Rav4 braking issue on gravel

[GregW1]

My daughter has her 2nd 2004 Rav4 2.4 Auto Cruiser, has over 300K country kms, but runs really well for age and kms done.  This was purchased only recently from a local seller after her first Rav4 was a write-off after an accident.  After Insurance excess this replacement Rav4 was not as good as the previous one, it is a cheaper replacement until an upgrade in next 2 to 3 years.  It has a few minor oil leaks identified that I will attempt to fix on the next service I do.  I do all of the routine maintenance and ensure only quality parts and oils are used.  After purchase a full replacement of oil, coolant, filters and plugs were done with a couple of water hoses replaced as well.  It is using more oil than the previous Rav4 (150K), but is probably acceptable given the 300K kms.  It still runs very well, good compression, good pickup, trans is clean and smooth.  So it is in pretty good nick for its age and kms.

I have come across an issue I have not had before.  The brakes appear good, the pads are fine, brake fluid looks clean, but I'm going to do a brake fluid flush to cross that off the possible issues.

The issue is that when on a gravel road and brakes are applied normally there appears to be little to no issue.  When only slightly harder than normal braking is applied you can feel through the pedal what feels like grabbing and releasing and grabbing again while the brake is being applied, it certainly feels bad. I'm not 100% sure of what I am hearing, it appears (or at least feels to hear) to be a knocking, rather than grinding.  This ONLY happens on gravel, hard application on sealed roads has no issues at all, no bad or poor feel at all in the brake pedal.  There is no obvious brake fluid leaks etc,  the level of brake fluid has not changed since purchase.

Does this Rav4 come with LSD?  If so I am thinking that is probably the issue in that it is not handling the loose gravel as it should.  Or is this an AWD issue?  How to tell?

I can't see any obvious visual issues, I will re look at the full brake system when I do the Brake fluid on the weekend.

If you have some advice on what the issue could be and a way to fix please let me know.  I'd rather work on what is most likely instead of fiddling around with what is ok 🙂

Cheers for you help 🙂

Greg

[ianskluger]

Hi Greg, from your description, this sounds to me like the Anti-lock Braking System(ABS)  kicking in. I live along 5km of gravel road, and the same thing would happen to me in a 2002 camry I used to own which had ABS and if I was going down a slight decline and had to brake. Did the previous RAV have ABS? I never had any brake issues with the Camry, and while it is disconcerting it wasn't a concern once I knew what it was. So unless there are any other obvious issues, it is probably just the ABS (correctly) kicking in due to the lack of traction.

 

Ian

[GregW1]

Thank you, that makes perfect sense, especially as the brake system works perfectly on sealed roads. I'm going to do some research about the ABS and see if there is anything I can take a look at and check what is normal.  We are pretty sure the previous Rav4 didn't have this issue, but I need to check if that had ABS, it was a Rav4 Sports wagon (if I recall correctly).

The main thing here is safety.

Thanks again

Greg

P.S. is there a way to check if the previous Rav4 had ABS or not?  I have the past rego papers so the VIN etc number are on that

Edited November 21, 2018 by GregW1

[Roustus66]

I'm not a mechanic but I agree with ianskluger that your problem sounds like the ABS doing what it's supposed to do. It could be that the type of tyres on the new car are different to the old one which may cause a difference in the grip on a rough/loose surface and hence the activating difference of the ABS, especially as you say it's okay with normal braking and only noticeable with a heavier application of the brakes. Researching the year model should turn up whether the previous car had ABS and may be easier to find than a VIN number.