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MG MGB Technical - Water has found its way in to my GT!

I have an MGB GT 1977. I got in it this morning to find a nice puddle in the passenger footwell. Didn't have much time but at a guess it may be coming through the bottom of the windscreen rubber.

The water is dripping down under the dash, but its dry on top of the dash itself.

Windsecreen rubber does look brittle and old, but am I missing any other common water entry point that should be checked?

If it is the rubber then whats the best way to replace it?

Thanks in advance

Graham
G Lewis

Is the drain tube for the vent clear of debri? How are the seals around the wiper boxes?
Kimberly

Before replacing the windscreen rubber...

Open the bonnet, and look at the corner of the
engine compartment where the gutter of the
fender (wing) meets the cowl and firewall.

The factory sealed the split (where the wing and
cowl meet) with a bit of putty. This putty eventually
dries out and become brittle and often cracks or
flakes away. Then water finds it's way past and
dribbles inside, near the wiper motor (behind the
dash).

I'll bet that ee-sealing this split with a spot of
silicone caulk will go a long way to stop your
dribbles.
Daniel Wong

Thanks for the replies, I'll check these first.

Kimberley - Where is the drain tube? is it easy to locate? Can't look at the moment, stuck in work.

Cheers

Graham
G Lewis

Graham

Also check your wipers and winshield washer nossle. I found I was getting water in there. It can run down defroster hose or a cable and be a bit harder to identify.

If this is a larger quantity, I would look to the vent box being plugged
Bruce Cunha

Yes it was a flood! Do you mean the vent at the back of the bonnet with the chrome trim?

G Lewis

Graham,
The vent in front of the windscreen is the intake for the heater. Obviously rain is going to go in there and a drain was provided to take this away. The drain exits up beside the right-hand side of the gearbox and terminates in a bulb thingy that is meant to prevent fumes entering the heater. This bulb (known as Tom's knob) gets blocked with leaves and other debris over the years. When it's blocked the rain empties out through the heater into the footwell.

On a '77 car you should be able to rod it out from above with a piece of flexible curtain wire. The chrome grille just prises off - use a flat blade screwdriver and rag to prevent damage to the paint. Looking down the vent you should be able to see the drain in the RH bottom corner.

However, you say the rain is dripping under the dash, which makes me think it isn't coming from the heater outlet on the tunnel side. So another point to check is where the wiper spindles go through the body. Flimsy rubber washers seal these and they can also let water in.

Mike
Mike Howlett

Shouldn't need to prise off the chrome grill unless you have a leaf guard mesh installed. Have a look at http://www.mgb-stuff.org.uk/wn_heaterframe.htm and click on 'Air box' for pictures and description of how to locate the vent. Paradoxically, when you have located it and rodded it through, and dirty gunge lies on the floor underneath, flush it through by pouring clean water in through the grille.
Paul Hunt 2

Great, thanks everyone. I'll get working at the weekend. Seems like the drain could be the problem as it does not happen in normal short rain showers, just long heavy ones like we had last night.

I guess its got just enough flow to drain the slow build up of water.

Nice web site Paul.

Thanks again

Graham
G Lewis

Count yourself lucky. It always pours out over the driver's side on mine and I get a wet left foot as soon as I go round a corner. Of course, by the time I have got home, I have forgotten about it and it never gets sorted out.
B D Hird

B D Hird - See you are local, I have moved to berks now, Intersested in any meets, do you attend any?

Its the love for the car, my wife just does not get it!?!

Graham
G Lewis

Graham

Here are some pics that might help

http://www.mg-bgt.co.uk/mesh.html
2nd pic shows the drain hole

http://www.angry-bear.co.uk/s/mg-bgt.co.uk/image%20respository/MGBGT%20017.jpg
shows the drain tube (left hand side of the pic)

Good Luck
Steve
Steve99

Tom's Knob!

Now there is a trivial fact you will not learn anywhere else.

Bruce Cunha

Tom's knob is a bit that isn't available any more,
but a midget 1275 top hose is a perfect fit and shouldn't block up.
K Harris

Well I had a fiddle with toms knob oh err and it was blocked and has sorted the flood problem.

However I still have a trickle during rain. After feeling around under the dash there seems to be damp rust at the bottom of the screen corner. There is no rust on the outside though.

Is it worth trying to seal around the screens rubber seal with a sealant? Or just better to relace it?

Thanks for all the help so far.

Graham
G Lewis

I wonder if you have corrosion of the bottom corners of the windscreen frame. It's not at all uncommon on the GT. The lip of metal that the rubber is held on rusts away in the corners. There is no cure except to remove the screen and get welding. So it is probably worth trying some windscreen sealer for the time being. It will be no good sealing between the rubber and the glass. You need to seal between the rubber and the car body, extending up an inch or two above the corner. Lift up the edge of the rubber and try to inject sealant in the gap. That's what I would try.

Mike
Mike Howlett

Mike, what sort of sealant should I use?

Cheers Graham
G Lewis

Probably a bit late now but I had a similar problem once that I eventually traced to a leaking heater matrix.
Simon Jansen

Graham

If you do have rust in the lower corner(s) and are not ready to pull the windshield and have the metal replaced I would suggest carefully wetting the rusted surfaces that you can get to with a phosphoric acid based rust treatment. This should greatly slow the corrosion in that area. You might want to consider also "painting" these surfaces with a paint such as POR-15 that "encapsulates" the rust to slow the rust process even more.

HTH

Larry
Larry Hallanger

Simon, I don't think its anything like that as I only get a trickle in prolonged rain fall. In small showers and dry weather its all dry.



Larry, I'll give that a go.

Anyone got any suggestions for a good sealant to use under the screen rubber?

Cheers

Graham
G Lewis

Try one of the bitumen based ones, you can buy a big tube of bitumen roof and gutter sealant from a DIY shop.

When you come to repair it, it will come off with petrol.

Don't use a silicon bath type sealer, these are difficult to remove, and are impossible to paint over.
M Layton

Use a proper windscreen sealant. It comes in a syringe that goes in a standard caulking gun. It's black and never goes completely hard. I think you could get something suitable from www.frost.co.uk

You might be able to buy it from a local windscreen fitting place.

Mike
Mike Howlett

This thread was discussed between 18/08/2006 and 23/08/2006

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