Jchiodi

I plan on checking out harsh shifting by checking modulator pressue.

Read the write-up on it and I'm wondering is there an item number on the fitting used on the test port? It mentioned getting one at a junkyard but i'd just as soon buy one.

Any help on that?

Thanks...

davek9

You should check for no vacuum leaks first before attempting any adjustments.
So start w/ firewall connection that goes to trans.
Does it hold a vacuum?
Also the how is the bowden cable adjusted, tight will cause a harder shift.

edit: just read an excellent post by "Tails" on the total adjustment process.

MainePorsche

Regarding hard auto shifts, and evaluating the modulation pressure, I would first check all components of the vacuum to the modulator. Check vacuum at the 'T' piece below the airbox, then isolate and evaluate if the line holds vacuum, and then I would check to see if the modulator itself holds vacuum. You don't want to go through the modulator pressure evaluation (this I believe is while car is at 70 km/h) if the modulator diaphragm is faulted, or any of the other vacuum components are faulted.

When you get to the point of wanting to measure the three different transmission pressures, this is a good kit to use. Click on the link.

PC-85-928S

What ate the 3 pressures that are measured?
From what I understand this type of gauge is hooked up, lines run through an open window, and then you drive.
Have you done this procedure.?

Jchiodi

I'm in the middle of mm replacement now, and to get to my modulator, i will have to remove exhaust and heat sheilds. while i have it up in the air, i will be able to check vac hose at modulator. havent even checked the vac hose from engine yet, having way too much fun punching myself in the eye, getting crud dropped on me, and eating pbblaster to work on tranny yet.

That kit looks prety cool, and not a bad price. Looks like it has enough adapters to fit almost anything.

Jchiodi

Btw, on the procedure, i've read it can be done with car/tranny warmed up on stands. This will be interesting if i do it since my exhaust is welded and they might be off from the headers back!

Jchiodi

also, I do have the bowden cable, and accel cable adjusted pretty well. I could tell a difference after doing this, and the symtoms (harsh shifts) are actually much more pronounced with light accelaration, under WOT, it does give a jerk at shift points, but doesnt feel that harsh!

I should be able to get back on this problem by the weekend, hopefully i will be done with MM's by then....

PC-85-928S

i'd go this route first:
http://www.harborfreight.com/mityvac...ump-39522.html

the rubber tansmission vacuum on the back of the firewall seems to always deteriorate or break where it connects the metal tube that runs on top of the torque tube, back to the transmission.

You can see it from the passenger side underneath

MainePorsche

They are the Operating, Governing, and Modulator Pressure. The Operating Pressure is the highest and is essentially the working pressure of the transmission. The Operating Pressure is the only pressure that can be measured while car is up.
I have measured the Operating Pressure recently as I have a major trans problem I'm working through.

MainePorsche

With this kit be sure to use the right angle adapter as well as the straight one.
A single straight adapter does not give enough length and clearance to get over the lip of the transmission. BTDT

MFranke

Also check that the vacuum line from modulator to intake is sourced to the correct nipple on the throttle body. This is important if the intake was ever worked. There may be closely spaced nipples right near the throttle valve that get different pressures base in valve position. If you swap them by mistake then the modulator will not get much vacuum when you lift off the gas pedal and you will get hard shifts even though there are no actual vacuum leaks. The source line for the 5-way should be from on a nipple downstream of the throttle valve.

Jchiodi

MFanke, that my be it! I've done a refresh of vacuum lines and I'll check that I've got it on the right "nipple". I didn't have a diagram of van lines from roger when I did mine, and it was very confusing with just the WSM. Not anywhere as clear, especially using the different fittings that he supplies...

As I mentioned, the harsh shifting seems much more pronounced with when I have very light pressure on accel, much smoothing shifts when under acceleration.. just got done with taxes and mm's so I should be on this today!
jc

Landshark87

can someone elaborate on this - i believe the P.O. put in some new vacuum lines and i have some hard shifting. i think i just fixed the flare (the throttle and bowden cables were WAYYYYY out of whack!), but i still have some hard shifts .....

Mrmerlin

OK its been mentioned a few times here and no report of what you found has been given....,

SO do this remove the aircleaner,
then the feed from the 6 way vacuum fitting that goes to the transmission,
NOTE the 6 way is near the MAF unit.
And attach a mytivac to it ,
See if it will hold a vacuum..

Please post the results of this test.

FredR

An interesting comment- have never checked this out but I would have thought both these nipples are downstream of the butterfly- will take a look this evening at my spare manifold to check this. Like you say noting in the WSM to differentiate that I remember seeing.
On my set up one of these nipples leads to a blank [unused] connector I seem to remember. That may be because of the useless stuff I have ripped out like the air pump system. There was a vacuum actuator on something that led from the air box
- was advised to get rid of it many years ago- cannot even remember what it did.

Would be interesting to know if anyone has similar views.

Regards

Fred