MG Sports Cars

I think he's counting on good news from Punxsutawney Phil. ;)

Lawyer logic is involved, I believe.

Lawyer logic? hmmm.....

Well, OK since you asked. Winter solstice is recognized by many societies as "Midwinter's Day". That means the March equinox would be mid-spring, therefore Feb. 2, being halfway between must be the first day of Spring. And just look, isn't the weather warming up nicely? Better get those cars ready!

I believe I'd mentioned that I ordered another posi unit, this one from Coventry West in Georgia, and at a cost of $350 and $60 shipping. Herein lies the reason for searching out a complete Jag rear suspension unit with the desired gears and posi unit before buying. A few more dollars well spent for the correct parts the first time around can pay off handsomely compared to piecing it together. Now that does mean a flange type driveshaft connection and a u-joint yoke is a bit expensive at perhaps as much as $80 depending on where you get it, but changing the yoke is easy compared to a complete setup of the gears. Likewise, shortened tubular half-shafts and lower control arms from an established custom parts supplier such as Concours West Industries (CWI) can make very good sense compared to making them yourself. Now as best I recall I had the IRS unit for somewhere around $250-300, meaning I just paid for a second one at the same price with enough change for the yoke, provided I found the same sort of a deal. Regardless, the total would easily pay for the desired unit and then some.

I have yet to do any more than pull the cover. They sent the entire differential unit including bottom brackets and brake brackets. These brake brackets are cast aluminum pieces with a one bolt attachment point. Obviously it used a different brake caliper, most likely a floating caliper, and I would very much like to get some more information on those, including what material was used for the body and what configuration of parking brake was used.

A cursory check shows up nothing obviously defective in the unit, but it was a core so was most likely removed due to noise. I will begin inspection and probable disassembly in a few days after I check backlash and the torque capacity of the posi unit. I doubt I can use it as-is but you never know.

As for the engine, head gaskets are on order, the mains are properly torqued and the last two head studs are in place. The pan should go on shortly along with the oversized pickup tube and a windage tray if I can fit one. Then I'll start work on the front cover. In about a week or so Charles at CamcraftCams will be able to recommend a cam grind, and checking my valve springs indicates I should have about 300lbs at .490" lift. I think that should work out well.

Jim

I found out why the Jag diff was a core. The cross pins for the spiders had both broken right across the center hole, so it probably made some very odd and hard to identify noises. It wouldn't have caused imminent destruction or anything like that but would have required a nearly full teardown to find the problem. Easier to replace the whole thing. Which works out good for me as there is very little wear, and I still have the cross pins from the trashed Ford diff. They have no center hole so should be stronger.



I removed the pressed on trigger wheel which I believe drove the speedometer but I'm beginning to have second thoughts about that. It might be useful for cruise control and would hurt nothing to put back in.



A very pleasant surprise was that this unit uses 7/16" ring gear bolts rather than the 3/8" ones used in earlier units, meaning it is fully interchangeable with Dana 44 parts, and I will not have to drill out the bolt holes to fit my 3.54 Dana gears. It also came with a set of very nice 3.54 gears, but I haven't yet removed the pinion flange to see if it is coarse spline like the older Jag units or fine spline like most of the Dana 44 ones. If it is fine spline, I might consider just using the new case as the pinion depth and backlash is already set. I guess pulling that flange is the next step.



Dan will be interested to know that the Olds motor he blew up is now gone, other than a few bits and pieces like the pan and front cover, and of course the induction system and blower. I sold the heads and the short block on ebay and the proceeds are helping to pay for the build on the 340. I might as well sell the blower too, I doubt I will use it on the other Olds 215 I have and I will probably sell the 215 as well. That is, whenever I get the time to disassemble it.

Jim

Not gonna blow the 340? What are you going to do with that big hole in the hood?

I have a bigger blower for the 340. It's a M-112 instead of a M-90. That's close to a 25% increase in displacement but the 340 is almost a 60% increase, so I'd have to spin it faster to get the same amount of boost, which would just be crazy, but I may call Magnuson to see what their engineers recommend. I haven't decided on whether or not to use an intercooler this time, I'm thinking it's going to be completely unnecessary though, with the lower boost levels and the higher static compression. Plus with less boost pressure there will be less heat for the intercooler to remove, so I'm thinking it's just more complication that isn't going to help much.

I'm not sure what I can get for the old blower setup, probably have to sell it with the drive including the crank trigger and front cover. That means I'll have to buy a new drive extension and I don't recall what the cost of that was. More questions to ask. Guess I'll need to start mocking it up as soon as my head gaskets come in. More calls to make.

I'm ready to begin assembly of the differential again. Interestingly enough, Jaguar used the same odd clutch stack in this Power-Lok as I found in the other one, a stack that gives 3 friction surfaces per side. Using a conventional stack gives 5 per side. Torque of the unit before disassembly was 40 ft lbs, possibly at least partially because of the broken cross pins, but I should have around 140. Well, this time for sure. Think I'll get a new set of side bearings too. Probably better start looking around for more stuff to sell....

Jim

Seems the details are very important in differential work. I just slapped the thing together but when I tested the torque of the clutches all it had was 75 ft/lbs. So I opened the case and swapped in the internals for the 2 series unit which had given me 140. When I tested it again I had picked up 15 but not what I had expected. So I broke it down again, cleaned the lube off all the parts and set to with dial calipers, dial indicator and micrometer to find out why, and discovered there are some significant variations in the parts, and not always as expected either. For instance, the newer and less worn plates with the inner spline were about .0015" thicker, but the older plates with the external tabs were .003-.005" thicker. The newer spider gears gave maybe .005" of extra height to the internal assembly, but the older cones that surround the side gears were .020" taller.

The stack-up didn't account for the difference in torque so it was probably in the depth of the bores in the case. That's something I couldn't change so I just reassembled with the thickest parts and this time came up with 120 ft/lbs. That's just about what it should be so I'm happy.

Then I slid on the set-up side bearings with a couple shims under each one (they had each had 3 in the other case) and slipped the unit into the gear case, snugged down the caps lightly and checked the play. Shoved all the way away from the pinion it felt like about .020-.030" backlash and shoved towards it there was none. Good so far. Next I'll add shims on the left until the backlash is in range, add to the right until the fit in the case is snug, and then check the pattern. That will tell me if the pinion is centered properly, and I will probably have to re-shim that and do it all over 2 or 3 times before everything lines up right.

If anyone tells you that there are no shortcuts in axle work, listen to them. It's probably someone who has tried it all and knows. And if you ever wondered why work takes longer than the quoted time, just consider the above. Much of this would be the same whether I was doing it or your friendly neighborhood shop, the only difference being they aren't going to give you a detailed description of just what went on because they don't want to look incompetent. Can't say I blame them one bit, I'm only saying when it takes longer than you expect there are usually some real good reasons for that which have nothing to do with the skills involved. All new parts do help, but even new parts aren't always what you expect them to be.

Jim

Sometimes you just get lucky. Too bad it doesn't happen more often, but I sure do appreciate it when it does.








The contact pattern looks pretty good. Evidently my interpretation of the somewhat ambiguous depth markings on the end of the pinions was on the money, so all that's left is to add a shim for preload and install the new bearings which should be in on Monday. It will be nice to have this part of the job behind me. Once it's buttoned up the hog's head will go back on the upside down MG body section to assemble the other parts and finish up the last few pieces. I should be ordering coil-overs sometime during the week as well. Shouldn't be long before the swap takes place. Then we'll see just how close actual practice comes to theory.

Jim

Here are some new photos of the engine.







Jim

Freeze plugs, oil pump shims and a few other small parts came in today, but I've switched off to the IRS again. On that, I turned down the hub centers and polished one of the drill rods down. If you'll remember those were 5/8 dia x 36" long and will form the heart of the forward extension of the lower control arm pivot. I actually have to polish four of them since the Roadmaster will also be using this arrangement. Happily, about the time I finished the first one I remembered a couple of tricks that should speed up the job on the 3 remaining ones, so hopefully I can get that done tomorrow.

So the hubs are ready to assemble to the uprights, and I have new bearings to install in the lower pivots, which means it's almost time to sort out all those small parts and figure out how they go back together. What fun. Once that is done I can put stuff together and look to see what has to be done to make the remaining parts. Quite a bit left to do, but with warmer weather it'll be easier.

Jim

OK, the hubs are assembled and the bearings need shimmed, seals and spacers for the lower pivots need installed, and then bolt it all up. I've decided on heim joints for the forward pivot and found some nice pieces that use an alloy body and oversize stud. That should be substantial enough, and I'll use spring eye bushings for isolation, like originally planned. There will also be a UHMW strip across the front of the forward cross brace for forward thrust against the lip of the panel below the driveshaft. All four of the lengths of 5/8" drill rod are at size but need to have the ends turned and threaded. Or maybe just threaded... more to think about. The rods will pass through the center of the cross brace and pinion angle will be fixed at 3 degrees. The angle braces will have a cut and welded angle at the heim joint and a slight bow where they go under the battery boxes. At 1" dia and .156" wall they should be strong enough but should they bend they can be upgraded to larger diameter tubing rather easily.

Next step is to lay out the holes in the tie bars and finish all that up and then I should be ready for the heim joints.

Jim

Hey, I accidentally found the sections of Jag IRS cage that act as tie bars... They are on the MGB-Roadmaster! Here I was searching all around for them and then ran across them by accident. Well, loads of progress. The uprights are assembled to the half shafts with the proper amount of preload on the timken bearings (as are the ones for the GT as well) and the trunion bearings and seals are also assembled. New neoprene seals are used rather than the old style felt and the housings will be filled with synthetic gear oil. It turns out the spacer tubes are the right length without any shims to give heavy preload to the trunions, and this is desirable because the bearings see only a few degrees of rotation and overheating will never be an issue. Lack of adequate preload allows the rollers to beat divots in the races resulting in looseness and torque steer. So here is an instance where heavy preload is a good thing. I'm stopping by Graingers in the morning in hopes of picking up a pack of .010" shims to take up the slack in the joint to the LCA and then these go together for the last time. This assembly method has reduced the parts count by at least 8 or 10 pieces per side and should be much more effective than the original design, while retaining the rigidity of the timken bearings.

I also found a couple of 30 year old pieces of stainless tubing that I was able to use to bush the shock mounting bolts down to 1/2", which fits the coil-over units I'll be using. With some serious hunting I was able to find enough to do both cars and that part is ready to be bolted up, hopefully as soon as the heim joint seals come in.

I stopped by Marmon/Keystone in hopes of buying some tubing for the diagonal links, and Tom Jackson remembered me and the Roadmaster. Since they had already given us some tubing for that project and because this piece was going to be used for the GT as well, he gave us the length of tubing for the Roadmaster and there is plenty extra to make the links I need for my roadster also.

I began to fit the brake calipers and I see what all the hubbub is about. While I was doing that I was also bead blasting the rotors (which barely show use but had a good bit of rust) when all of a sudden the compressed air system blew a hose off the feed line to the big tank and vented a couple hundred gallons of 140 psi air. That was some excitement, with the loose 3/4" hose whipping the fiberglass insulation off the walls about 12 ft up in the corner of the building, so with all that glass in the air I concluded it was time to quit for the day, cut the lights and locked up. Tomorrow I'll apply a more permanent sort of bypass to the leaky chiller unit that caused all the trouble in the first place.

I'm hoping to get everything on the IRS more or less finished up in the next couple of days, but that kinda depends on deliveries. I got a lot closer today though. It's nice being able to do the work with the whole shebang turned upside down.

Jim

Today I learned the trick to changing Jaguar brake pads. Using the two holes in the rotor, you just unbolt the stub axle housing and pull the whole works out the side. Pretty slick, I just need a little more clearance in the crossmember. I also need to relocate the top shock mount, thread the pivot rods, paint some spacer tubes, a few more small details and it's ready to go together for the last time. Couldn't be too soon, this week maybe for sure. ;-)

Jim

More good news about those Jag brakes, the pads can be changed easily and without removing the calipers. Most sensible of the old chaps considering what a pain it is to pull the works. So clearly frequent pad changes to avoid rotor damage is the regimen.

I threaded one of the pivot rods today, a bit of a job but now that I know how to properly accomplish it the other three will come easier. Also got the spacer tubes painted and organized parts for assembly. Put the brake/stub shaft assemblies together with new brake pads and wouldn't you know, haven't been able to lay my hands on the safety wire and pliers. Well, they'll turn up, hopefully tomorrow. Also drilled the crossbar and prepared the spring eyes, so those parts can be welded up and I think a gusset is in order as well.

So here it is nearly Thursday. Will it go together by week's end? Stay tuned.

Oh, the cam came in also. Looks to be a decent performance grind, hopefully it will compliment the engine well.

Jim

All the pivot rods are done finally, and so is relocating the upper shock mounts and widening the notches so that the brakes can be easily changed. I could have gotten by with only widening one side but went ahead and did both, and I dropped the IRS out of the Roadmaster and did the same mods on it as well.

Now here's a photo where I trimmed the bell of the upright on the Roadmaster IRS:



The piece cut off is laying below. This is something I've been considering ever since Evan mentioned it a couple years back. The goal in building this IRS was a pure bolt-in swap and cutting the bump stop hump away does not qualify as bolt-in. However, trimming the bell makes it unnecessary except in extreme cases. There is still further testing to do, but with my 17" Corvette wheels and 275 tires, the sidewall hangs on the hump. However, at full compression the sidewall still contacts the inner wheelwell, indicating that most likely this hump removal only results in a gain of about a quarter inch. Well, if a quarter inch is the difference between clearing and not clearing it can be removed but most folks do not run that close, especially on the inboard side. We're talking 7-1/4" of backspacing here. At 7" or less it should clear easily, certainly 6-3/4" should be more than enough, and you have to run at least an 8-1/2 or 9" rim to do that, maybe even 10". Even with flares most can't fit such a tire.

So the reason for cutting the bell was to clear the hump, which it did interfere with slightly. Now with that obstruction gone, interference with the tire as above is the issue, and it isn't much of one. What we have is a case of one or the other. If the hump is trimmed, there is no need to trim the bell and vice-versa, although as noted it makes a slight difference in tire space. For the Roadmaster and all bolt-in applications this is clearly the way to go. For my car, with the 275's, that 1/4" just might be needed. It'll be close, and I need to do more measuring. I'm already pretty sure the 7-1/4 is going to need to be pulled out to 7" with a spacer or change of wheels but how close I'll be to the lip outside is still undetermined. But I think it'll be close. Everything hinges on the control arms, quite literally, and I can't really determine the outcome until the unit is bolted in.

Wheels with this combination will be everything, and I don't know where that will take us. But if an 8" wheel with a 6-1/2" offset is a possibility and can be made to fit the car with standard flares then I think we have a winner. If we can bring the uprights in another 2" it would work with the standard bodywork with no problem. Without a doubt there is a combination somewhere in between that will work reasonably well and eventually we may find it. Just not today.

Jim

The diagonal braces are in the paint booth (the ones for the GT will have to wait their turn on the mule for fitting and welding). I think they will turn out to be quite strong and rigid despite a slight bow to fit beneath the battery boxes at full compression. There's still some fiddling with the shock mounting hardware, and I've decided to run diagonal straps from the rear tie bar to the outboard ends of the crossmember, most likely using the original shock mount holes to do so. I should have some photos in a day or so.

Jim

Ready to install (still some shock hardware to sort out)









The one for the GT is on the mule and will be in the same form in a day or so.

Jim

Looks good. Have you weighed it?

Also, Curtis gave me good input on getting the shock mounts out of single shear... would be pretty easy to do on this from the looks of it.

Jim, that is really nice. Great work.

Jim, that setup looks pretty stout and should hold up very well to the 340!

Great looking work!