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Cummis8.3
Active Member
11 Posts |
 Posted - 03/20/2011 : 7:22:34 PM
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I am having an issue with high RPMs. I am at 2500 RPMs at 60 MPH...2800 RPMs at 65 MPH. I am at red-line just to drive at highway speed.
1992 Cummins 6CTA8.3, Allison MT643. All Mechanical. Rear End is a 391. Tires 9R22.5, PAC Brake not connected to Tranny.
It is shifting all 4 gears but this is what I'm feeling:
I can feel it shift from 1-2, then from 2-3, and while in 3rd the rpms drop a second time, about 200-300rpms before shifting into 4th. I believe the drop in RPMs is the converter locking.
THEN;
After it shifts to 4th gear I get the initial drop in RPMs but don't get the second drop like I do in 3rd gear. Tranny not locking in 4th? I think it suppose to lock in 3rd and 4th. Though RPMs are still high in low gears.
I can remember having to downshift to get up a couple of hills by my house last time I drove it 2 years ago, but now I don't have to down shift, the RPMs are high like it's in a low gear but I know its shifting to 4th gear, MAYBE the tranny isn't locking correctly? I have no idea but RPMs seem high even in 1st gear.
PAC brake is turned off, I even removed air line to make sure it wasn't on.
Tranny Service is 3 years old, only about 1000 miles since having it serviced. Fluid looks good and no smell of burning. I don't feel any kind of slippage either.
Below are the RPMs each time it shifts. I think the RPMs are too high even in 1st gear. I thought at first Tach was off, but engine seems to be screaming and peddle is at the floor to get to 66 MPH.
0-12ish MPH 2500ish RPM 1st Gear
12-20ish MPH 2300ish RPM @12mph it shifts to 2nd gear
20-25ish MPH 2300ish RPM @20mph it shifts to 3rd gear
25-35ish MPH 2500ish RPM @35mph it shifts to 4th gear
Any ideas would be appreciated. I'm afraid if I drive it I will damage something. Engine is already leaking diesel it never leaked before, I think the High RPMs may have caused an injector and high pressure fuel line to leak.
Someone else with the same Engine and tranny as me said he is at 1900 RPMs @ 60 MPH.
Here are the links to pictures of Dashboard showing speed and RPMs.
http://i238.photobucket.com/albums/f...IdleRPMs-1.jpg
http://i238.photobucket.com/albums/f...mph1800rpm.jpg
http://i238.photobucket.com/albums/f...mph2300rpm.jpg
http://i238.photobucket.com/albums/f...mph2500rpm.jpg
http://i238.photobucket.com/albums/f...dlefloored.jpg
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Spar
Active Member
20 Posts |
Posted - 03/21/2011 : 09:04:12 AM
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Must be Monday because my brain is on vacation - not like it helps much when it's here ;P
Is the "kick down" linkage stuck like you're in passing gear? That would be my first check, scratch that second check. First would be fluid level but you did that already.
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It's a machine, not a werewolf. |
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08 Thomas EF
Top Member
533 Posts |
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IBTMech
Top Member
USA
973 Posts |
Posted - 03/21/2011 : 2:49:36 PM
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If you're leaking fuel, you're out of service anyway!
I would question the operation of the lockup clutch. The piston could be seizing in it's bore. |
If it doesn't fit, FORCE it.
If it breaks, well, it needed replacing anyway.
Pullin' wrenches for 45 years. |
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stovebolt
Active Member
37 Posts |
Posted - 03/21/2011 : 9:54:21 PM
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IBTmech hit the nail on the head, your converter is not locking up.
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Cummis8.3
Active Member
11 Posts |
Posted - 03/26/2011 : 7:29:52 PM
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UPDATE ON RPM's
I bought a handheld Digital Tach and verified my Dashboard Tach is working correctly. I had my wife hold the rpms at 1000, 1200, & 1500. The dash Tach matched my handheld tach reading off a pulley on the engine.
Now I know I have a much bigger problem than just a bad tach!
I know it's shifting all 4 gears and I don't feel it slipping at all, is there anything else on a mechanical Tranny ( my MH doesn't have a computer ) that could cause the high rpms?
The rpms seem high right from 1st gear to 4th gear.
I guess I'll change the tranny fluid and both the filter inside the Pan and the external Filter. Do I just drop the pan and change the filter like I do on all automatics? I'm not sure if the MT643 needs to be done a different way. I'll also change the external screw on filter.
I drove the coach for 2 hours at 2500-2800 RPMS not realizing I had an issue!! Now I have 2 diesel fuel leaks and I am guessing it was the high Rpms that caused them. 1 High Pressure fuel line is leaking and 1 injector.
Here is a picture of the high pressure line leak.
http://i238.photobucket.com/albums/ff24/patcherman/injector_leak_3.gif
The injector is leaking quite a bit. Here is a couple of pictures, I used a paper towel and plugged the opening below the injector. The paper towel absorbed all the diesel fuel that was leaking down the engine to the ground. Heres a picture of the injector leak top and bottom.
http://i238.photobucket.com/albums/ff24/patcherman/injector_leak.gif
http://i238.photobucket.com/albums/ff24/patcherman/injector_leak_2.gif
I will post the diesel leaks in the appropriate forum for help, also might help someone else.
Now that I know for sure the RPMs are really high please post any ideas you might have on the reason for it. Any idea would be a help! i would like to do this without bringing to the shop.
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Cummis8.3
Active Member
11 Posts |
Posted - 03/26/2011 : 7:34:46 PM
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quote:
Originally posted by Spar
Is the "kick down" linkage stuck like you're in passing gear? That would be my first check, scratch that second check. First would be fluid level but you did that already.
The RPMS are high enough to seem like it's in passing gear. IN FACT, I CANNOT get it to drop into passing gear. I test drove to see if it down shifts and it DOESN'T!!
This could be my problem. I know its shifting into 4th gear because I am counting the shifts, But No downshift for passing gear.
What do I look for on Tranny? My MT643 is mechanical, No Computer on my year.
IBT/STOVEBOLT: I also don't get the second drop in RPMS like I do in 3rd gear (I think the Torque Converter Lock isn't happening in 4th. RPMS are still real high in 3rd.)
FYI, I didn't drive it for about 2 years. I had the tranny fluid changed over 3 years ago and haven't put 1000 miles on it. I was going to change the fluid again myself and drop the pan and change the Filter & also change the secondary screw on filter. If I do that is there anything else I can look for or change that could be causing my problem, i.e. modulator, etc.
Thanks! |
Edited by - Cummis8.3 on 03/26/2011 8:01:15 PM |
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Cummis8.3
Active Member
11 Posts |
Posted - 03/30/2011 : 10:19:07 PM
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hey guys, what if I disconnect the kickdown cable, would that tell me if it's an issue with the kickdown?
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tigger2
Advanced Member
USA
470 Posts |
Posted - 03/31/2011 : 08:50:23 AM
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| Yes that may help, the cable in some styles is hooked to a sliding wedge (long straight style or a rotary ramp on the small round style) that is usually plastic that works a pin that goes to a valve on the valve body. When you take it off of the transmission fluid will come out. We got a kick down assy. from a junk yard that had the cable cut off for a test plug. You may also want to check the mounting at the throttle linkage to see if it is bound up at that end as well. |
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Cummis8.3
Active Member
11 Posts |
Posted - 03/31/2011 : 1:09:43 PM
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quote:
Originally posted by tigger2
Yes that may help, the cable in some styles is hooked to a sliding wedge (long straight style or a rotary ramp on the small round style) that is usually plastic that works a pin that goes to a valve on the valve body. When you take it off of the transmission fluid will come out. We got a kick down assy. from a junk yard that had the cable cut off for a test plug. You may also want to check the mounting at the throttle linkage to see if it is bound up at that end as well.
Attached is a picture of the Kickdown cable at the throttle. If moves back and forth with no binding at all.
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Edited by - Cummis8.3 on 04/01/2011 11:16:22 PM |
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Cummis8.3
Active Member
11 Posts |
Posted - 04/01/2011 : 11:15:51 PM
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UPDATE:
I think the Rpm mystery has been solved. As I said in an earlier post I used a handheld laser tach on the Crankshaft to verify tach was accurate. I tested at Idle, 1200, & 1500 Rpms. All Rpms matched Handheld and Dash Tach. But, with a suggestion of another poster to check the Tach at Full Throttle ( governed RPM ), with the peddle pressed to the floor the Dash Tach was at 3000 Rpms and the Handheld was at 2550 RPMs. Apparently the Dash Tach is not accurate at the higher RPMs. I hope this is the real issue and my experience (wasted time) helps someone else. Next is to figure out what is wrong with the VDO tach, or possibly the alternator is sending bad information. Strange that it was accurate at least to 1500rpms but not at full throttle. Thanks for all the help! |
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Allison MT643 running 2500 RPMs at 60 MPH, Help!
