Bill Ball

Well, George's "new" tranny didn't need any adjustment.

You need to also verify that the modulator itself holds vacuum. This is why I recommend the static test at the end of the line in the engine compartment. If you put a vacuum gun on it you easily can determine if the line and modulator are air tight without having to get under the car. If so, then some adjustment of the modulator sounds like next step, but I agree, it would be a good idea to check with Greg.

Sorry if I sound like broken record harping on the vacuum issue.

the flyin' scotsman

thx Stan for the clarification.......not sure where I read the order previously, here somewhere.

I would believe then the order of cable adjustment is same with the std gbox?

Bill Ball

Stan's cable adjustment guidelines are great, as always. Still, I don't think this affects partial throttle shift harshness, which I believe is the only issue being reported here. It would affect shift and downshift shift points more than anything else. Please correct me if I am off-base on this.

When throttle cables are loose, the primary effect is that you will reduce throttle plate opening a bit and not trip the WOT switch, preventing the WOT fuel enrichment map from engaging. Snugging the cables to eliminate excess slack will fix that, and the Bowden cable will need to be readjusted so shift points are not adversely affected.

I know I've beaten the vacuum thing to death, but that's my simple-minded view of this issue. If it's not that, then hallelujah, it will be a good lesson when you find the resolution.

MainePorsche

I do note that the new transmission feels just like the old one did when it functioned. In urban, stop and go driving, (I think) she shifts late from 1st to 2nd and slightly less noticeable from 2nd to 3rd at low rpm/low speeds. I've never touched the cable quad other than do replace a snapped CC bowden cable. It is my feeling that the cables need to be orderly reset, and I feel this will remedy the issue. I perhaps am not reliably, and specifically describing the issue correctly. I feel it must be the cable quad issue for both transmissions to behave in the exact same manner. On this, there is no mistake. Even my son says it feels just like the old one.

Bill, I will test the line at the proximal end. I know the line is good. Regarding whether the modulator holds vacuum, I would be very surprised if the modulator was faulty.

I do not want to trouble Greg for I feel the problem lies outside of the transmission, and is remediable.

My Thanks again to the Masters for your help and patience.

Bill Ball

OK, I guess I misread your problem report. If the shifts are late then, yes, the cable adjustment is very relevant. Sorry about that.

Kevin in Atlanta

If you have access to a vacuum gauge, "T" it in at the manifold where it goes to the shift modulator and with enough vacuum line you should be able to bring it into the cabin to see actual vacuum under load. I did this years ago to verify a vacuum issue with my 86.5 auto.

MainePorsche

Hey Guys,
I come to you, especially Bill, with my tail between my legs.
I stated with surety that my new vacuum line I placed was 'good'. Well it wasn't. There was a tiny hairline crack that I did not observe along the long length of the line. I then protected it and installed. Funny that it held vacuum distally, but not at the proximal end. A new braided quality line was placed. I also adjusted the cables per Stan's instruction for the throttle cable was slightly lengthened at the ball. Going to take her for a run soon. Embarrassing.

Bill I owe you a cold one.

Schocki

Good that you found the vacuum leak source. What is the dynamic vacuum at the front under the hood?

It should be good to go now. One or two little harsher shifts when cold in the morning. But after a minute or two smooth a silk, unless you floor it

MainePorsche

At the 'T' it is 19.25 mm HG, and 19.25 mm HG at the distal end of the line before the modulator.

GregBBRD

No matter what is new or what got replaced, the first step is to always check for vacuum at the modulator....we've learned that brutal lesson here, several times.

I won't even take one for a test drive before I check this.....

MainePorsche

Would the vacuum pressure I listed above be adequate for proper modulator function ?

GregBBRD

Sounds correct.

While I'm certain that Porsche has a "standard" setting for the modulators (and all of these transmissions that we have used have worked /shifted virtually perfectly) it is certainly possible that you might have to do a bit of adjusting to make them work perfectly.

However, it would certainly not be the first thing that I'd start fussing with.....

MainePorsche

Agreed.

MainePorsche

Well Guys,
I don't know what else to do. Looks like I'll have to adjust the modulator.
Now have absolutely reliable vacuum to modulator.
Cables adjusted per Stan's recommendation.
At low speed local driving the car feels like it gets hit in the rear when shifting. The first shift when I pull off from a start is truly jolting. Even somewhat noticeable at quicker starts and when I'm up around 35-40.
I can't think of anything else to consider other than manipulating the modulator.
Is there anything else to consider ?

Bertrand Daoust

Hi Craig,

Here's a thread on adjusting the modulator:

https://rennlist.com/forums/928-foru...-pressure.html

I would definately take a look at the modulator.

I had harsh shifting on mine.
I played a bit with the "T" on the modulator and it made a huge difference.
I would recommend to use a pressure set though.

The linkage on the throttle bracket adjust the timing of the shift, and the modulator adjust the harshness - totally independent functions.

I'm sure you'll get it right. Just a question of time.