Technical the misery of rear brakes

[wapper]

I know there's a lot of topics about poor rear brakes on barchettas, have read them all but my MOT problem still not solved.
MOT shows rear brake are very weak, like 10% or less. At the same time parking brake is a lot better at about 15% or so.
Everything that brakes has been replaced recently: parking brake cables, rear brake calipers, pressure regulators. The disks and pads are ok. The actual braking on the road is just great, no worse than my much younger everydays car.

I passed the MOT this time somehow, but what options do I have next year, other than putting some bags of sand to the trunk?
My b is 1996 year, with ABS (not sure if its working) and simple pressure regulators without levers or springs.

Appreciate all thoughts, except for bypassing pressure regulators.

 

[Dave-M]

Have you replaced the flexible rubber pipes, they can collapse and restrict the hydraulic pressure to the callipers.

 

[JMSG]

For noowing if ABS is working is simple , just go to the road and insuring there is no trafic at the moment lets say roling about 60 KM/H brake the hard you can and if it works you will notice the brake pedal bumpimg fast and the brake marks in the road !!
About rear brake problem it can be also the main brake pump failing in the rear circuit , the hidraulic brake circuit is divided in 2 for safety reasons ! it is comon the seals inside the pump start internal leaking and losing brake pressure !
I presume you have bleeded the rear brakes since you have replaced the calipers ...

 

[wapper]

Have you replaced the flexible rubber pipes, they can collapse and restrict the hydraulic pressure to the callipers.

Good point thanks, will check, however I don't expect these hoses to be the problem as they were inspected by the garage who changed calipers. Also I think it is unlikely that both hoses would collapse in the same way (both my left and right brake are weak). I'd rather believe there's manufacturing defect that causes hoses to bulge or expand and lose pressure. Will check.

About rear brake problem it can be also the main brake pump failing in the rear circuit

Oh my that means new master cylinder, doesn't it.
Yes my brakes have been bleeded properly and there is nothing to complain about the quality of braking on the road.
ABS - I think it doesn't work. Tried to trigger ABS on sand-coated track once or twice, nothing. Also, I wasn't able to connect to ABS ECU with my OBD adapter. However the ABS warning light in the dashboard will not indicate any faults.

 

[JMSG]

Yes it will mean new master cylinder ! there are repair sealers kit but if the housing is worn out it will not be a lasting fix and it will take more labour hours !! so , i really don't advise it !
does the brake pedal feals spongie ??
strange ABS not working and no warning light !!?
have you checked if the bulb in the dash is ok or worse if it was removed on purpose for hiding the ABS problem ?! does it come on wen you turn ignition on (check ligths test ) ??

 

[blackydog]

My handbrake is pants. It cause me grief at MoT every year (well documented on here).

 

[Dave-M]

I have rear brake problems also, handbrake is fine, new cables sorted that. My problem is uneven braking on the rear wheels, so failed the mot. I think it's the brake compensation valves that are either siezed or the seals have gone, Biggest suprise is the cost of them £200+ for the pair. Apparently they are like hens teath, also ordered a new master cylinder so will be fitting this lot in the next few weeks.

 

[blackydog]

I have rear brake problems also, handbrake is fine, new cables sorted that. My problem is uneven braking on the rear wheels, so failed the mot. I think it's the brake compensation valves that are either siezed or the seals have gone, Biggest suprise is the cost of them £200+ for the pair. Apparently they are like hens teath, also ordered a new master cylinder so will be fitting this lot in the next few weeks.

I replaced mine years ago with a couple of copper pipe loops, never experienced any lockup. Unless you drive like a nutter I don't think it would be a problem.

 

[Dave-M]

I did consider doing the bypass idea, but wasn't sure if it would be picked up at the MOT test, I have bought now so will be fitting the new ones,

 

[wapper]

so will be fitting the new ones,

So did it pay off to have replaced master cylinder and compensation valves? Rear braking is better now?
My MOT is coming soon...

 

[Dave-M]

Well yes in short my car passed, the rear brake compensation valve's were the the culprits both were worn, unfortunately you can't replace the seals so new are required. I replaced also the master cylinder and changed the hoses for braided items.
Hope this helps.

 

[wapper]

Good to hear this. But how could you tell that your valves were worn?
What kind of compensation valves do you have, the "active" proportioning ones with brackets and springs, or "passive" pressure regulators, like I do.
Regarding master cylinder, I'm not sure it can cause weak rear brakes because to my knowledge, we have diagonal split system for brakes and there's also ABS in between, so there is no "front" and "rear" sections in master cylinder.

I have new valves and rear calipers, so the only reasons I can think of is air in the rear system, or bad hoses that don't hold pressure. Both seem unlikely though, knowing that rear braking force is equal, although too weak.

 

[Dave-M]

My car doesn't have ABS, the valves are the type that have a lever and spring attached that from the rear trailing arms to the body of the car. When I removed the valves, the piston inside gave no resistance so concluded that the rubber seals within had perished, I changed the master cylinder as a matter of course. As I have in the last 6 years replaced all 4 calipers. The valves and master cylinder were the last items.

 

[Alfa1968]

I have the regulators with the levers and spring (non abs) but the spring on the right hand side has come off. Any idea where you can get another from?

 

[s130]

Should be available directly from Fiat (see below). However possible also available as a generic part from other suppliers.

(Note! 2014 ePER information)

7739610 SPRING
Famiglia: CX01 - SUNDRIES-BRAKE SYSTEM
Availability: Product that can be ordered Minimum quantity per package: 2
Macro-family: G Discount code: B
Weight (grams): 50 Listed price(1): 6.41 GBP
Measurement unit: Num Price including taxes: 7.69 GBP
FIAT - PK BARCHETTA (1995-2004)

33102/00 - BRAKE HYDRAULIC SYSTEM

FIAT - 1A PUNTO BZ. GAMMA '97 (1997-1999)
FIAT - NW PUNTO GT (1993-1997)