Soft compound brake pads Volvo 131?
 

Hi all,
Just had my local garage give my 1966 131 a roadworthy test. While Ive been testing the brakes on the road the rear wheels lock up before the fronts discs. The garage tested the brake efficiency and found that the fronts needed considerably greater foot pressure to lock than the rears. The front calipers and flexible hoses have been replaced recently.

The garage suggested trying some softer pads on the front to change the balance between fronts and rear braking balance.

Any ideas about which softer pads would be suitable for my car? or any comments on the braking efficiency?

Many thanks
Phil

Phil;

The Rear Brake Valve should decrease brake sys pressure to rear axle to prevent rear lock-up...before you go adjusting front brake pad formulations, I'd have them check function of Rear Brake Valve.

Cheers

Either your pads or discs could have become glazed so efficiency is lost. Not easy to cure it on the discs without surface grinding, They may already be too thin to accept that treatment. If the pads are glazed you can sand those back to remove the glazing. If that looks to be the case on inspection it's a no cost option to try. Glazing can come about if new pads aren't bedded in properly but using a good amount of hard breaking initially. Light breaking just smooths and polishes them therefore = glazing. It may also be possible that the pressure limiting valve at the rear is stuck and so doesn't limit the pressure to the rear brakes. It's there to stop premature locking. Refurb is possible by someone who is aware of the pitfalls. Rob at Amazon Cars removes them from rally cars but probably not the best idea for road cars.
I was writing this when Ron posted. Non asbestos pads now days tend to be harder. Genuine Volvo ones are good but they too are quite hard. I prefer soft pads as I'm not a demon braker but they do make a lot of dust. Trouble is there is no indication on pads to denote how hard they are. Expect those sold as sports or race pads to be hard.

Installed EBC "Green Stuff" pads and have used them for the past two seasons on our '67 1800s without a booster. After 15K + miles on the road and 900 miles of road racing and hillclimbing use these pads have held up and worked great, and haven't worn the rotors. The only noticeable dust buildup happens after a weekend of racing.

Would a '66 car have the brake valve? If not you could have the wrong rear wheel cylinders fitted.

Thanks for the replies. I'll see if there is a brake pressure valve fitted.

Andy,
According to Brookhouse there are two different brake cylinders depending on the whether the car originally had a brake servo fitted. 7/8" bore if it did and 1" if there was no servo rather than the brake pressure valve. I guess I might have to be brave and try to get the drums off but I am a bit wary given what happened to by 1800 recently (https://www.volvoforums.org.uk/showthread.php?t=304683)

Also many thanks for the choke axle which arrived this week. Should help no end during the winter months.

Phil

Hi all
Finally got under the car and found that there is in fact a brake pressure relief/reduction valve. I wonder if that is where the problem lies. Not sure why my '66 has a PRV ad it doesn't have a servo.

Does anyone know if there is any way to check the PRV. Is it adjustable or repairable?

I happen have a NOS PRV, which I bought or my 1968 1800s (with a servo) and never used. Checking the invoice is was listed as part 671894, which is the Amazon part number, rather than 672969, which is the 1800 parts number. Are these likely to be the same but with a different part number for the different models.

In the meantime have some new pads to try first, nit that i think that will cure the problem (rears locking up before the fronts).

Thanks
Phil

Brookhouse say this re the single rear PRV:
SINGLE CIRCUIT REAR BRAKE PRESSURE REGULATOR. NOTE SOME AMAZON CAR CAME FROM THE FACTORY WITH A REGULATOR FITTED AND OTHERS DID NOT. ONLY USE IF YOUR CAR ALREADY HAS ONE FITTED.
I got a couple of rebuild kits from them for my twin circuit car, they probably have a rebuild kit for the single prv, by all accounts it's a simple job, although I have not done it yet. It is adjustable, well, mine are.

My first amazon a 65 model bought for £150 in 1974 had the same problem.
On wet surfaces the rear wheels would lock under hard braking. Single circuit, with rear limiting valve,front discs, no servo.
Mine was cured by having the front discs lightly skimmed as Derek has mentioned.
The discs were not heavily pitted or rusty, but were not perfect. W/shop manual gives the minimum disc thickness allowed and the present thickness can be quickly checked with a micrometer with the wheel removed. I have had a few Amazon's since the 70s, some have been stood idle and unloved and I have never had to adjust or replace the limiting valve.
An mot type single axle rolling road can check for an imbalance between nearside and offside brakes but cannot give a comparison between the front and rear axle.
Chris.

The limiter valves are pre adjusted to set the pressure. This gives the correct pressure bleed off to stop too much pressure to the rears. Yes, when these are fitted the rear brake cylinders are different. 1" instead of 7/8" I think. Please correct me if it's the other way round. Obviously replacements can be of the wrong size if that bit of knowledge isn't known.
Rebuild kits didn't used to be readily available even from Volvo for safety reasons. The adjustment screw shouldn't be tampered with. Cleaning everything and fitting new seals should be all that's needed. Rust or damage will mean replacement.