Late Sprint rear brake cylinders

[PaulB]

Am I correct that late Sprints had a different rear brake cylinder to earlier Sprints?

I cannot find any reference to this in the parts book and Rimmers don't indicate any difference either.

If they are different, what is the difference and when did they change. Part number for the late cylinder would be much appreciated.

Thanks.

[xvivalve]

The Sprint was the only model in the range to keep the same cylinder throughout: GWC1121

[Carledo]

Unconfirmed information is that dual circuit brake cars use the 1850 rear cylinders which have a slightly smaller bore. But my parts list is only a 76 one and though it shows the tandem master (for foreign markets) it only shows one rear cylinder. Perhaps someone will come on who has a very late parts list (80 or 81) though I suspect BL had gone over to microfische by then.

Steve

[xvivalve]

It's the other way round Steve, later dual circuit 1850s used the Sprint cylinder.

[Richard the old one]

For 1500 cars it is the same the later cars with a dual braking system use the smaller rear brake cylinders.

[MIG Wielder]

I have the late Dolomite parts book dated Feb 1981, RTC9822CB, which, as Alun says, only lists the GWC1121 for the Sprint.
The same GWC1121 is also listed as fitting 1500 / 1500HL / 1850HL for WF68200 and onwards for RHD cars. ( WF68823 for LHD cars. )
Tony.

[gmsclassics]

There have been a number of previous posts on this and there ARE two different diameters fitted depending on whether the master is single or tandem. The problem is that as the smaller diameter for later cars can be retrofitted (in pairs) to earlier cars without issue, BL seem to have continued with the same part number. As BL would in the later times have only sold the smaller diameter which work without problem on earlier cars, they never considered the implications that in 35-40 years time copies of the earlier, larger diameter cylinders would be made with the potential for them to be fitted to later cars.

As this post reports, both 3/4" and 5/8" cylinders are being sold under GWC 1121
viewtopic.php?f=4&t=15689

Interestingly, when I measured mine, I came up with sizes 1/16 larger for both, but I'm sure that is my cack-handed measuring.

You definitely need to ensure that only the 5/8" (smaller) versions are fitted to dual circuit systems as if you fit 3/4" versions, you could suffer dire consequences if the front circuit fails as you are effectively back to a single circuit system with the master unable to push enough fluid to fill two larger diameter rear cylinders!

I presume you need to ring any potential supplier and ensure that the GWC1121 they have for sale is the 5/8" (smaller) version if you are fitting to a later car.

Geoff

[Yellow Banana]

Geoff, my Sprint is a Feb '75 production with single line brakes. A few years back I replaced a leaking left rear cylinder which has let go again. On removal I see it is a 3/4" bore (it was not a genuine Girling/Lockheed part and the manufacturer is unclear). I am about to purchase 2x NOS Girling 5/8" bore cylinders - reportedly with newer seals fitted - and plan to replace the opposite side as well - which is not currently leaking. Question is: Is the 5/8" bore
going to work OK?

[Yellow Banana]

Here are two pics of the cylinder to be replaced:

[Yellow Banana]

The 2nd pic above is vague - here is a clearer pic:

[Carledo]

Geoff, my Sprint is a Feb '75 production with single line brakes. A few years back I replaced a leaking left rear cylinder which has let go again. On removal I see it is a 3/4" bore (it was not a genuine Girling/Lockheed part and the manufacturer is unclear). I am about to purchase 2x NOS Girling 5/8" bore cylinders - reportedly with newer seals fitted - and plan to replace the opposite side as well - which is not currently leaking. Question is: Is the 5/8" bore
going to work OK?

The problem is, they all LOOK the same! The only way you can tell the difference is by measuring the bore. The reason for the change is that a dual circuit master has 2 travel gaps on the 2 concentric pistons, making for a longer pedal. Since it would be folly beyond even Triumph's capacity to reduce the front caliper pistons to compensate, the only leeway is in the rear cylinders.

The same thing applies if you have the "Trackerjack" vented disc conversion, the bigger 54mm pistons of the Ford calipers (stock is 48mm) make for a longer pedal, fitting the smaller dual circuit rear cylinders helps to compensate for this. Of course, if you have dual circuit AND Trackerjacks like I do, you just have to live with a slightly longer pedal.

In terms of brake efficiency, you are unlikely to notice any difference using the 5/8" cylinders. The pedal bite point may be a touch higher and that's IT!

Steve

[Yellow Banana]

Thanks Steve. I have measured the cylinder bore diameter and it is 3/4" but, as per the pics, it was an unknown aftermarket part. Not sure what I have on the other side yet. Think I'm going to get a pair of the 5/8" wheel cylinders and replace them both. Makes sense I suppose as I have only to bleed the system once.