cwiert

I just don't know if this is normal or not. Say the car is in Park and you select "R" to back up. On my car there is a full 1-1.5 second delay before the car shifts into reverse. Then, if you select "D," there again is a full 1-1.5 second delay before the car goes in drive. Is this normal with the 928?
If not, what should I look out for? BTW - my AT fluid level is perfect and fluid looks clean.

blown 87

Most likely the seals are hard inside the trans and the only thing that will fix that is a build.

Bill Ball

That short of a delay is probably normal. The fluid and filter should be changed every 30K miles. Since many of our cars get driven so little, that might not be enough to keep the valve body from gumming up. It could help to throw in a can of "Trans Medic" or similar AT conditioner. I have gotten very good results from doing this when I had a sticky 1-2 shift valve (no downshift into 1st) despite a fluid and filter change.

dr bob

My car has a slight lag going from park/neutral to a drive gear. It's done this since I've owned it (from 22k miles) so I don't consider it abnormal.

Echoing Bill's recommendation, make sure your trans service is up to date. It's easy to take the AT for granted. Many decice that service is needed only when the trans starts to shift funny or slip. Kinda like waiting for a rod knock before changing the engine oil. The service isn't difficult for a good DIY, but if you don't have really clean workspace, car, and work habits, you may want to trust it to a specialist.

cwiert

thanks for all the replys. i'll plan for a fluid and filter soon...just to be safe. thanks.

blown 87

He said a second and a half, that is a long time.
Does it only do it cold? or does it do it hot and cold?

Mike Frye

This is typical of those cars that can only shift in one plane. If your pattern looked like this shifting would be instant:

R-2-4
|--|--|
1-3-5

Mrmerlin

the delay is a function of the MB transmission, Steve Cattaneo would have a better explaination

cwiert

Yeah, I thought it was kind of long too... hence the post.
It does it both hot and cold.
And when it does shift into gear, it does so kinda heavy. There's definitely no mistaking that its in gear.
I was reading the John Pirtle HVAC write-up and in there it states:

"The 928 essentially has two vacuum systems. One system is based on the variable engine vacuum and includes the fuel pressure regulator, the two fuel pressure dampers, and the automatic transmission. This vacuum is provided from the intake manifold and a problem in this system will create issues with idle, general performance, and harsh A/T shifting."

So I was wondering if I had a vacuum leak that was causing the delay.

anonymousagain

Even current MB transmissions get "ding'd" during reviews for having ~1.5sec delay D to R. The payoff is a very strong unit though.

blown 87

Mine goes right into gear????

Tampa 928s

Same on my 85 Euro, use the trans medic it does wonders for shifting.
Remember to drain your Torque converter and loosen your top drain plug with a 17MM hex to make sure you can get it off first.

SQLGuy

Sounds like your delay unit is burned out! Better get that seen to.

blown 87

I will put that on my list of things broken.

dr bob

The longer you focus on the perceived lag, the longer it will be in perceived seconds. While it's possible it really is more than a full second I guess, mine is just a fraction in realtime.

The vacuum for the trans is used to help determine how much load it will need to shift. There's a vacuum-operated "modulator", commonly referred to as "the modulator", that bleeds off some control pressure under low vacuum (high engine load) shifts. If/when the modulator fails or you have a leaky or disconnected line from the engine, the trans will shift very hard even al low engine loads. The modulator is adjustable, making it possible to break trans parts with too-harsh shifts, or burn clutch packs and brake bands if set too soft. Generally, by the time you feel the need to adjust the modulator, you are compensating for something that's already damaged.