Will a 95 transmission be compatible with a 90Q???

[nuQ]

considering buying a fellow members rebuilt 95 transmission (as a backup) for my 90Q. wondering if it will fit with no problems and eventually take the 93 first gear start TCU???

[Q45tech]

It will bolt up. There might be some rev limiter/shift speed problems in 1st and 2nd gears as the 94-96 transmission has less aggressive gearing in those gears..........but really only 7% so it should barely make it without hitting rev limiter......6500 x 1.07= 6955..........really depends on 95 transmission condition [how fast it shifts].........at the worst you just get a 94-96 tcu.

The acceleration will slow but only a few tenths.

[elwesso]

Get it!!! You may want to get a hold of a 94 TCU, which I may have available sometime soon!

[nuQ]

two questions before i take the plunge,,,,,,will a 94 or 95 TCU be compatible w/ a 90 ECU, and would a 93 (first gear start) work with the 95 transmission????????thanks

[elwesso]

NO... You want a 94 TCU (will work fine with the ECU)

Its the TCU that controls the 1st gear start, and if you use a 93 TCU you will definitely have messed up shift points..

A 94 TCU should be real easy to find!

[nuQ]

i was under the impression that only the 93's had the first gear start. does your 94 wes start in 1st???????

[elwesso]

Yes.... 93 and on had 1st gear start..

Thats the main reason they made the lower 1st and 2nd gear, for still silky smooth 1st gear starts...

For 90-93 owners, 93 WAS THE ONLY TO START IN 1st, and thus for 90-93 owners woud be the only TCU worth going after...

[elwesso]

BTW Jeff, can I have dibs on your old transmission?

[nuQ]

if and when she implodes, she's all your's wes!!! LOL actually i was looking at the 95 rebuilt transmission as a backup to have around, just in case of disaster. sometimes i think mine shifts a little funny (i have that classic "burp" when cruising at a steady highway speed that i'm hoping is the KS'ers that will be replaced soon), most times i think it's all in my head. just want to be sure i'm making the right decision, cause i wont if all is well with the trans i'm buying until something bad happens with mine!!!!jeff

[rsiwicki]

Dennis....I installed a 93 TCU into my car last night and drove it around all day and all went great. No problems at all with functionality. I did several WOT runs to test the frst gear redline and did not notice any difference. The car still seems to shift right at 6,750-6,900 rpms. My rpms have never gone into the redline territory so if your theory holds true about the change in redline due to gearing.....then I figure that when I install the 92 transmission and run my 95 TCU against it, my new redline should be somewhere around 7,400. I should definetly notice this if it is true. After I get 500+ miles breaking in my transmission I will test it with both TCU's to see if I can't get it above the 6,900 redline point.

Please let me know if my thoughts are correct that the 95 TCU with a 92 transmission based on your comments should move it to a 7,400 redline.

Thanks...Rob

If nothing else...I might have a 93 TCU to sell to somebody if I can't determine a difference between the 93 vs. 95 TCU.

[Q45tech]

Redline [fuel cut] is set by ecu at 6,900 rpm [or 7300 with JWT ecu].

Just as speedo is optimistic so is tach to compensate for gravity and acceleration on needles.Have to use Consult to accurately read rpm and even that may miss because of data collection refresh cycle [0.03 seconds].

[rsiwicki]

I figured as much that I would need a consult to determine the true rpms....

To understand this correctly....the JWT ECU does not determine the shift point...just the fuel to rpm cut off point. So if I had a JWT ECU on a stock (OEM TCU & transmission) setup I would still shift at 6,900 regardless that the JWT ECU can now go to 7,300rpms becuase the TCU tells it shift at 6,900.

Now if I use the JWT ECU, 92 transmission, & 95 TCU the shift point should be moved up to about 7,400 rpms but the fuel will be cut off at 7,300 rpms. Is this correct???

I tried hard to see a difference in the shift points, but was not able to determine any noticeable difference when I put in the 93 TCU. I know that the rpm gauge is not correct as when my TC acts up the rpms drop about 250 but on the consult is was only dropping 50 to 100 rpms...I can't believe how strong the 50 to 100 rpm drop for that split second feels under a hard acceleration. I get the new transmission installed early next week and after the breakin period I can see if it truely is the TC. This was the best guest from the head tech as this was the TC was the only parameter that changed exactly when the rpms drop while we were running the consult and duplicating the problem.

[Q45tech]

The oem TCU shifts by vehicle speed rather than rpm.Notice all the graph in section AT reference SPEED..........notice the 5mph range plus the sloped range vs. TPS voltage [% of throttle opening= load].

The rpm of engine and torque convertor output is primarily to decide lockup clutch activation and to avoid a down shift that would over rev the engine.

Everything is interrelated as a safety check but speed sensor is the primary signal source.Notice that the speed ranges correlate to a 6,000-6,300 rpm shift range!..............the get ready to shift operation begins in this range [in D4] position, the actual shift start is a function of the time to rev of the motor [condition], just as the 0.6-0.9sec [or worse] shift time is a function of transmission health.

The adaptive portion of software is supposed to pick early or late starts [6,000, 6100, 6200, or 6300] to the operation so that everything is complete before the red line is [could be] approached.

Worn out trannies can't keep up..........the other problem is JWT ecu creates more torque so acceleration is faster in the 6,000-6,300 rpm range and the engine may get to redline before the transmission initiates the shift due to JWT ecu EXTRA ignition advance.

Why some trannies don't like JWT ecu and need the Trimode which is meant to be used with JWT ecu.

[rsiwicki]

Dennis...thanks for all the info as I am not starting to undertand how it all works.

Can you tell me more about the downshift points in relation to speed and engine rpms???? What really drives me nuts is my car will not downshift from about 30+mph into first and just sits there in 2nd gear when I hammer it slowly accelerating. I think that it should be programed to downshift till at least 40mph as the acceleration in 2nd gear from 30+mph is so slow. Also the same is true when I try to manually down shift it into 1st. I put it into first but the transmission will not engage into 1st gear until the speed drops to about 30mph.

Does the JWT TCU tell the car to downshift easier so that the next time I am going 35mph and WOT it that don't get stuck in 2nd gear and it downshifts into 1st gear??? Also will the higher TC that I am installing (2,400) help with this problem and make my car downshift easier? I have been beat on the street so bad by cars that I should have no problem with only to have my car stuck in 2nd gear when we start racing around 35mph. If I could get it to downshift to 1st then I would fly by these guys.

[Q45tech]

To protect the transmission - increase life, automatic downshifts to 1st gear are locked out above 23-26 mph [what would result in 3400 rpm].

The transmission power handling capacity is speced at 290 lb/ft max so this was added when they found out the engine could produce 300-307 lb/ft stock...........the JWT ecu gets you to 330-337 lb/ft so you want this protection.......as a 16% overload is not good.

The newer 5 speed is speced right at 333 lb/ft..........the QX56 has a different more robust version good for 390 lb/ft.

Just manually shift into 1st gear, the tcu is self protective in that no shift will occur if an over rev is possible [no shift to 1st at 50 mph].

[rsiwicki]

Okay I understand that...but with my car I can be cruising at 40mph and then if I manually downshift it to 1st the car still will not go into 1st gear unless my speed drops below 30mph. Believe me...I have tried several times to get it into 1st gear when I am already above 30mph and I can't...I have never been able to do this..even when I bought the car back in 1998 and was autocrossing it. It drove me nuts to come out of a turn at 35mph and to just sit there stuck in second gear with no way of getting it into 1st. On of the reasons I stopped autocrossing it was becuase I was tired of just sitting there in 2nd gear barely accelerating out of the turns.

So what you are telling me is that if I manually downshift the car at 40mph that it should go into 1st gear??? My car has never been able to do this.

I understand about the computers protecting the transmission from these 1st gear downshifts, but is there a way to override this function or does the JWT TCU lift the protection things to allow the car to automatically down shift?

[elwesso]

My car can downshift to 1st with the shifter at about 35..... Sometimes its evil and does, most times it does.....

[rsiwicki]

Can somebody tell me for certain that if you manually put the transmission into 1st gear that it will go into first gear....even if you are at 40mph?

My car has never been able to do this and I would like verification on this to see what is up.

I am currently running a 93 TCU in my car which works fine. I will test it out on the way home to see if I can get the car to drop into 1st at 40mph by doing it manually.

[elwesso]

I am leaving the house soon, and I will see if I can.....

[rsiwicki]

okay ....I just tried it with the 93 TCU installed and I get the exact same response....the car will not downshift into first gear until the speed is 30mph or less...I tried several times putting it into first from 40mph and nothing happens and then I let the speed slowly decrease and as usual...when the speed decreases to 30mph...the transmission will move itself into first gear while it is already selected manually into 1st gear.

[Q45tech]

In 90-93: 30 mph x 1333 rpm [per 10 mph] [1st gear] = 4,000 rpm. The exact rpm where the torque peaks..........any higher would be a waste to acceleration.

WHEREAS the 94-96 : 30 x 1250 rpm= 3750 rpm

Very few trannies of any brand allow you to down shift beyond torque peak......except older American iron which has a much lower torque peak rpm.

My trimode tcu with the reman transmission will down shift at 38-39 mph not helpful but dramatic.

[rsiwicki]

Ahh thanks for the info...I must get my hands on a JWT TCU to try to engage the dowshifts. I would love to get what you have Dennis...a down shift at 37-38. Even 35mph would be great...but when you start at 30mph and are stuck in 2nd gear...it just seems so slow until the rpms get up there again.

[elwesso]

my Q does it at 35mph... I tried it thrice.....

[nuQ]

just tried mine too,,,,,35mph

[Q45tech]

Function of whether you have the throttle WOT when you pull it into 1st or are letting the engine brake with no throttle.......obviously some differences with TCU...........why they each have different part numbers.

[rsiwicki]

Well I don't know why my car will not downshift into 1st gear at 35 mph like the rest of yours....It has never done it and probably never will. Maybe something is setup differently in a 95 versus the other years.

Okay...Q45tech is correct about the change in shift points using a 93 TCU on a 95 transmission. It does lower the shift points. After several trials, it definetly does appear to lower the rpm redline by about 500rpms. I don't know why I could not tell the first day I had it in my car, but this weekend I have noticed that the car now shift right at 6,500 vs. the usual...6,750-6,900 rpms. Even my 2nd to 3rd gear shifts are at 6,500 rpms.

JWT called me to tell me that my new ECU would be mailed out this week so all is good there and this should allow my engine to redline to 7,300rpms. Also with the 92 transmission running with a 95 TCU then I would suspect the redline should increase to around 7,300 or 7,400.

I will have to try the 1/4 mile runs with each TCU to see which option is the quicker setup and will go with that setup. I will also be running the 4.08 gears so I think that because I will create an extra shift before I finish the 1/4 mile that I might not want to run out the car to 7,300rpms. I am thinking that based on the HP & torque curve that I would have more power in the say 4500-60000 rpms range versus somewhere in the 6,000-7,400 rpms range and would therefore benefit by shifting sooner and benefiting from the higher HP at the lower rpms compared to HP at redline.

That probably does not make a whole lot of sense what I just said but the overall goal will be to obtain the highest average HP & torque over the entire 1/4 mile across the total possible rpms range. Since I will be creating 2 shifts during the run, I will need to keep the rpms in the range where I would benefit the most...which I think would be around 4,500-6,000 versus 6,000-7,400. If I did not have this extra shift then running a higher redline would probably definetly help, but since I have to shift I think that I would benefit from greater HP & torque at mid rpm range.

[rsiwicki]

Also....if this is all correct that running a 95 TCU against a 92 transmission will raise my shift points...then I would think that with my JWT ECU that I would almost be duplicating what a JWT ECU/TCU combo does with raising the shift point. I know the JWT TCU does some other things, but the for others out there not wanting to spend $450 on a JWT TCU and they have the 90-93 transmission's then you could buy a 94-95 TCU for less than $100 and basically raise the redline point, get the first gear start, and keep everything else the same. I will know in about a month after my transmission has 700 miles on it to test the above to see if this works.

[Q45tech]

The [gear spread/span] the ratio drop from gear to gear is always too wide on a 4 speed............

2.784>1.544=55.46%; 1.544> 1.000=64.77%;

Unless the torque falls faster [% amount] from peak to redline, you are always bettter off staying in a gear to redline.

In any iteration the Q engine doesn't lose torque as fast as a gear shift would. Do the math!

[rsiwicki]

Ahh thanks for the help Q45tech....Always much appreciated. I guess I will be running it to redline and then some. I will still try it out with both TCU's in the 1/4 to see what the difference is just for curiousity.

[lockwood7]

rsiwicki - drop me a line when you want to get rid of the 93 TCU. Tell me again why this is the only year I can put in my 1990...