Dolomite 1500 wheel cylinder types.

[GlenM]

I need to replace the wheel cylinders on my 1978 1500HL. Looking at wheel cylinders online I noticed that there are single and tandem system types listed. What is the difference between the two?

I want to convert it to tandem brakes eventually anyway, so it might make sense to do it now with the correct cylinders.

Glen.

[Carledo]

The difference is in the piston diameter, I think the dual circuit cylinder is a slightly smaller bore. But the difference on the car is marginal, you may notice the pedal is a tad firmer or less travel with dual circuit cylinders on a single circuit car. Or the difference may be SO slight, you won't notice at all!

Steve

PS I'm just about to buy some smaller bore 1850 rear cylinders for my Sprint, to help compensate for the bigger pistons on my TJ conversion calipers! (already have a tandem master which helps too!)

[cliftyhanger]

The difference is in the piston diameter, I think the dual circuit cylinder is a slightly smaller bore. But the difference on the car is marginal, you may notice the pedal is a tad firmer or less travel with dual circuit cylinders on a single circuit car. Or the difference may be SO slight, you won't notice at all!

Steve

PS I'm just about to buy some smaller bore 1850 rear cylinders for my Sprint, to help compensate for the bigger pistons on my TJ conversion calipers! (already have a tandem master which helps too!)

Steve, surely you need larger bore if you want more braking force? (force=pressure x area, and bigger calipers use bigger pistons etc...)

[soe8m]

Smaller diameter rear to have less pedal travel caused by bigger front calipers.

Jeroen

[GlenM]

The difference is in the piston diameter, I think the dual circuit cylinder is a slightly smaller bore. But the difference on the car is marginal, you may notice the pedal is a tad firmer or less travel with dual circuit cylinders on a single circuit car. Or the difference may be SO slight, you won't notice at all!

Steve

PS I'm just about to buy some smaller bore 1850 rear cylinders for my Sprint, to help compensate for the bigger pistons on my TJ conversion calipers! (already have a tandem master which helps too!)

Thanks Steve. I am probably going to convert it to a tandem system with a slightly larger bore master cylinder anyway, so I guess I might as well go for the smaller bore wheel cylinders. Ultimately, when the engine is changed, it will also have TJ front brakes and a Sprint axle, so I might also need to change to the 1850 cylinders.

[gmsclassics]

Not sure about other models but on the Sprint I always understood the change to a smaller diameter rear cylinder with the introduction of the tandem brake master was to ensure in case of a front brake fluid failure/loss of fluid, there was enough fluid in the master to operate the rear brakes – smaller diameter rear cylinders being required to achieve this. Obviously if using a non standard master, that situation may change, but perhaps best to err on the side of caution?
Geoff

[Carledo]

The difference is in the piston diameter, I think the dual circuit cylinder is a slightly smaller bore. But the difference on the car is marginal, you may notice the pedal is a tad firmer or less travel with dual circuit cylinders on a single circuit car. Or the difference may be SO slight, you won't notice at all!

Steve

PS I'm just about to buy some smaller bore 1850 rear cylinders for my Sprint, to help compensate for the bigger pistons on my TJ conversion calipers! (already have a tandem master which helps too!)

Steve, surely you need larger bore if you want more braking force? (force=pressure x area, and bigger calipers use bigger pistons etc...)

What Jeroen said!!!^^^^^

Steve

[Carledo]

Not sure about other models but on the Sprint I always understood the change to a smaller diameter rear cylinder with the introduction of the tandem brake master was to ensure in case of a front brake fluid failure/loss of fluid, there was enough fluid in the master to operate the rear brakes – smaller diameter rear cylinders being required to achieve this. Obviously if using a non standard master, that situation may change, but perhaps best to err on the side of caution?
Geoff

I think this may be urban myth! The divider in the master would have been designed to be high enough to maintain sufficient fluid to operate the rear brakes in the complete absence of fluid in the front circuit, with a considerable safety margin as well, ie to allow for extra travel in the cylinders from failure of the self adjusters to do their job (as is invariably the case) else there is no point in having a tandem system!

I'm pretty sure the smaller cylinders on the tandem brakes were to allow for the extra pedal travel inherent in the tandem cylinder from taking up 2 lots of piston free play instead of 1!

Steve

[GlenM]

So, with a bit of free time this morning and, finally, a break in the weather I thought that I would fit the new tandem wheel cylinders and get the car mobile again.

Unfortunately, bore size aside, they don't appear to be the right type. The casting is totally wrong, where the trailing shoe fits is totally different and the fork where the handbrake lever pivot fits is too wide.





The ones on the car look more like 1300 wheel cylinders, from what I can see on the internet.

I am now worried that the shoes are wrong, so going to go and check those.

[Carledo]

The wheel cylinders you have are the 1300 type for manual adjustment, the ones you have bought are correct for automatic adjustment. If your car has manual adjustment brakes, NOTHING from the self adjuster style will fit, the differences go right back to the backplate and out to the drum.

I would be inclined to think that at some point, someone has swapped a much earlier (or 1300) axle into your car, a 78 1500HL SHOULD have self adjusting brakes, no ifs buts or maybes!

Steve

[GlenM]

Thanks Steve.

I checked the shoes and they are indeed different, so I was starting to come to the same conclusion about it being a 1300 axle.

It's very odd as the car has only done 42,000 miles and was stored away for 25 years, up until a couple of years ago. It certainly doesn't look as if anything has been disturbed under there recently, so it must have been changed many years ago. Or maybe they fitted the wrong one at the factory.

Not sure whether to stick with the 1300 axle, which will be quite low geared, or change it for a 1500 one. Ultimately it is going to be swapped for a Sprint one anyway.

[Carledo]

Honestly, nothing would surprise me! I once (around 74) found a brand new Marina with a drum brake on one front wheel and a disc on the other!

So anything is possible, factory error, customer spec, someone may have swapped the case and backplates just to get rid of the unreliable self adjusters! The 1500 diff will bolt into a 1300 case and accept the 1300 halfshafts no trouble at all. Someone sometime could have done just that, maybe to get over a cracked axle case or broken ears or even accident damage. Who knows after all this time? I would have thought it unlikely that anyone would have voluntarily put a 4.11 1300 diff in a 1500 car, it would be screaming it's poor little big ends out at 70!

Sprint diff going in? Tell me more! Something tasty going in up front?

Steve

[GlenM]

Steve,

The braking on the Marina must have been horrific with one drum and one disc! I remember my Grandad's Volvo dealership buying a new Marina van in 1979, it went back about 3 times to have the rear axle changed because they were so badly assembled that they sounded worn out. He also knew a guy who ran an engineering shop that manufactured camshafts, they supplied BL and Volvo. Volvo would quality check the camshafts and rejected quite a high percentage, BL just took everything!

There is no sign of any major accident damage on the car. I am hoping that maybe its the right diff and 1300 brakes, so I have ordered the 1300 wheel cylinders and shoes. I only test drove the car a couple of miles round some lanes when I bought it, so I have no idea how it's geared. Good to know that I could pull the half-shafts and fit a 1500 diff, if I need to.

Yes, Sprint axle going in for a Nissan turbo conversion eventually, either CA18, or SR20. Got to build a garage first though, so won't be for a while.

https://forum.triumphdolomite.co.uk/vie ... 19&t=35575

[GlenM]

Honestly, nothing would surprise me! I once (around 74) found a brand new Marina with a drum brake on one front wheel and a disc on the other!

So anything is possible, factory error, customer spec, someone may have swapped the case and backplates just to get rid of the unreliable self adjusters! The 1500 diff will bolt into a 1300 case and accept the 1300 halfshafts no trouble at all. Someone sometime could have done just that, maybe to get over a cracked axle case or broken ears or even accident damage. Who knows after all this time? I would have thought it unlikely that anyone would have voluntarily put a 4.11 1300 diff in a 1500 car, it would be screaming it's poor little big ends out at 70!

Sprint diff going in? Tell me more! Something tasty going in up front?

Steve

I managed to get the brakes back together yesterday and took the car for a run this evening. At an indicated 50 MPH it is doing 3000 RPM. Is that about right for a 1500 axle?

[Richard the old one]

Edition 6 of the Official Triumph dolomite 1500HL handbook gives the 10mph engine revs as being 594 for the 3.89:1 rear axle and 554 for the later 3.63:1 axle. These figures are for a car without overdrive with OD they drop to 473 and 441. So if your car is non O/D you have an early 1500 axle fitted as 594 x 5 = 2970.