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-   -   Why no 4th gear? (http://www.peachparts.com/shopforum/diesel-discussion/341636-why-no-4th-gear.html)

jkubica 07-23-2013 09:52 PM
Why no 4th gear?
 
Hi all

I have a 1985 300td that I'm working on.

The current problem is that I don't seem to have 4th gear. Starting in Drive I seem to have three smooth shifts - but then at 55MPH I am showing 3100 RPM - which seems to me like 3rd gear - instead of 4th.

Any suggestions or info appreciated.

Joseph

Govert 07-24-2013 05:48 AM
When you put the selector in S when you are driving 55 mph, does it shift back to third gear?

You can also try accelerating using kickdown of with the accelerator pedal fully pressed (only with a fully warm engine), upshifting should occur at 4000-4500 rpm. You should still be in third gear at 55 mph. Releasing the accelerator pedal at that point should cause the transmission to upshift to fourth gear.

Does the tachometer show around 750 rpm at idle?

Skippy 07-24-2013 06:33 AM
Quote:
Originally Posted by jkubica (Post 3181056)
Hi all

I have a 1985 300td that I'm working on.

The current problem is that I don't seem to have 4th gear. Starting in Drive I seem to have three smooth shifts - but then at 55MPH I am showing 3100 RPM - which seems to me like 3rd gear - instead of 4th.

Any suggestions or info appreciated.

Joseph
Three shifts would indicate fourth gear. I suspect your tach is reading high. Mine does that intermittently.

Also, these transmissions (and automatics in general) tend to last longer when adjusted to give a firm shift.

jkubica 07-24-2013 07:24 AM
Quote:
Originally Posted by Govert (Post 3181161)
When you put the selector in S when you are driving 55 mph, does it shift back to third gear?

You can also try accelerating using kickdown of with the accelerator pedal fully pressed (only with a fully warm engine), upshifting should occur at 4000-4500 rpm. You should still be in third gear at 55 mph. Releasing the accelerator pedal at that point should cause the transmission to upshift to fourth gear.

Does the tachometer show around 750 rpm at idle?
Hi Govert

I am showing 750 rpm at Idle. I'll follow your suggestion tomorrow when I have time for another test run -and report back.

Thanks, Joseph

jkubica 07-24-2013 07:31 AM
Quote:
Originally Posted by Skippy (Post 3181162)
Three shifts would indicate fourth gear. I suspect your tach is reading high. Mine does that intermittently.

Also, these transmissions (and automatics in general) tend to last longer when adjusted to give a firm shift.
Hi Skippy
My thinking was also that 3 shifts would have me in forth gear - but it felt like the engine was running fast - and the tachometer idles at 750 and otherwise seems to be working.

Do you suggest adjusting the Bowden? Or the Vacuum modulator?

Thanks, Joseph

Shortsguy1 07-24-2013 08:38 AM
These photo tachometers are cheap and if you think your car's tach is off, would give you a way to tell for sure. It would be hard to use one while driving, but parked with the hood open, the work really well. You stick a small reflective piece of tape (included) to the crank and point the tach at the crank. Maybe a friend could sit in the car and hold the rpm at some elevated level, and you could verify the actual rpm compared to the indicated rpm.
CyberTech Digital Photo Tachometer Non Contact Tach bundle CyberTech Cable Tie: Amazon.com: Automotive

vstech 07-24-2013 09:34 AM
it may be your diff that's off...

in 85 it should have a 2.88 giving you about 2800RPM at 60
if you are actually showing 3100 RPM at 55, then wow, yeah something is wrong. my bet is somebody wanted faster acceleration and pulled the diff out of a NA vehicle bumping your ratio to 3.46, or maybe just put in a 3.07 from a standard year turbo.

Doktor Bert 07-24-2013 10:31 AM
Quote:
Originally Posted by Skippy (Post 3181162)
Also, these transmissions (and automatics in general) tend to last longer when adjusted to give a firm shift.
Yes....

SD Blue 07-24-2013 01:38 PM
Would a stuck downshift switch, behind the accelerator pedal, give you this sort of problem. I've never had this problem but IIRC it has been mentioned here on the forum.

winmutt 07-24-2013 02:49 PM
I had this same problem and I think its specific to 85's. Never fixed mine, put a stick in. Guy I sold my auto to put it in an 83 and never had a problem with it.

Verify speedo based on gps.


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