Attention: TDR Forum Junkies Transmissions not all equal
Our automatic transmissions are the product of production line assembly and quality. The design is quite strong as witnessed by the design being used since the 60's behind all kinds of powerplants including the bigblocks in muscle cars. But our Cummins engine with it's huge torque numbers at low rpms pulling a heavy truck is the toughest duty for the Auto trans.
Being a production line product, not a custom hand assembled product there are huge variations from trans to trans. The +/- allowable tolerances often add up to creating a very loose, internally leaking transmission that will have a rather short life. But occasionally all the tolerances come together and create a very good transmission that will hold up to a lot of abuse.
Our auto trans' live on pressure, the clutch packs are held by pressure, one of the big items done when a trans is upgraded is to raise the line pressures to hold more power. Also taking care of pressure loss from internal leakage means that the pressure gets to the clutch packs to do the intended job.
What is often misunderstood is that the pressures in the trans varies a lot based on throttle pedal travel. With a stock trans when you are running at say 45 mph OD, the line pressure will be somewhere around 60-80 psi. If you almost floor the pedal to accelerate but not hard enough to get a downshift into third gear, the line pressures will be in the 120-140psi range. This is a product of throttle pedal movement.
With a stock Cummins engine, a large amount of throttle pedal movement is needed to get good acceleration, but with a fueling box, only a very small amount of pedal travel will produce a lot more torque than stock, but the pressures in the trans are much lower, therefore the trans can slip and shudder. If it slips and shudders enough, the trans will self destruct.
What all the above distills down to is this: don't 'baby' the trans! Keep the rpm's up, and when you want to go, GO! use a lot of pedal, so the trans will have enough pressure to hold the power you are producing.
Some of the transmissions I've overhauled and upgraded have had fueling boxes and injectors installed for over 100K miles. They were driven with the above knowledge and survived longer than expected. But I have also overhauled and upgraded low mileage transmissions that were in very poor condition behind stock engines.
Some auto transmissions are much better than others. Just like some stick shift stock clutches hold a lot more power than others.
I hope this explains some of the experiences of our TDR members with their auto transmissions.
Greg L The Noise Nazi
Our automatic transmissions are the product of production line assembly and quality. The design is quite strong as witnessed by the design being used since the 60's behind all kinds of powerplants including the bigblocks in muscle cars. But our Cummins engine with it's huge torque numbers at low rpms pulling a heavy truck is the toughest duty for the Auto trans.
Being a production line product, not a custom hand assembled product there are huge variations from trans to trans. The +/- allowable tolerances often add up to creating a very loose, internally leaking transmission that will have a rather short life. But occasionally all the tolerances come together and create a very good transmission that will hold up to a lot of abuse.
Our auto trans' live on pressure, the clutch packs are held by pressure, one of the big items done when a trans is upgraded is to raise the line pressures to hold more power. Also taking care of pressure loss from internal leakage means that the pressure gets to the clutch packs to do the intended job.
What is often misunderstood is that the pressures in the trans varies a lot based on throttle pedal travel. With a stock trans when you are running at say 45 mph OD, the line pressure will be somewhere around 60-80 psi. If you almost floor the pedal to accelerate but not hard enough to get a downshift into third gear, the line pressures will be in the 120-140psi range. This is a product of throttle pedal movement.
With a stock Cummins engine, a large amount of throttle pedal movement is needed to get good acceleration, but with a fueling box, only a very small amount of pedal travel will produce a lot more torque than stock, but the pressures in the trans are much lower, therefore the trans can slip and shudder. If it slips and shudders enough, the trans will self destruct.
What all the above distills down to is this: don't 'baby' the trans! Keep the rpm's up, and when you want to go, GO! use a lot of pedal, so the trans will have enough pressure to hold the power you are producing.
Some of the transmissions I've overhauled and upgraded have had fueling boxes and injectors installed for over 100K miles. They were driven with the above knowledge and survived longer than expected. But I have also overhauled and upgraded low mileage transmissions that were in very poor condition behind stock engines.
Some auto transmissions are much better than others. Just like some stick shift stock clutches hold a lot more power than others.
I hope this explains some of the experiences of our TDR members with their auto transmissions.
Greg L The Noise Nazi
