Brakes on 90

[graham2306]

A mate of mine has recently bought a really nice 90.  It has a 300 tdi engine, discs all round and the rear axle is a Range Rover one (shocks at opposing angles).  The vehicle was built on a galvanised chassis and a has a 2" suspemnsion lift.

At the moment it is almost undriveable as it locks up the rear brakes long before the fronts, making it bloody dangerous.  It has new discs and pads all the way round and all the brakes work fine.  the master cyclinder is different to the one on mine and on a 110 we have looked at, it has 2 pipes out and is very long compared with mine which has 3 pipes out.

Other than that all the plumbing seems to be the same as mine.  What does the block on the chassis rail below the master cyclinder do? 

Any ideas what the problem might be anyone?

[V8MoneyPit]

Hi

The 'block' on the chassis rail is a pressure reducing valve for the rear.

Mine have a Disco disc brake rear axle, but standard brakes everywhere else. In the wet, mine can lock the rear first. I'm not sure if there is a different valve available for the disc rear axle.

[Axetamer]

Mine does the same locking the rears first even in the dry under heavy braking, mine was originally a 2.5 petrol with drums on the rear, but now is a 200tdi with a td5 defender rear axle converted some 10 years ago I am told, Like V8moneypit hinted at there is a different bias valve for discs all round, but I'm not sure of any part numbers, I have enquired about this down my local 4x4 specialist and it seems to be a bit of a minefield.....but like has been said bloody scary when you need to jump on the brakes!!

[V8MoneyPit]

We are in the automotive industry and have contacts at a major LR wholesale company so I'll do a bit of investigation next week and let you know what I find. I really should sort mine out anyway!

[graham2306]

Thanks guys.  We guessed it was some kind of restrictor valve and have since looked at several different vehicles, they all look the same, but I bet they aint the same inside.

[V8MoneyPit]

I've got my specialist on the case, but have done a bit of digging in the mean time. When discs were fitted to the rear of a 90 (LA930456 onwards) the bias valve changed to part number to NTC8836. This is pre ABS.

The disc/drum valve was NRC8215. But, apparently, this was hardtops only  :-k

So, there is a difference, but I can't say what it is!

The front brakes may have changed at the same time though and this would also affect the front/rear balance. I'm still running the solid discs on the front. I have read on another forum that someone fitted 110 calipers to the front which solved the problem.

I might try one of these NTC8836 valves, but they ain't cheap!

[ChrisW70]

I *think* the valve is the same across different set-ups, the way the valve is piped up does differ though.

If you have it, have a look at the diagram of the brake pipe set-up in Rave as this does show how the valve is connected with the different set-ups.

[V8MoneyPit]

The NTC8836 is visually different to the earlier one that I currently have fitted. It has a bleed screw on it and the ports are in different locations. Obviously, I can't tell if it operates differently though.

If it's like an early Mini one, it would not limit rear pressure under normal braking. But when the brakes are hit hard the piston would deflect further and restrict the outlet port.

[V8MoneyPit]

Just looked a bit more....

NTC8836 has 3 pipe ports on it. The older ones only have 2. How are the 3 ports plumbed?

But....
NRC8215, which appears to be the earlier one was not only fitted to drum rear 90's, but also to 90's fitted with vented front/solid rear discs from  LA930456 to LA939975. So, on this basis, it should also work fine with solid discs all round as long as the pistons in the front calipers are the same diameter and the pads are the same size..... I'll keep digging  :D

Update:
There doesn't appear to be a master cylinder change at the same VIN as rear disc introduction. Equally, the front caliper pistons and pads didn't change. The caliper part number changed because it had to be wider for vented discs, but the pad and piston areas seemed to remain the same.

This all suggests that the earlier NRC8215 valve should be fine.

I'm beginning to wonder if it is just faulty and the disc brake conversion just highlights this.

[graham2306]

Brilliant stuff, Keep going MoneyPit, the answer is there somewhere I hope.

Cheers Guys

[V8MoneyPit]

I'm going to see if I can track down a freebie used one to take apart. Then I will understand how it works and might be able to offer some more guidance....oh, and maybe solve my problem too  :lol:

[graham2306]

BTW the one with the 3 outputs seems to be plumbed, one to each front brake and then one to the rear which then splits at centre of the axle, that is whats on the 110 we looked at.  The one with the 2 outputs seems to be one to front that then splits and one to back that splits in middle of the axle.

[V8MoneyPit]

BTW the one with the 3 outputs seems to be plumbed, one to each front brake and then one to the rear which then splits at centre of the axle, that is whats on the 110 we looked at.  The one with the 2 outputs seems to be one to front that then splits and one to back that splits in middle of the axle.

The NRC8215 2 port one is simply for the rears. The pipe from the master cylinder goes to one port, then the other feeds out to the rear. The front brakes are fed directly from the master cylinder.

Where was the master cylinder pipework going on the 3 port one you saw? It must have a pressure feed from the master. IIRC, some 110's had a 4 way valve (PDWA).