Weird transmission problem
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From: Milroy, PA
Weird transmission problem
Interesting thing my truck has started doing, it seems to have lost its ability to do any kind of engine breaking unless its in OD, for instance, driving on the interstate at 75 mph, and you let off the gas, the engine stays at the appropriate rpm, and deaccelerates, now if i was going 75mph, or 60 mph, and i take it out of OD, the rpms instantly go to idle, and there is no "engine drag", which also holds true for putting it in 2nd, or first, now the truck does however go into that gear, because when i step on the throttle again, it goes to the appropriate rpms, in the selected gear, but when i let off, goes directly to idle......... anyone else seen this?? It actually happend in the middle of a trip, i noticed it because i generally put it in 3rd going down a hill, for less brake usage, and i did, then later in the same trip, it started doing this, and its done it for 6 months
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From: Columbia, MO
That seems pretty typical of a diesel engine. Since a diesel does not have a throttle body, it has nothing to restrict airflow into the engine which would cause engine braking. My truck has always been like that since I've owned it. No engine braking. This is the reason you'll see an exhaust brake on a lot of diesels that pull heavy loads a lot. The exhaust brake will restrict exhaust flow and cause engine braking. Several people here on the forum, including myself, have converted their EBPV for use as an exhaust brake. Run a search for it and you should find some good info on it. You may also see a link for it in the sticky thread at the top of the 7.3 forum page.
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From: Milroy, PA
Well the problem is, is it does in OD, but not 3rd, 2nd, or 1st, and it changed as to were it did in all but now its in the above condition, when you let off the throttle, and are in a reduced gear, it goes to idle, and doenst drag any, so if i was going 95 mph, and put it in 3rd, 2nd, or 1st, it would immedietly drop to idle and coast........
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It isn't the engine, and it isn't the torque converter unlocking. The torque converter unlocks in OD when coasting, and it has braking there. The engine WILL NOT drop to idle when the torque converter unlocks, as long as the rest of the trans is working correctly.
The problem is the coast clutch. Since it doesn't have braking with the shifter in 1 or 2, it means the coast clutch is gone. Unfortunately the trans has to come out and be rebuilt or replaced to fix this.
The problem is the coast clutch. Since it doesn't have braking with the shifter in 1 or 2, it means the coast clutch is gone. Unfortunately the trans has to come out and be rebuilt or replaced to fix this.
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From: Milroy, PA
Originally Posted by Casey
It isn't the engine, and it isn't the torque converter unlocking. The torque converter unlocks in OD when coasting, and it has braking there. The engine WILL NOT drop to idle when the torque converter unlocks, as long as the rest of the trans is working correctly.
The problem is the coast clutch. Since it doesn't have braking with the shifter in 1 or 2, it means the coast clutch is gone. Unfortunately the trans has to come out and be rebuilt or replaced to fix this.
The problem is the coast clutch. Since it doesn't have braking with the shifter in 1 or 2, it means the coast clutch is gone. Unfortunately the trans has to come out and be rebuilt or replaced to fix this.
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Originally Posted by jtharvey
That seems pretty typical of a diesel engine. Since a diesel does not have a throttle body, it has nothing to restrict airflow into the engine which would cause engine braking. My truck has always been like that since I've owned it. No engine braking. This is the reason you'll see an exhaust brake on a lot of diesels that pull heavy loads a lot. The exhaust brake will restrict exhaust flow and cause engine braking. Several people here on the forum, including myself, have converted their EBPV for use as an exhaust brake. Run a search for it and you should find some good info on it. You may also see a link for it in the sticky thread at the top of the 7.3 forum page.
Warren
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Originally Posted by Casey
It isn't the engine, and it isn't the torque converter unlocking. The torque converter unlocks in OD when coasting, and it has braking there. The engine WILL NOT drop to idle when the torque converter unlocks, as long as the rest of the trans is working correctly.
The problem is the coast clutch. Since it doesn't have braking with the shifter in 1 or 2, it means the coast clutch is gone. Unfortunately the trans has to come out and be rebuilt or replaced to fix this.
The problem is the coast clutch. Since it doesn't have braking with the shifter in 1 or 2, it means the coast clutch is gone. Unfortunately the trans has to come out and be rebuilt or replaced to fix this.
Warren
Last edited by warrens250; Jul 5, 2006 at 09:08 PM. Reason: forgot a sentence
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From: Milroy, PA
Im not an auto expert, and i really dont know much about them more then doing the tranny service, which has been done a little earlier then fomoco requires, but from what i understand it could be the coast clutches, but from what i understand 1st, and 2nd are together and 3rd, and OD are together? correct me if im wrong, however this all happend in one shot, and it does engine brake in OD still so it would tend to lead me away from this theory, another thing, or the t/c really because it indeed still does in OD. Another way to prove that is i recently did the t/c lockup mod, which is cool, and with it engaged it still doesnt keep the rpms up inless its in OD. None the less a cool mod, love to hear the engine lug.
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From: Milroy, PA
Talked to a local shop that is known for reliably rebuilding autos, he said they could do it for around 2k, he said he beefs them up alittle also with some better clutches, and bigger planetarys...... Glad i dont have to pay to get it fixed, gotta love the company truck principal, just hope it doesnt have to go that route, due to down time.
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The coast clutch is used for braking in 1,2, and 3. It is not on for 4th, and there is engine braking without the coast clutch in 4th.
In 3rd gear with the OD off the coast clutch is turned on by the coast clutch solenoid. In 1 and 2 it is energized by the manual valve, the solenoid isn't used. That's why I said it was the clutch and not the solenoid. If the solenoid was bad you would have braking in 4th, not in 3rd, and you would again have it in 1 and 2. Since it doesn't work in 1,2, or 3, the clutch itself is the problem.
In 3rd gear with the OD off the coast clutch is turned on by the coast clutch solenoid. In 1 and 2 it is energized by the manual valve, the solenoid isn't used. That's why I said it was the clutch and not the solenoid. If the solenoid was bad you would have braking in 4th, not in 3rd, and you would again have it in 1 and 2. Since it doesn't work in 1,2, or 3, the clutch itself is the problem.
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Originally Posted by Casey
The coast clutch is used for braking in 1,2, and 3. It is not on for 4th, and there is engine braking without the coast clutch in 4th.
In 3rd gear with the OD off the coast clutch is turned on by the coast clutch solenoid. In 1 and 2 it is energized by the manual valve, the solenoid isn't used. That's why I said it was the clutch and not the solenoid. If the solenoid was bad you would have braking in 4th, not in 3rd, and you would again have it in 1 and 2. Since it doesn't work in 1,2, or 3, the clutch itself is the problem.
In 3rd gear with the OD off the coast clutch is turned on by the coast clutch solenoid. In 1 and 2 it is energized by the manual valve, the solenoid isn't used. That's why I said it was the clutch and not the solenoid. If the solenoid was bad you would have braking in 4th, not in 3rd, and you would again have it in 1 and 2. Since it doesn't work in 1,2, or 3, the clutch itself is the problem.
Warren
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From: Columbia, MO
Originally Posted by warrens250
No, Harvey, look at his post again. He HAS engine braking in OD, but not in the other gears. The diesel engine effect you speak of does result in a weaker but still real engine braking effect. My 02 effectively controls my 12000 pound trailer in 2nd gear down grades up to 6 % without assistance from either the truck or trailer wheel brakes. He obviously has a automatic transmission problem which started happening 6 months ago. I hope other members who are tranny experts will chime in with thoughts about what the failure is.
Warren
Warren
The coast clutch was my next thought, which I completely forgot about....guess that's what I get for trying to post at almost 2:00 am. 
I had no idea what the coast clutch was until I asked Brian what that band looking thing was when he had my trans apart down at BTS.
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From: N. Georgia
Originally Posted by Casey
The coast clutch is used for braking in 1,2, and 3. It is not on for 4th, and there is engine braking without the coast clutch in 4th.
In 3rd gear with the OD off the coast clutch is turned on by the coast clutch solenoid. In 1 and 2 it is energized by the manual valve, the solenoid isn't used. That's why I said it was the clutch and not the solenoid. If the solenoid was bad you would have braking in 4th, not in 3rd, and you would again have it in 1 and 2. Since it doesn't work in 1,2, or 3, the clutch itself is the problem.
In 3rd gear with the OD off the coast clutch is turned on by the coast clutch solenoid. In 1 and 2 it is energized by the manual valve, the solenoid isn't used. That's why I said it was the clutch and not the solenoid. If the solenoid was bad you would have braking in 4th, not in 3rd, and you would again have it in 1 and 2. Since it doesn't work in 1,2, or 3, the clutch itself is the problem.
Joe
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From: Milroy, PA
Originally Posted by JOE-M
Did he burn up the coast clutch by downshifting into first? I've read a few posts where the transmissions were shifted into first to hold back a load while going at low speeds and burning out the coast clutch. I've been advised not to downshift into first to hold'er back, only when needed to pull.
Joe
Joe