Brittany Chen Li

Hi my 1986 928 Automatic shifts very hard with a hard jerk feeling as it goes through the gears. It has always been hard but yesterday it got worse to the point it’s uncomfortable to drive any length of time. Does any one have any suggestions? I hope it can be adjusted to smooth it out some. Please some one can help me with any information. Does any one else have a 1986 I have other questions that will only relate to that engine.
Peace, Brittany Chen Li

Thank-you to all of you wonderful new friends who help me with this prob. Bless you all ! I have not fixed it yet but I hope to have time soon Thanks again! Britt

slevy951

When was the last time you changed the fluid in the transmission? It may be old.

Randy V

Scott,

Do you have any of those odometer gears for the 928? (ref. your link in the above post)

Brittany - if the trans fluid/filter service doesn't correct it, you probably need to have the vacuum modulator adjusted - simple to do.

Brittany Chen Li

Never did? Wow it this doon is ther detailed info somewhere on the web on this?

Randy V

Put down the coffee cup and try again - hah!

(click on the 'edit' icon - little pencil/paper - within your post to make any corrections.)

Randy V

I'd suspect a fluid change, then the vacuum modulator - not the same as the 'shift point' adjustment on your model.

Brittany Chen Li

You said I need to have the vacuum modulator adjusted - simple to do. Where can I find detailed Info on this so I can do this at home? I saw some wed sites, but the 928 is a different year does that matter with this?

Brittany Chen Li

Yes I Need A cup of Coffie. Now I understand Sorry. Please can you show me links to this information I need
Peace, Brittany Li

Tom. M

Hi,
Before you go tearing into the vacuum modulator adjustment, check if your system is holding vacuum. If it doesn't then the tranny will also shift very hard. (Does the cruise control hold speed?--sometimes vacuum related)

There is a one way check valve at the brake booster. Get a vacuum tester and see if it holds vacuum for an while. From the valve the lines go a bunch of places (tee's etc.) including one line back to the tranny.
If the vacuum is fine then try adjusting the modulator.

Good Luck
Tom
midlman@seanet.com 87S4 AT

Brittany Chen Li

I went last week through the vacuum line that I could reach around engine many were loose. I will check near the tranny next. Thanks

Jerry 87 928S4

The trans can be adjusted. The details are at the bottom of Tony's page.

tony's page

Elsewhere on his site he shows how to change the trans fluid also.

Good luck

Randy V

One-stop-shopping for all your 928 Tips:

Greg Nichols' 928 Tips

Let us know if you need further assistance, or what you did to correct the problem with your car.

Steve Cattaneo

Brittany,
If you have hard upshift, through all the gears, it is Definitely vacuum related. To confirm, the best method is to check the vacuum at the modulator. Drivers side rear of car you will find the vacuum modulator. You will have to move the heat shield out of the way. With a long needle nose Pliers pull the vacuum hose off of the modulator. Check the hose for vacuum. You will probably have none. You will need to find the leak in the engine compartment.

The vacuum modulator cap number 9264 is part of the vacuum system. If it's missing or cracked (it likes to crack) you will have hard shifts or erratic shifts. MB part #1262770081.

Good Luck,
Steve C
The Great White

2V4V

I would add only one thing to the vacuum line tracing. There are 2 pieces of flexible tubing in the vacuum line to the trans.

There's the one you can see going from the hardpipe that runs the length of the torque tube to the modulator. There's also the one you can't see (at least until you drop the exhaust and remove the front heatshield).

This second little piece of hose makes the transition from the hard vacuum pipe off the intake to the hard pipe that runs the length of the torque tube. It is, ummmm, challenging to replace without lowering the torque tube (but it can be done with the help of small hands and LONG curved needle-nose pliers).

If you still have a vacuum leak after checking everything else, that is likely the culprit.

HTH,

Greg

Thom1

Hi Brittany,

Sounds like you are getting good advice on vacuum and mechanical fixes and adjustments. Transmissions tend to slip, not jerk when fluid is bad. However, fluid and filter must be changed every 60kmiles. Synthetic fluids can help performance. See the fluid ideas below:

Synthetic Fluids Plus:

Mobil 1 synthetics are good for: Automatic Transmission (Use the same “ATF” for power steering.), Rear End (Use the same “75w-90” weight gear oil for Timing Belt Tensioner.). Mobil 1 has a good rep, and is less expensive than most - $7/qt for gear oil $5-6/qt for ATF and motor oil. Castrol Synthetic Blend motor oil is good. The blend is about half the price of the 100% synthetic - $2.6/qt. I have heard that you can change oil less frequently with synthetics. Distilled water and aluminum safe antifreeze - like Prestone (non synthetic) work for Radiators, but NOT the new Prestone in older cars. (Check the archives for other antifreeze recommendations, if you want something more exotic.) Use Valvoline synthetic Wheel Bearing grease. Use ATE Super Blue Racing brake fluid, alternate flushes with Gold. It is German with a high boiling point.

Replace caliper and master cylinder bleeder valves with check valve type for easier bleeding. Crush washers for the differential fill and drain plugs were 17mm id.


HTH,
Good luck,