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Exmo "updates" - Some Questions


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Hi all,

 

I've got an Exmo which has been sitting in the garage for far too long awaiting the completion of a K-Series engine transplant, and I'm now thinking about some finishing touches/improvements, given the experiences of others in the past.

 

1) Fix the front strut top mount issue with some plates and proper thrust bearings.

2) Think about retro-fitting the rear coil-over shocks to the rear... anyone know what specs the original 'optional' rear coil-overs were? Poundage, length, etc - is there an off-the-shelf option that fits the bill or is it a case of ring up someone and get a pair made up to spec?

3) As a knock-on effect from going K-series, the standard master cylinder had to come out to clear the TB's/air filter (no bad thing). After much searching I'm going to give OBP's pedal boxes a try with an adjustable bias on the brakes and twin master cylinders. Has anyone ever done this? If so did they find the normal M/C types of 0.625/0.7 ok with the standard Sierra vented discs/drums setup?

4) I suspect the standard diff might be a little tall given the increased rev range now available, if memory serves me rightly the diff to have was from a Sierra Estate (3.9?)- is that right? If I can find one... was it in anything else?

5) Bonnets - can you still get them? Lolocost don't seem to have it listed, or have I missed it... reason being some muppet decided to knock over a pile of tyres which landed on the bonnet and put a nice crease into it, so would be good to replace it if I can... but not essential, the old one just looks a bit tatty :(

 

Any thoughts/experiences much appreciated...

 

Cheers,

Dan

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Guest Dan_Beeston

Hi Dan,

 

I've just swapped to a twin Master cylinder pedal box and have had a bit of messing around to get a balance I am happy with.

 

I started with 0.625 rear & 0.75 front, but needed more stopping power in the front so swapped front brakes for Wilwood Powerlites and then changed the master cyl for a 0.7.

 

Plenty of stopping power now but still locking up the rears under very heavy braking (there is a lot of weight transfer from rear to front under heavy braking so it makes it progressivly easier to lock the rears) I'm going to re-fit the standard Seirra proportioning valve in the rear line as that worked really well at allowing decent power to the rear brakes under normal driving while still preventing the rears locking up when 'giving it death', as you would put it :)

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Hi Dan,

 

I've just swapped to a twin Master cylinder pedal box and have had a bit of messing around to get a balance I am happy with.

 

I started with 0.625 rear & 0.75 front, but needed more stopping power in the front so swapped front brakes for Wilwood Powerlites and then changed the master cyl for a 0.7.

 

Plenty of stopping power now but still locking up the rears under very heavy braking (there is a lot of weight transfer from rear to front under heavy braking so it makes it progressivly easier to lock the rears) I'm going to re-fit the standard Seirra proportioning valve in the rear line as that worked really well at allowing decent power to the rear brakes under normal driving while still preventing the rears locking up when 'giving it death', as you would put it :)

 

Now that's interesting. Ignoring your move to Wilwoods, you put the .75 on the front and the .625 on the rear, which is at odds with what most people suggest and does seem at first sight to be the wrong way round - but without knowing the slave cylinder sizes of the standard rear drums and Sierra sliding-pot fronts I can't say for sure. Did you ever try them the other way round (.625s on the front, .75's on the rear)? Was it better or worse?

 

I'm ok with the balance as it is when it was on the sierra master cylinder, my main concern is keeping reasonable pedal effort and not going too hard, but the balance for me seemed fine previously.

 

Does anyone know the standard Sierra's master cylinder diameters front/rear? Anyone know the piston diameters at the caliper/slave cylinder ends?

 

I can see a bit of suck-it-and-see'ing here.... :)

 

Cheers,

Dan

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Guest Dan_Beeston

I have to admit I took a punt on which way round it should be, I was working on the principle the pistons at the front were much larger than the ones at the rear, so used the smaller master cylinder on the back to keep the forces similar

 

I guess it makes sense to use it the other way round, when you consider it takes much more pressure for effective braking on discs than drums, I'll swap them around & see what happens! :p

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I have a twin m/c setup with .625 front and .700 rear. Balance is good. The rear drum slaves need very little fluid volume to activate and the m/c rod moves very little before the rears come on. The fronts need more movement. The smaller bore m/c exerts more pressure but shifts less volume. This means you have to set the bias bar fully back on the smaller front m/c side and fully forward on the rear m/c side. Don't set it up with the bias bar square to the rods or you don't get the stroke volume needed for the fronts. I am thinking of trying a .700 for the fronts as well to get more fluid shifted but it will reduce front braking. I don't know if the balance will still be OK or within the range of the bias bar to compensate. Time will tell.

 

Nigel

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I have a twin m/c setup with .625 front and .700 rear. Balance is good. The rear drum slaves need very little fluid volume to activate and the m/c rod moves very little before the rears come on. The fronts need more movement. The smaller bore m/c exerts more pressure but shifts less volume. This means you have to set the bias bar fully back on the smaller front m/c side and fully forward on the rear m/c side. Don't set it up with the bias bar square to the rods or you don't get the stroke volume needed for the fronts. I am thinking of trying a .700 for the fronts as well to get more fluid shifted but it will reduce front braking. I don't know if the balance will still be OK or within the range of the bias bar to compensate. Time will tell.

 

Nigel

 

Hmm, thanks. Maybe a .75 on the rear would have been a better bet.... I'll give it a try and see how we get on then. The OBP pedal box came today but it needs a bit of modification to clear the steering column, and the clutch pedal needs a bit of bending to move it away from the centre of the tub...

 

Anyone any ideas on the other queries, particularly the rear coil-overs?

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Guest woolly

as a by the way about the brakes.

if i remember correctly there was 3 different sizes for the rear brake wheel cylinders which will have a effect on your master size.

 

woolly

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