Measuring Transmission Slip

[BlkMax]

I want to know if there is a way to see the transmission slip when running a 5 speed Alison in 5th gear.

Is there a way with EFILive to measure or calculate the slip RPM? I had this ability with my old Banks System and it was kind of handy to see when you were starting to have problems with 5th gear. To be honest, until I totally smoked the tranny, I never saw any slip in gears 1-4, that is why I am specifically asking about 5th.

I do a lot of highway driving with trailers, campers, etc. where I am going too fast to take a downshift to 4th, so the engine will just drag along in 5th when you accelerate hard (hence you could see when there was too much foot in the pedal by the slip gauge). I have about 300 miles on the new transmission, and do not want to go through that pain again anytime soon....

[Big Mike]

Look through your trans PID list. You're looking for trans input shaft speed, output shaft speed, and converter slip (in RPM's). Log these in tow/haul. If the converter slips while its in lockup you'll see it. A healthy trans will have minimal slip aprox 0-25 RPM or so and the trans input and output shaft speeds will both be linear (but not the same).

If you see much in the way of erratic lines in the log from logging these specific PIDs then you've got trans issues.

[BlkMax]

Thanx for the help....

[Mitco39]

I made a 05 Tranny slip PID for the Allison awhile back and posted it over on dieselplace... heres the post



I just finished making my own tranny slip PID!... took most of last night to figure out but I got it. I need to try and recall my C++ schooling to try and get it to work for every gear but im working on it.

This PID will read bogus numbers untill you get to 5th gear, then the gear ratios will align and you will get a accurate slip RPM (I took into account the slip in the TCC as well). Like I said im going to work on it to get it to work for every gear (I didnt realize it was alot like C++).

Im going to post up this PID for you guys and let me know what you think.


Thanks goes out to Blacky off the EFI site for his informative post.


To get this to work on your Scan tool download the corresponding .rar file. Extract it to you EFI Live User Configuration and over-write your exsisting calc_pids.txt file. My efi live user configuration folder was located at

C:\Users\Your user name\Documents\EFILive\V7.5\User Configuration

Yours will probably be similar if your on Vista or Windows 7.


After you have the file copied to that folder all you have to do is open your Livescan and you will see a PID called "Trans Clutch Slip" with code "CALC.Trans_Slip". You will need to also log 3 other parameters to get this PID to work. They are

Transmission Converter Clutch Slip Speed ---- GM.TCCSLIP
Transmission Input Speed ------------------- GM.TIS
Transmission Ouput Speed ------------------ GM.TOS


After you are done this go out for a drive (you will have to wait till you get into OD for the time being) and you will see a real time calculated slip of your transmission. There seems to be a minor variance +-20 RPM... that is just the error of either the tranny or the Flashscan, but if you slip the tranny you will see the RPM spike very fast.


Well I hope this helps alot of you, Depending on the feedback and popularity of this I will hopefully release one that will work with all the gears.

Any comments or suggestions would be greatly appreciated.


Goodluck

Mitch

[joecar]

Mitch,

Thanks, good job, that's short and simple... ...I take it 0.71 is the overdrive gear ratio.

That will also work for the Hydra-Matic 4L80E which has the TIS sensor located after the TC.

Where is the TIS sensor located on the Allison transmissions (is it the same for all models...?)...?

[Mitco39]

Thanks Joecar, Im not really sure why someone didnt beat me to it, because as you saw there wasnt anything to it.

Yes 0.71 is the OD gear ratio, I am going to try and get it to work for every gear. However, as soon as you start trying to do that there is quite a bit more arguements that you have to make, such as referencing the right gear ratio depending on the gear your in. I have looked at the arguements that the guys at EFI live has made availible to us and it is definatly do-able, it just requires alot more effort to figure out. I have taken a couple courses in C++ and the code they use resembles that fairly well.

The TIS is located just after the TCC on the bellhousing according to my service manual I have.

[joecar]

You may be able to use the lookup() function (see scantool user manual pdf).

So your TIS sensor reads from the input shaft (i.e. it measures angular speed on the input to the transmission itself
(i.e. the output of the TC, and not the shell of the TC and not the engine flexplate))...?

[Mitco39]

I would assume so.. I attached the picture I was looking at. I would say the engine rpms are measured by the crank angle sensor (or some other engine mounted sensor)... these are then fed to the TIS to calculate the amount of TC slip.



And yea I was looking through all the functions availible, I am sure there is a way to get it all to work... lol just have to remember all my schooling.

[Mitco39]

sorry heres the legend for the numbers

(1) Turbine Sensor Harness Connector
(2) Power Take-Off (PTO) Connector
(3) Output Speed Sensor Harness Connector
(4) Transfer Case Selector Shift Control Switch
(5) Transmission Connector Harness
(6) Park/Neutral Position (PNP) Switch Connectors
(7) Allison Transmission
(8) Engine Harness
(9) Automatic Transmission Input Shaft Speed (ISS) Sensor

[DURAtotheMAX]

there are three speed sensors on the allison.

input speed
turbine speed
output speed

the difference between input and turbine speed determines how much the CONVERTER (not the trans itself) is slipping. Obviously if its unlocked you are going to see a lot of "slip"...because thats what a torque converter does. Once its locked you should see zero difference, or something small, like +/-5 rpm. If the converter is slipping, you'll see a number thats ~15rpm or higher when its locked up.

The turbine speed sensor basically measures the input speed of the trans itself...like the RPM of the "other end" of the converter (called the turbine)...the output speed sensor measures the speed of the output shaft. The transmission has a fixed set of ratios. The TCM is constantly calculating the "actual" ratio of the turbine vs. output speed based on which gear the trans is in to determine if the trans (clutchpacks) are slipping or if there is some other internal problem in the trans that is preventing it from transmitting the proper gear ratio equivalent for a given gear/speed. This has NOTHING to do with the converter slip.

The ratios of the allison are as follows.

1st gear - 3.10:1
2nd gear - 1.81:1
3rd gear - 1.41:1
4th gear - 1.00:1
5th gear - .71:1
6th gear - .61:1

So, if the trans is working properly and not slipping, the ratio/mathematical equation between the turbine speed sensor and output speed sensor should correlate with what gear the trans is in. For example if its in 3rd gear (regardless of wether the converter is locked or unlocked, remember the allison is a clutch to clutch automatic trans, it is ALWAYS locked positively in one gear...there is NO freewheeling or overrunning so the ratios are always constant/fixed), which is 1.41:1, the turbine speed should be 1.41 / the output speed.

Say the turbine speed is 2500rpm. 2500rpm / 1.41 = 1773rpm. SO. the output speed sensor SHOULD read 1773 rpm if the trans is not slipping and working properly. The TCM constantly calculates this ratio, and does it for all of the other gears too. If the ratio gets too far out of range, it interpenetrates this as the transmission slipping and goes into limp mode and sets an "incorrect ratio" DTC.

make sense???

ben