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Loss of engine braking- TRANNY OR ENGINE ISSUE?

Can Can

Can Can

Pusher Man
Joined
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Cochrane, Alberta, Canada
A couple of years ago I replaced the injector pump on my 6.2. The truck has always shifted a little wierd but I've owned the truck for 7 years so I'm used to it. The diesel shop tried to "fix" my shifts(it's a 700r4), but I made them re-adjust it back. I DO know that they played around with the TV cable as well as the TPS(Throttle Position Switch).

Anyhow, it never seemed quite right. It feels like the tranny totally disengages if I let off the throttle, eg. going down a hill. It's almost like I have a standard and I'm pushing in the clutch- when I get to the bottom of the hill and re-apply throttle, the tranny seems to re-engage.

This became very evident last weekend when I took a load of lumber across the mountains. If I let off the throttle the truck would actually pick up speed going downhill, and the wierd part is that I could slow the truck down by pressing the gas pedal........ /forums/images/graemlins/confused.gif

So here's my question-

Is this problem diesel related or 700r4 related? And how can I fix it?

This is posted in the diesel forum as well. At this point I'm not sure if it's a tranny issue or a diesel issue....
 
was the 700r4 ever offered behind the 6.2?
maybe it is something to do with that. i have never seen a factory 700/6.2 now i also have not seen many 6.2's out there so maybe i just missed them all.
grant
 
thats cool. i dont know much about ethier, well except this.
1. i want a 6.2
2. i dont want a 700r4.

hope you can fix it, and soon.
grant
 
I don't know anything about diesel, but I'm leaning toward tranny.
I'm thinking torque convertor not locking, but I don't think messing with the TV cable would do that. I haven't looked at a tranny book in like a year and a half, much less fooled around with one, so I'm lucky I can remember they lock up...
I think the convertor not locking might also make the tranny feel like it's acting funny.
Does your mileage seem worse, too?
 
Mileage is the same if not better since the new injection pump went in. And the TC locks and unlocks without a problem as far as I can tell. Got any other good ideas, Ratch??? /forums/images/graemlins/wink.gif /forums/images/graemlins/rotfl.gif

I'm starting to think it has something to do with the TPS. Does anybody know EXACTLY how a TPS affects shifting on a 6.2? /forums/images/graemlins/1zhelp.gif
 
Nah, I traded most of my good ideas for cheap wine and cigarettes, then quit smoking...

What year is your truck Paul? I wasn't thinking in terms of sensors or anything, but duh, injector pump should've been a hint...

Speaking from my rectum /forums/images/graemlins/crazy.gif; With a TV cable, would the TPS do anything for shifting? The Cable should act like the tranny's own personal TPS, right??
 
Compression braking is not a normal function of current automatic transmissions, and hasn't been since about the late 50s. That's one reason you can't push-start a vehicle equipped with an auto. They are not intended to have a compression braking effect on deceleration. It has nothing to do with TC lockup. Your transmission is not malfunctioning.

If compression is what you want, it can be done with an aftermarket shift kit. Two good ones that come to mind are TransGo and B&M. A shift kit will also give you more control over how your transmission shifts, and as a general rule will extend the life of your transmission. You will get more positive shifts, less slippage, and less heat buildup.
 
Uh, I've got an '80 Turbo 400, a '90 700R4, a '91 700R4, and a '94 4L60E in my junk. ALL of them provide compression braking just fine. I downshift and use compression braking every day just to get down off the mountain that I live on without smoking the brakes... /forums/images/graemlins/shocked.gif
 
Years ago I heard of a similiar problem on a tv show. I do remember that the fix was adding a valve into the exhaust that would shut on deceleration and greatly add to the engine breaking effect. It was also an automatic. Maybe this would be option to look into.

BTW I know nothing of diesels, so if what I'm saying is totaly wrong, sorry.
 
TPS shouldn't affect shifting on a 6.2 at all.

TV cable affects line pressure in the 700R4, TPS would affect ONLY the lockup if its setup that way. Might not even be used for that.

You get the most compression braking in 1st gear as I recall, and since the 700 converter isn't locked in 1st gear, if you don't slow down shifting into 1st, you have problems.

I believe what you are experiencing is normal in OD, and perhaps D, but you put it in 2nd or 1st, guarantee you slow down. Just depends on how steep the hill is if the truck speeds up or not with no throttle.
 
[ QUOTE ]
Uh, I've got an '80 Turbo 400, a '90 700R4, a '91 700R4, and a '94 4L60E in my junk. ALL of them provide compression braking just fine. I downshift and use compression braking every day just to get down off the mountain that I live on without smoking the brakes... /forums/images/graemlins/shocked.gif

[/ QUOTE ]

I guess I should have clarified a little better. You will get a limited amount of compression braking, especially in the lower gears, in a stock transmission. But it is nothing like you will experience with a manual transmission. Put in a good shift kit and you will be amazed at the difference. It's dramatic. You will experience REAL compression braking.
 
I see what you're saying, but believe me when I tell you that the truck USED to have a lot better compression braking before the diesel shop played around.

Also, why does it feel like the tranny just drops into neutral when coasting down a hill? And why does the coasting stop if I press the gas pedal? You'd think that applying throttle would speed the truck up, not slow it down.....
 
Just to get this post back on track for Paul...the amount of compression braking he used to have is now non-existant. He isn't looking for new products, or for the truck to do anything that it hasn't done for the 7 years he has had it. This is a recent development after a tranny shop made some adjustments...

I would guess the convertor is unlocking when the throttle is released, which points to the TPS.

Rene
 
AHAH!!! That's what I'm looking for.....

Now how do I remedy the situation, brother? Fill me in!!! /forums/images/graemlins/thumb.gif
 
[ QUOTE ]
I see what you're saying, but believe me when I tell you that the truck USED to have a lot better compression braking before the diesel shop played around.



[/ QUOTE ]

The first thing I would suspect is that it's low on fluid, but I'm sure you've already checked that. Instead of asking people on this forum to speculate long-distance I suggest you take it back to the shop and ask them what they did, then ask them to undo it. Mechanics are human and make mistakes. And some are just plain incompetent idiots. Be nice to know which worked on your truck.

JP
 
The 700r4 is not affected by the TPS. It sounds like your TV cable is out of adjustment. You are basically upshifting too soon. You will not see engine braking with it adjusted like that. Push the TV cable in 2 clicks and see if it improves your shift. TV cable adjustment is critical in this trans. Also when you bring it back to the shop have them verify that the TCC Brake switch is operating when you depress the brake pedal by watching it on the scan tool.
 
I had the 700 fail in my Blazer with those symptoms.

Complete freewheel when you left off the gas. Additionally I could drop the shift lever from OD to 1 at freeway speeds (while coasting) with no affect. Try it at slower speeds/forums/images/graemlins/ooo.gif, I discovered this fact after lots of troubleshooting/experimenting.

My tranny had blown the sprag(sp?).

More symptoms were the TC lock going in and out.

And I had this symptom happen on a trip to Chico over XMas.
I drove over a snowy Ashland Summit to get back to Seattle. I was so tweaked after coming down that pass with no compression braking I thought I was gonna hurl. Scarier than hell.... /forums/images/graemlins/eek.gif
 
Thanks for the input, Dave, but I can manually upshift and downshift my tranny with no problems. Arveetek was able to give me some good TPS-related info in the diesel forum, but I still need someone who can tell me exactly how to set the TPS back to where it was before the diesel shop messed with it.
 
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