Dangerous brake pulsing on long downhills

[ericm979]

I live on a very steep twisty mountain road. There's some Christmas tree farms on the road. Each fall when tree season starts you can tell because of the smell of burning brakes. Every few years a large truck loses its brakes on the road and crashes. You have to go down this road in a lower gear than "D" or you will burn up your brakes. And you need to not drag the brakes all the way or they will be smoking at the bottom of the road.

I've downshifted for steep downhills on every vehicle I have owned since I started driving in the '70s. Even before I moved to my current place a lot of those miles were in mountains as I worked for the USFS for a while and spent a lot of time in the mountains. I've yet to damage a transmission or engine from downshifting for downhills.

I have monitored trans temps in a number of vehicles including my GX. Downshifting on downhills does not raise transmission temps significantly. It's going up the hill that heats up the transmission.

 

[Poop Bubbles]

GXs seemingly have a weak point with transmissions

LOL You have clearly never owned a Ford or any other vehicle that has actual "weak points". Call me when you've cracked two transmission in half in 30k miles.

 

[185]

LOL You have clearly never owned a Ford or any other vehicle that has actual "weak points". Call me when you've cracked two transmission in half in 30k miles.

Thankfully nothing as serious as that. But always concerning to see things like this

GX460 P2714 P0761 Ultimate Summary and Hope For A Fix Thread

BREAKING NEWS**** Check out page 6 and @BamaPaul’s info on the solenoids and Sonnex kit!!!!! Lexus GX460 P2714 P0761 Collection of Info Hey crew! I know many of us have been affected by this issue with some replacing their transmission at around 80-180k for $7-8k. On all forums and groups...

forum.ih8mud.com

I live on a very steep twisty mountain road. There's some Christmas tree farms on the road. Each fall when tree season starts you can tell because of the smell of burning brakes. Every few years a large truck loses its brakes on the road and crashes. You have to go down this road in a lower gear than "D" or you will burn up your brakes. And you need to not drag the brakes all the way or they will be smoking at the bottom of the road.

I've downshifted for steep downhills on every vehicle I have owned since I started driving in the '70s. Even before I moved to my current place a lot of those miles were in mountains as I worked for the USFS for a while and spent a lot of time in the mountains. I've yet to damage a transmission or engine from downshifting for downhills.

I have monitored trans temps in a number of vehicles including my GX. Downshifting on downhills does not raise transmission temps significantly. It's going up the hill that heats up the transmission.

appreciate the trans temp data point. Notes taken.

@swild

RR Racing Front Big Brake Kit for Lexus GX460 GX470 & Toyota 4Runner - https://www.rr-racing.com/RR-Racing-Front-Big-Brake-Kit-for-Lexus-GX-4Runner-p/gx4fbk0002.html

Just for comparisons sake.

Seems like they are claiming they upsized from stock 27mm to 32mm rotor/heatsink size (jury is out on this since some of the aftermarket standard replacements are 31-32mm) while shifting up to a 6 piston caliper vs 4 piston stock and adding bigger and aggressive pads (increasing the contact patch and cf).

 

[Rednexus]

I typically get 70-90K out of a set or rotors....and 40-75K plus out of pads.....on every vehicle I've owned. My GX has over 50K on a set of aftermarket, OEM-style Bosch rotors. Zero warping, zero pulsing etc. It's been out to CO twice, down most of the alpine loop, and has towed our camper thousands of miles. We have very steep/twisty roads around here too that - IMO - are more stressful on brakes than long mountain descents out west. I have not done the 460 brakes upgrade. I gear down the transmission all of the time, including putting it in low off-road when it doesn't have enough engine braking in high range.

So....my experience....if you are regularly warping rotors or developing deposits on them in a 460 or a 470 - that's a driving style issue caused by riding the brakes, stopping too short, driving too fast, etc. These rigs don't need big brake kits.....mine stops just fine with 33s and EBC pads, and also stops just fine pulling a 4K camper, with 4 people inside, and bikes on the top of it.

Full disclosure - I have replaced both the front calipers (one had an internal leak) and rear (one had a sticky piston). But, the calipers it had never caused a pulsation issue. The only time I really use my brakes hard is for panic stop scenarios - which due to my driving style of avoiding being distracted and trying not to tailgate folks - happens rather infrequently.

 

[GrizzlyClint]

Downshifting rightfully has its place, however imo brakes are cheaper then transmissions. With the GXs seemingly have a weak point with transmissions, I would avoid undue stresses and/or expect to use a higher quality fluid/transmission cooler/more frequent drivetrain fluid exchanges.

With that in mind, the GX brake package can be little bit more stout, German marque-esque to handle the extra brake taxation, whether with better airflow to the brakes, bigger heatsink/rotor, and more aggressive pads (for a luxury program targets a ceramic brake pad offers decent performance, low noise and dust when cold over say a semi metallic) it pay dividends for those who constantly ascend and descend any significant altitude.

Keep your fluid changed on regular intervals, don't hot rod it when it's cold (or in general), and most of all be reasonable with your downshifts and I have zero concern about the trans. I literally live in the mountains and have 6-8% grades on the paved roads all over the place so engine braking is used. I don't notice any spikes in trans temps.

On the subject of brake fade. The only time I've ever had brake fade with these heavy duty brakes is coming down a few thousand feet on a mountain USFS road barely wide enough for a GX and a bicycle. Too many sharp turns and switch backs to engine brake so alas brake fade was inevitable. Had to stop periodically to cool off. LOL

 

[HVLA]

Thank you for pointing that out Clint!
As I said before, I love using the manual shifting!

Same. I only started using it recently when I started towing my KRX on a trailer, but now I basically drive in manual mode everywhere.

 

[mtnco]

Re-reading through this thread from the start and considering the original scenario, I 100% agree downshifting is called for when one finds themselves needing to frequently use their brakes to regulate speed during long, steep descents. And it's beneficial in many other scenarios, even if not as critical.

Regarding pads, since I do occasionally get mild pulsing in my CO mountain driving on the OEM pads (probably not doing it right! ) I am going to try something like the Z36 pads on stock rotors.

 

[Rednexus]

On the subject of brake fade. The only time I've ever had brake fade with these heavy duty brakes is coming down a few thousand feet on a mountain USFS road barely wide enough for a GX and a bicycle. Too many sharp turns and switch backs to engine brake so alas brake fade was inevitable. Had to stop periodically to cool off. LOL

Putting it in low-range should provide more engine braking in that scenario. I dropped off many, many thousands of feet on USFS and other rough roads last month in CO and had zero brake fade. But, even on relatively groomed roads, I still put it in low-range (with the CDL unlocked) and used gears 1-4 for engine braking.

My general rule of thumb for my rig....if there is any doubt at all....put it in 4LO! It makes going up and down hill much easier at <25 mph speeds than in 4HI. I've also found that it can significantly lower trans temperatures as the rig doesn't have to work as hard to get going and the engine/fan/water pump are spinning faster and therefore moving more coolant around.

Back to engine braking - it should generate no increase in trans temp. It should fade back to it's normal/ambient temp when engine braking. The only time these things generate heat is when they are going up a hill with the TCC unlocked. I watch mine like a hawk.

 

[r2m]

Downshifting rightfully has its place, however imo brakes are cheaper then transmissions. With the GXs seemingly have a weak point with transmissions, I would avoid undue stresses and/or expect to use a higher quality fluid/transmission cooler/more frequent drivetrain fluid exchanges.

With that in mind, the GX brake package can be little bit more stout, German marque-esque to handle the extra brake taxation, whether with better airflow to the brakes, bigger heatsink/rotor, and more aggressive pads (for a luxury program targets a ceramic brake pad offers decent performance, low noise and dust when cold over say a semi metallic) it pay dividends for those who constantly ascend and descend any significant altitude.

IMHO, there should be little impact on the GX trans since it won't let you down shift if you're going too fast. It'll just Beep-beep. When the speed is at an acceptable speed, then it'll let you down shift.
I've haven't seen any issues with trans associated with using the gears, it's mostly from trans temps getting too high. For me, it seems shifting helps keep the trans to run cooler then just leaving it in auto mode.

 

[GrizzlyClint]

Putting it in low-range should provide more engine braking in that scenario. I dropped off many, many thousands of feet on USFS and other rough roads last month in CO and had zero brake fade. But, even on relatively groomed roads, I still put it in low-range (with the CDL unlocked) and used gears 1-4 for engine braking.

My general rule of thumb for my rig....if there is any doubt at all....put it in 4LO! It makes going up and down hill much easier at <25 mph speeds than in 4HI. I've also found that it can significantly lower trans temperatures as the rig doesn't have to work as hard to get going and the engine/fan/water pump are spinning faster and therefore moving more coolant around.

Back to engine braking - it should generate no increase in trans temp. It should fade back to it's normal/ambient temp when engine braking. The only time these things generate heat is when they are going up a hill with the TCC unlocked. I watch mine like a hawk.

Didn't think of using 4LO as a pseudo engine brake. Good tip!

 

[Poop Bubbles]

Didn't think of using 4LO as a pseudo engine brake. Good tip!

Always use 4low when offroading, uphill or down. Saves a TON of stress on the trans, and brakes. (Gravel roads don’t count as offroading)

 

[r2m]

Didn't think of using 4LO as a pseudo engine brake. Good tip!

When off tarmac, I'll often drop into 4LO unless I'm on fast trails, speeds greater than 20 or 30 MPH.
It gives good engine braking and it's nice to get the 'juices' flowing in the low range for a few miles.

 

[GrizzlyClint]

When off tarmac, I'll often drop into 4LO unless I'm on fast trails, speeds greater than 20 or 30 MPH.
It gives good engine braking and it's nice to get the 'juices' flowing in the low range for a few miles.

I'm usually 20~25 on these USFS roads / trails. I suppose I could go slower and use 4LO when the brakes get hot.

 

[Rednexus]

I'm usually 20~25 on these USFS roads / trails. I suppose I could go slower and use 4LO when the brakes get hot.

Yes, do switch to 4LO on mountain gravel descents, and you won't need to use your brakes at all. 4LO in 4th gear will limit you to 20-25 mph or so when coasting downhill. Any faster than that and you should be in 4HI in 1st gear.

 

[Kid]

Flat lander driving , when they move to the mountains or even hilly area they are awful to be behind , they do not know how to drive hills and curvy roads .
They are the ones who burn up their brakes .
We get a lot of them here , Oh my god , to be behind a flat lander , that's when I get impatient .
Especially if I can not pass them

 

[Poop Bubbles]

Flat lander driving , when they move to the mountains or even hilly area they are awful to be behind , they do not know how to drive hills and curvy roads .
They are the ones who burn up their brakes .
We get a lot of them here , Oh my god , to be behind a flat lander , that's when I get impatient .
Especially if I can not pass them

Yup, lots of Texas plates here in Colorado, always clogging up the road, can't drive for s***!

 

[GrizzlyClint]

Not everyone from Texas "can't drive for s***". If we want to go there trust me I can easily call out how crummy [insert state here] drives. I've seen s***ty drivers from about every state.