15 speed to 13sd

boo boo

New member
i've got an 86 359 i changed the 15spd to a late model 13. now it wants to run hot in 13. i run it in 12. truck has 370 rears. what am i missing. need some direction. thanks
 

Truck Shop

Well-known member
What model of 13 speed, RTLO16913A? What temp is it running? Is it running hot with a load or empty?
If have a laser temp gun check the temp with it to verify the gauge is accurate. And was this gear box
just rebuilt or a used take out?

Truck Shop
 

Truck Shop

Well-known member
To stop any confusion the top four gears are 5th direct,5th over 6th direct, 6th over 7th direct, 7th over 8th direct, 8th over. So when you are in 8th direct your calling it 12th, 8th direct
power runs straight through the main shaft in the rear section. 8th over power or torque is divided between the two counter shafts in the rear section. Now if this is a late model high
torque transmission {built after say 1990} the counter shafts use tapered or Timken bearings. Those bearings have to have the proper preload set with shims, to preload the counter
shafts. If the preload is set to tight it will cause heat to be generated.

Because the trans makes heat in 8th over is because the counter shafts are transferring torque through them which will case heat. It should run a normal temp of 150* to 190*.
When operating in 8th direct the torque or power flows straight through the output main shaft, the two counter shafts are not flowing any power through them so the trans builds
less heat in 8th direct. Thus if the counter shafts were set up on the tight side of end play it will cause heat in 8th over. That's why I wanted to know if it is a newly rebuilt trans.

With all of that said Quote{Eaton Corp says 250* to 260* is OK on a short pull but should cool down quickly to 200* after cresting grade} Hope this helps and no confusion.

Truck Shop
 

JasonG

Well-known member
To stop any confusion the top four gears are 5th direct,5th over 6th direct, 6th over 7th direct, 7th over 8th direct, 8th over. So when you are in 8th direct your calling it 12th, 8th direct
power runs straight through the main shaft in the rear section. 8th over power or torque is divided between the two counter shafts in the rear section. Now if this is a late model high
torque transmission {built after say 1990} the counter shafts use tapered or Timken bearings. Those bearings have to have the proper preload set with shims, to preload the counter
shafts. If the preload is set to tight it will cause heat to be generated.

Because the trans makes heat in 8th over is because the counter shafts are transferring torque through them which will case heat. It should run a normal temp of 150* to 190*.
When operating in 8th direct the torque or power flows straight through the output main shaft, the two counter shafts are not flowing any power through them so the trans builds
less heat in 8th direct. Thus if the counter shafts were set up on the tight side of end play it will cause heat in 8th over. That's why I wanted to know if it is a newly rebuilt trans.

With all of that said Quote{Eaton Corp says 250* to 260* is OK on a short pull but should cool down quickly to 200* after cresting grade} Hope this helps and no confusion.

Truck Shop
Wow Truck Shop. That's an education.
I feel like I owe you some money, take a :beer ?
 
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