle gear ratio of 89. Really wakes up the early 240hp car. On tech aspects of S4 swap into 84, Bowden cable adaption is easy, as you just shorten it, whacking off cable and hardened cover shroud.
On the 16 v cars a bare cable wire is held at throttle linkage by a jam screw. No end needs to be applied.
On a 32 V 85/6 swap, as OP is contemplating, the S4 bowden cable must actually be lengthened, and an end fitting like on 85/6 be applied, as it attaches way up front near radiator, not with jam screw. Whereas S4 attachment is near engine, so it's too short. Not hard to do, I suppose, but expect to deal with it.
83/4/5/6 auto trans shift cable should be swapped with S4 version. Early cable can just barely fit but it's an unhealthy stretch against the larger S4 TC case, and you have to omit any cable routing bracket/guides, both early or S4, to make it reach.
Retrospectively, if I had a choice of units back when forced to swap, I'd still take that choice to utilize the S4 unit, esp the 89, but probably also any other S4 year.
T Tube works. I'm using 84. 85/6 will also work. Good time to refresh bearings, esp if you can swing a set of Constantine's bearings. Mine has the Constantine clamp, seems it was available back then, before he offered the bearings.
That 1-2 shift on my 85 and 86 auto cars was always a point of concern due to shock esp on moderate to heavy throttle. But even driving conservatively. Maybe just my perception of wear happening. After driving and riding new stuff like C8 vette that seems undaunted, I'd go that route for sporty launches, stay off flirting with razor edge f breaking 928 parts. Even if you cant own one, score a ride in one...it cured me from trying to pretend with 928.
Try to find 89 transaxle but any S4 should work for you if you have to swap
You can laugh and belittle me as much as you want, with your vast experience in rebuilding 4 speed automatic transmissions. (Have either one of you actually ever taken one apart and studied it?)
I never expect anything else, from you two.....it's a continuous, never ending, thing.
I simply am reporting, to the other people on Rennlist, what I see and what I have to buy as replacement parts for vehicles that are subjected to continuous 1st gear starts. Those people are free to do as they please, with that information.
Very simple stuff, me providing data from a vast reservoir of experience.
Which makes your continual personal attacks not only mysterious, but malicious in nature.
You considering belittling anytime someone doesn't agree with you.
I live and breathe data for a living. Anecdotal evidence is anything but, and that's all you've got here.
1985 - 1986 produced 9,341 928's. What, about half of those are automatics? So let's say 5,000 just to keep things simple.
Exactly how many 85-86 automatic transmissions have you concluded failed due to first gear start?
Why did Porsche change from 1st gear starts in 1986 to 2nd gear starts in 1987 (with the option of kicking down into 1st gear by flooring the throttle, if needed? Porsche just stupid? Porsche wanted the car to be slower? Better fuel economy by requiring more throttle opening to accelerate in 2nd gear, the same as it would in 1st gear? Anyone have any clue? Because after rebuilding dozens and dozens of these transmissions that were driven stock with 2nd gear starts, versus rebuilding dozens that were modified to start in 1st gear, I do know, for certain!
I don't know exactly how many "dozens & dozens" is, but lets just settle on 4 dozen or 48.
That's less than 1% sample size, typically you want at least 10%. You're not even close. But if we're going to count anecdotal data, I know more than a dozen owners of 85/86 cars with over 100k on the odo & the trans has never been rebuilt.
Back to your evidence
How much service history do you personally have with the "dozens and dozens" of cars that suffered this failure?
We all know setting up an automatic 928 to shift perfect isn't necessarily hard, but you need to know what you are doing and as time goes on, most of these cars not serviced by an experienced tech are driving around with transmissions not shifting optimally. How good is it for a transmission to operate for tens of thousands of miles not shifting properly?
Is there anything significantly different between the 85/86 boxes compared to the 87's in this regard?
Is lack of 1st gear starts the only change they made from 86 to 87 with regards to the transmission?
So you're telling me Porsche did this to save the transmission, so now if you want to take off in a more spirited manor, you must roll away in 2nd, mash the pedal dropping it into 1st (under full load) - this is OK for the transmission
VS
Coming to a complete stop, the transmission goes into first, then you remove your foot off the brake and floor the throttle - this breaks dozens and dozens of transmissions
That would be fun to try in a manual trans car. Roll away in 2nd, then shift into first and dump the clutch.
How hard is it to rebuild a 85 transmission? Is there any videos on this Auto rebuild? while you're in there are there any performance parts that you can place in there to make it shift quicker? My transmission is currently flaring in third gear. I've done the spring replacement in the valve body. Transmission shifts fine otherwise. It does not slip into 3rd. just flares and then goes in. That's only when I'm stopping on the gas. If I'm driving it easy it j shifts normally
There is plenty of information w/r to transmission work including steps for pump seals, piston, band services in this forum, if that is what you’re interested in. I’ve done some of that by way of help from the WSM, plus advice from the forum’s Gandalfs. Most of these services are also backed up with detailed steps in the WSM. If you have expertise rebuilding automatics, I would suggest posting specific questions about internal tweaks. Otherwise, I suggest posting what you want to accomplish, how much of your transmission you expect to tear down.
Despite the tenor of the conversation in this thread, Greg, Stan (MrMerlin) and others who more regularly tear down transmissions have common, WSM based advice that helps the casual rebuilder make sense of this delicate work and get through the job.
…On a 32 V 85/6 swap, as OP is contemplating, the S4 bowden cable must actually be lengthened, and an end fitting like on 85/6 be applied, as it attaches way up front near radiator, not with jam screw. Whereas S4 attachment is near engine, so it's too short. Not hard to do, I suppose, but expect to deal with it.
So, I’ve done the trans swap in reverse. I put the 88 auto trans into my 86.5. A trans failure plus necessity made strange bedfellows. The 86.5 Bowden cable fitting at the transmission is totally different as well as the cable fitting at the engine. The best method is to have both type cables, complete. The cables are each cutoff so the 86.5 connects to the transmission internal KD lever and the 88 cable connects at the engine. The two cables, appropriately shortened, meet in the middle via an adaptor. I can send the diagram of my adaptor to anyone interested who PMs with their email address.
Originally Posted by Landseer
83/4/5/6 auto trans shift cable should be swapped with S4 version. Early cable can just barely fit but it's an unhealthy stretch against the larger S4 TC case, and you have to omit any cable routing bracket/guides, both early or S4, to make it reach.
From experience, trying to make one MY trans shift cable work with a different unique MY is just saving some cash at the expense of a lot of aggravation. Buy the correct shift cable for the transmission in use.
Originally Posted by Landseer
T Tube works. I'm using 84. 85/6 will also work. Good time to refresh bearings, esp if you can swing a set of Constantine's bearings. Mine has the Constantine clamp, seems it was available back then, before he offered the bearings..
while you’re going thru (I emphasize) ALL THIS WORK, get the drive rod with non-tapered ends. There is almost universal agreement that this is a desirable upgrade. Yes, Constantine has nice ones and there are other sources.
10-28-2023, 06:10 PM
