164 brakes
 

A bit of thought-sharing appreciated.

I have fully rebuilt the brake system on my 1973 164 fitted with ATE brakes & master c. Trouble is despite repeated bleeding by the book, following the order of bleeding to the letter, the pedal is still soft, the brakes next to useless.

I’m at a bit of a loss where to look next. One specific question - the small bolt on top of the master cylinder that acts as a lock for the piston assembly - is that also for bleeding the master cylinder? Openly I’ve not experienced needing to bleed a master cylinder but cannot think what else might be needed?

Any other thoughts?

Full disclosure, I have a 1971 142, not a 164 so no direct experience. But, I expect the systems are similar.

First off, I have never touched the little bolt on the MC.

I highly recommend using a pressure bleeder for the Volvo dual diagonal brake systems. I have had 3 Volvos with that system which originated with the 140 and it makes bleeding a snap compared to the alternatives. The pressure bleeder eliminates the need for that pre bleeding of the MC that a of people like to do.

Did you rebuild the master cylinder or is it new? I have had no luck rebuilding MCs, ending up with leaking past the primary piston seals back into the reservoir.

If you removed / replaced the MC check the push rod adjustment on the brake booster. The service manual specifies a clearance between the front tip of the push rod and the back of the piston in the master cylinder. You will need a depth gauge / vernier caliper to do this measurement because you can't check the clearance when it is assembled. If you have excess clearance between the push rod and the MC piston you will have 'lost motion' and will not be able to generate as much brake system pressure.

I presume that you have checked for weeping around all the brake fittings and are not experiencing a drop in reservoir level after doing your testing?

The Volvo system can be a royal pain to bleed. I expect that the likely cause is residual air in the brake system. A pressurized bleeder tool is much more effective at moving trapped bubbles quickly through the system than the foot pump method.

164 brakes
 

Thanks for this.

I have a vacuum bleeder but didn’t seem to do much so reverted back to the old method of wife in car on pedal but seems I either need to do as you say with pressure bleeding or get the vacuum type to work.

It’s the existing mc with new seals fitted. Pushrod clearance didn’t give a thought to tbh so if a further round of bleeding doesn’t work and I take it off again I will look at that for sure.

Not aware re mc pre-bleeding - not come across before.

It could be I just need to persevere!

Did you replace calipers? Check that they’re on the correct side.

https://www.volvoforums.org.uk/showt...t=Bleed+brakes

164 brakes
 

Yes I had all four callipers off but kept them ordered to go back on correct sides however I will double check to be sure tomorrow and thanks for the heads up. From last recent bleed I’m 99% sure all nipples are at the top on each wheel as now fitted - so 99% sure they are correctly fitted but certainly worth a double check. Cheers

A couple more thoughts for your consideration.

I see you’re following the bleeding sequence, so I assume your bleeding from all 3 bleeders on the front calipers? I ask because I initially missed the third one when I bled mine.

Also it’s possible the rear brake proportioning valves can impede the bleeding. Recommendation is to raise the rear of the vehicle when bleeding to assist air to be expelled.

When you fitted the new seals, did you use a cylinder hone to remove the ridge that forms at the normal end of piston travel? If you didn't, chances are you have damaged the new seals and need to replace or rebuild the MC .

Over years of operation, a wear ridge develops in the cylinder walls at the normal end of travel on the MC piston. If you do a brake bleed using the pedal pump process you need to put a block under the pedal to stop it from travelling beyond its normal range of operation (a bit of a guess as to where that is). If you repeatedly push the pedal right to the floor as part of the bleeding process without having reamed the cylinder you force the seal over the ridge eventually leading to seal damage and leakage back into the reservoir. Been there, done that - bought the new MC! That is the primary reason I now use a pressure bleeder when I do my semi regular brake fluid flushes on old cars.

I have used the hand vacuum pump on a car that I didn't have a correct master cylinder adapter cap for doing a pressure flush. That was a simple brake system flush replacing old fluid with new fluid and did not involve removing any air from the system. It probably took 20 - 30 minutes at each wheel for a single bleed port (not a Volvo) leaving me with an incredibly sore forearm at the finish. The rate of fluid flow with the hand pump was so slow that I don't think it would do a very good job of removing trapped air in the system.

To echo C1800, when you did the bleed 'by the book' did you use the Volvo service manual procedure and you got all 3 bleed ports on each front caliper? When I completely rebuilt my 142, I got lots of experience repeatedly bleeding the system as I repeatedly discovered new leaks at the various flare fittings in the system. With the pressure bleeder, on the 140 I never had to resort to elevating the rear of the car to complete the bleed process.

And another thought…
Did you remove the brake warning switch in the brake line junction block under the hood? The switch detects an imbalance in the fluid pressure in the 2 systems, and may have activated , which requires removal to reset. Remove for bleeding, and reinstall when done.

164 brakes
 

Many thanks constructive points.

Brief update - bled again today and slightly better so I do think it’s a matter of residual air still. Gave up with vacuum bleeder, despite just cracking nipple open it still drags in air (should Hv renewed these, no doubt) so cannot get a clear idea if bleeding done. Went back to basics, however have since made a pressure bleeder system to attach to MC and will use that tomorrow to see if improves.
Rear of car was elevated.
All nipples bled in order, 3 on each front corner and one on each rear.
No, brake warning switch not removed - thought would just let air enter through there? Or it it not opening into hydraulic system just into space between both circuits?
Cylinder NOT honed but surface was good, no ridge. Car has been stood many years so was fairly sure seals were shot and leaking by under pedal pressure.

I think pressure is the way forward so will update tomorrow if my Heath-Robinson setup does the job. Had a spare MC cap so will rig on there fed by spare wheel so no over-pressure.

Heath - Robinson would be proud.

I use about 10 psi air from my compressor. That pressure will depend on how well your H - R constructed cap seals. Also, check where your reservoir pushes into the MC housing. Its a rubber friction retention and if the rubber seals are tired it does not take too much air pressure for the reservoir to pop itself out of the MC launching brake fluid all over the place.

Watch the reservoir level like a hawk. The bleeding goes so quickly that you can empty the MC reservoir in a jiffy and fill your system up with air. I have a two part bleeder. It has a separate 1 l reservoir filled with brake fluid and that reservoir is pressurized forcing fluid into and also pressurizing the MC reservoir. Easy to check the external reservoir and refill it before the MC reservoir starts to drop. If I ever did empty both the external reservoir and MC reservoir before checking, serves me right for having to start the whole process over again.