Front Brake Problem

[Trevor W]

My Harrison Cob76 has had front braking problems from the start.
Front left hand caliper locks skids wheel and releases
1. @ 60 km/h with hard sharp breaking
2. @ almost stopping say last 3 meter with medium braking from 40 km/h
Front R/H does not Lock
Regular in traffic braking no problems no pulling even with hands off Steering Wheel.
Components are
Calipers Commodore VT.
Booster Ford FX
Master Cyclinder New after market (Protex P10212)
Flexible lines - Braided
Plumbing Bundy Annealed
Connection to Master Cyclinder front Bottom to R/H Caliper Front Left connection to Left Caliper. Correction Attempts Swap pads L/H to R/H
Remove Caliper to Brake Prof, no faults. Remove L/H Disc checked out of true OK. Bled calipers many time when cold and warm.
Had Booster Serviced. Removed R/H Braided Line air purged into clean tissue no residues.
Last option I can think of is to reverse connection on Master Cyclinder I have been told won't help.
I have read many interesting Threads and answers over the years so if any one has experienced this type of problem and won I would be very pleased to hear.
Regards Trevor W

[stiffy]

Trevor,

Call me on 0412249950


Rohan

[Gaz64]

Maybe your RHF is the problem.

Also your rears aren't efficient, what proportioning valve are you using?

[Treeve]

Are the pads worn evenly? Do the sliders on the calipers slide freely? Are the disc thicknesses the same? Having swapped pads L > R, have you swapped rotors?

Just some thoughts.

Treeve

[David Hodgson]

I'm with Gaz, check why your r/f is not working correctly and then sort the bias issue.

Have you had the calipers ovehauled? Pull them off and like Treeve says check everything, sliders for binding but also pull the pistons out and check for burs or rough surface on piston

[Trevor W]

Have Nissan R32 Rear Brakes with Green Stuff Pads No Proportioning, Gary
Calipers removed and checked by a Brake Coy,all ok. SLIPRY
Swapped pads roughed up with emery,discs new, haven't swapped rotors good thought Haven't measured over disk pads they look ok but will do so when I swap rotors, Treeve.
Next test I can think of to remove wheels lock back discs and check if there is diff, movement l/h to r/h slides. I have had one member advise his engineer wouldn't pass the car with Holden Front Calipers!!!!
Thanks all for your Thoughts
Trevor W

[letsboogie351]

Trevor, have you read this thread by sambo?

Harrison brake bias - solved!

[07cob]

Trevor

The front L/R bias issue appears to be a problem with some but not all Harrisons. Sambo's solution attacks the front/rear bias problem which seems to be more common. This may well overcome your (our) front bias problem but could just be a disguise. Paul, if you read this, did you have front L/R bias issues as well as not enough rears?

I also have some slight front L/R bias issues under extreme breaking and have done most of the above tests with little difference. I have had some success with adjusting corner weights by winding up/down the shocks on the appropriate diagonals. Next for me will be to do a complete corner weight test.

Merv had a similar issue and the AP brakes he fitted to the front sorted it out.

However, I would be very interested if someone came up with a solution as to WHY these front L/R bias issues are occurring. The only thought I have (and feel free to shoot me down in flames) is that since the rears do little work, very slight differences in chassis and weight distribution affect the balance on the fronts very dramatically and, depending on the build, different cars are affected differently. This is the reason that I would like to corner weigh the car and go from there.

2.2c

Geof

[Trevor W]

Geof
Have done the corner weights with the Club Scales& Merv"s computer program and finished up on the cross over almost 50% balance. After listening and reading I think the Commodore Calipers are simply not right for the Cobra. So it would seem that put Nissan Gtr's on the front with small mods to the mounts and different Discs may be the way to go.
Letsboogie thanks for that thread looks a pretty dramatic change ok for racing mine only a street car.
Trevor

[schipps]

Originally Posted by Trevor W

Geof
After listening and reading I think the Commodore Calipers are simply not right for the Cobra.
Trevor

Trevor,

I have VT SS commodore calipers on the front of my Harrison and they are brilliant. No locking under very heavy breaking.

regards

Mick

[Trevor W]

Hi Mick
Long time no see sorry have'nt got my act together to organise a run up to your neck of the woods.Can't get Darth Vader and his Black Adder out, now he has a Shell on his back.
Well Iam amazed you havn't had the problems that many speak about behind closed doors !!! May be your calipers were early in production and didn't get the Colly Wobbles the later ones experience.
My set up locked the rollers front and back at the Pit testing but if I give them a quick hard jab the front l/f side grabs real bad.
Thanks for your thoughts
Trevor

[Treeve]

I wouldn't go changing calipers until you actually know what is happening - if it really is weight distribution causing it (or a crimp in a brake line possibly) then new calipers won't solve things, just annoy you since you will have spent money and not resolved it.

pressure in the line would creep past the crimp, but not under the initial lock-up, then you've got the locked wheel already locked, so keeping it locked takes less pressure (the tyre has less friction once it's sliding).

Treeve

[Gaz64]

Does it have this problem with 2 equal weight passengers?

[schipps]

Originally Posted by Trevor W

Hi Mick
Long time no see sorry have'nt got my act together to organise a run up to your neck of the woods.Can't get Darth Vader and his Black Adder out, now he has a Shell on his back.
Well Iam amazed you havn't had the problems that many speak about behind closed doors !!! May be your calipers were early in production and didn't get the Colly Wobbles the later ones experience.
My set up locked the rollers front and back at the Pit testing but if I give them a quick hard jab the front l/f side grabs real bad.
Thanks for your thoughts
Trevor

Hi Trevor,
My apologies, I didn't realise that it was you! Yes long time no see. Are you guys still meeting for breakfast and a run afterwards?
I will have to come down and join in if you do.
regards

Mick

[Trevor W]

Trying to, Mick but other things have been cropping up will let you know
Trevor

[Trevor W]

Originally Posted by Gaz64

Does it have this problem with 2 equal weight passengers?

No hav'nt tried that approach but I rotated the disc's yesterday and was very surprised with the change. R/h started to lock instead of the l/h then after a few more try's they both swapped sometimes one side then the other may be it was the road surface variations. Will have anther go on the week end.
Trevor

[sambo]

Originally Posted by 07cob

Trevor

The front L/R bias issue appears to be a problem with some but not all Harrisons. Sambo's solution attacks the front/rear bias problem which seems to be more common. This may well overcome your (our) front bias problem but could just be a disguise. Paul, if you read this, did you have front L/R bias issues as well as not enough rears?

Geof, I recall a slight bias to the front left but after the upgrade to the back brakes it seems to be gone. Which may support the idea that the Nissan rear brakes are really undersized for this car, amplifying any left/right differences at the front end.

Maybe put a 100kg bloke in the passenger seat and see whether that gives more traction to the front left?

[Rossba]

Have you checked the callipers inlet hole? I have heard that they sometimes had obstructions (casting faults)