I've searched until I can't search no more. so I'm looking for any and all knowledge that might help.

Warning: this explanation could be long and potentially useless to anyone who knows what they are talking about.

I've got a '97 D90 with the requisite auto box, about 108K. running 285 rubber and stock drivetrain (to change as soon as rovertracks gets the testing done and shaffer gets my arb's to the door).

At highway speed (remember stock 3.54 gearing for now), when I jam on the gas to go uphill, I get smooth shifting from 4th to 3rd. Then when I attempt to go from 3rd to 2nd (peddle to the floor), I get initial gear change (smooth again), power increase for 3-5 seconds until I hit about 3600 to 3800 RPM. Then, the truck loses all but minimal power, until I take my foot off the gas and it can shift up to the proper gear for the speed. The RPMs will continue to climb if I keep the foot on he peddle, no noises seem to eminate when this happens besides the engine revving. I can predicatably make the behavior happen every time right at the same RPM threshold.

The Auto has been flawless up until now. Fluid is fairly recent (about 4K miles), remains clean (not burnt) and doesn't smell like vinegar pee. It's not over filled by any means. In fact I took a bunch out after the shop had filled it a while back (as I've read that ZF auto's don't like to be over filled).

I've tried working the box manually up through the gears and can get the same reaction either in 2nd at the same RPM, or 3rd, at the same RPM. Doesn't happen in 1st, as I can take it past 4K.

I plan to replace the kickdown cable shortly as a possible reason (really I'm looking for the cheaper fix). I've talked to a few that say the box probably needs a rebuild which is $$$:mad: .

So my thoughts are this. If indeed it is a clutch plate or two slipping, why would it be so predicatable (even at max torque at that speed)? If clutch plates were going, wouldn't I get burnt fluid? Additionally, a few times, I've been able to get it to shift down like normal. But this has only happened maybe 2-3 times since this issue popped up.

I'm going with 4.11's soon. My initial thoughts were to wait and see what the 4.11's inside do when the RPM's are naturally running higher. But that kinda scares me too for some reason.

At this point, I interested in any and all possibilites besides rebuild. Or, just tell me to rebuild if it is necessary... Any thoughts are appreciated. The obligatory :flipoff2: applies because I'm noob.

Thanks. ;)

I'm not sure what the problem is, however, I will tell you that replacing the kickdown cable is not going to be the easiest thing to do with the transmission in the vehicle-it's hard enough with the transmission out of the truck. You'll need a pair of hemostats to thread the cable around the bellcrank it rides on.

Given the same situation, I'd try the kickdown cable first as well.

Thanks PT. Your right. I just had a look at that section in the workshop manual. Maybe I'll need to attempt "adjusting" the existing cable a little more first.

Call these guys, all they do are ZFs. May be able to help trouble shoot. http://erikssonindustries.com/

Tis

Originally posted by PTSchram
I'm not sure what the problem is, however, I will tell you that replacing the kickdown cable is not going to be the easiest thing to do with the transmission in the vehicle-it's hard enough with the transmission out of the truck. You'll need a pair of hemostats to thread the cable around the bellcrank it rides on.

Given the same situation, I'd try the kickdown cable first as well.

Uhm so the engine stumbles at a certain rpm. and maybe in a certain gear? try the throttle position sensor

TomW

I'm with TomW here...

I don't know how you test it..but you should test it.

The other thing to note is that when my throttle pot went, it only showed symptoms under load...when it was parked, you could rev it all day withouit any stumble...until you put it under load.

This would also make sense, since you are stating that it only happens up-hill.

Dave

My impression from reading your explanation is that the transmission slips once you hit 3600-3800 rpm in both 2nd and 3rd gear. I don't think the kickdown cable has anything to do with this and it sounds to me like the bands are slipping. I would guess you're in for a rebuild or new tranny.

Another option is to try some of the "magic snake oil" tranny repair stuff they sell at a lot of auto parts stores. The way I see this is you're out $$$ anyway for the tranny, so why not see if a $5 can of mystery gunk will help it along for a bit.

Anyway, that's my $.015 (not even worth two cents. :flipoff2:

Good luck!

-John

Thanks guys. Please keep the ideas coming... Good or bad, snake oil or the ultimate fix. I'd like to give them all a try.

If you are going down the level highway and come to a hill and hit the gas to pass the 18 wheeler and the truck just seems to flat out die then come back to life a second later then it is likely the TPS. I bought a used one from a wrecked 95lwb and installed it, it took the ecu about 10 minutes to meet and greet the TPS then it ran like a champ again. I thought it was going to be ZF $$$ issues too. Don't use snake oil and introduce a new variable to question later if you have ZF issues, you'll always wonder if it is the snake oil causing it , also - it can do weird things to your seals. My lazy way to clean out the ZF is to keep on draining and filling it often, after 4 or 6 times you should have flushed it. ( someone else can do the math to see if 4-6- drains equals total capacity, like I said - I am lazy ;) Someday I'll get to the TRANNY, yes tranny tran tran tranny filter ( that's for you PT) but after 170 thousand miles it isn't broken yet so I am not fixing it, but I do drain and fill often.

I saw a guy on the short-track run the whole race after he got a hole in his tranny and lost all his fluid - he had always used synth tranny fluid - If I hadn't seen it I'd never have believed it.

Thanks Tallbrad, I wonder if the TPS going bad would set off codes/check engine in a '97 GEMS rig? Were you getting anything prior or was it just the running condition that let you on to the issue?

Would the consensis believe that a bad TPS would cause the ECU to start reacting: i.e. check engine, etc.?

At this point, $70 part is worth trying as opposed to the $1000 plus rebuild.

Again, any thoughts appreciated.

Thanks!

Originally posted by dmarch
Thanks Tallbrad, I wonder if the TPS going bad would set off codes/check engine in a '97 GEMS rig? Were you getting anything prior or was it just the running condition that let you on to the issue?

Would the consensis believe that a bad TPS would cause the ECU to start reacting: i.e. check engine, etc.?

At this point, $70 part is worth trying as opposed to the $1000 plus rebuild.

Again, any thoughts appreciated.

Thanks!

The TPS will only throw a code if it becomes completely unresponsive (in my experience).

All of the responses have definitely forced me to look at this issue from other perspectives and it could well be the VSS or the TPS.

If it always does it at the same engine speed, it's most likely the TPS.

If it always does it at the same vehicle speed, it may be the VSS.

TPS' are available at Autozone for $75. Haven't found a VSS yet (but I'm looking).

I am also a proponent of the dump/fill, repeat method as I have changed a tranny :flipoff2: (thanx TallBrad!) filter and don't want to waste the better part of an entire day to do it again if I'm not being paid to do it.

Peace,
Paul

Dmarch you said -

"In fact I took a bunch out after the shop had filled it a while back (as I've read that ZF auto's don't like to be over filled"

overfill it again and see if the problem goes away.. it is a rover. That might be it right there.

Will do Tallbrad.

I replaced the TPS last night. While the truck seems to idle better and in general run stronger (this is all perceived of course), the down shift issues remain.

Under load, up hill, jam on the skinny pedal, downshifts correct, gives initial power, the drops out with the RPM continuing to rise. Returns to the right gear after I pull my foot off the pedal and accelerates again. Ugh.

Thanks,
Dave

Originally posted by dmarch
Will do Tallbrad.

I replaced the TPS last night. While the truck seems to idle better and in general run stronger (this is all perceived of course), the down shift issues remain.

Under load, up hill, jam on the skinny pedal, downshifts correct, gives initial power, the drops out with the RPM continuing to rise. Returns to the right gear after I pull my foot off the pedal and accelerates again. Ugh.

Thanks,
Dave

Sounds like you are going to neutral or the tranny is slipping. Will it manaully hold a gear? Any Gear?

j

It'll manually hold the gear in 1st. In 2nd, it slips at 36-3800 RPM. In 3rd and 4th, I can't really get it that RPM, at least on the roads around here. But it does hold 3rd.

Okay, I'm back. And not happy about it.... :(

I decided to rebuild the trans, and so went through with it. After exhausting what I thought were all avenues, this seemed to be the answer. Trans rebuild was great. New torque converter. Installed, and the truck drives a 100% better than before (110K miles). No more slack, actually downshifts and has noticeable torque in 1st and 2nd, in low range.

Well, low and behold, on my way through the Pocono's, I again noticed the very same issue reported above. It seems that as soon as the truck hits 3600 RPMs, it begins to "bog down". This is completely predictable and I can recreate it everytime. I still get a rise in the RPM's, and slight power, but it's almost like something is limiting the power transfer right at that RPM. I just can't get the power out of the downshifts on up-hills that I used to. So far, I've rebuilt the trans, new torque converter and replaced the TPS. Truck runs better than ever, but this problem still exists.

Are their any limiters or other sensors I should look at? VSS maybe? Anyone have any further suggestions?

I'm heading out to CO in October, and if I can't hold 50 mph on the mountain passes in PA at 2K feet, I'm going to have a helluva hard time holding any speed out there...bummin.

Check the fuel pressure....I had a loss of power at @3100 due to fuel pressure at @28lbs.....about 10 low...Drove fine except for higher RPMs....Worth a shot....
KAan..

Check your air filter and replace.
Clean the small hole in the side of the barrel opening of your MAF with carb cleaner and them wd 40. That is the NTC opening. could be you are not getting enough fuel at high RPM due to dirty MAF. Maybe substittute another and test. Can you say compression test?

Good luck.
JP

Dave
Are the revs going up a bit during the percieved "slip" or is the motor bogging... I've seen the Vehicle Speed sensors do wierd stuff like this before.. If the engine bogs and is unresponsive and the revs don't move much at all (VS. actual Speed) it could be the VSS.. I'm betting it is the notorious VSS... Well it ain't my buck:)
Hmm but then again maybe it is.........

Keith