Thread: ser 2a brake upgrade

So the optimum braking system, without moving to discs, would be the wide TLS 11" drums on the front, and reversed TLS 11" drums - wide or narrow - on the rear, mated to either a dual circuit + PDWS or single circuit (depending on personal preference) master cylinder on a suitable (Series III or 6 cylinder IIA?) vacuum boosted pedal box.......?

Originally Posted by Warb

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Is the booster type pedal box on the 6 cylinder 109" 2A the same as the Series 3 dual circuit version?
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Yes. But I am pretty certain the single circuit system will fit without body modifications - it is the length of the dual circuit master cylinder plus the booster that needs these.

Copper pipe is not approved for brake pipes because of the ease with which it work hardens and breaks, especially on corrugated roads. As Diana points out, there is copper alloy tubing formulated to avoid this and specified for brake use that is OK.

As to fitting rear brakes with two trailing shoes, I am not too sure how necessary this is, certainly with an 88. I have never found it a problem with my 2a 109 with unboosted brakes, so I'm not too sure why it would be needed with boosted brakes on an 88!

John

Originally Posted by JDNSW

As to fitting rear brakes with two trailing shoes, I am not too sure how necessary this is, certainly with an 88. I have never found it a problem with my 2a 109 with unboosted brakes, so I'm not too sure why it would be needed with boosted brakes on an 88!

Probably not needed at all! However I seem to have acquired a large number of Land Rovers, some of which are suitable only as part donors. Given that I have the backplates available, and also intend to fit all new moving parts, the increase in cost and effort between keeping the standard brakes and upgrading them is really quite minimal. On that basis alone, given that this is not a "restoration to factory specification" project, it seems like an easy decision!

Originally Posted by Warb

Probably not needed at all! However I seem to have acquired a large number of Land Rovers, some of which are suitable only as part donors. Given that I have the backplates available, and also intend to fit all new moving parts, the increase in cost and effort between keeping the standard brakes and upgrading them is really quite minimal. On that basis alone, given that this is not a "restoration to factory specification" project, it seems like an easy decision!

OK, but two leading shoes on the front and two trailing on the back means that effectively you only have two wheel brakes when going forward - certainly it is the front two, which do most of the braking going forward, but are you sure that you really want to be in that situation? Bearing in mind that in a swb virtually all the load in the back is on the back wheels only.

John

John

I think you will find that the boosted pedal box requires the modified front mudguards, irrespective of whether it is single or dual circuit.

Diana

Originally Posted by Lotz-A-Landies

John

I think you will find that the boosted pedal box requires the modified front mudguards, irrespective of whether it is single or dual circuit.

Diana

You may well be right - I must admit I have never actually seen one, believe it or not! But there does not seem to be anything about it being needed in the optional equipment parts book.

For those not familiar with the setup, the unboosted pedal box is the same as the clutch one, with the pedal pivot below the master cylinder and the m/c back towards the driver. The boosted pedal box has the pivot above the m/c, and the m/c pointing forward. Add the thickness of the booster to the length of the m/c, and at least with the dual circuit one, you run into sheet metal! Series 3 has a modified inner guard which has a bend in it to provide room, where the 2/2a has a flat sheet (with a bent over edge to add stiffness).

John

Originally Posted by JDNSW

OK, but two leading shoes on the front and two trailing on the back means that effectively you only have two wheel brakes when going forward - certainly it is the front two, which do most of the braking going forward, but are you sure that you really want to be in that situation? Bearing in mind that in a swb virtually all the load in the back is on the back wheels only.

A valid point. From a braking perspective, the "leading shoe" generates a self servo effect which acts to push the shoe against the drum, where a trailing shoe is pushed away from the drum. So in the original brakes there was a 10" drum with a single leading shoe and only "pedal effort" fluid pressure. This is being replaced with no leading shoes (going forwards), but on an 11" drum and with boosted fluid pressure - though the fluid pressure is the same for all wheels - so the rear braking is still reduced in comparison to the front, but by how much?

The other factor is that the 88" has minimal weight on the rear axle at rest - two of us can scoot the rear of a 88" sideways relatively easily, the front is another matter! Even with a load the weight is transferred to the front axle under braking, so the rear brakes are possibly not adding much. The harder the braking, the more the weight transfer unloads the rear axle, and the more likely the rear brakes are to lock up.

If the front brakes are upgraded to allow harder braking, and therefore more weight transfer to the front, and there is no rear brake limiter to offset the weight transfer effect, is a slight reduction in rear braking necessarily a bad thing?

Another point of interest is that moving from a single slave cylinder (SLS) to two slave cylinders (TLS) means that more fluid is required to apply the brakes. With a single circuit system that means more pedal travel to move 8 slave cylinders instead of 6. With dual circuits, the SIII 88" master cylinder has equally sized front and rear pistons (all wheels are single slave cylinder?), but the 109" has a larger "front" piston to move more fluid to the twin slave cylinders on the front wheels. So potentially with a 109" dual circuit master cylinder the extra pedal travel will be further increased?

More to think about! Lucky I'm still sandblasting the chassis and not yet ready to fit the brakes!

Originally Posted by Warb

A valid point. From a braking perspective, the "leading shoe" generates a self servo effect which acts to push the shoe against the drum, where a trailing shoe is pushed away from the drum. So in the original brakes there was a 10" drum with a single leading shoe and only "pedal effort" fluid pressure. This is being replaced with no leading shoes (going forwards), but on an 11" drum and with boosted fluid pressure - though the fluid pressure is the same for all wheels - so the rear braking is still reduced in comparison to the front, but by how much?

There is very little braking effort resulting from a trailing shoe. In the one leading/one trailing brake, almost all the braking effort is from the leading shoe.

The other factor is that the 88" has minimal weight on the rear axle at rest - two of us can scoot the rear of a 88" sideways relatively easily, the front is another matter! Even with a load the weight is transferred to the front axle under braking, so the rear brakes are possibly not adding much. The harder the braking, the more the weight transfer unloads the rear axle, and the more likely the rear brakes are to lock up.

Front braking will be limited by tyre adhesion. Once the front tyres break loose deceleration does not increase, so neither does weight transfer.

If the front brakes are upgraded to allow harder braking, and therefore more weight transfer to the front, and there is no rear brake limiter to offset the weight transfer effect, is a slight reduction in rear braking necessarily a bad thing?

Problem is, it is not a slight reduction. As you suggest, it is a good idea to not have the rear wheels lock before the front ones. This is arranged on the original 10" drums by having smaller diameter wheel cylinders on the back, and on the 11" brakes by having two leading at the front and one leading/one trailing at the back (with appropriate cylinder diameter). To further reduce this by having no leading shoes at the back will mean even less braking effort at the back.

Another point of interest is that moving from a single slave cylinder (SLS) to two slave cylinders (TLS) means that more fluid is required to apply the brakes. With a single circuit system that means more pedal travel to move 8 slave cylinders instead of 6. With dual circuits, the SIII 88" master cylinder has equally sized front and rear pistons (all wheels are single slave cylinder?), but the 109" has a larger "front" piston to move more fluid to the twin slave cylinders on the front wheels. So potentially with a 109" dual circuit master cylinder the extra pedal travel will be further increased?

More to think about! Lucky I'm still sandblasting the chassis and not yet ready to fit the brakes!

If you want two trailing shoes at the back, you will also have to change the master cylinder. For a dual circuit one, you will need the same diameter piston for both circuits, and for the single circuit, a larger than standard one to move the additional fluid. Avoiding this sort of design problem is a good reason for sticking to a standard setup - OK to put 109 brakes on an 88, but an entirely new design becomes a whole new ball game.

You need to think about what you mean by "improving" the brakes. There are three separate considerations:-

1. Pedal pressure. This is what most people think of.This depends on what proportion of the shoes are leading, the lining composition, the overall leverage (for this exercise, cylinder diameters) and the power assistance. Just fitting a booster to an 88 is a major improvement. Problem with increasing the leverage is that it increases pedal movement.

2. Resistance to fade. This depends mainly on drum surface area - 10" vs 11" and wide vs narrow.

3. Braking effectiveness. Once pedal pressure is light enough that the driver is not limited by this, it mainly depends on getting the appropriate proportion of braking between front and rear. Ideally the front should lock just before the rear. Without load proportioned braking this is virtually impossible, so cars such as the Series Landrover are invariably designed to be a bit underbraked on the back. Since most of the braking is required on the front, this is not as big a problem as it sounds, although it gets more so as disposable load becomes a bigger proportion of maximum load on any one axle.

There are other factors, but for this installation they are pretty much the same regardless of what you change.

Hope this helps,

John