RPM drop/rebound ?

cl4Rk

cl4Rk

Member
Over the last week or so, I've noticed something that I can reliably reproduce.

I'm in a 2000 automatic 4wd. I've had the truck for about 2 months now. I don't remember noticing this issue until about a week ago, but it's also possible (likely) I wasn't paying attention to it.

Anyway, with O/D Off, at about 1500 RPMs and 35 MPH, I'll experience a momentary rev drop/rebound when I apply brakes.

Here's the full picture:

Recent work (within last year, previous owner and myself):
- new radiator
- new valve cover gaskets
- new timing belt
- new battery
- new water pump
- new driveshaft
- new cat
- recent oil change
- power steering fluid exchange
- new starter
- new MAF sensor
- new spark plugs
- new coil boots
- new pcv valve
- new fuel filter
- cleaned throttle bottle/IAC
- fixed various vacuum leaks (one that thew a P0171 and another that prevented my 4WD from engaging)

Things that don't seem to matter (this happens either way):
- Coolant temp
- ATF temp
- ECT norm/pwr

Pre-conditions:
- O/D Off
- 3rd gear
- Cruising about 35 mph
- RPMs about 1500

Steps to reproduce:
- Apply brakes to slow down to about 30 mph

Symptom:
- The moment I brake, the engine quickly drops to about 900 RPM before correcting and quickly climbing back up to about 1200 RPM.

Torque converter?
Any thoughts? Something about locking/unlocking/re-locking the torque converter? since i'm in O/D Off, then brake, but not enough for a downshift? Trans fluid is at the correct level, looks pretty nice and red. I'll be adding a Magnefine filter shortly, doing a drain & fill, and adding a B&M external cooler in series. Have not tested this with 4wd engaged.

Also, is this something to be worried about?

Thanks!!
 
Last edited:
Register to hide this ad
cl4Rk said:
...
Anyway, with O/D Off, at about 1500 RPMs and 35 MPH, I'll experience a momentary rev drop/rebound when I apply brakes....
Click to expand...

No idea why.

But why drive at 35mph with OD off?

I only turn OD off when climbing or I need to pass another vehicle at highway speeds, it does not help my vehicle's performance at 35mph. I can't find another time to use it that it makes a difference but hey who knows....
 
jgue467 said:
But why drive at 35mph with OD off?
Click to expand...

Thanks for the reply.

Why OD off at 35mph? No good reason. Just experimenting and learning as I go. I've been really enjoying fixing up this truck, and this forum has been massively helpful.
 
cl4Rk said:
Thanks for the reply.

Why OD off at 35mph? No good reason. Just experimenting and learning as I go. I've been really enjoying fixing up this truck, and this forum has been massively helpful.
Click to expand...
Torque converter locking/unlocking under those specific conditions would be my best guess
 
The torque converter is not locked at 35mph, OD on or off.

It does have something to do with the torque converter going from loaded under power to coasting. I mostly notice mine doing it in 4th/OD going from cruising to coasting.

Not 100% sure it is normal, but it hasn't caused any problems with my truck in the last ~300k miles...

-Charlie
 
phattyduck said:
The torque converter is not locked at 35mph, OD on or off.

It does have something to do with the torque converter going from loaded under power to coasting. I mostly notice mine doing it in 4th/OD going from cruising to coasting.

Not 100% sure it is normal, but it hasn't caused any problems with my truck in the last ~300k miles...

-Charlie
Click to expand...
Do you know what mph the torque converter will lock up with overdrive off?
 
Bad Luck said:
Do you know what mph the torque converter will lock up with overdrive off?
Click to expand...
Officially from the Toyota manual (OD on) (for V6 4WD):

Code: 
Lock−up point (Throttle valve opening 5%), O/D gear (NORM and PWR)
Lock−up ON    72 − 78 km/h (45 − 48 mph) 
Lock−up OFF    65 − 71 km/h (40 − 44 mph)

It doesn't have a spec for when OD is off, but in my experience it is about 5mph lower and will hold for higher throttle openings.

-Charlie
 
Double check your brake booster vacuum hoses for cracks or loose fitment. Do you also get too soft of a brake or too firm of a brake at the same time?

Mine revs down but never down that low. More like to around 1200 RPM's at the lowest.
 
gamefreakgc said:
Double check your brake booster vacuum hoses for cracks or loose fitment. Do you also get too soft of a brake or too firm of a brake at the same time?

Mine revs down but never down that low. More like to around 1200 RPM's at the lowest.
Click to expand...

Hmmm great question. I’ll check for brake feel during this maneuver. I want to say I get a soft brake feel, but I’ll test it out.

All my vacuum hoses are pretty worn out, being 21 years old.. I recently ordered this silicone hose kit and will be replacing all my hoses soon.
 
HiLife said:
Only when you hit the brakes the drop/rebound happens?
What about just cruising along then taking foot off the gas pedal, no rpm drop/rebound happens?
Click to expand...

Yep. Only if I use the brakes. Doesn’t happen if I let of the gas as far as I remember. I will double check that scenario though.

I mostly notice it after I crest a hill and begin the descent, but traffic ahead prevents me from continuing at the same speed, so I push the brake to slow down a little.

All day today I kept O/D On, and did not experience this at all.
 
gamefreakgc said:
Double check your brake booster vacuum hoses for cracks or loose fitment. Do you also get too soft of a brake or too firm of a brake at the same time?

Mine revs down but never down that low. More like to around 1200 RPM's at the lowest.
Click to expand...

Update: was just able to test. Brake feel is normal.
 
HiLife said:
Only when you hit the brakes the drop/rebound happens?
What about just cruising along then taking foot off the gas pedal, no rpm drop/rebound happens?
Click to expand...

Update: confirmed that it only happens in this very narrow set of circumstances, only when I hit the brakes. Letting off the gas does not reproduce the issue.
 
Last edited:
cl4Rk said:
Update: was just able to test. Brake feel is normal.
Click to expand...
Try letting the truck sit for a while. Without starting the truck...step on the brakes. You should have vacuum assist on the first push of the brakes and gradual hard on the second push.
You could have a leaking brake booster check valve or leaking booster. Bottom line is booster cannot hold vacuum.
 
HiLife said:
Try letting the truck sit for a while. Without starting the truck...step on the brakes. You should have vacuum assist on the first push of the brakes and gradual hard on the second push.
You could have a leaking brake booster check valve or leaking booster. Bottom line is booster cannot hold vacuum.
Click to expand...

Ok I’ll check it soon and post my findings. Thank you!
 
Last edited:
Just to update this thread, I have not really noticed this symptom since finishing the frame swap. So I won't be able to get to the root cause unless it starts happening again.
 
Hey everyone Check your Coils you could have a failing coil and the coil is working and as your slowing Down the coil looses power then regains Power and Current spikes on the secondary winding after recovery seen this on Cylinder 1 coil and because it's a waisted spark system 2 cylinders are loosing power momentarily and then recovering to fast for a misfire..... hope it helps all if you need coil ohm specs let me know....



cl4Rk said:
Over the last week or so, I've noticed something that I can reliably reproduce.

I'm in a 2000 automatic 4wd. I've had the truck for about 2 months now. I don't remember noticing this issue until about a week ago, but it's also possible (likely) I wasn't paying attention to it.

Anyway, with O/D Off, at about 1500 RPMs and 35 MPH, I'll experience a momentary rev drop/rebound when I apply brakes.

Here's the full picture:

Recent work (within last year, previous owner and myself):
- new radiator
- new valve cover gaskets
- new timing belt
- new battery
- new water pump
- new driveshaft
- new cat
- recent oil change
- power steering fluid exchange
- new starter
- new MAF sensor
- new spark plugs
- new coil boots
- new pcv valve
- new fuel filter
- cleaned throttle bottle/IAC
- fixed various vacuum leaks (one that thew a P0171 and another that prevented my 4WD from engaging)

Things that don't seem to matter (this happens either way):
- Coolant temp
- ATF temp
- ECT norm/pwr

Pre-conditions:
- O/D Off
- 3rd gear
- Cruising about 35 mph
- RPMs about 1500

Steps to reproduce:
- Apply brakes to slow down to about 30 mph

Symptom:
- The moment I brake, the engine quickly drops to about 900 RPM before correcting and quickly climbing back up to about 1200 RPM.

Torque converter?
Any thoughts? Something about locking/unlocking/re-locking the torque converter? since i'm in O/D Off, then brake, but not enough for a downshift? Trans fluid is at the correct level, looks pretty nice and red. I'll be adding a Magnefine filter shortly, doing a drain & fill, and adding a B&M external cooler in series. Have not tested this with 4wd engaged.

Also, is this something to be worried about?

Thanks!!
Click to expand...
 
You must log in or register to reply here.

Members online

Total: 346 (members: 2, guests: 344)

Forum statistics

Threads
278,309
Messages
3,554,075
Members
248,016
Latest member
Advally Service

Share this page

Trending content

Back
Top