Forum Discussion
- The ZF 8 speed in the Rams(and in my BMW) have a torque converter so the "would" part of that has no bearing in what is being discussed.
There is some slippage in the torque converter locks up clutches and in the clutch packs of the transmission as they lock together. That is what clutches do, they slip as they come together and then lock up. Even though it is very quick on the ZF 8 speed, it still isn't instantaneous and there is some slippage especially when the TCM programs smooth shifts. There is less slippage in sport modes that have a firmer and quicker shift.
Increasing line pressure for long periods of time under heavy load to keep these clutch packs together causes more friction and will increase the fluid temp. High engine temps will also heat soak into the trans as well. Too much heat will break down the fluid and decrease its ability to keep these clutches together which will cause them to slip. I am not saying that it will likely happen in any of these trucks any time soon, but it will eventually happen as the clutch material over time.
If these 8 speeds didn't have some slip or heat caused by what I stated above, then why is this Ram Rebel's trans temp is at 203F at 31:00 of this video towing just 7k lbs with snow falling?
Ford Raptor vs Ram Rebel on Ike wilber1 wrote:
Samsonsworld wrote:
wilber1 wrote:
Samsonsworld wrote:
Shift speed doesn't matter. The gears aren't what slips. The torque converter acts like a clutch. If you've ever been in a vehicle with a shift kit, you'll understand. No slip = very hard shift.
ZF 8 spdAll sequential upshifts and downshifts with this design involve just releasing one shift element and engaging another. In engineering literature, this is referred to as a “clutch to clutch” shift. Many skip shifts are also possible in the same way, e.g. a shift from Eighth to Fourth involves releasing brake A and engaging brake B while leaving clutches D and E engaged. This transmission therefore shifts very quickly. If the torque converter is replaced by a launch clutch, this transmission would be equivalent to a dual clutch transmission.
Yeah...so?
So this.
If the torque converter is replaced by a launch clutch, this transmission would be equivalent to a dual clutch transmission.
Shifts are clutch to clutch, the torque converter isn't involved.
Exactly. I just tried to explain it, probably to long winded. Clutches in an auto are what is used to get between the gears. Programing and line pressure is what determines what type of shift and overlap. In other words firmness and time.Samsonsworld wrote:
wilber1 wrote:
Samsonsworld wrote:
Shift speed doesn't matter. The gears aren't what slips. The torque converter acts like a clutch. If you've ever been in a vehicle with a shift kit, you'll understand. No slip = very hard shift.
ZF 8 spdAll sequential upshifts and downshifts with this design involve just releasing one shift element and engaging another. In engineering literature, this is referred to as a “clutch to clutch” shift. Many skip shifts are also possible in the same way, e.g. a shift from Eighth to Fourth involves releasing brake A and engaging brake B while leaving clutches D and E engaged. This transmission therefore shifts very quickly. If the torque converter is replaced by a launch clutch, this transmission would be equivalent to a dual clutch transmission.
Yeah...so?
So this.
If the torque converter is replaced by a launch clutch, this transmission would be equivalent to a dual clutch transmission.
Shifts are clutch to clutch, the torque converter isn't involved.wilber1 wrote:
Samsonsworld wrote:
Shift speed doesn't matter. The gears aren't what slips. The torque converter acts like a clutch. If you've ever been in a vehicle with a shift kit, you'll understand. No slip = very hard shift.
ZF 8 spdAll sequential upshifts and downshifts with this design involve just releasing one shift element and engaging another. In engineering literature, this is referred to as a “clutch to clutch” shift. Many skip shifts are also possible in the same way, e.g. a shift from Eighth to Fourth involves releasing brake A and engaging brake B while leaving clutches D and E engaged. This transmission therefore shifts very quickly. If the torque converter is replaced by a launch clutch, this transmission would be equivalent to a dual clutch transmission.
Yeah...so?- I have a 9 speed in my 1998 dually.
Samsonsworld wrote:
Shift speed doesn't matter. The gears aren't what slips. The torque converter acts like a clutch. If you've ever been in a vehicle with a shift kit, you'll understand. No slip = very hard shift.
ZF 8 spdAll sequential upshifts and downshifts with this design involve just releasing one shift element and engaging another. In engineering literature, this is referred to as a “clutch to clutch” shift. Many skip shifts are also possible in the same way, e.g. a shift from Eighth to Fourth involves releasing brake A and engaging brake B while leaving clutches D and E engaged. This transmission therefore shifts very quickly. If the torque converter is replaced by a launch clutch, this transmission would be equivalent to a dual clutch transmission.
- Shift kits generally up line pressure, it reduces friction of the clutches, by reducing clutch slip. That is why you get the hard shift. You get longer clutch life but depending on the transmission you can get broken hard parts.
It effectively takes the overlap out of shift so you lose the smooth soft shifts.
It is generally installed in the valve body.
Automatic transmissions have clutch packs and that is generally the first thing to wear out.
A torque converter is fluid coupler. It allows the engine to spin almost independently of the transmission. It is responsible for pressurizing automatic transmission fluid, the pressure supplies the force necessary to the clutches and bands. So as you apply gas the torque converter spins and the pressure comes up moving the vehicle.
On newer vehicles you maybe able to get away with a tune to change it, but stuff like the 4L80E and 4l60E can still have it installed in the valve body.
But here
http://www.txchange.com/transgo.htm
and here
https://www.mistertransmission.com/what-are-shift-kits/ - Shift speed doesn't matter. The gears aren't what slips. The torque converter acts like a clutch. If you've ever been in a vehicle with a shift kit, you'll understand. No slip = very hard shift.
- Everyone keeps saying that all manufacture's sent their strongest power plant the 5.7 for the RAM the 6.2 for GM, but Ford did not send their strongest power plant. The 3.5 Eco is a great power plant yes I own 2 of them and they are no doubt the best truck power plants I've ever owned.... but there is a 3.5 High Output that is available in the higher trim just like GM's 6.2 which produces 450 horses and 510 ft/lbs of torque. Put that against GM's 6.2 with only 420HP/460Ft/Lbs......Just something to chew on :B
ShinerBock wrote:
wilber1 wrote:
ShinerBock wrote:
wilber1 wrote:
Higher RPM's mean more line pressure and less chance of slippage.
The line pressure within the clutch housing is dictated by the valve body and increases pressure within the clutch housing based on engine load/throttle input. Line pressure is one of the things I monitor on my CTS2. I can drop down a gear and be close to max rpm applying the same throttle and the line pressure to the clutches will hardly even change. In contrast, I can be at low rpm going up a hill which requires more throttle and my line pressure at the clutches will jump close to max 225 psi even though my rpm didn't change much.
I should have phrased that differently. If RPM is too low the transmission will not be able to make enough line pressure. This is always an issue with diesels that make huge torque at low rpm.
It would have to be pretty low, because I can make the line pressure in my tuned Ram 2500 CTD go to 200+ psi at just 1,000 rpm. Stock valve body max line pressure for my truck is 170 psi.
It was certainly a problem with the old 4 spd transmissions which were basically just reworked gas engine transmissions.
Anyway I was responding to the comment that higher rpm puts more stress on a transmission. There is no reason for a transmission to get hotter unless something is slipping, or the torque converter is unlocked. My transmission temperature changes very little between towing on the flat making very little HP and pulling a grade at full throttle.
