home register FAQ memberlist calendar

Go Back   Turbobricks Forums > Mechanical > maintenance & nonperformance

Reply
 
Thread Tools Display Modes
Old 12-15-2019, 02:40 PM   #1
TimS
Board Member
 
Join Date: Dec 2017
Default master cylinder questions and line routing

I need to replace the master on my 85 244 turbo. I noticed that it is a stepped bore cylinder. (.625/.875)
With the stock system one of the bores feeds half of each front caliper, and one side of the rear. So does that mean that the rear calipers are at 2 different line pressures?
TimS is offline   Reply With Quote
Old 12-24-2019, 01:29 PM   #2
dbarton
Dejected by Volvo
 
dbarton's Avatar
 
Join Date: Nov 2002
Location: North of Dallas
Default

Quote:
Originally Posted by TimS View Post
I need to replace the master on my 85 244 turbo. I noticed that it is a stepped bore cylinder. (.625/.875)
With the stock system one of the bores feeds half of each front caliper, and one side of the rear. So does that mean that the rear calipers are at 2 different line pressures?
One would think the pressures might be different, but my guess is they must be equalized by the other lines. If not, the brake failure sensor would trigger on every push of the pedal.

Here's a diagram I made for my page below.
Dave B

__________________


'84 242ti, fourth owner, mine since 2003. Always garaged since brand new. Old-school rounds because I like. B21FT, SDS EFI/IGN, TD04HL-15G, T5Z trans with modded 0.73 OD, 3.91 diff, unmodified G80.
Volvo Ambivalence of Volvo Enthusiast Community: prancingmoose.com/#novolvo
Dave's Volvo Page: davebarton.com
240 Mods and Fixes Pages: 240turbo.com/volvo240mods.html
dbarton is offline   Reply With Quote
Old 12-24-2019, 02:25 PM   #3
hiperfauto
The Librarian
 
hiperfauto's Avatar
 
Join Date: Nov 2011
Location: So Cal
Default

Volvo developed the stepped bore master in order to eliminate the increase in pedal travel when one circuit fails.

The entry into the SAE Transaction register from 1975 explains that the pressures are equal in the 2 circuits when the system is intact.

Quote:
HS-018 270

STEPPED BORE MASTER CYLINDER--A WAY OF
IMPROVING DUAL BRAKE SYSTEMS

Dual brake systems are required in motor vehicles in the
United States. These systems increase the safety of motor
vehicles by overcoming the loss of braking effect which oc-
curs when a brake pipe or hose in a single-circuit system
breaks. However, a disadvantage of the dual system is the
extra pedal movement and increased pedal force which are
required when one circuit has broken down. Since the max-
imum deceleration which can be obtained is dependent on the
largest pedal force that the driver can produce, or the max-
imum friction force which can be exerted at the braked
wheels, a deterioration in deceleration normally occurs when
one circuit breaks down. A dual brake system which includes
a tandem master cylinder was introduced on the Volvo 144 in
1966. This system still caused rather large pedal stroke losses
when one circuit broke down, resulting in a feeling of un-
resiliency in the pedal. A new type of master cylinder was in-
troduced on the Volvo 244 model for 1975. The function of
this new cylinder is based on the use of two pistons, loosely
connected with one another, and with different diameters, in
one cylinder. When the brakes are applied with an intact
system, the pressures in both circuits are the same. The pres-
sure equalization necessary to obtain the same pressure in
both circuits is achieved in the stepped bore master cylinder
with a secondary piston, which floats within certain limits. The
stepped bore master cylinder gives high brake fluid pressure
with a moderate pedal force with one circuit out of function. It
is probably most suitable when used with disc brake systems.
With drum brakes, a good automatic adjusting device is
needed.

by Ante Larsson; Lars Larsson

AB Volvo

Rept. No. SAE-750385 ; 1975 ; 8p

Presented at the Automotive Engineering Congress and

Exposition, Detroit, Mich., 24-28 Feb 1975.

Availability: SAE
hiperfauto is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump


All times are GMT -4. The time now is 04:00 AM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, vBulletin Solutions Inc.