Jump to content

Residual Pressure after installing Brake Proportioning Valve


Recommended Posts

I've just changed my Brake Setup and installed the US Spec rear wheel cylinders ø22,2 mm with the 230mm Drum to get more brake in the rear.
Now I have a little bit too much at the rear so I installed a Tilton Proportioning Valve 90-2003 and now I have an issue with residual Pressure in the system.
There is no residual Pressure Valve in Main Cylinder or in the line.
The rest of the Braking system is untouched and has been run before, so the only change has been the installation in the line to the rears.
I have confirmed the orientation in-out is correct. Brakes have been bled thoroughly with a pressure/vacuum bleeder
(+pressure at the MC and vacuum at the wheel cylinder)  Brake Pedal feel is ok.

What I've recognized and confirmed is that I get a residual pressure in the rear circuit if the proportioning valve is turned in
more than 2.5 Turns (of the 7.25 Turns possible).
So the rear drum is free - I close the Proportioning Valve 3 turns- I press the Pedal and afterwards the rear drum is stuck. I could feel it in the test drive, and now have confirmed with the wheel off. When I attach a tube to the bleeder at the Wheels cylinder and open it I get a volume of ca. 0,5 cm³

As I need a rather closed Proportioning valve to get settings right this won't work for me.

Do you have an Idea what's wrong? When I'm only closing 2.5 turns the drums are free after releasing the pedal.

Edited by uai
Link to post
Share on other sites

The rear shoes are held in adjustment by the eccentric adjusters in the backing plates.

 

Residual pressure just holds the hydraulics against the shoes, nothing more.

 

The shoes aren't supposed to drag- if they do, they'll heat things up, and then bind.

 

It's a very manual system, compared to most.

 

t

 

Link to post
Share on other sites

I have been talked by the vendor in buying another one (lever type this time to avoid being from the same charge) same issue. Have been talking to tilton yesterday - no idea from their side.
If you want to have a look I made a video. (I bled the system to get the pressure out before the video)
https://youtu.be/JB-HrYsSRas

Link to post
Share on other sites

I wondered about that too, but they would have had to do that with both of the valves he tried.


I tried to find other information online and was excited to be reading of someone on a Porsche forum having the same problem... until I realized that that guy had the same name!  :D 

 

Tom

  • Haha 2
Link to post
Share on other sites
15 minutes ago, '76mintgrün'02 said:

I tried to find other information online and was excited to be reading of someone on a Porsche forum having the same problem... until I realized that that guy had the same name!  :D 

you could probably find another BMW owner on a german forum having the same issue...

 

  • Haha 2
Link to post
Share on other sites

2002's had a residual pressure valve on the master cylinder for the rear drums.  You're does not??  Have you checked that the problem is on both rear wheels?  I have used the Wilwood (same design as Tilton) proportioning valves on lots of 2002's with no issues.  I think the valve is not the problem.  Maybe try backing off the brake shoes a bit.  Or you could switch to the 19mm wheel cylinders from an E21.

Link to post
Share on other sites
24 minutes ago, jireland2002 said:

2002's had a residual pressure valve on the master cylinder for the rear drums.  You're does not??  Have you checked that the problem is on both rear wheels?  I have used the Wilwood (same design as Tilton) proportioning valves on lots of 2002's with no issues.  I think the valve is not the problem.  Maybe try backing off the brake shoes a bit.  Or you could switch to the 19mm wheel cylinders from an E21.

Yes, I have no residual pressure valve in the system. And yes both rear wheels are affected. Brakes shoes adjustment (backed off or not) does not affect the symptom. 
Does anbody have a pic from the e21 Wheel cylinders (from the connection side).
If the 19mm e21 wheel cylinders is shaped like the upper on in the pic they might do the trick.

index.php?action=dlattach;topic=186495.0

 

Link to post
Share on other sites

Just saw this as I have been away.

 

The brake balance is a common problem when owners depart from the OE setup. Changes in front calipers, pad material, rear drum size, and rear hydraulics all serve to mess up that balance.

 

When I didn't know any better, I did the front caliper / E21/Turbo rear drums and hydraulics  "upgrade". i observed the same thing, the rears locking up. i even purchased a Tilton valve, but never managed to install it.

 

While investigating the brake proportioning valve used in the Turbo / E9 and its associated pressure curve, I decided to do some delving into the engineering of the hydraulics, which I had done on my M3 years ago.

 

i found that the balance is actually pretty good on an OE system, but is heavily dependent on a) how many people are in the car, b) how much "junk is in the trunk" and most importantly c) what friction material you are using for the front pads and the shoes. and d) What kind of tires you are using and their coefficient of friction.

 

First I recommend you finding out what material you have so an analysis can be done. Many times you can solve your issue by not having a tilton valve. In the case of the Turbo (essentially Tii M/C, caliper pucks, E21 drums and hydraulics) the balance is designed for the Factory specification of 4 people in the car, a full tank of gas and additional weight in the trunk. so, the proportioning valve (odd that it is used in both the turbo and the heavier E9) serves it purpose when the car is "light" in the rear from the specification.

 

By knowing how you "normally" drive your car,  just changing the friction material might suffice.

 

I have found that Hawk HP+ (or whatever it is nowadays Mu of ~0.5 @ 100 deg F.) in the front along with something like a  porterfield R-4 in the rear creates a pretty good balance F/R.

 

the Hawk pads are great in that they achieve their maximum friction at close to ambient temperature...no waiting for them to "get up to temp".

 

As an aside, my M3 achieves -1.4G with stock calipers, HP+ pads and sticky tires without the need for a "big brake kit".

 

If you want me to run an analysis, PM me.

 

HTH

 

Ted

  • Like 2
Link to post
Share on other sites

Hi Ted, I had spoken to somebody from Tilton yesterday. They are trying to replicate the symptom in their lab.
 

My brakes are pretty much different from stock and I would be very glad with the balance if I could just take a little bit from the rear. In wet condition I think it would already be good, but on dry grippy tarmac I need a little less in the rear to be on the safe side.

My Brake setup:

Aluminium Hubs

E21 vented Rotors front with custom built venting ducts
Porsche 911s ATE Aluminum Calipers (2nd series like Alpina used) with TiCN coated 6AL4V titanium pistons 48mmø
Pagid RSH42 pads front - very satisfied with them.

230mm Drums with (17,46 before) now 22mm wheel cylinders rear with standard ATE Friction material
19mm Master Cylinder without booster
Motul RBF 660 Fluid
I tried to avoid importing rear shoes from the US as there are no hawk or porterfield rear shoes available here you'd have to have the friction material custom glued to your shoes.
A benefit of the valve would be the ability to adjust to conditions. 

 

For Junk in the Trunk: I have a 100 Liter Tank right above the axle between the wheel housings.

 

Perhaps I'll go and try another manufacturer (ap Racing) for the valve or go back to smaller wheel cylinders and order shoes with a little higher friction coefficient from the US




 

Link to post
Share on other sites

Hi. How many pistons on each caliper?

 

Have you weighed your car f/r with full and empty?

 

I would be willing to get you shoes or whatever you need  if that would help.

 

Let me run some numbers tomorrow.
Hth

ted

Link to post
Share on other sites
Posted (edited)
19 hours ago, Einspritz said:

Hi. How many pistons on each caliper?

 

Have you weighed your car f/r with full and empty?

 

I would be willing to get you shoes or whatever you need  if that would help.

 

Let me run some numbers tomorrow.
Hth

ted

Thanks Ted, here are the numbers. The weight is in kg with me, 50 liters in the 100 liter tank, spare wheel and tools.
Main cyl is 19mm, fronts calipers are 2 pistons ø48mm each, rear wheel cylinders were 17,46 now changed to  22,2
Discs are 255x22, drums are 230mm diameter

 

IMG_5310_k.JPG

Edited by uai
Link to post
Share on other sites

Hi, the pad depth is 55 mm, so the medium friction diameter is ca. 200 mm

Thanks Uli

PS: Tilton was able to reproduce the behaviour when the volume that goes through the valve on compression exceeds a certain value.

My drums do not need any adjustment at the moment (as soon as the excenter touches the shoe it starts dragging) therefore if this occurs even when properly bled I probably need to switch the supplier of the valve. The ap racing is much larger - I assume It can take more volume - that will be my next trial.

Edited by uai
  • Like 1
Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...