Sprint LSV

[marshman]

Went for a run out yesterday to meet up with a few other owners here in the South East. On the way back had the rear wheels lock .. twice. First time a blind person pulled out in front of me (assume they were blind as the looked right at me and still pulled out), didn't have to brake really hard, but harder than normal and almost immediately the rear end locked up. Thought it was a one off as not happened before, maybe have been some oil/diesel on the road (insert your own rational thought/excuse here!). But then a a good few miles further on a young scrote in a black BMW thought he didn't need to look both ways before pulling out, that required a much more rapid reduction in forward momentum, again the rears locked instantly and this time the back end made moves to get in front, but still managed to stop in time and stay on my side of the road. Driven a good few thousand miles in the car and never had this before, the roads were dry and not at all greasy, so no excuse for the premature lockup - same tyres all round.

Brakes were all fine at the last MoT in Feb, all nice and even with good effort, handbrake as well, so I am assuming the LSV is not doing it's job and the oversized rear drums are putting in their maximum effort all the time.

Before I dive undo the car to investigate further a question (or 2):

How do you test the LSV? and if faulty/seized/knackered what do you do about it?

A quick scan of the forum indicates that Hens teeth are more readily available than a new LSV so can the old one be revived/reconditioned/repaired? if not what are the alternatives.

Not interested in changing the brakes from the standard setup - they have been absolutely fine up until now, just want to fix what's wrong.

[Mad Mart]

Yes, they can be repaired. The club sells seals kits. I can strip & rebuild it if needed.

[marshman]

Yes, they can be repaired. The club sells seals kits. I can strip & rebuild it if needed.

Thanks, good to know. Will get a seal kit and get it sorted ASAP.

[GrahamFountain]

the rears locked instantly and this time the back end made moves to get in front

Well that appears to conclusively prove Steve's point that the std rear brakes on a Sprint are more than adequate, seriously so without the LSV.

And that gets even more the case when you upgrade the front brakes, so there's potentially less weight on the back wheels at the limit of braking.

Graham

[Carledo]

the rears locked instantly and this time the back end made moves to get in front

Well that appears to conclusively prove Steve's point that the std rear brakes on a Sprint are more than adequate, seriously so without the LSV.

And that gets even more the case when you upgrade the front brakes, so there's potentially less weight on the back wheels at the limit of braking.

Graham

Also my point about a Dolomite's propensity to try and change ends under these conditions, which I firmly believe is due to the design and layout of the rear brake hard lines.

My dislike for the LSV is based on this situation where there they have a habit of seizing solid (and indeed BEING seized for years at a time) without anyone noticing and only ambushing you when you need them to work most, IE under emergency stop conditions. This applies also to the hardline design, hydraulic theory only breaks down at the limit, again, when you need it most to work right!

I make no bones about the fact that EVERY LSV i've had in my possesion or on a car in my custody has been seized solid. I currently have more than 10 in my possesion in this state and will probably end up with more. As I either fit TJ conversions that make them redundant or use the Vauxhall pressure limiter valve that DOES work for more than a week at a time!

Back in the bad old days, an MOT would show it up, then, it was obligatory to have an assistant or the owner in the car to wiggle the steering and press the brake whilst the tester looked and felt things. I'm not aware of any change in the rules that stopped this practise, but none of the testers I know have an assistant available any more during tests, so it doesn't get noticed anymore! Even the brake testing rollers won't condemn the LSV as at normal operating ride height (where the LSV seizes and where the rollers test) there is still plenty of fluid getting to the rear brakes and they give a good reading.

I don't see a solution to keeping the LSV AND standard front brakes that doesn't involve overhauling the LSV annually at the very least. Especially on a low mileage car, as most are these days, the thing doesn't move around far enough in service to keep it free and it seizes up, worse still there are absolutely NO outward signs that this has happened. Until it BITES you! Even checking it for movement takes 2 people, one to press the pedal and one to watch the effect.

Alun and I have made enquiries regarding the possibility of sleeving the LSV cylinder in stainless, but the design, with the big nut screwed into the sleeve, precludes this, it just ain't possible without a total redesign of the casting itself. I'm even making enquiries myself, about a new casting, but progress is glacially slow. Although, to be fair, i'm not pursuing it that hard, as I have workarounds that are cheaper and easier than making a new casting!

Steve

[new to this]

Steve

Do you have a picture of the Vauxhall pressure limiter valve ? and how have you mounted them ?

Dave

[Carledo]

Steve

Do you have a picture of the Vauxhall pressure limiter valve ? and how have you mounted them ?

Dave

Dave, I'll take a pic or two and post them. On my dual circuit cars I mount it in the gap in the front to rear pipe caused by the deletion of the PDWA on the bulkhead. But it's an inline fit and small enough (2.5" long and 1" in diameter) to go almost anywhere in the front to rear pipe. The only snag (if it is one) is that it runs on metric unions, so will need bespoke pipes to fit it! You can get them on ebay for less than £30 last time I looked.

Steve

[GrahamFountain]

Is there any possibility to fit the TR7's automatic brake balance thingamajig? That is meant to limit the back brakes to only starting to bite after the front brake calipers have fully clenched. I think it needs dual circuit brakes, though.

How successfully that reduces the tendency for the back wheels to lock first on a dry, clean road might be questionable, but I've never had that happen in a TR7, even with the big Princess four-pots on the front, keeping the std., 5-speed rear pistons, and with wider tires; all of which should add to the transferring to the front under braking, and the rear wheels tending to lock first.

Of course, there is the simple option of only ever doing emergency braking on wet and or dirty roads, which is the preferred one in Lancashire. That will ensure the front wheels will lock before the weight is transferred off the back wheels.

Or what about always having two biggies in the back to move the CoG backwards - they have to be strapped in though.

Or then there's cadence braking, if it's not too much like the rhythm method.

Graham

[matt of the vivas]

Next time someone is advised to remove the LSV on a Sprint axled Dolomite as "it's not needed and it'll pass the MoT without one anyway" they need to read this thread.
It's needed, it's dangerous without, and yes they can be repaired as suggested above.
Suggestions about it being caused by the layout of the rear brake lines rather than the valve are ludicrous.
Matt.

[Carledo]

Next time someone is advised to remove the LSV on a Sprint axled Dolomite as "it's not needed and it'll pass the MoT without one anyway" they need to read this thread.
It's needed, it's dangerous without, and yes they can be repaired as suggested above.
Suggestions about it being caused by the layout of the rear brake lines rather than the valve are ludicrous.
Matt.

I've never tried to suggest that the LSV or some reasonable facsimile is not needed on a standard Sprint (or any Dolomite running a Sprint axle) It most certainly DOES and I have the brown trousers to prove it. The TJ kit bypasses the need, but then the car isn't standard any more.

It's a sad fact that the way the MOT is MOSTLY conducted these days, a seized LSV is likely to slip through, a seized solid one will give excellent readings on the rollers. It SHOULDN'T pass with a seized one, or a deleted one, but chances are, it will, unless you are faced with a tester like yourself who knows a Sprint from a pile of rocks!

I never at any time suggested that the rear brakes prematurely locking is down to the pipe layout, please READ my post again! I hold the pipe layout responsible for the car trying, sometimes successfully, to change ends during an emergency stop scenario. I have known this happen, even on a 1500 Dolomite, which doesn't HAVE an LSV OR overpowered rear brakes. What it did have, was 1 piston seized in each front caliper, drastically reducing the front brake effort. Oddly enough, that car had a fresh ticket on it too!

I don't mind you disagreeing with me Matt, everyone is entitled to their opinion, but I don't like being told i'm talking rubbish when YOU'VE misread what i've written!

Steve

[Magenta Auto Sprint]

Does anyone have a part number for the Hyundai LSV? I have not come across any for sale on Ebay or a Google search.

Malcolm

[new to this]

This is my setup

[Ralph]

Excuse my ignorance here, but just been reading through this thread and as I understand it an LSV allows more pressure to the rear brakes when the car is loaded (4 people and luggage), and is usually connected to the rear axle mechanically. Same system as was used on many vans in the old days, nowadays superceded by Anti Lock braking systems.
Replacing that with an in line valve such as the Vauxhall item is surely just a pressure reducing valve which would only allow the same limited pressure through regardless of load being carried.
All of which begs the question, why fit bigger rear brakes in the first place if you then have to add other devices to limit their effectiveness?

Just thinking out loud,
Ralph

[Carledo]

Excuse my ignorance here, but just been reading through this thread and as I understand it an LSV allows more pressure to the rear brakes when the car is loaded (4 people and luggage), and is usually connected to the rear axle mechanically. Same system as was used on many vans in the old days, nowadays superceded by Anti Lock braking systems.
Replacing that with an in line valve such as the Vauxhall item is surely just a pressure reducing valve which would only allow the same limited pressure through regardless of load being carried.
All of which begs the question, why fit bigger rear brakes in the first place if you then have to add other devices to limit their effectiveness?

Just thinking out loud,
Ralph

The LSV lets more fluid/pressure through when the car is loaded, but also less when the back end is unloaded by heavy braking/nosediving. If the LSV was fit for purpose and worked reliably and over a sensible time period, I'd have no quarrel with it at all! Unfortunately it doesn't!

The Vauxhall pressure limiting valve is, frankly, a pale shadow of the LSV, but it's cheap, easily available, simple to fit, works indefinitely and solves the problem of premature rear lockup. That's why I use it!

The Sprint, being an afterthought itself, is even more of a "parts bin special" than the rest of the range. The FACTORY fitted rear brakes that were too large for the car, then were forced to fit the LSV to make it work. Urban legend has it that the axle AND the brakes were robbed from the TR4 wholesale and that's why the imbalance (the TR4 has bigger wheels and therefore much bigger front discs than will fit a Sprint)

I don't believe the urban legend for several good and sufficient reasons, but that's another story!

Steve

[GrahamFountain]

I've never tried to suggest that the LSV or some reasonable facsimile is not needed on a standard Sprint (or any Dolomite running a Sprint axle) It most certainly DOES and I have the brown trousers to prove it. The TJ kit bypasses the need, but then the car isn't standard any more.

I get what you mean that increasing the relative effort of the front brakes is, in a sense, the same as reducing the effort from the back and will make it less likely that the rear wheels will lock first.

However, there are a couple of other issues:

Firstly, if the increased effort from the front brakes allows for more deceleration from the greater overall braking effort, that has the reverse effect, i.e. it tends to increase the likelihood that the rear wheels will lock first. Or at least, it tends to cancel the effect of moving the brake balance from bigger front brakes. That's because, at a higher deceleration, there's a greater transfer of weight off the back wheels onto the front, and (through Amonton's 1st law of friction) the increased downforce on the front wheels increases the brake force needed to make them lock, but reduces the brake force needed to make the rear wheels lock. And that double effect can exceed the effect of changing the brake balance; especially if the full potential of the improved front brakes can be turned into greater deceleration.

The other issue is that the LSV also compensates for any change in the height of the centre of gravity of the car and load. That matters because the higher off the road the CoG is, the greater the transfer of weight from the front to the back under braking, because the weight of the car acts through that CoG and, with that being higher up, has more leverage. Hence, raising the CoG increases the tendency for the back wheels to lock in the same way that moving it backwards reduces it. That means the LSV limits the tendency for the back wheels to lock over a large range of circumstances; where upgrading the front brakes is a simple one for all fix.

But, given the point about how unreliable the LSV is, how does the Vauxhall pressure reducing valve work?

I understand the TR7's (and SD1's) brake bias valve, which does much more than just reducing the pressure to the back wheels, and see how that should stop the back wheels locking first in an extreme braking event, more or less whatever you did to grip, front brakes, and CoG. They are a bit expensive at £150 or so new. But, because it's self-contained, and does not connect to the suspension, just working off fluid flows, it should be a lot more reliable than the Dolomite's LSV.

Graham