Daveinet
il
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Is there an easy way to change the shift point for my TH475 transmission? I'm not sure if there is something wrong with the trans, or if it was designed/setup this way, but it tends to shift to the higher gear much sooner than it should. Even if the vehicle is floored, it will shift @ 3500 RPM, even though the engine will pull hard well above 4500 rpm. Under normal driving, it seems to shift way early as well. The modulator does seem to work - I had the vacuum hose come off and it stayed in first gear. Its actually better since I installed the new engine, but it still does not seem to be right. I've never been inside an automatic trans, so if I get into it, I'm starting from scratch.
Dave
FMCA F298817
'83 Revcon Prince 31' FWD
502 w/Thorley's & Magnaflows,
Howell/Edelbrock MPFI, Koni FSD,
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st687
tampa Fl
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Joined: 10/09/2003
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Dave,google Bowler Transmission and talk to them, I have a buddy that has there trans in his Chevy truck with a big block and he said it is a killer trans.
Doris &Bill
97 U270 Foretravel
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Adam H
People's Republic of California
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Joined: 02/12/2007
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Ok, that's an issue. Under normal driving the modulator controls shift points and you can buy adjustible ones. At full throttle they are governor shifts and the modulator has nothing to do with it. Assuming you are talking about the rig in your signature, I would assume you have a TH400. In order for a TH400 to know you are a full throttle and give you governor shifts it uses an electrical switch on the throttle pedal (usually there) to activate a solenoid in the valve body to lock out the modulator and give you full governor shifts. Make sure that connector is plugged in at throttle pedal and left side of transmission case. Check the wire for opens with an ohm meter. Repair as necessary. If all looks good there, turn key on and have someone floor the throttle pedal and make sure voltage is present at connector at trans. If all is still good you will need to pull trans pan off at this point, might want to go to shop. If you want to venture further, pull pan and check connector inside of case and continuity to solenoid. If all that is ok, replace solenoid and put back together. If the trans is a TH400 it will be the ONLY solenoid inside. Good luck, I hope this makes some sort of sense.
Adam
BTW it is not a good idea to drive the vehicle until this is fixed or you WILL damage the trans. Still assuming it is a TH400
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Seanman
Arroyo Grande, California
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Joined: 05/02/2007
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Dave, Been through a 400 but not a 475. That being said, I think your setup is shifting as designed. It is good that it shifts no higher RPM than 3500rpm due to the weight. From the "MOTOR" Domestic Transmission Manual it states....
A VACUUM MODULATOR is used to sence engine torque input to the transmission automatically. The Vacuum modulator transmits this signal to the pressure regulator, which controls line pressure, so that all torque requirements of the transmission are met and proper shift spacing is obtained at all throttle openings.
The DETENT SOLENOID is activated by an electric switch at the carburetor. When the throttle is opened sufficiently to close this switch, the solenoid in the transmission is activated, causing a downshift at speeds below 70 mph. At lower speeds, downshifts will occur at lesser throttle openings without the use of the electric switch.
I have had 3 P-30s....two of them had the detent solenoid switch not on the carb but on a bracket under the throttle pedal. It would engage only when I had my foot to the floor. I would suggest leaving everything as is. If you require the shifting you wish I would do it manually. Hope this helps.
Sean
87 Holidy Rambler Imperial
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Seanman
Arroyo Grande, California
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Adam H wrote:Ok, that's an issue. Under normal driving the modulator controls shift points and you can buy adjustible ones. At full throttle they are governor shifts and the modulator has nothing to do with it. Assuming you are talking about the rig in your signature, I would assume you have a TH400. In order for a TH400 to know you are a full throttle and give you governor shifts it uses an electrical switch on the throttle pedal (usually there) to activate a solenoid in the valve body to lock out the modulator and give you full governor shifts. Make sure that connector is plugged in at throttle pedal and left side of transmission case. Check the wire for opens with an ohm meter. Repair as necessary. If all looks good there, turn key on and have someone floor the throttle pedal and make sure voltage is present at connector at trans. If all is still good you will need to pull trans pan off at this point, might want to go to shop. If you want to venture further, pull pan and check connector inside of case and continuity to solenoid. If all that is ok, replace solenoid and put back together. If the trans is a TH400 it will be the ONLY solenoid inside. Good luck, I hope this makes some sort of sense.
Adam
BTW it is not a good idea to drive the vehicle until this is fixed or you WILL damage the trans. Still assuming it is a TH400
Ya! What he said
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Daveinet
il
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I've driven another Revcon and it shifts normal, so I can't think the shift points are right. I just ran outside and checked the switch. The switch is OK, supplies 12 volts when the pedal is pushed. The same location is 20 ohms to ground, so the solenoid is OK, -well the coil is OK, we can't know if it fires or not, but It does downshift if you tromp on it, even at 60 or so.
When I first got the coach, it would shift out of 1st @ ~15 mph even at half throttle, or so it seemed. It would also bang really hard from 1st to 2nd. After putting 50K miles on it, it has gotten some better, but still shifts early in all cases. its like there is too much vacuum, or the position of the modulator is wrong or something, not that I have any idea if that is possible.
Shifting out at 3500 RPM wastes a lot of power, the torque peak is around 3800 RPM, so it never hits peak torque, let alone peak HP. But even under normal driving, it shifts earlier than normal, and earlier than the other Revcon I drove.
I'm pretty sure the only difference between the TH400 and the TH475 is the output shaft is for a 4WD. It also has straight cut gear in 1st and 2nd. Yes, they whine when taking off.
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zmotorsports
Utah
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Joined: 11/29/2007
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Dave, when I have built transmissions for extreme duty such as towing/hauling or clients with heavy right foot I will install slightly stiffer springs on the governor and then as already mentioned install an adjustable modulator to fine tune the part throttle shifts. There are a couple of other little tricks that I do if I am inside the trans. already but the governor springs and modulator are where I would start without having to drop the pan. As far as the detent solenoid this is for kickdown or passing gear whichever you prefer to call it only. The speed I usually try to shoot for is around 15-20 MPH (approx. 2800-3000 RPM) for a 1-2 shift and about 35-40 MPH (approx 3000-3300 RPM) for a 2-3 shift. These are for part throttle shifts not full throttle. Mike.
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1fastdad
mo.
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Joined: 08/27/2007
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When the trans is in detent(all the way to the floor with detent switch engaged) the trans will shift on the govener just like when you take the vac. line off. For what you want they make an ajustable vac. modulator. It has a small screw in the end of the vac. tube to ajust the spring tension. This way by turning the screw in or out you can make it shift at any RPM you want at normal driving conditions. They do make kits to change the gov. shift point to if you want to play with that. I owned a tran. shop and built a lot of perfomance transmisions for street and drag racing so I know there is a lot you can do with these tranmisions.
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Daveinet
il
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zmotorsports wrote:... but the governor springs and modulator are where I would start without having to drop the pan... Mike. Ok, so the vac modulator location is obvious, but where is the governor location? It can be accessed without dropping the pan?
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thomasinnv
where ever i stop
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the governor is on the side of the tranny behind a small round cover. probably has a wire clip holding the cover on.
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