1966 131 Single circut but with BRV - Rear brakes lock up before fronts
Username
Do you already have an account?
Forgot your password?
  • Log in or Sign up

    Results 1 to 14 of 14
    1. #1
      Junior Member
      Join Date
      Jul 2020
      Location
      Hampshire, UK
      Posts
      10

      1966 131 Single circut but with BRV - Rear brakes lock up before fronts

      Hi all,
      First time poster, long time Volvo owner.
      Two moths ago I bought a low mileage (16k), two owner 131 Amazon here in the UK.

      My local garage gave my 1966 131 a roadworthy test and found that the rear drum brakes were locking up before the front disks. I had found the same while briefly driving the car. The garage found that while the front will lock they require more pressure than the rear. Obviously this present a severe skid risk in the wet and one I would like to solve.

      The front calipers and flexible hoses have been replaced recently (before my ownership) and the single circuit system has a Brake Restrictor Valve (BRV)

      The garage suggested trying some softer pads on the front to change the balance between fronts and rear braking balance.
      Others have suggested skimming the front disks, or replacing a potentially faulty BRV may solve the problem.

      Has anyone experienced a similar problem and has a solution to share?

      Many thanks
      Phil
      1966 Volvo 131
      1968 Volvo 1800S

    2. Remove Advertisements

      Advertisements
       

    3. #2
      Junior Member
      Join Date
      Jan 2013
      Posts
      344
      You need a functioning BRV

    4. #3
      Junior Member
      Join Date
      Jul 2020
      Location
      Hampshire, UK
      Posts
      10
      Cairg
      Do you think the symptoms suggest a non-functioning BRV?
      Phil
      1966 Volvo 131
      1968 Volvo 1800S

    5. Remove Advertisements
      SwedeSpeed.com
      Advertisements
       

    6. #4
      Member
      Join Date
      May 2013
      Location
      Saskatchewan, Canada
      Posts
      2,432
      A 1966 131 with 16,000 miles? That is a nice find. The two previous owners must have been grandmothers who only drove on Sundays.

      Having the rear brakes lock up before the fronts during maximum braking was pretty normal in pre ABS cars and much more preferable than having the fronts lock up first. That is assuming that the rears are locking up under extreme / maximum brake application with full weight transfer to the fronts. If lock up is occurring under non maximum brake application or much earlier than expected then that is a problem. How are the tires? If they are 15 years old then you might have some traction issues. A more aggressive pad in the front might help; but, I would pull the existing pads first to see if they are glazed or other wise contaminated. I have no experience with the BRV so can't advise on repair / replacement.
      A 142 of course. What do you expect? I'm the 142 guy. / 1971 142 E 102 color

    7. #5
      Junior Member
      Join Date
      Jan 2013
      Posts
      344
      Quote Originally Posted by Fishyboy View Post
      Cairg
      Do you think the symptoms suggest a non-functioning BRV?
      Phil
      HI Phil, the BRV might be the problem. I see your thread on the Volvo UK forum. Have you had the front discs checked and/or skimmed? I would do this first and see if it fixes the problem. I haven't rebuilt my BRV's (1800E has 2 of them) but have the kits in hand. From all the research on these I have done, given the age of our vehicles, the valves could be gummed up and malfunctioning. I did read an article (sorry cant find it now) that detailed the rebuild of the valve, and the significant point I remember is that when disassembling, there is a strong spring inside which can eject from the unit, so care must be taken.

      You should be able to find a rebuild kit from the various suppliers.

      But get your front brakes in top condition first, as suggested by Derek on the UK forum.

      EDIT. heres a link to look at for pictures, wasn't the article I was thinking of, but might give some insight. You'll have to scroll down the page,

      https://p1800s66.wordpress.com
      Last edited by craig300; 08-28-2020 at 11:47 AM.

    8. #6
      Member
      Join Date
      May 2013
      Location
      Saskatchewan, Canada
      Posts
      2,432
      BRV - I was a little confused because Volvo just refers to it as the brake valve in the 140 service manual.

      Removal and cleaning in brake cleaner may help. Rehabilitation of the brake valve is covered in the Volvo service manual. At least it is on the later 140 cars. Check first to see if you can find the rebuild parts because if you remove the internal piston and damage the seal on the piston then you are buggered. If you take it apart for cleaning, do not fiddle with the adjustment for the spring in the top part of the valve. That sets the pressure differential between the front and back circuit. If a previous owner did maintenance on the system which included complete disassembly of the brake valve they may have altered the preload on the spring which alters the pressure differential.

      The correct operation of the brake valve can be checked on the vehicle; but, you need two pressure gauges capable of operating system pressures. On the 140 you connect one gauge to a bleed port on a front caliper and the other to a bleed port on a rear caliper (same circuit on the 140 dual system). Use a pedal jack to apply brake pressure and monitor the front and rear pressures. As the brake valve setting point the front will continue to increase in pressure while the back stays relatively level. The Volvo service manual should have the pressure test values for your 131. If the pressure in the rear continues to stay at the same value as the front then the brake valve is leaking internally or stuck / seized in the open position. If the rear pressure limits at a value higher than spec then somebody may have fiddled with the spring setting in which case you should be able to adjust the spring setting to bring it into spec by adjusting the spring preload and retesting the pressures.

      Before you do any pressure testing I would advise that you flush the brake system with clean brake fluid as a minimum. Whether you choose to remove and clean the valve before testing is your choice.
      Last edited by 142 Guy; 08-28-2020 at 04:01 PM.
      A 142 of course. What do you expect? I'm the 142 guy. / 1971 142 E 102 color

    9. #7
      Junior Member
      Join Date
      Jul 2020
      Location
      Hampshire, UK
      Posts
      10
      Hi 142Guy and Craig,
      I didn't get the disks skimmed as Derek suggested because when I asked my local garage they said it wouldn't help and it was difficult to find someone nearby who could do it.
      Instead I decided to rebuild the rear brakes, as they probably hadn't been done in at least 20 year! I have now finished these but unfortuely I managed to snap one of the brake lines and that has taken a while to get sorted (my pipe bending skills are lacking) I ended replacing all the solid lines and the one flexi hose back to the BRV. At that point I thought I might bite the bullet and replace the BRV. Unfortunately today I found out that no one of this side on the Pond has one in stock and Skandix, who probably supply most other "suppliers" say they won't be available till the end of September.

      Hopefully at least now I can at adjust the new shoes and bleed the system properly and see if that makes any difference. Then I have a new set of front pads which I will install try and see if they make any difference. At that point if there is no improvement i know the problem lies with BRV. The car also has brand new tyres!

      The link Craig posted is a blog by Ove Ericson only 50 miles from me and our local Rep for the Volvo Enthusiasts Club. I might give him a call and investigate the rebuild route. I'll probably leave this until the new BRV's are in stock otherwise I have no backup if a brake the BRV during the rebuild. However, I happen to have a NOS BRV that I bought for my single brake circuit, 1968 1800S. I have assumed that it is'nt the same as the one on my Amazon at it is listed with a different part number. I'll dig it out and take a look.

      Thanks for all you input.

      Phil
      1966 Volvo 131
      1968 Volvo 1800S

    10. #8
      Member
      Join Date
      May 2013
      Location
      Saskatchewan, Canada
      Posts
      2,432
      Tip on doing your on hard lines - use nickel copper alloy lines. Relatively corrosion resistant and very easy to do nice bends with a simple hand tube bender.

      Having a back-up BRV in case you bollix the rebuild is a good plan. However, are there no rebuild kits for your BRV? I think that the only thing that you could really mess up is the piston seal. There are rebuild kits for the valves on the 140 which is admittedly a later design. At least there used to be kits.

      Your 1968 1800S BRV may be the same piece as your Amazon BRV; but, if the front / rear weight distribution on the 1800S is different than the Amazon it may have a different preload on the BRV adjustment spring and hence a different part number.
      A 142 of course. What do you expect? I'm the 142 guy. / 1971 142 E 102 color

    11. #9
      Junior Member
      Join Date
      Apr 2016
      Posts
      443
      Guys;

      I agree with Craig...the first thing to suspect when rears lock up before fronts (presuming relatively similar friction at the road surface), is the BRV...and if you are going to rebuild it (which I have never attempted, so cannot offer any specific advice other than the typical..."it hydraulic and for the brakes, so if you are going to attempt it at all, super-cleanliness is required") you will then know its internals intimately (they are also shown and function detailed in the factory green manual)...and also know that the beefy preload spring (which should be "respected" during dis and reassembly!) is adjustable for the 122 or 1800.

      Roadtests with hard brakings to lockup would show in what direction the adjustment should be made...admittedly, such rebuilds and adjustments are not for everybody, and certainly not for someone who is not willing to take the brakes to lockup...on the other hand, racers adjust their front/rear brake bias with a knob on the dashboard, to compensate for fueltank level-caused front/rear weight variations...

      I also agree with 142G on the "CuNiFer alloy brakelines.

      Cheers
      Last edited by Ron Kwas; 08-29-2020 at 08:59 AM.

    12. #10
      Junior Member
      Join Date
      Jul 2020
      Location
      Hampshire, UK
      Posts
      10
      Hi all,
      It turns out the NOS BRV that I got for my 1800S is part number for 671894, which is the same part number listed for the 131. On comparing the NOS one with the one on my 131 they look identical apart from the long tube that I think holds the spring which is about 1/4"longer on the Amazon. Any ideas if this NOS one would work on the 131? They do at least have the same part number!
      Phil
      1966 Volvo 131
      1968 Volvo 1800S

    13. #11
      Member
      Join Date
      May 2013
      Location
      Saskatchewan, Canada
      Posts
      2,432
      The only definitive way to determine if the visually different / same part number BRVs are the same in terms of their operation is the static brake pressure test - which can be a fair amount of effort if you don't happen to have two high pressure gauges just hanging around.

      Skandix cross lists the 671894 BRV to the 131 and 1800 single circuit systems

      https://www.skandix.de/en/spare-part...lator/1053764/

      so I would be inclined to try your 1800S part in the Amazon and see if that resolves or improves the rear lock up problem. That would at least provide some data that the problem is the BRV and not something else.

      With your 1800S valve in the car, you can then try cleaning and refurbishing your original 131 BRV . Skandix does not list rebuild kits for the early BRV; but, others might have them or you can 'test' to see what parts from the later valve kits might fit. The critical piece would be the piston seal.
      A 142 of course. What do you expect? I'm the 142 guy. / 1971 142 E 102 color

    14. #12
      Junior Member
      Join Date
      Jul 2020
      Location
      Hampshire, UK
      Posts
      10
      Hi all,
      Yesterday I finally managed to get the rear brakes back together and also replaced all the brake lines and flexi-hose from the BRV to the brakes drums. Me and my son spent a while bleeding the system I finally got a brake pedal I was happy with. Adjusted the rears to the Green Book specs (just able turn wheel with one arm and then back off 4 clicks). Went out for test drive and the brakes were performing very poorly and could get neither the rears or the fronts to lock on emergency braking.

      Back in the garage I decided to take a quick look at the front calipers, disks and pads. Took out the old pads and got my son to gently press the pedal while I observed the piston's movement (using a brake caliper tool to make sure the pistons didn't pop out). And guess what only the large single piston moved, the two smaller pistons appear to be stuck. I assume both should move. I assume that the other caliper will be the same as they car doesn't pull to one side on braking. Maybe the inactive pistons and reduced braking efficiency of the front disks is the cause of all the problems (rears locking up before the fronts) that I've been experiencing.

      Phil
      1966 Volvo 131
      1968 Volvo 1800S

    15. #13
      Member
      Join Date
      May 2013
      Location
      Saskatchewan, Canada
      Posts
      2,432
      With the type of test you are performing, three things are going to conspire to mess up the test.

      -The first is that with only a single press of the brake pedal the physical movement of the pads / pistons is miniscule and hard to detect visually. When you hit the brakes the pistons / pads probably move only a couple hundredths of an inch.
      -The second is that I am going to assume that Volvo designed the calipers so that the surface area of the two single pistons is equal to the area of the large piston (balanced force across the disc face). However, the two small pistons have a combined greater circumference than the single large piston which means that they have slightly higher stiction. In a free movement test like you are doing where brake fluid pressures are relatively low a small difference in stiction will affect piston movement significantly.
      - The third factor is that I believe the brake supply line enters the big piston first. In a low pressure test the slight flow restriction between the two sides of the caliper may conspire to cause all the movement on the big piston.

      Short answer, I don't think that your visual inspection of apparent non movement of the piston confirms that there is a problem.

      With the pads removed from the caliper can you push the two small pistons back into their cylinders? If you can move the pistons back then they are not seized. With the pads back in the caliper, slip a feeler gauge between the pad on the two piston side and the disc and have someone press down on the brake pedal a couple of times to move the pads into there normal running position - almost contacting the disc. The feeler gauge will probably have to be the thinnest one you have. Then have that person press down on the brake pedal as in normal stopping and try and pull the feeler gauge out. If you cannot withdraw the feeler gauge with someone pressing on the pedal then that suggests that your calipers are operating correctly.

      Assuming your calipers are functioning, pull out the pads and have a look at the backing to see if you can determine the manufacture and the model. You do not want high performance brake pads. To resort to the vernacular, high performance brake pads suck for day to day driving. Their first problem is that they typically require a specific break in procedure to work properly and the second problem is that they don't really work well until they get hot. I initially had some high price performance pads in the front calipers on my 142 and braking was not adequate for stop and go driving. I switched them out for some Beck Arnley semi metallic pads that I picked up from Rockauto on clear out special for around $10 which resulted in a miraculous improvement in braking for regular driving.
      A 142 of course. What do you expect? I'm the 142 guy. / 1971 142 E 102 color

    16. #14
      Junior Member
      Join Date
      Jul 2020
      Location
      Hampshire, UK
      Posts
      10
      Hi all
      Sorry for not updating earlier.

      Rear brake rebuild went fine. New shoes, fixing key and brake cylinders. Ending up putting two new drums on as well. I even managed to get the brakes pipes to fit after a fashion.

      With a friend we looked again at the front calipers, which I thought had sticky pistons and found that the pistons were actually moving fine and I was just not pushing the pedal far enough. Installed new pads (and hopefully softer) and bled the system several times.

      Took the car for a test run. Warmed up the brakes and tried a few stops and rears were still locking before the fronts and concluded that the BRV must be faulty.

      Booked the car into my local classic-friendly garage and asked them to check over my work and change out the Brake Restrictor Valve for the NOS one I had for my '68 1800S (same part number as for the 131 and had "1800 and 121" written on the label). Car came back from the garage and now the rears no longer lock up, the front of the car dips under heavy braking and I can if i really stamp I can get the fronts lock up first.

      Drove 200 miles in one day in the car and all seemed OK, but I still don't feel that brakes are as efficient as another non-servo 60's car I have with the same set up. I'll see how things are when the brakes are fully bedded in (if they aren't already).

      Thanks for all the advice and I will update if there are any changes.

      Phil
      1966 Volvo 131
      1968 Volvo 1800S

    17. Remove Advertisements

      Advertisements
       

    Similar Threads

    1. "Issue #131" ??
      By PRCvolvo in forum V70 & XC70 (2008 - 2016)
      Replies: 3
      Last Post: 09-07-2012, 03:57 PM
    2. Replies: 11
      Last Post: 10-03-2010, 07:33 PM
    3. Replies: 4
      Last Post: 04-23-2008, 01:06 PM
    4. I know S60s have rear backup sensors, but...what about fronts?
      By funglenn in forum R Forum (2004-2007)
      Replies: 11
      Last Post: 01-18-2008, 03:50 PM