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MG Midget and Sprite Technical - Phantom grip advice

moving my PG into a 4.2 diff, I have the road springs it was shipped with and some stronger competition springs. Originally it also had some washers in the blind holes for the springs.

When compressing the plates with the stronger springs to the maximum, the assembley will nor fit into the diff assy. with the road springs, I have to remove the washers for it to fit.

anyone have any experience?

also is there a wrong way round for the shaft to go in? cut-out faceing the crown or away?

thanks
d cusworth

Not used a PG but have read the fitting instructions on the PG site, IIRC they have a specified clearance between the sun gears and the compressed PG and that clearance may require machining (surface grinding) of the sun gears to achieve. You may not need the washers but it would depend on the resulting clearance.
David Billington

David, where did you read this?


thanks

Danny
d cusworth

http://www.phantomgrip.com/index-3.html

Tech tip #1 has a link to get the installation details.

http://www.phantomgrip.com/images/Phantomgrip_manual_2008.pdf
David Billington

thanks!
d cusworth

My PG which came direct from Rivergate who developed the product for the Spridget and it did not come with any washers to sit under the springs. Certainly it fitted without any washers.

I don't understand your comments about the unit not fitting. Surely you are assembling it with the keepers in position and then installing it and removing the keepers? It cannot NOT fit because the keepers set the distance just right to fit the Spridget.

There are books with this kind of stuff in.




Daniel Thirteen-Twelve

Daniel,

It may be a tolerance issue on the inner faces of the sun gears. I wouldn't expect those faces to be tightly controlled as they don't have any function normally. The PDF file I posted a link to earlier gave a clearance of 0.003" - 0.005" so not much. It may be Dannys gears are at the upper end of their size so causing a problem. The fitting details do mention that some machining may be required to get the correct fit.

David Billington

Dave,

Danny's description of fitting the PG isn't the correct way of doing it. The Keepers on the PG control the compressed size of the unit not the springs. If the PG won't fit inside the diff with the keepers in place then YES you are correct. However, Danny is talking about washers in the reliefs for the springs - they cannot change the compressed size of the unit because the compressed size is controlled by the keepers. I'll e-mail you a photo since you don't have a copy of a book with this stuff in....
Daniel Thirteen-Twelve

My understanding from another gentleman who got a PG for his Sprite (and who happens to be a profesional reparier of differentials) is that there are two styles of Spridget diff with two different dimensions there, so PG sells two different units depending on the application. Sounds like you should look for another Spridget diff to try.

I do not know whether it applies to the spring sets you have, but when I got mine there was one set of springs available for street use and one that was so tight that it was only suitable on cars that were being driven in anger (virtually locked all the time). Unless you plan to trailer your car, you might be better off with the lighter springs.

I imagine that the washers are there to help match spring rate and travel. Probably one set of the springs needs them and the other set does not.
David "lots of conjecture" Lieb
David Lieb

Daniel,

Danny hasn't mentioned the keepers and I would imagine it would be a sod to fit the PG without them in place in a one piece diff cage. If he is compressing the unit fully and it doesn't fit then the keeper distance won't help. Ultimately it's about the load applied to the sun gears by the springs and that is determined by the amount they're compressed.

Danny,

About your flat orientation question, I presume you mean the flat on the cross pin allowing lubricant into the planet gears, I wouldn't expect it to matter. Must make that glass axle case so I can see the splash lubrication distribution in action.
David Billington

2 sorts of midget diff and so 2 variants of PG? - first I've heard of it, and Rivergate never mentioned it when I bought mine some 5 years ago. Swapped mine around a couple of timers and not had any problems yet
David "now where did I safely store those keeper springs" Smith
David Smith

News to me, too, David S. PG has two different listings with two different part numbers, one of which says that it is a custom unit made when ordered. The guy I was talking to told me this, "I got a call from John at Phantom Grip. I guess he is the big cheese. It turns out that I did have the wrong unit. He said there are some Spridget diffs that are a little thicker than the normal ones so they have a different kit. He isn't sure why there is a different version out there since they are all supposed to be the same other than ratio. They are putting the correct unit in and sending it back to me."
David "is your name not David? Bound to cause a bit of confusion! Minds if we calls you David?" Lieb
David Lieb

Just hijacking this thread very slightly.

The 2 sets of springs supplied with the PG are (as I understand) meant for different power (torque) outputs. I have used the lower rated springs (from memory up to 150BHP) in my Midget diff.

Would the stronger springs be too much for a Midget diff, perhaps turning it into a fully locked diff?

Thoughts anyone?

John
John Turner (Midget & MGB)

Hi

i got my PG from Bill Perry.

i have used the clips.

i made mew clips which clamped the assy to the max (coilbound springs) with the heavier springs, i need about 1mm more space between the gears.

will probably fit with weak springs for now.

does anyone know which way around the cutouts on the shaft should be?
d cusworth

wheelspin is not only a function of engine power output but also of road surface friction. If you look at the design of the PG it seems to me that it will never give a fully locked diff, far from it. The two sets of springs were billed as Road use and Competition use when I bought mine. If it was linked to power output I can't believe the 150bhp as that would surely limit their potential sales to only a handful of cars worldwide!
David Smith

There are defintely two different diff housings. The change came when BMC introduced ratio higher than 4.22 - the pinion had to be offset from the crownwheel further on account of the larger pinion head needed for the higher ratio. This housing was used for all ratios between 3.55 and 4.22.

The other (earlier) housing was used for all ratios 4.55 and lower.

The internal gears, thrusts etc, cage are all the same.
Paul Walbran

Danny, why did you make new clips (keepers)?
Daniel Thirteen-Twelve

Daniel,

To be honest, i can't find the originals!

until today i had not read anything to say the clips' measurements were critical for setup( the rivergate instructions did not mention anything like that) what are is the pitch with the factory clips?
d cusworth

The clips/keepers control the thickness of the unit before it is fitted to the diff. Once in the diff the clips are removed and the springs push each half of the unit back to the gears.

If the clips/keepers are too long then the springs are not compressed enough for it to fit in the first place.

However, before you make some shorter clips/keepers you should establishe whether or not the PG unit can be fitted with no springs in it at all - you won't need clips for this test fitting. Only if the PG unit can't be fitted with any clips whatsoever do you have a clearance problem.
Daniel Thirteen-Twelve

Daniel, I made the clips so that the 2 halves were as compressed as possibe, and still the gap was too small. I have now fitted the PG with road springs.

Thanks for help
d cusworth

Do you have a measurement for the gap or the uncompressed height of a gold spring?

If you do I can make comparative measurements.

Whichever springs you have fitted, the clips control the compressed height - so did you make shorter clips when you used the road springs?
Daniel Thirteen-Twelve

Daniel,

free length of 'competition' springs is 26mm

d cusworth

measurements from mine:
width of assembly when strapped closed = 24.3mm
free length of comp spring = 25.4mm
there are no washers in, or supplied with, mine.
David Smith

d cusworth is right on a problem with the competition springs - I've had the same problem.

I'm racing a FIA Midget 62, I bought the PG last year, mounted it with ordinary springs and they fitted without a problem.

My first race and the PG moved around in the diff, and broke the crosspin.

Preparing a new diff I thought that I'd better fit the competitionsprings - but I experienced that problem - it is not possible to press the comp. springs as much as the regular ones - the spring itself is to thick.

Now for race I did not dare to machine the sun-wheels, and the PG would be way too thinn at the arc to machine the PG.

So what did I do? I shrew the PG in a box - where it is still laying
Ole Aaen

thanks all
d cusworth

This thread was discussed between 15/05/2009 and 18/05/2009

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