George Helser

I drove a 1971 914-1.7 for 11 years.
When I bought the car in 1974 the brake pedal was spongy. I replaced the rubber brake lines with Aeroquip braided steel lines but it made no difference.

The 914 has an adjustable regulator which limits the brake pressure to the rear
wheels to prevent rear wheel lockup. I experimented with setting the regulator
for higher pressure (turning the bolt clockwise). As the pressure went higher my
brake pedal became less spongy and my car stopped faster. Then I removed the original adjusting bolt (which had little range) from the regulator and fitted a longer bolt. (Sorry, I cannot find my records on the length of the new bolt.) I increased the pressure adjustment as far as the longer bolt would go. The brake pedal was no longer spongy and my rear brakes were doing more work to stop the car faster. I never locked the rear wheels with the higher pressure setting in 50,000 miles of dry, wet or snow driving.

Note my rear springs had sagged (common problem with early 914s) so I lowered the front end (adjustment screw on the front torsion bars, raised the steering box & aligned). My lowered 914 may have been better suited to higher rear brake pressure. A higher 914 might not tolerate the higher rear wheel braking force without locking the rear wheels?

If you adjust the rear brake pressure regulator be careful not to induce rear
wheel lockup which would tend to cause the car to spin.

Good luck!

Regards,
George
In sunny Arizona
(Currently in the market for a 993 with LSD)

George Helser

I just found the spot in my notebook on this brake regulator adjustment. The bolt I used was 40 mm long. It was screwed all the way into the regulator with a 2 mm thick washer between the bolt head and the regulator.

Regards,
George
In sunny Arizona
(Currently in the market for a 993 C2 with LSD)

JGriff

Great tip... since my 914's pedal also feels soft. (I just bought the car, and haven't checked the brakes yet... they may need to be bled etc.)

Two questions:

1. Where is the pressure regulator?

2. I know you mentioned 40mm long, but what size is the bolt... i.e. 8mm or 10mm ? Will one sourced from Home Depot suffice... or should I get one from an auto parts source?

Thanks.

Jim

George Helser

Jim,

WHERE?
My “recollection” is the brake pressure regulator is on the firewall near the bottom on the driver’s side. It is cylindrical with brake lines attached.

BOLT
I did not note the bolt size. It is a standard metric thread/diameter you can find in the hardware or auto parts store.

Good luck!

Regards,
George
In sunny Arizona

DERSIX

George, Great tip on adjusting the bias valve.I will try it out on my 2 liter. One must be careful when turning the screw for the Germans usually epoxy it so you will have difficulty moving it. You and I are probably the only ones who feel that replacing the rubber OEM lines with the steel braided lines does not remove the spongy feel to the pedal.The metal lines are great for racing for they are not easily damaged, but you can not see them begin to fail and should be replaced every two or three years.
Pete

vinceinhiding

I too have the spongy brake pedal problems. I have changed all brake pads, rotors, hoses, and have rebuilt the rear calipers. I even played with the adjustment on the brake pedal (which I now think was wrong). My next thought was to replace the proportioning valve that you guys mentioned, but I've read and heard that its not safe to play with the valve. Is that true? Also, how could the valve go out of adjustment, isnt it epoxied?

I'm getting real frustrated with these brakes, please help!

George Helser

Joey,

I don’t have answers to you questions.

I am not saying that the adjusting bolt in the rear brake pressure limiter came loose. The locking nut was in place when I experimented with it. I simply found evidence that:
- my rear brakes were contributing little to stopping
- when I increased the bolt length on the pressure limiter my pedal became firmer
- when I increased the bolt length on the pressure limiter my stopping improved
- when I increased the bolt length on the pressure limiter my rear wheels never locked.
My car was lowered (stock rear 71 springs sagged and I leveled the car by lowering the
front) and maybe this was a factor.

Good luck!

Regards,
George
In sunny Arizona

P.S. Just a thought: The rear springs in 71 914s were defective and sagged. Maybe the
rear brake pressure limiter also had a defective spring?

DERSIX

Joey Vargas,
The lock nut on the adjustment screw is epoxied, but the epoxy can be removed to afford adjustment. My belief is that the spongy pedal is due to air entrapment in the bias valve. By opening up the valve with the screw allows for easier removal of this entraped air when bleeding. These valves can be easily replaced with the adjustible type;eg,Kelsey-Hayes.
Pete

vinceinhiding

Are the adjustable type valve safe for everyday freeway driving???

John D.

Hi Joey,

DERSIX is absolutely correct (again ;^).. The proportioning valve is exactly that - there is a "valve" in the assembly that relies on pressure to activate. Without that pressure or without activation - that same device will/can also trap air bubbles that lead to the "spongy pedal". You have a couple of options...

You can try pressure bleeding the system (pressure bleeder are sold with a hand pump, or use a home-built air supply (a spare tire works;^) to pressurize the brake system - or you can open the valve (yes, you'll have to remove the epoxy).

Are after-market proportioning valves safe for the street? Probably fine, in my opinion - but know how to set it up so you can dial in the correct bias given the brake calipers you are running. Even with a BMW 320 converted system - the factory bias seems to be just about right - but if you go further up the upgrade scale, the factory setting will most likely be off by a bit..