Hello,

My 86.5 auto trans sometimes slips when it shifts into 3rd gear. When I bought the car, the modulator vacuum line was dead and it had bone-jarring hard shifts. I ran a new vacuum line and it now shifts smooth, but does sometimes slip when going to 3rd.

I was given a trans filter kit with the car. Friday, I pulled the pan and found the engage return spring lying in the pan (see other topic on that one). I re-attached the spring, drained the torque converter and when I went to replace the filter, I realized that the filter kit I was given did not fit this car. The old filter stayed in, pan went back on with old gasket and new fluid went in. I filled to the proper level when warm and drove it Saturday. It's only problem is the occasional slip into 3rd. No other problems that I can tell. I will order a new filter kit and will do filter and gasket this coming week.

Current status- new fluid, old filter, car still slips sometimes when shifting to third.

Questions-
could old filter cause this?

Could other vacuum leaks in car cause overall vacuum pull at the modulator to be below suction needed?

Could the modulator be adjusted slightly to firm up the shift to third, or will that also make 1st-2nd become too hard of a shift?

I probably should have waited until the new filter was in to post this, but since I'm going into the thing again to do the filter, I was wondering what else I should be looking for and testing.


Thanks for any help anyone can give,

Greg

 

From the Workshop Manual:

Condition:
Transmission slips in 3rd gear

Correction:
1. Remove shift valve housing, check sealing bushings on plug tubes and replace same if necessary.

2. Repair clutch K2 dpending on findings. Visually inspect oil distribution sleeve, replacing if necessary.

 

Thanks Wally.

To be specific, it slips going into the next gear. Once it has shifted, there is no additional slippage. Would that info change your assessment of the problem?

I noticed this morning that it did this when shifting into 4th. I think now that it has been doing this when it goes to 4th and not third this whole time.

Sorry for the confusion, I'm used to overdrive automatic transmissions which won't usually hit final gear at 35mph like this one will do.
Now, I'm counting the shifts and it seems that it is the 3rd to 4th shift where it sometimes slips going into 4th and then is fine with no additional slippage once it has shifted.

BTW fluid was quite clean and minimal sludge was found in pan. There were no plastic or metal bits / shavings.

Greg

 

I'm bumping this to the top so if Steve C. is in the house, possibly he will add his thoughts to this problem.

 

Have you tried adjusting the shift modulator for firmer shifts?

Sounds like you may have gone from one extreme to the other.

Tony has a good write-up here (scroll past the kickdown switch stuff):

<a href="http://members.rennlist.com/v1uhoh/kickdown.htm" target="_blank">http://members.rennlist.com/v1uhoh/kickdown.htm</a>

 

Randy,

I am leaning towards that direction. I guess that I would expect the trans to slip at each gear change, not just 3rd to 4th if the modulator needed to be adjusted. I'm going to try it because maybe the other shift changes are just on the edge of slipping and a small turn won't firm then up too much. I also want to test the modulator for leakdown.

The positive thing about this is that when vacuum was not present at the modulator, is shifted .Real Firm and there was no slip. In fact, it shifted with such a bone-jarring kick, that I suffered a temporary case of turetts syndrome each time the car changed gears! So, I think the main internals of the trans are probably OK.

Thanks for the reply. I'm hoping Steve C. will also give me his ideas on this one as well.

Greg

 

Greg,
Start with the basic, level and condition of the fluid, if it is black and smells burnt, it’s internal. If the oil were clean, I would check and adjust the TV cable, no slack.
Check the modulator cap for cracks, check the modulating pressure A28.01 04 \ 4.4bar
A28 02,05,06,09,11 /4.0BAR. Check working pressure15.3/ 16.9bar.
Change the b-2 servo

EXTERNAL
Modulating pressure
Vacuum response
B –2 servo
VALVE BODY
3-4 accumulator piston seal
3-4 feed control valve
Rear clutch control valve

INTERNAL
K-1/k-2 clutches
Seals leaking.


You my have to go into the valve body, there are no guaranties ,it sill can be internal.

And it’s a 3\4 slip?

Steve C
The Great White

<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

 

Hi Steve,

Thanks for taking a look at this thread.

Yes, it is definitly a 3/4 slip. Once it completes the shift, 4 is fine, no slip. When I changed the fluid Friday, it was clean, not black or burnt.

I'll start with the TV cable. The PO had said that he tried to adjust the cable to solve his hard shift problem, it turned out that I found no vacuum at the modulator and ran a new line, that's when it went from bone-jarring shifts to smooth shifts and the 3/4 slip started.

Then I'll move to vacuum and modulator checks. I have the work shop manuals and a transmission service book.

I'll let you know.

Thanks again,
Greg

 

Greg,

You wont find a section in the manuals under vacuum response test. Here is the procedure: Connect the vacuum gauge to the disconnect vacuum line at the modulator, with the engine idling in park, normal vacuum readings would be 14 to 22 in HG. Quickly open and close the throttle, the vacuum should drop to below 5 in, then rebound , with no lag to your highest vacuum reading, 14” to 22”


All pressure test are with no vauccm to the modulator.



Steve C
The Great White
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

 

Thanks Steve.

I can't tell you how much I appreciate your knowledge about transmissions and your willingness to share it.

Hopefully by Sunday, I'll have somethig to report.

Thanks again,
Greg

 

Greg
the symptions that you are experiencing are very similar to what i was going through last week.
now my tranny is worse.
Steve C has generously given me some very good advice to try and help me save my tranny beore it is too late.
i strongly recommend that you read the post titled the great white.

good luck

tim

84 s2 euro auto

 

Just an update.

Problem still exists, not as frequent though. Seems to happen when feathering the throttle.

I have replaced fluid and filter. Trans fluid is at proper level.

Modulator checks good and holds vacuum.
Vacuum line is good to trans.

TV cable appears to be adjusted properly, but I want to review the procedure in the manual this weekend to be sure.

I gave the modulator "t" handle 1 turn clockwise. 1st to 2nd seems a bit firmer, but by 3rd to 4th, it is still slipping sometimes. In fact, it seems that the frimness diminishes as I get from 1st to 4th. 1-2 firm, 2-3 not as form, 3-4 sometimes slip. The slip is a 1 second engine rev-up and then a solid 4th gear forever.

I'm still working through Steve's list of things to check.

Greg

 

Update- Trans is A28-07

Steve, if you read this,

I adjusted the cable. Very sensitive, shifts later now, but still has the slip.

I performed the vacuum response test- Checked O.K.

I replaced the modulator as a preventative measure. Then I performed modulator pressure adjustment with a transmission gauge 4.4 BAR

I then checked the working pressure. reads within limits, but needle wobbles between 15+ and high 16 BAR. Is this O.K.?

I drove the car. This shifts seem a bit quicker, but the same pattern of 1-2 being firmer than 2-3 and 3-4 having an occassional slip remains.

Also, with the motor running, I re-attached the modulator vacuum line to the modulator. With the vacuum attached, there is a sound that is not present with the vacuum line disconected. It sounds like a pulsating vacuum leak. I tested the modulator with the mityvac, and it holds vacuum fine. I was thinking that maybe the o-ring seal on the modulator may not have sealed when I installed it, or maybe it got pinched. I don't remember the old modulator making this sound.
The modulator seems to work fine though. Is this O.K.?

***With the car on blocks, I ran it up to speed and noticed that the working pressure dropped with each gear change to about 10 BAR in 4th. Is this O.K.? There was no resistance on the drivetrain, as it was on blocks. I tried to create a bit of drag with the parking brake, ran it up and got roughly the same result.***

I will have to read the book and get familliar with the other things on Steve's hit-list.

Thanks, Greg

 

BTW, the working pressure and modulator pressure test was with the fluid warm.

 

Greg,
With a 28.07 transmission your working pressure should be 16.9 + or – 1, trans fluid hot, car in drive at idle (not moving) with the vacuum line off the working pressure should be 16.9, one full turn on the modulator will raise the pressure by 0.4 bar. If it’s on the high side of 16, it’s ok. If not then raise it.

The o-ring on the modulator seals transmission fluid, not vacuum. On some modulators you can install the hold down clamp in the wrong place (on the modulator). It will not be pushed into the case far enough, check it. Check the old modulator for any signs of where the bracket went. The pulsation could be fluid related. Every time adjustments are made, always recheck working pressure.

The car should be driven on the road at 50km for the modulator check (4.4 bar + or - .05). It’s normal for the pressure to drop between shifts.

This is the first step in troubleshooting a transmission problem.

Next, your going to have to check the B2 piston seal. Ill post pictures by next week.

Good Luck,
Steve C
The Great White
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />