New 4.08 Rear diff install now have ABS issues, what to do?

[qsiguy]

Title says it all. I got the 4.08 swap done and obviously there are ABS issues that need addressing. I don't recall reading about this on other 4.08 installs. Is there something I need to change or is it possible the sensors on the new diff have a problem?

[maxnix]

You have TCS on this car, right?

[sijoko]

Title says it all. I got the 4.08 swap done and obviously there are ABS issues that need addressing. I don't recall reading about this on other 4.08 installs. Is there something I need to change or is it possible the sensors on the new diff have a problem?

Welcome to the land of ABS issues after a differential swap..........I've been there on my 95 Q. Here's the situation that I had with my differential.

The one that I picked up from a junkyard was for a different year and the ABS reluctor rings had a different pattern than the diff that was originally on my car. I didn't realize this till after I did the swap.

If you look closely at the rings, you can see if they have the same spacing. If not, then that is the problem. The one in my 95 had small teeth but the one from an earlier Q had wider teeth. I don't know if you can simply swap out the stub axles to fix the problem.

[qsiguy]

I'll take a look at the gears and compare.

I have TCS but it's been inoperative for a while now, I've just pulled the fuse, don't really want it.

[maxnix]

Yeah but it uses the same sensors.

I've always wanted to convert a a TCS to non-TCS to keep the sensor per wheel ABS. Probably way too much trouble.

[qsiguy]

The sensor rings are different old vs new. My originals were much thinner. I'm thinking it may be easier to build some electronics to adjust the frequency to offset the pulses and bring it back to spec. I really don't want to pull that diff out again.

[Q45tech]

Meditate on your statement, as the sensor rings are on the output [equivalent to being on wheel] so all 4 tires rotate at ~ the same rate...............probably a pulse LEVEL problem not a frequency problem.

[qsiguy]

Well the old diff's sensor rings had smaller teeth than the new one which means that it will send more pulses per revolution. ABS computer now thinks the rear tires are turning slower than the front. I have yet to verify any of this, just theorizing at the point. I plan to put a scope on it and figure it out. Maybe I can just count the teeth on the old vs new and do the math. I realize this issue doesn't really have anything to do with the diff, just the sensors.

[Rex]

Welcome to the land of ABS issues after a differential swap..........I've been there on my 95 Q. ...

I was in the same world, though mine might have been due to a bad sensor. Ultimately, I just considered it a "cost" of the rear end swap.

FWIW, the one on Greg's old Q, didn't throw an error for the new owner (pinched cable or something).

[rhinoone]

Well the old diff's sensor rings had smaller teeth than the new one which means that it will send more pulses per revolution. ABS computer now thinks the rear tires are turning slower than the front. I have yet to verify any of this, just theorizing at the point. I plan to put a scope on it and figure it out. Maybe I can just count the teeth on the old vs new and do the math. I realize this issue doesn't really have anything to do with the diff, just the sensors.

Can you post some pics?

[T45]

Have you investigated the front sensors and compatibility between the Z32 and Q? May be able to swap the fronts over and solve your issues if it's a pulse-width issue.

[qsiguy]

No I haven't but that could be an easier swap than pulling the diff again. For now I just pulled the ABS fuse..

[jamesmost]

i have been w/o TCS since my 408 swap code comes up right rear wheel sensor but there is nothing wrong with the sensor

[carlosinseattle]

I bought a parts car a couple of years ago, and I'm having a problem where that I can't figure out, but I think you guys might have an answer for me.

94 Q45a, w/TCS 141Kmiles.I'm getting the right wheel sensor code from the diagnostics.I'm also getting the code for speed sensor malfunction from the transmission computer. Could this be due to a diff swap by the previous owner? Do you guys get the transmission code if you perform a transmission diagnostic?

And if so, how/where can I get an original differential with the plugs for the tCS on it?

[Q45tech]

Has the AT speed sensor been replaced to correct for diff ratio change?

[qsiguy]

I would diagnose the actual components and wiring before suspecting a diff swap. I don't think you'd get a right wheel code with a diff swap but I could be wrong. Both sides would be throwing a code.

Tech, not sure if you are responding to my issue above or "carlosinseattle's" post but I did change my speed sensor to the correct one for the ratio change. The speed is right on. Checked it with a stopwatch as well as GPS.

[Q45tech]

Then you get to use a 4 channel digital oscilloscope and compare the frequency and amplitude of the 4 wheel sensors simulataneously as the Q is driven straight at a very very steady speed.

That's what the traction control computer does, except each channel has an A/D, so wheel rpms are translated to a VOLTAGE for comparison.

http://www.astm.org/BOOKSTORE/...4.pdf

http://cp.literature.agilent.c...E.pdf

[500hpSilvia]

hey, can you end me a link on where you bought the 4.08 gears for your Q45?? thanks.. you can email me @ [email protected]

Mike

[qsiguy]

I got mine from a donor Q45 that I picked up, parted and sold. It was done by Unitrax but they said they no longer have the parts available to do this for the Q45. Most people use Z32 rear diff parts to do this mod.

[500hpSilvia]

z32 rears have what gear ratio?

[MinisterofDOOM]

NA Z32 has 4.08, which is what most of us are running. TT Z32 has 3.69.

[500hpSilvia]

CAN YOU PULL THE GEARS AND PUT THEM ON YOUR DIFF?

[elwesso]

its not just that simple to put the gears into a diff, it has to be setup just right.

I really dont recommend 4.08 diffs to anyone. high stall TC's are way better and less hassle! If it were easy itd be one thing, but its a huge PITA for a 15% difference in gearing, which for all benefits and purposes doesnt really do that much.

[qsiguy]

I concur. I don't know about the torque converter but at least for the 4.08 rear diff it did not have the effect I was looking for. I will most likely put my stock one back in some day. Highway cruise is a bit annoying, RPMs are too high, I liked it before better nice quiet cruise at 70-80-90, now it's at around 3k+ by about 80 mph. I don't think I'd like the torque converter with my turbo.

My transmission is getting tired, been noticing some whining lately. It will most likely be getting built in the near future or swapped for a 5 speed but budget will determine what I can do. I think the transmission could make a huge difference in my application.

[elwesso]

shane do you still have the dropping resistor removed, or some other resistor in its place???

I really think the high stall TC would make a HUGE difference in your application. Think about nailing the gas and instead of having to go from 2000-3500 RPM or whatever to be in boost, you just nail the gas and you're already in boost. It would make a HUGE difference down low and for all intents and purposes take away any spool up time you had (which seems to be minimal)

Dragon torque converter= best mod for your money outside of an ECU, HANDS DOWN

[qsiguy]

The dropping resistor disconnects only during WOT. All other times it's stock. I am going to experiment a little with higher resistance values to see how high I can get it without getting the "trans malfunction" warning. I think I can get firmer shifts all the time without the warning. That would be nice.

I guess I'm not totally clear on how the high stall TC works. How would the TC allow me to be in boost as soon as I hit the gas? I have to get a load on the motor before it will really make any boost and if it's not hooking up the transmission until a higher RPM how would that help? Can you break it down for me? I think Siju has a high stall TC on his car and he wasn't sure he liked it. I could be wrong.

[500hpSilvia]

its not just that simple to put the gears into a diff, it has to be setup just right.

I really dont recommend 4.08 diffs to anyone. high stall TC's are way better and less hassle! If it were easy itd be one thing, but its a huge PITA for a 15% difference in gearing, which for all benefits and purposes doesnt really do that much.

MY PROBLEM IS THAT I HAVE A S13 SR20DET AND KEEP SNAPING AXLES.. SO I UBGRADED TO THE Q45 REAR END, HUBS, AND SHAFTS. NOW THE GEARS ARE WAY TO LONG.. SO IM LOOKING FOR SHORTER GEARS TO PUT IN THE REAR END.. ANY IDEAS? SORRY FOR THE CAPS.. DIDNT KNOW..

[maxnix]

SORRY FOR THE CAPS.. DIDNT KNOW..

IT'S THE CAPS LOCK KEY!

Usually on the far left side of the keyboard. Please don't engage it next time.

[elwesso]

when we hit the gas from a stop, compare your car to my car

My car:http://www.youtube.com/watch?v=8g76s8WXh_8

Your car:

http://www.youtube.com/watch?v=SLBGWe_Q5eo

When you nail the gas, your RPMs only go up to about 2000 RPM where mine go almost to about 3000 RPM

What youd want to do is get a dyno and have your stall speed just below your peak torque, or maybe just before you start hitting boost, which might be about 3000 RPM...

Notice how on my car when it gets to 3000 RPM it sits there for just a split second.. This is when the torque converter is catching up to the engine.. In this time, by the time your engine catches up you're going to be in boost. I think this would be an ideal way to sorta get the turbo lag out of the way sooner... Siju doesnt have quite as high of a stall rate as I do, mine is about 2800 RPM.

BTW do you have something that shows your setup to bypass the dropping resistor at WOT? Did you just wire up a switch to the kickdown thing?

[Q45tech]

The problem is torque convertor efficiency is directly related to stall and cruise speed. For best highway MPG the stall speed should be close to 55-65 mph rpm [1830- 2165 in 4th with 3.538 diff and stock tires] so that locked-unlocked clutch survives.

A higher stall speed creates more ATF heat so the cooler should be upsized by the percentage of increased stall 2200>3,000 needs 35% more btu capacity. Probably get away with 20% more area.

The Consult shows the difference in rpm between engine and transmission..........TC slip amount which should be limited to 2-4% [less than 100 rpm] at cruise load unlocked.