940 Brake Pedal.

[Steve940estate]

I've had an exciting evening, thats a lie actually I have been out in the garage comparing the lengths of of 2 brake pedals I have.

I read on here whilst searching various brake topics that late 940's had modified brake pedals to cut down pedal travel. I am currently trying to make my brakes better and wondered if this might be of help.

Amongst my spares I have a late pedal box I grabbed when I first thought of making my car manual, sure enough the pedal is slightly longer and the pivot is higher up in the pedal box.

It isn't much different, around 10mm but if my understanding of levers etc is still correct you get slightly less pedal travel and slightly less force acting on the master cylinder.

Volvo must have done this for a reason so I might give it a try to see if it makes the brakes feel any different.

The pedal itself is different as is the pedal box and you need both to convert your car. The only other difference is that there isn't a return spring on the pedal itself. Not sure how this might help but it might make the pedal slightly softer and might take away some of the free play in the pushrod assembly.

Cars fitted with these parts are from 1995, has anyone noticed a difference before I go to the trouble of swapping parts ?

[crogthomas]

Could you measure the distances between the pivots and pedal? I'd like to work out the difference in the pedal ratio.

[Steve940estate]

I will measure them properly later on. I sat looking at the pedals last night as I couldn't work out how the differences affected things. The overall length is greater but the pushrod is still the same distance from the pedal pad. I need to get the technical Lego out so I understand it !

To add to the confusion I found a technical spec page on Vadis saying there were 2 versions of brake servo that have different input /output ratios.

[Steve940estate]

I've done a bit of measuring.

Shorter Pedal

Distance from pivot to center of pedal pad = 335mm
Distance from pivot to pushrod = 83mm

Longer Pedal

Distance from pivot to center of padal pad = 346mm
Distance from pivot to pushrod = 94mm

The pivot to pushrod figures are accurate, the one from the pushrod to the pedal pad are 252mm. This is as close as I could get, and then I added the pivot to pushrod figure to get the pivot to pad measurement.

To get the mechanical advantage figures you devide the total length by the pivot to pushrod length.

335 DEVIDED BY 83 = 4:1
346 DEVIDED BY 94 = 3.7 :1

If this is right it proves the shorter pedal has more mechanical advantage and a longer travel.
If it doesn't I'm a dunce and need to sit in the corner with the special hat !

[Steve940estate]

Just to prove I am mad.

Pedal Up

Black pieces of Lego are the pedals linked to the same pushrod to show effect.



Pedal Down

Short pedal has traveller furthur to move the pushrod the same distance, it's easier to push against the spring as well !

[crogthomas]

Just measured up the pedal in my '95 940 turbo, it's the longer one. I assume that the pedal in my old 740 was the shorter type. The 740 definitely had a longer pedal travel, but it also will have had a different master cylinder and brake caliper piston size, so not very conclusive.

I like the use of Lego to visualise how the ratio changes. Very useful stuff. Lego made me the man I am today. Now make a differential!

[Steve940estate]

My M reg turbo spares car had the shorter pedal and it's that one I've got in my car now. They change from chassis number 203140 for the saloon and 145131 , mine is a bit too old.

The lego is a bit too old to have the bits to make a diff. Plus almost all of it's still built up.

[Ian21401]

Originally Posted by Steve940estate

My M reg turbo spares car had the shorter pedal and it's that one I've got in my car now. They change from chassis number 203140 for the saloon and 145131 , mine is a bit too old.

The lego is a bit too old to have the bits to make a diff. Plus almost all of it's still built up.

I'm impressed by the use of the Lego. Now if you were old enough you would have used Meccano, had an electric motor in it and put a body on as well.

[rod25]

Originally Posted by Ian21401

I'm impressed by the use of the Lego. Now if you were old enough you would have used Meccano, had an electric motor in it and put a body on as well.

Meccano ,

Now there's a blast from the past .
Are the parts still made from tin ,

[Steve940estate]

I'm glad someone was impressed !
I did have Meccano but it used to wind me up. My parents bought that set for me while we were on holiday. It rained every day and I think they felt a bit guilty. Most of it got put together in the back of the car !
I was trying to work out when it was, I must have been about 8 years old as they came out in the late 70's I think.

Makes you wonder how much stuff has been developed using meccano and lego. Before the advent of computers that could model everything someone had to make things to test.
Thinking about it thats why I don't have a decent job now !

Like all my cars it didn't stay standard for long, it got a jack up kit and sidepipes, thats what happens when children buy Street machine magazine and don't have real cars to play with !