518 Automatic Adjustment Question

[RSchwarzli]

Y'all know I like my manual transmissions. But I ended up buying a 1993 D350 dually auto, that has 40k miles on it. It lived a harder life as a company truck, but on the overall it has survived well.

Having an issue with the trans and looking for guidance. My solution for automatic problems has always been swap to a stick (and that may yet happen, will see if this is fixable lol) so despite being versed in 1st gens, I am lost on this one.

When driving down the highway at 75 mph, I cruise at say 20% throttle pedal depression. If a small hill comes, or I try to speed up to go around someone in the left lane, I may press the pedal to 40% of full. When I do this, the trans kicks out of OD, and I drop to 60 mph as if I hit the brakes. I get the .68 OD ratio to direct is a big step so that part makes sense.

So I adjusted the mechanical kickdown cable to service manual spec at rear of engine, and I did the drill bit spacing spec as the truck was sitting at full bottomed out when I got the truck. Test drive. Better. But still drops down too easily. Adjusted it as far as it could go the other way. Was worse. Would drop in and out of OD with only 15% depression. Now have it sitting at say 55% throttle depression and it kicks out but I would like it closer to say 80%. I really dont want it kicking out of OD unless I am climbing Veil Pass. lol

Does this sound more like an internal adjustment, or maybe a TPS signal to kick out? Odd that I can change the point at where it kicks out of OD by changing the cable length on the adjuster if it is a TPS issue.... but I am a bit lost as to where to look next.

Thanks!

Robert

 

[cerberusiam]

The kick down cable just adjusts the shift points via TV pressure, won't impact the OD shift which is all computer controlled. To adjust OD engagement you have to adjust the TPS setting, more advance equals quicker OD engagement and holding. When you modify the engine enough to where the TPS won't correlate with throttle position, or the the parts and wiring gets so old it doesn't like adjustments anymore, then you wire in a POT and set it where you want it to go to OD and stay in. Could be partly the VSS signal thta is causing the issue also, the POT just fixes that so you have to use the manual OD off if needed. With the engine powered up a little never could get them tuned correctly anyway, adjustments just to coarse for the needs.

 

[RSchwarzli]

Ahhhh interesting. That explains why the cable adjustment hasnt changed the response much. lol

Given this truck is 100% stock engine, tamper caps and all on, I would say maybe needs adjustment of the TPS. Makes most sense to start there. How is this done?

Thanks for the reply Cerberusiam

 

[cerberusiam]

IIRC, there is an adjusting nut on the bottom of the TPS, hold the shaft and adjust that nut a little each way until the results change. Can't remember if it is hold the shaft and turn the the nut or hold the nut and turn the shaft, when you look at it the adjustment is obvious.

 

[RSchwarzli]

That is perfect. Gives me enough to play with it. Thanks for the clarification on all this. I feel like a Gen 1 newbie again. Been a long time since I had questions on Gen 1 systems. lol

 

[RSchwarzli]

This is what the old girl looks like.

 

[DavidC]

That looks mighty perty. Jump seats in the back ?

 

[Nigel]

Look very nice Robert. Time to change your signature.

Nigel

 

[Ozymandias]

Check out this >>> https://www.genosgarage.com/product/dodge-cummins-tps-apps-delete-kit/electrical-sensors-2

Then you are in charge when it shiuld shift into OD.

 

[RSchwarzli]

That looks mighty perty. Jump seats in the back ?

Yes, there is! I thought all club cabs came with them. Did they not?

Look very nice Robert. Time to change your signature.

Nigel

Yes. It is time. You are correct.

Check out this >>> https://www.genosgarage.com/product/dodge-cummins-tps-apps-delete-kit/electrical-sensors-2

Then you are in charge when it shiuld shift into OD.

This is brilliant Ozy! May have to do just that if the adjustment doesnt work. Did reading last night on how to do the adjustment. Once I try tonight and it works, I will post here how to do it.

 

[DavidC]

Yes, there is! I thought all club cabs came with them. Did they not

I believe so although some removed them that is why I asked.

 

[RSchwarzli]

I believe so although some removed them that is why I asked.

Ahh. Makes sense. Here are my jump seats.

 

[DavidC]

That truck is in unbelievable great condition, Congrats.

 

[RSchwarzli]

That truck is in unbelievable great condition, Congrats.

It is now. Wasnt when I got it. Have about 200 hours into cleaning it up. Thankfully had a lot of parts left over from the crew cab build with same color interior.

 

[RSchwarzli]

Update:

So adjustment is actually really easy. Via the FSM:

Step one is to ensure that the throttle lever is sitting on the stop pin.
Step two is to ensure that at WOT, the break over spring is tripped.
Step 3, at idle, you need to measure the center wire on the TPS connector. Idle should be 1v or slightly higher. Use a sharpened paperclip and stick it into the back side of the connector to get your signal.
Step 4, at WOT, it should read 2.25-2.75v over idle.
Step 5, adjust the 10 mm nylon nut on the bottom side of the tps until the voltages read in Step 3/4.

My step I am adding:
Have a helper slowly push down the pedal as you monitor voltage. You may find a giant dead spot in your TPS as I found. lol

Thanks for the link Ozy - Delete kit on its way. I much prefer controlling my own shift points and if I have to replace the TPS anyways..... lol

 

[cerberusiam]

Yep, typical issue with the TPS is the dead spot. Done carefully you can take the TPS apart, clean up the carbon that is causing the dead spot and glue it back together, beats $170 for a new TPS if it works. I just built mone from RS parts before kits were available, kit makes it easier though.

 

[RSchwarzli]

Ah. I may pull it apart then for the experience. Either way ordered the $35 TPS delete so I can control when and how it shifts. Felt that based on your comments, may be needed anyways if I start adding power.

 

[cerberusiam]

Yep, it likely will.

 

[Ozymandias]

Ah. I may pull it apart then for the experience. Either way ordered the $35 TPS delete so I can control when and how it shifts. Felt that based on your comments, may be needed anyways if I start adding power.

Absolutely, you can set the shift point according to road, traffic, load (trailer) and your personal preference.
I think that is a great addition.


And as you are "new" to Autos, I like the old 727 Trans, aside from lack of gears. It's a very simple and reliable transmission with some upgrades. And you can rush through as many HP and TQ as you want if properly built.

 

[RSchwarzli]

Absolutely, you can set the shift point according to road, traffic, load (trailer) and your personal preference.
I think that is a great addition.


And as you are "new" to Autos, I like the old 727 Trans, aside from lack of gears. It's a very simple and reliable transmission with some upgrades. And you can rush through as many HP and TQ as you want if properly built.

Yes, my 1990 started life as a 727 truck. I lived with it in there for the first 8 years I owned it. Those are simple transmissions and about the extent of my automatic skills. I like those transmissions as well. Minus the lack of speed capability. lol This PCM and electronics of the 518, thats all new. But I learn quick....