Bleeding brakes and rear spring bolts

[James Eastwood]

The long process of rebuilding all the steering, suspension, brakes and drive shafts on BE475 is now complete and I've test driven the car to work several times  :D :D

I have a couple of things I need help with;

1) Bleeding the brakes; they're 'ok' but wouldn't win any competitions for firmness. I note that the rear brake cylinders have the bleed lower-most on the cylinder, can others confirm this is correct and are there any tricks to bleeding this arrangement?

2) I'd like to replace the rear spring bolts to fit longer items, in order to fit a small lowering block. How do I dissemble these bolts, as they appear to be captive within the differential casing?

Many thanks.
James Eastwood

[TTM]

1) To reach the nipples at the rear which nest almost hidden in the middle of the parking brake "tower brackets" I was not able to find anything better than a "perforated elbow spanner" which should allow reaching the nipple while retaining enough rotation clearance. The spanner obviously needs to be perforated to allow fitting through some generic transparent tubing to let the fluid out while leaving the spanner on the nipple.



I do not have the original dedicated spanner and the nipples on my car were replaced and are no more of the standard size.

[AC Ace Bristol]

.
James..

Yes,  the bleed nipple is at the bottom ,  and not he easiest access when bleeding, too make life easier I replaced the rear brake nipples with extended units, then I use a shortened  but deeply cranked ring spanner . One can comfortably bleed the rear brakes as  the bleed hose doesn't interfere with access to the spanner .

Keith

[TTM]

Should the nipples at the rear really point downards?
They point upwards on mine and they do not look like they would be accessible at all if they pointed downwards.
I have also never seen a car where the nipples ever point downwards...

[AC Ace Bristol]

.
TTM  & James

Rear  Girling brake cylinders part number 390150W & 390151W are used on various cars during the 1950s/1960s.   fitted to the front of  the car  with the  bleed nipple at the top as one would expect, However on the Ace they are fitted towrds the rear, therefor the brake nipple is at the bottom with the  hand brake Adjuster and cylinder to  the rear .
BEX333 has never be rebuilt other than general maintenance( plus  Engine gearbox and diff rebuild)  I assume BEX  is as she left Thames Ditton in 1957.
The few  Aces I have worked on and or inspected have been the same.

Please note:   I run Drums all round therefore use 1 " cylinders to the rear, Whereas Disc braked Aces will use 7/82 Rear Wheel Cylinders.

Keith

[James Eastwood]

Many thanks. I had worried that I was about to be told I had everything on the wrong side! At least that's not the case.

I do think there's probably a volume of air upper most in the cylinder, and whether bleeding upwards into the master cylinder may expell it or getting inside the drum and pressing down on the upper piston. I will let it all settle some time and have another go.

My other question was the rear spring bolts - can I remove them to fit longer items to fit a lowering block in place? I just haven't seen how they are removeable??

[B.P.Bird]

Keith et al,
Many years ago Ken Davies and I were chatting to Derek Hurlock at Thames Ditton. At the time Ken was racing AE 108 very successfully and seeing off the Bristol and Ford engined cars. Our conversation turned to brakes and Derek remarked how much trouble they had taken, with Girling, to get the rear brakes to lock first. Ken and I were speechless as Derek went on to explain the philosophy: As the front wheels did the steering it was essential that they did not lock. Afterwards we both realised that many Aces and Acecas and Greyhounds we had driven had indeed suffered from this rear locking malady.
It was common practice, at the time, for Ace racers to fit smaller rear wheel cylinders to get a better front to rear balance. The usual fix being to go to a 7/8" cylinder instead of the 1". However Ken had also tried to improve his lap times by fitting disc front brakes to '108 and this necessitated a further reduction in rear brake effort by going down to 3/4" cylinders. When it transpired that the front drums had produced better lap times than the heavier discs he reverted to the Alfins, but retained the 3/4" rear cylinders. This combination turned out to be the best of all with a hard pedal and good front to rear balance.
I recollect that the smaller size Girling slave cylinders sometimes had three mounting studs instead of two, the extra stud was simply cut off as the remaining two fitted the rear mounting holes. By the bye, just a reminder, these studs fit in to slots which allow for the cylinder to shift. It is important not to do the nuts up tight. Originally there were spring washers under the nuts, but these are now most often missing. The wheel cylinder movement is essential to allow the linings to centre up in the drum.
So far as brake bleeding goes I gave up pumping brakes pedals and wasting pints of fluid trying to get the air bubbles out, years ago. I use a simple hand operated vacuum pump - there are several on the market, mine is a 'Mityvac' and it has worked fine for a long time. Just remember to put the bleed nipples in with PTFE tape around the threads so that air cannot be sucked in during bleeding operations with the nipple released.
James to fit replacement spring mounting bolts you will need to remove the diff from the rear spring tower. Fitting lowering blocks to the springs is not the way it was done in period and by reason of the Ace's unconventional suspension geometry might well be detrimental to cornering performance. The correct procedure was to re-temper the the springs to a lower arch and to shorten the main plate and the lap plate to retain the negative camber, or even increase it.
Barrie

[James Eastwood]

Barry, many thanks for this detailed information.

I get the idea of trail braking the rear of a car, I'm just back from an outing this evening at Buckmore Park go kart racing. Go karts of course typically only have a rear brake and this can be used to great affect to initiate turn-in. Perhaps this style of driving was more driven by cross ply tyres and the need to set the tyre up with more 'angle of attack' than radials.

My car also locks the rears first, good to know that's the design intent!

I had seen the slots in the rear uprights and assumed Thames Ditton must have fixtured this to set the cylinder in the slot, but it's interesting to note they should float, thank you.

I was aware of the shimming vs spring resetting argument; the shimming changes the roll centre and gives more roll induced positive camber which is undesirable. The upside of the shim is that I can play with ride height before commiting to having the spring 're-set' which necessitates a 3 week turn around to send the spring to Jones Springs in the Midlands, as my local place, Brost Forge in London has just closed last year. I'm also only looking at a 1/2 inch shim at present. But I'm not taking the diff out, so I'm going to have to think about the studs.

[Klassik Metall]

Regarding orientation of the bleed nipple, I've always fitted the cylinders with the bleed nipple pointing upwards. I take the common sense view that any air in the system will collect at the highest point. However, as the rear cylinders are mounted vertically rather thank horizontally this is less of an issue than it could be. The other reason for mounting them this way up is it's much easier to see what you're doing when bleeding the cylinders & I've always found that the original AC bleeding tool works really well for this job.

As to the actual bleeding, I just follow the procedure in the AC handbook & firstly wind in the adjusters so that the shoes are pushed fully against the drums, which in turn forces the pistons as far as possible into the wheel cylinders.Using this method I've always managed to achieve a good pedal.Occasionally it's also been necessary to bleed air from the master cylinder by just cracking the brake pipe nut on the cylinder outlet, whilst a helper depresses the brake pedal.

Lastly, as Barrie stated it's very important that the rear cylinders can "float" on the back plate so that the shoes can self centre within the drum. I've found that rather than plain nuts with spring washers the original fitment here were very slim 1/4 BSF Aerotite or Simmonds lock nuts. These nuts are now somewhat hard to source but Barry Howsley had some available a couple of years ago.

Regards Luke.