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Dropping the propshaft out and rear brake cylinder


RichardS
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Our work on the new Mk3 1973 GT6 continues, as does my confusion.

I've been doing the brakes (they didn't seem very good!) and leaking diff oil seal today and have come across two issues which I've never encountered before so any help would be most appreciated.

Firstly, the prop shaft. It seemed like it would be a simple job to drop/remove the prop shaft to access the oil seal. However, two issues have arisen. 

The prop shaft is too wide in diameter to drop between the chassis rails. Presumably this means that the only way to remove it is to remove the body and lift it upwards. I have never know a car where the prop shaft cannot be dropped downwards. Is this normal for a GT6?

Our second thought was to pull the prop shaft apart at the splined joint and slide it out backwards. However, this doesn't work either as the sliding splines extend a couple of inches and it then locks suggesting that there is a snap ring or similar. We've not forced it as we can drop it out of the way enough to do the oil seal but should it simply slide apart.

Secondly, the rear brakes shoes are self adjusting and there is a groove in the self-sdjuster which the brake shoe locates in. However, the piston itself does not have a groove but it simple a smooth "button" which the shoe appears to slide off and damage the rubber dust cover. I've never seen non grooved brake pistons before so I'm wondering if there is something missing on my car .... or do I take the angle grinder and fashion a groove in the button?

Many thanks for any clues.

Richard

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pretty much all trailing shoes sit on the plain piston its held in place by  the return springs fitted on the back of the shoe   and the sprung /pins 

the prop i would have said does slide out from underside past the diff, i may be you exhaust it the snag 

do make sure the trailing shoe is not upside down 

Pete

 

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8 minutes ago, Pete Lewis said:

pretty much all trailing shoes sit on the plain piston its held in place by  the return springs fitted on the back of the shoe   and the sprung /pins 

the prop i would have said does slide out from underside past the diff, i may be you exhaust it the snag 

do make sure the trailing shoe is not upside down 

Pete

Thanks Pete

We've removed the exhaust system. It sounds as if the prop shaft is supposed to be wider than the the chassis rails which seems incredible but it is what it is but it does mean that we can't simply leave it hanging down out of the way.

Is there a snap ring on the splined joint as there's no chance of sliding it out under the diff if we can't slide the joint apart?

The brake shoes and the springs all seem to be in the right place but the middle locating spring is not sufficient to stop the top of the shoe sliding off the smooth button. The large spring between the two shoes at the top is not really exerting a force in the plane required to stop the shoe sliding off. In fact, it is probably making it more likely.

The only thing I can see which would stop the top of the shoe moving outwards would be the hooked end of the handbrake actuating arm which goes through the rectangular hole in the shoe but the hook sticks out through the hole by about a cm which allows sufficient space for the shoe to move outwards. If the actuating arm was a bit shorter it would be a perfect alternative to the usual grooved piston but it isn't.

I've stripped down and rebuilt brakes and removed prop shafts on dozens of cars over the last 50 years but it seems that Triumph certainly liked to plough their own furrow. 🙂

Richard

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The prop. should normally come out OK.  I can't remember if it just drops out or if unbolting from each end gives enough room to tilt/wiggle it so it can slide either back/forwards and down/out where the chassis rails spread further apart.

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Just now, johny said:

What about the tee pins and washers that retain the shoes? They should hold them against the backplate...

Worth noting I had some brand new hold-down springs and washers on one of my cars (no idea where they came from, I didn't buy them) and the springs were ridiculously weak. 

I had to dig around in my box of "stuff" to find some mucky old ones that worked perfectly

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1 minute ago, clive said:

Worth noting I had some brand new hold-down springs and washers on one of my cars (no idea where they came from, I didn't buy them) and the springs were ridiculously weak. 

I had to dig around in my box of "stuff" to find some mucky old ones that worked perfectly

I replaced the pedal return springs on a Herald this morning, and the new springs were so poor I put the old ones back on. Why do we put up with this?

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20 minutes ago, clive said:

Yes, prop pulls out from the diff end, and indeed the front flange will scrape along the top of the chassis. But it will come out.

I understand .... but the gearbox flange is still connected. It's the actual diameter of the propshaft which is wider than the gap between the frame rails. We could pull it out under the diff if the splined section would come apart but it doesn't appear to.

Richard

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25 minutes ago, johny said:

What about the tee pins and washers that retain the shoes? They should hold them against the backplate...

The springs are not that strong and are some way down the shoe so not exerting such a great force at the top end. 

I'll probably buy new ones anyway as I think I'll replace the slave cylinders as one of them was seized and I've had to refurb the piston. In the meantime, I think I'll try a spacer on the handbrake actuating arm as that will provide a positive end stop.

Richard

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10 minutes ago, RichardS said:

I understand .... but the gearbox flange is still connected. It's the actual diameter of the propshaft which is wider than the gap between the frame rails. We could pull it out under the diff if the splined section would come apart but it doesn't appear to.

Richard

The splined section does separate but access to it is limited so it's normal to undo the gearbox flange bolts and this might be best done from inside the car...

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12 minutes ago, RichardS said:

I understand .... but the gearbox flange is still connected. It's the actual diameter of the propshaft which is wider than the gap between the frame rails. We could pull it out under the diff if the splined section would come apart but it doesn't appear to.

Richard

The prop drops far enough to slide out under the diff.  But as mentioned you have to detach from the gearbox first.  It's bolted to the gearbox flange with 4 bolts and I reckon you'd need to remove the tunnel cover (and all that entails) to gain access.  There is a sliding splin joint in the propshaft and that is retained by a screw-on cap.  That is probably impossible to access in situ, and even if you could access it I'd strong advise trying to dismantle it that was as it needs to go back in exactly the same position and some (though by no means all) have ball bearings and spacers in there as well......

To keep the prop out of your working area, zip-tie it up to the handbrake linkage.

Self-adjusting brakes....... good luck.....

Nick

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4 minutes ago, Nick Jones said:

The prop drops far enough to slide out under the diff.  But as mentioned you have to detach from the gearbox first.  It's bolted to the gearbox flange with 4 bolts and I reckon you'd need to remove the tunnel cover (and all that entails) to gain access.  There is a sliding splin joint in the propshaft and that is retained by a screw-on cap.  That is probably impossible to access in situ, and even if you could access it I'd strong advise trying to dismantle it that was as it needs to go back in exactly the same position and some (though by no means all) have ball bearings and spacers in there as well......

To keep the prop out of your working area, zip-tie it up to the handbrake linkage.

Self-adjusting brakes....... good luck.....

Nick

Ah ... That explains why we can't slide the prop shaft apart. It's not a problem as you say, we can tie it out of the way.

I've just looked at Rimmers to see about ordering some new brake parts and there is something called an H-Tappet which I don't have fitted to either of my rear brakes. I wonder if this has anything to do with shoe location? I'll do some further online investigation.

Many thanks

Richard

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1 hour ago, RichardS said:

Ah ... That explains why we can't slide the prop shaft apart. It's not a problem as you say, we can tie it out of the way.

I've just looked at Rimmers to see about ordering some new brake parts and there is something called an H-Tappet which I don't have fitted to either of my rear brakes. I wonder if this has anything to do with shoe location? I'll do some further online investigation.

Many thanks

Richard

OK .... I've found a great photo on the internet and it is the H-shaped spacer / H-tappet which is completely missing from both my rear brakes. It fills that gap I mentioned between the the brake actuating arm and the shoe and so stops the shoe slipping off the piston. Another problem solved !

Many thanks to all.

Richard

IMG00018-20110626-1544.jpg

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and if the pins are poor i have in the past replaced with a 4mm setscrew and nyloc nut  just twiddle to get spring compression you want and so much easier to assemble than the push and twist idea.  its lasted years 

and yes that little H  blighter is often lost   519760   only used on the self adj shoes 

pete

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8 hours ago, Peter Truman said:

They are fitted to my dolly sprint had one missing so had to make one subsequently I’ve seen them on ebay

Neither my Mk2 Spit or Mk2 Vitesse have them never thought of them as a retro fit

 

53 minutes ago, Pete Lewis said:

and if the pins are poor i have in the past replaced with a 4mm setscrew and nyloc nut  just twiddle to get spring compression you want and so much easier to assemble than the push and twist idea.  its lasted years 

and yes that little H  blighter is often lost   519760   only used on the self adj shoes 

pete

 

A great idea to look on eBay and the 519760 H-Clips are indeed available but they are £12.50 for a pair plus £3.50 p & p whereas Rimmers charge £4.50 + VAT + p & p which seems seems better value, especially if I order the other brake parts at the same time. In the meantime, I will fashion something suitable from my bits box until the next time I have the wheels off ... which probably won't be very long. 🙂 

Richard

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12 hours ago, RichardS said:

Ah ... That explains why we can't slide the prop shaft apart. It's not a problem as you say, we can tie it out of the way.

The prop won't drop straight down; it will slide backwards into the wider space at the diff and then slide down below it at a sufficient angle to slide the entire thing out. It can only come out in one direction and be replaced the same way, upwards and forwards. I've found a good photo that will give you some idea of the dimensions.

s-l1000-2.jpg.d55eaff3f609d3d5281978bb6c8fa7e3.jpg

 

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55 minutes ago, Colin Lindsay said:

The prop won't drop straight down; it will slide backwards into the wider space at the diff and then slide down below it at a sufficient angle to slide the entire thing out. It can only come out in one direction and be replaced the same way, upwards and forwards. I've found a good photo that will give you some idea of the dimensions.

s-l1000-2.jpg.d55eaff3f609d3d5281978bb6c8fa7e3.jpg

 

That's very interesting, Colin. I wonder if there is any other chassis/propshaft combination where the prop shaft is wider than the chassis rail clearance? It's not something I have ever come across before and my first thought was that I have a non-standard propshaft. I'm delighted that I haven't as I could foresee problems with getting new UJs etc in the future. Thanks for posting.

Richard

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Just to add an interesting postscript to this thread, we attacked the diff oil seal this afternoon and I use the word attacked advisedly. It turned out to be composed of three layers of metal with an outer metal skin and an inner corrugated metal tensioner thing. Between the layers of metal were layers of leather. I therefore wonder if this was the original seal from 1973? If so, I'm not surprised that it was leaking rather a lot!

Richard

 

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8 minutes ago, johny said:

I'm surprised such a late diff has that early type of seal as I thought they would have gone over to lip seals by then! What's the serial number stamped length ways on the underside of the front casing?

+1

I would expect a late GT6 diff (probably any GT6 diff) would have a rubber lip seal. While you have access, as well as looking for the serial number, it would be interesting to check the final drive ratio and confirm it really is 3.89:1 as expected.

Nigel

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