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Rolling backward holding brake ?
- Thread starter jefferylay
- Start date
OP
Thread Starter
#3
Thread Starter
#3
Garaged. Cold start. Foot on brake. Car in park. Start car. Release electronic parking brake. Select reverse while still holding brake. Car rolls backward. Don’t see a scenario where a car rolls - ever - while holding a brake pedal. That’s NTSB level stuff. No?
Yes, it certainly can roll back a foot or two in that scenario, especially if on an incline. The issue is sufficient engine vacuum to the power brake booster. When you start the engine, the throttle is opened slightly to increase idle speed such that it takes several seconds for the vacuum to build enough for the booster to apply enough assistance for the brakes to be fully powered.
Many of the newer turbocharged vehicles have a true engine or electric powered vacuum pump which builds vacuum almost instantly at first rotation. The Explorer does not. It still uses the age old engine vacuum to assist the brakes.
I recommend waiting at least 30 seconds after startup before putting the trans in reverse and report back on the issue you’re seeing.
Many of the newer turbocharged vehicles have a true engine or electric powered vacuum pump which builds vacuum almost instantly at first rotation. The Explorer does not. It still uses the age old engine vacuum to assist the brakes.
I recommend waiting at least 30 seconds after startup before putting the trans in reverse and report back on the issue you’re seeing.
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The problem does not have anything to do with vacuum or lack thereof, nor does it take any time after the engine is started "for the vacuum to build". Even then, the brakes are not dependent on vacuum to stop the car, or you wouldn't be able to stop the car if the engine failed suddenly or the throttle were stuck open. It might require more pressure from your foot to stop but it will absolutely stop. The vacuum boost allows you to use less pedal pressure to slow the car.
If your vehicle is truly slipping a "few feet" backward with your foot on the brake, you're either not using enough force on the pedal or you have a major malfunction. As @Dale5403 says, get it in for checkup ASAP.
If your vehicle is truly slipping a "few feet" backward with your foot on the brake, you're either not using enough force on the pedal or you have a major malfunction. As @Dale5403 says, get it in for checkup ASAP.
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OP
Thread Starter
#10
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- Location
- Rancho Santa Margarita, CA, USA
- Vehicle
- 2020 Explorer ST
This has happened to me a few times, but it's intermittent so I can't replicate it. @jefferylay when it happens, does it feel like your car has manual brakes? And when you take your foot off the brakes, do the sensors and servos (the ones under the car that sometimes make noise when the car is off) start clicking? It happens to me occasionally when I start the car and don't take my foot off the brake until I'm in R or D. Never happened if I start and take my foot off the brake before shifting.
I have to take it to the dealer next week, so I was going to ask them about this.
I have to take it to the dealer next week, so I was going to ask them about this.
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I have had something like this happen- I believe it has something to do with a software glitch in the switch-off between automated braking and manual braking. It has only happened in reverse. It does brake, but the pedal feels soft and isn't consistent until I've come to a complete stop. I think it has to do with the rear sensors "thinking" there is some obstruction rearward. In that case, the automated braking takes over but seems to get confused with the manual braking. I add that the only time this has happened is after an alert for collision in reverse.
I didn't bring it up since I didn't think it was the same case as the OP.
I didn't bring it up since I didn't think it was the same case as the OP.
OP
Thread Starter
#18
Thread Starter
#18
Update - there was a tech in the shop who had previously dealt with the axle bolt recall. He said he knew how to replicate the issue and had dealt with something similar to this. He did in fact replicate the issue. It's related in a few ways to the hard shifting recall as well. Though the car did not come up via its VIN for the hard shift or the axle bolt recall, it's how to fix it. They have to order a handful of things to include axle, A frame, etc (I'm not an expert on the parts, but it wasn't an easy thing). 3-5 days to order parts, and another 2 days or so in the shop. The clicking / clunking noise we hear going from P to R along with the stutter / shutter of the car is coming from the front left axle so that's part of it. They're still going to look into the axle splines but are asking "which" axle splines as they're in different places, so if anyone knows about this (is there a grease fitting perhaps?) please let me know. More to follow. JL
How do I put this? There is no way that even if you did have a bolt fracture issue on the differential that it would impact the brakes not stopping your vehicle the way you describe. Can't happen that way. Think about it. The brakes are not mounted to the differential.
Applying the brakes would still stop the car unless the driveshaft was detached and the differential had somehow snapped all the bolts (all 4) and was freely rotating..
I'm not sure we're getting the complete information from either you or the tech. I see that you also just posted:
https://www.explorerst.org/threads/...t-fracture-poll-closed-6-4-22.3727/post-55871
I was thinking it could be a braking issue, but after that post, it doesn't make any sense. You also say you are not tuned, have a 2020 (with 4 bolts) and yet you continued to drive this vehicle with completely fractured rear differential and only noticed this happening in reverse where "holding the brake down firmly, the car rolls backward a few feet then catches itself." Either your tech is bullshitting you, or you are bullshitting this forum.
Applying the brakes would still stop the car unless the driveshaft was detached and the differential had somehow snapped all the bolts (all 4) and was freely rotating..
I'm not sure we're getting the complete information from either you or the tech. I see that you also just posted:
https://www.explorerst.org/threads/...t-fracture-poll-closed-6-4-22.3727/post-55871
I was thinking it could be a braking issue, but after that post, it doesn't make any sense. You also say you are not tuned, have a 2020 (with 4 bolts) and yet you continued to drive this vehicle with completely fractured rear differential and only noticed this happening in reverse where "holding the brake down firmly, the car rolls backward a few feet then catches itself." Either your tech is bullshitting you, or you are bullshitting this forum.
OP
Thread Starter
#20
Thread Starter
#20
Really? I'm not "bullshitting" anyone. I came here as an owner, and advocate of the ST. I do have an issue, and yeah - I did post in another forum. When they said "this" about the fracture, I posted here. Sorry to ruffle your feathers. I'm having two issues ... 1) the P to R ... and 2) a "hard shift" while driving. I'm not actively driving the car either. It's in the shop while they figure this out, and I'm in a GMC rental without my beloved ST. I also flew F-14's and F-16's in the Navy and Air Force and am not abusing my ride. So cut me / the tech some slack.
