p928

Could someone tells me the signs of a faulty brake pressure regulator? What does this part actually do?

1981 928
Auto

Mrmerlin

Hithe pressure reg is to limit the amount of fluid pressure sent to the rear wheels, to prevent lockup when the brakes are applied and the car is in a rear wheel unloaded situation

p928

Thanks for the answer. After doing some heavy research, I believe the brake booster is finished. Please..someone help me verify the problem before I spend $350.

The brake pedal travels half way to the floor before it gets hard.

When I depress the brake pedal with the car off, then start it, the pedal doesn't move.( I tested this theory on a 2004 vehicle and it moves when starting)

With the car running, I pulled the vacuume line out of the brake booster and covered it with my finger. The car sounded better than ever!

Please help so I can get my shark back on the road.

Thanks in advance!!!

TRUESCOTSMAN

Sound like the diaphram in the brake servo is leaking.

p928

Excellent!!!! What part is that? Where is it located? I'll get a new one on Monday!

TRUESCOTSMAN

What model and year is your 928?

TRUESCOTSMAN

Sorry i see it in your first post. For your year the p.n is 928 355 023 06. There is no repair kit listed for the servo so it would meen replacing the unit. Do a few checks first, pull out the line as it enters the servo and chek for vaccum leading up to the servo, just to make sure there is enough there, If that is ok then try pulling a vaccum with something else i.e one of these manual oil pump guns, pulling instead of pushing, that should show up whether your servo is leaking. These things can be opened up but it is a lot of work, they are normally swaged together but if you are willing to spend the time splitting the two halves of the unit, the diaphram can be repaired with a bicycle patch. Have done this in my younger days to good effect. (no money to buy expensive parts) Good luck

Mrmerlin

Hi call 928 international they have used parts. Stan

bunlacken

Anyone have brakes lockup on them lately. Did a MC rebuild, full fluid flush dot3 rode ok right after and to-day the brakes first started dragging then almost frose up completely... after sitting for about an hour (cool down) everything works as usual... afraid it will happen again. any ideas.

Vlocity

Is brake reservoir over full?

Possibly your brake fluid is heating and expanding with no where to go so is is pressurizing a caliper.

Ken

Mrmerlin

this sounds like different fluids have mixed , and have caused the seals in the brake system to swell, I would recommend that you only use ATE or Castrol brake fluid in your car, we have seen other M/C start getting sticky then the brakes locking up from the owners using the cheap stuff in the M/C for a quick refill. If you can get some new seals for the master try rebuilding it first ,if the brakes still are locking up then you may have to rebuild all of the calipers as well and this would be the ideal situation and dont forget to flush the lines before you reconnect the calipers

TRUESCOTSMAN

This is a classic case of air in the system. Air expands more than brake fluid when heated. The expansion causes the pads to rub on the discs , causing more heat, causing more drag, causing more heat,etc, etc. After cooling down everything goes back to normal, untill ran again, and it all starts over....... Bleed the system again.

Mrmerlin

yes it could be air in the system but then the brake pedel would be very spongy, so try bleeding the system first if their is no air removed by bleeding then try a rebuild on the master

Mrmerlin

dont forget to bleed the master first then do the wheels start at the furthest wheel then work to the master and use Castrol or ATE fluid

SharkSkin

You didn't put DOT 5 fluid in there, did you? Unlike ATF, where Dexron applications can use the later, higher numbers (Dexron II & III) you cannot put DOT 5 brake fluid in a system designed for DOT 3.