Hi all!
My 1994 RX7 FD3S has developed a major problem with the ABS and brake balance...
[1] ABS: Feels like there is no ABS whatsoever, although actually I think I may be getting an fraction of a second of initial pulse then nothing other than locking brakes. ABS warning light has I believe illuminated just once at my tuner, though I have never seen it.
[2] Brake balance: Basically the fronts lock up really really easily with just a moderate tickle of the brake pedal.
I'm now wondering whether the car has had the balance problem for some time and that this has just been masked by the ABS, but either way the car is essentially undrivable.
Car has a stock brake setup other than Mintex Extreme pads all round. My tuner and I have so far failed to find the fault(s) :(
:sign0085:
Any ideas as to what will have caused this and how we can diagnose the specific problems?
Sorry to hear you have an issue.
Starting with the basics first to establish the brake system is OK,
Do you have a long pedal that goes down a long way before doing anything ?
Does the pedal pump up higher?.
Do you know if any one disc that is hotter than the other.
I have to ask if the brake pads are OK and not worn down low.
Because if these are Extreme pads then they are very very old as these were discontinued years ago
Is it both front that lock or just 1? Over the years i have some strange brake results from perished oem brake hoses. 1 bursting on mot test and x2 collaspse internally...1 causing a serious bind and other no flow atall. Not much help but replacing components sometimes the only way to find faults.
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Quote from: clive on December 28, 2020, 08:59:03 AM
Sorry to hear you have an issue.
Starting with the basics first to establish the brake system is OK,
Do you have a long pedal that goes down a long way before doing anything ?
Does the pedal pump up higher?.
Do you know if any one disc that is hotter than the other.
I have to ask if the brake pads are OK and not worn down low.
Because if these are Extreme pads then they are very very old as these were discontinued years ago
Hi thanks for the response!
Pedal feel/position is unchanged... not running long/soft and not pumping up. No sign of excessive heat/binding on any corner either.
Pads were indeed very old and have just been changed to Ferodo 2500s as a precaution but no change in the issues...in fact my tuner could not even take the pads through their bed in process due to the dramatic locking.
Quote from: boosted on December 28, 2020, 08:59:34 AM
Is it both front that lock or just 1? Over the years i have some strange brake results from perished oem brake hoses. 1 bursting on mot test and x2 collaspse internally...1 causing a serious bind and other no flow atall. Not much help but replacing components sometimes the only way to find faults.
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Hi thanks for the response!
Yes it is both fronts locking generally, although depending on road conditions and being super-gentle one can be made to lock on it's own.
Thanks re the view on the pipes. I was thinking that the problem was fluid distribution related maybe abs pump proportioning valve or something else.
Are the front binding at all defo is a strange 1. And after locking no bind that frees itself over time.
Thing is the only thing that amplifies the braking input is the servo...there is a checkvalve on the pipe servo to engine vacuum line to shut off boost worth checking too...but ive no idea how that would react to seeing boost instead of vacuum.
Is this a stored car being recomissioned? Or A fault thats just appeared? Any works recently done?
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Another thing that springs to mind is a master cylinder upgrade in the past for a bbk that has been removed...mazda 929 cylinder fitted and not removed but bug calipers have. Piccys would help.
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The problem has been there for several months, potentially longer and maybe I only noticed when the ABS itself failed (ie. might have been masking the balance problem). Car gets used minimum once every couple of weeks, although has never done that many miles. Only works done over the last year are to exhaust and electrical and dashboard things like replacing failed gauges, HVAC, central locking/immobiliser, and varex active exhaust back box.
I damaged an abs front sensor awhile back...and had the abs light on dash...i had a trackday day booked..so i pulled the abs fuse...it caused front lock ups...
Fuse in was fine. I replaced the sensor and all back to normal.
Does you abs light come on and go off with ignition.self check ok.
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OK, you have DS2500 in the front but what have you got in the back.
You really need something like a Hawk HP+ in the back to keep the brake bias in check and stop locking the fronts!.
something like 25 years ago I fitted decent pads in the front and the ABS didn't have a clue about what was going on.
Ive got ap 6 pots on mine Clive and abs seems fine but this has jogged my memory and mine was locking up when i had the abs wheel sensor fault...pulling the fuses seem tome to make it worse... i credit it for my combe crash.
Are you getting abs light system check on start up?
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Yes ABS light system check on start up is fine ...ie. light comes on then goes off. Is there a way to test the abs sensors btw?
I did a resistance test and there is a Volts test..meter on volts connect across sensors 2 wires and turn wheel slowly see a small difference in mVs as the sensor picks up the ring high spots.
There was if memory right a main fuse and smaller fuse. Worth checking the local grounds too.
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Quote from: boosted on December 28, 2020, 01:41:53 PM
Ive got ap 6 pots on mine Clive and abs seems fine but this has jogged my memory and mine was locking up when i had the abs wheel sensor fault...pulling the fuses seem tome to make it worse... i credit it for my combe crash.
Are you getting abs light system check on start up?
Yes, but you have decent rear pads that give the rear some bite ;)
Oh yes!! It was just a weird fault with mine made no sense..no modulation atall apply brakes front lock...i sort of what the hell im skidding...and pulling fuses so abs dead seem to make it worse.
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Hi all, so the saga of the brakes has taken time but is sorted so I thought I'd do the decent thing and report back (so annoying when you read a thread without a conclusion ain't it?).
A couple of specialists tested everything and everything came up working with no indication of problems. Eventually Chris at RE:WORX swapped out the ABS pump with a good used one he had and hey presto ABS is back as good as ever. It's weird because with the old pump all the solenoids and other items tested fine.
Double shout out to Chris @ RE:WORX Portsmouth in the UK!
R