Brake behavior when hot?

[jmnetus]

So I went up/down a little nearby mountain today. On the way up I wasn't doing a very good job and managed to get my "TRANS TEMP" light on due to excessive slipping (I assume), but other than that had no problems. But---

On the way down, my brakes were behaving a bit oddly. I rode them too much early and I'm sure they were toasty hot - and my pedal started feeling mushy. Sometimes I had to press it all the way down to get it to brake significantly, but if I pumped it a couple times it felt 'normal' again. To minimize braking I got it into 4LO and coasted down with the trans in "2" - when I got back to flat pavement the fluid in the master cylinder was fine and I couldn't immediately see any issues. As I drove on highways, the brakes fairly quickly resumed normal operation (as they cooled down, I assume.)

Is this an expected behavior for hot brakes, or is something wrong here?

 

[tjkj2002]

Normal.

Would be wise to get the brake fluid flushed with new.

 

[jmnetus]

Good to know. Hoping to do a thorough fluid flushing soon anyway.

I'm not used to this whole automatic transmission thing - was much easier to use compression braking in my old stick shift XJ.

 

[SMETNA]

Sorry to thread-jack but

Wouldn't activating hill descent control on a KK help mitigate this? (Due to the system applying individual brakes to each wheel intermittently as needed)

Ps. I know the OP has a KJ. I'm asking on behalf of myself

 

[tjkj2002]

Sorry to thread-jack but

Wouldn't activating hill descent control on a KK help mitigate this? (Due to the system applying individual brakes to each wheel intermittently as needed)

Ps. I know the OP has a KJ. I'm asking on behalf of myself

Hill desent works only at very low speeds if I remember correctly.Downshifting the trans and using the brakes in short bursts only(no riding the brakes for more then 5-10 seconds) is the only way to prevent overheating the brakes on steep desecnts.

 

[SMETNA]

Yeah it works between 1mph and 7mph depending on where you set it

 

[jmnetus]

On a side note to the main answer I got on this thread, at what temperature does the TRANS TEMP light come on?

 

[J-Thompson]

The brake issue is called
"brake fade" and is normal if you ride them
The trans temp light is also normal for the 42rle
Both are corrected by driver not by Jeep
1st gear on your selector will prevent all of these issues
Off road 4wd Low range will prevent them even further

 

[jmnetus]

I acknowledge bad driving in both cases, I was not being careful at all and was slipping too much on the way up. I do want to know how hot the trans got to turn the light on so I can know of any effect on fluid life. I did park and idle in neutral when the light came on, and the manual seems to treat it as a minor warning, not a "YOU ARE IMMEDIATELY KILLING YOUR CAR" type of thing - just want to make sure that is the case.

 

[Ry' N Jen]

On a side note to the main answer I got on this thread, at what temperature does the TRANS TEMP light come on?

I acknowledge bad driving in both cases, I was not being careful at all and was slipping too much on the way up. I do want to know how hot the trans got to turn the light on so I can know of any effect on fluid life. I did park and idle in neutral when the light came on, and the manual seems to treat it as a minor warning, not a "YOU ARE IMMEDIATELY KILLING YOUR CAR" type of thing - just want to make sure that is the case.

Ya, that damn trans temp light!

If I were you, you better get the transmission fluid professionally flushed.
Or you run the risk of frying the ****** if you leave the fluid too long and you
over heat the ****** one or two more times.
You might also want to consider installing a new radiator so you can plumb in
the in rad transmission cooler (Along with the stand alone ****** cooler if you
do allot of off roading!)
The stand alone transmission cooler is not in the most optimal position way
down there at the bottom of the radiator, being obstructed by the vehicles
cross member and not in the direct air flow.
Trust me, it's less expensive now to do some upgrades to the cooling system
(Again, especially if you are an avid off roader) and consider adding the
heavy duty clutch/viscus fan in addition to the electric fan.
Sure, you will need the H/D rad shroud as well, but it is less costly than a rebuilt
transmission and the installation labour if you don't do the work yourself.



On a side note, I see in your signature line that you possibly want a trash lock rear diff?
Save your money and buy a better unit!

 

[jmnetus]

Nah, it came with the trac-lok, hoping to get a better one some day.

 

[seabass1858]

definitely or to not have the sprung weight or the clutch fan, you could install twin electric high cfm fans like I did to my xj along with an hd trans cooler. My xj never saw past 190 again after that and the transmission stayed at optimal temperature even climbing up shanadoah valley VA with a 4500lb trailer. A temp gauge for the transmission will not hurt and it will give you an idea on its limitations.

 

[jmnetus]

I do want to monitor transmission temperature more closely in the future - can anyone with a Scangauge II see if the XGauge codes for the JK 42RLE work on the KJ 42RLE? Maybe a longshot, but I want a bunch of the features on the scangauge anyway - if it keeps me from needing to weld stuff to my transmission pan I'll take that as a plus.

Here's the thread on wranglerforum giving codes to get transmission temperature on the JK/42RLE:

Scangauge II 42RLE temperatures - Jeep Wrangler Forum

 

[seabass1858]

should work but dont quote me on that

 

[J-Thompson]

B&G makes a trans temp guage kit
Easy and works
Flex lite makes and external cooler
easy and works
I have both along with a 10" electric fan in front of
the cooler ,for those really hot long climbs
I have not had an issue ever in my TJ

 

[jmnetus]

Thanks, I'll look into that cooler...

I would still appreciate it if someone could test those XGauge codes for me, since the autozones around here are being their usual unhelpful selves and not letting me demo one to test the code on my own Jeep, all the while pointing out that their return policies won't take it back the second I open it I want it for more than the trans temp, but that would clinch it being worth it to me.

 

[jmnetus]

*bump* - one last try before I just let the thread die. Guess I don't even know if anyone here has one of these things.

Let me know if running both of the following XGauges (at the same time) on your Scangauge 2 gives transmission temp:

Wake Up ECU
TXD: 07E01092
RXF: 045025920000
RXD: 3808
MTH: 000100010000
NAM: ECU

Transmission Fluid Temperature (Degrees F)
TXD: 07E022B010
RXF: 046205B00610
RXD: 3010
MTH: 000100400000
NAM: TFT

These codes work on a JK wrangler with a 42RLE, and I hope they'll work on my KJ - but if they don't give the temp then the $160 I'd pay for the Scangauge will probably go to some other piece of the Jeep first

 

[J-Thompson]

????
I gave you a $20 solution for monitoring trans temp
I guess simple and effective is just good enough

 

[jmnetus]

The kits I'm seeing aren't in the range of $20 - more like $50-60. I also like the idea of one piece that monitors a lot of stuff rather than finding places for a bunch of analog gauges.

 

[J-Thompson]

The kits I'm seeing aren't in the range of $20 - more like $50-60. I also like the idea of one piece that monitors a lot of stuff rather than finding places for a bunch of analog gauges.

Every thing you need to know is right there
in the dash ,besides trans temp
which with the 42rle is important