Pedal height - brakes

[michaeljc]

I have put a second hand brake booster in, put new seals in the rear callipers, bled the system all round and I think the pedal feel and braking is ok ..... But I am sure the brake pedal goes heaps further down than it used to. Also I had to adjust the brake light switch quite a few turns to stop the lights being on all the time.
I have not got around at the moment to investigating all the ways in which this change may have come about because this forum normally has the correct answers faster than I work them out 

Qn:  Should I have adjusted length of the rod on the booster rather than just swap it over as it was. .... I did not look to see if it was adjustable, but I do still have the original to check out when I get a spare moment.
Qn:  is there adjustability somewhere else in the system.

Thanks in advance to knowledgable alfisti ...... Mick

[GTVeloce]

I don't believe there is any adjustment at the front (i.e. pedal, m/c) but certainly the rears need to be adjusted properly or they won't work as well as they should.

It could also still be just a tiny amount of air in the system but I would start with making sure the rears are adjusted properly. Do you have the Haines manual?

[rowan_bris]

Brakes routinely have a low pedal at first when caliber seals have been replaced.  Assuming the adjustment on the rears is right it will improve with use

[michaeljc]

Thanks for the feedback. I did follow the Haines manual when setting the rear brakes up. I guess I just better drive it around braking a lot, hopefully without breaking a lot.

[Domenic]

The Alfetta boosters do have an adjustable rod just like most Fiat's it has a thread so that you can adjust the length of the rod.

The V6 boosters don't have an adjustable thread like the 4 cylinder cars, but the rod can be adjusted as there are shims behind the pin.

So check the length of your old one and also check the depth of where the rod goes into on the master cylinder as it might be different from manufacturer to manufacturer.

[michaeljc]

Finally got around to pulling the replacement booster out. It is an anodised one (not painted) and has the output shaft (the one that inserts into the master cylinder) with a thread and 8mm hex-domed cap (see photo).
The original booster I took out was a black painted unit and the output shaft has no thread (see other photo).
My GTV is Nov 1983 build date with the later (not-split) dash.

I measured up both booster units and the dimensions are pretty much identical, except for:
a)  distance from 'centre of 10mm dia. yoke pin on booster inlet shaft' to 'domed tip of outlet shaft': OLD booster = 195.5mm   /   REPLACEMENT booster = 194.5mm

My brake pedal travel is about 42mm to hard down. With the pedal pivoting length being approx. 440mm, and the pivoting arm connecting to the booster being 91.5mm long, this means that 42mm brake pedal movement = 8.7mm piston travel through the booster.

Both OLD and REPLACEMENT boosters have about 2.5mm slack between pushing the inlet shaft before the output shaft starts to move. This means that the first 12mm of brake pedal travel is just taking up slack before even pushing in the master cylinder piston.

With the boosters being dimensionally the same I have not worked out why the brake pedal sits lower than it used to. Extending the booster outlet shaft however may however reduce the total stroke needed to get full braking.

Previous reply to this post mentioned some shafts were adjustable. Please refer to the 2 photos attached. My gut feel is that neither of these is adjustable. I think the one with the threaded section has been factory crimped to hold the shaft in a fifed position. I feel that if I held the shaft and used an 8mm socket to turn the domed head I risk breaking the shaft.

I am therefore interested in your thoughts as (by my measurements) the overall combined input + output shaft length of the new REPLACEMENT booster is 1mm shorter than the OLD one I took out .... and it would be a bit helpful if I could lengthen the shaft by 1 - 2 (or maybe 3) mm .... noting that for each 1mm I lengthen the shaft in the booster, it means 4.8mm less brake pedal travel required.

Of course correct me if I am wrong :-)

[aggie57]

My standard practice to reset pedal height after track time was to press firmly down on the pedal and pump the handbrake. after all these years I can't recall the details of why but my recollection is that it was to do with the way the self adjustment mechanism works.

Whatever the logic it pretty much always worked.

[ACE]

Michael,

You mentioned that the "pedal sits lower than it used to"

If you have had the pedal box out or the "torsion bar" connecting the pedal to the servo's lever arm, Did you possibly misalign the pedal arm on the end of the splined shaft when reassembling?
It should not be possible as the shaft has a spline groove missing which should act as a key, but you never know ...

Otherwise, many Alfisti advocate a pressure bleed to get residual air out of the system.

[LukeC]

Jack the rear of the car as high as you can possibly get it  (like really high!!!) when you are bleeding the rear calipers. When an Alfetta is level, the bleeder nipples at the rear are not at the highest point. The front passages between the two halves are... Done properly, you can get them almost perfect first go. An additional bleed (also with the rear raised) after a couple of weeks use will get them perfect.

[michaeljc]

Many thanks to all for those comments. It gives me a bit to work with.

I will try the following and when I get success I will feedback on this thread.
1    I'll pump the handbrake and see how I go.
2    I'll jack up the rear REALLY high and have another bleed
3    I'll suss out the vacuum bleed option

Otherwise:
1    No, I didn't have the connecting rod out .... well ... not that I can remember .... I had the rear end / engine / gearbox / exhaust all out at the time but there was no need to remove the rod. Plus the change in angle from one spline to the next would probably be a HUGE change.
2    As far as I can tell by feeling with a small screwdriver, the inside of the master cylinder piston is contoured similar to the end of the booster rod. Hence a shim needs to be similarly contoured or it will bridge the curve and effectively act as a much thicker shim. But if curved shims are available I am game to have a go.
3    Any comment on the 2 - 3 mm of free-play in the booster between when the input shaft is pushed to when the output shaft starts to move. It is similar free-play on old and replacement boosters.
4    Another point of note is the output shaft on a)  OLD booster is fairly solidly fixed axially and just moves in/out b)  REPLACEMENT booster is pretty sloppy and the tip can be moved radially very easily. Of course, once inside the master cylinder there will be no radial movement.

Thanks again to all. I am looking forward to enjoying my brakes. .... Mick