As some of you may recall last spring I related the saga of converting my TVR
Vixen to a BUICK 215 V8 engine and B-W five speed transmission. The recent
comments about driveline redesigns has prompted me to relate my current
project of completing the conversion, with the addition of an XKE differential,
to handle the additional torque. (another saga)
When I made the engine swap I was convinced the GT6 differential was to small
to handle the increased engine output but I did not want to make the rear end
conversion at the same time. My personal experience is that I should only
undertake a reasonable size task each winter because the summer is too short in
the north east to risk any LBC driving time. So it is now winter number two and
the differential conversion is under way. The TVR has a fibergalss body, a
tube frame and independent rear suspension using a GT6 differential (3.9 ratio)
two u-joint splined axles and TVR design aluminum casting stub axle carriers at
the wheels. I decided to replace the GT6 differential with a Salsbury (sp.)
unit from an XKE, as it was originally fitted to the Griffith 400. I found a
good used one at our local MGCC car show flea market for the bargain price of
$200. It is from a 2+2 automatic with the exact ratio I wanted of 3.3 and
limited slip. Thanksgiving week I started the job in my drive in basement
shop. First I removed the body, a seven hour task (my second time). After
stripping off everything I lifted the body off with my engine hoist and floor
jack (and every piece of wood blocks I had) until it just cleared and I could
pull the chassis out from under it. Since I had not removed the engine and the
chassis goes up well into the body the lift was around three feet. This is the
point that the unplanned expenses started, since the body is off I decided to
have it repainted!
Now the chassis is up on stands and leveled carefully for future reference in
the modification process. The Jag. differential is HUGE compared to the GT6 but
it does fit and is installed from the top.(meaning any future removal will
require again removing the body or cutting the rear floor!) I removed the GT6
diff. and stripped the rear chassis bare after carefully measuring all the
dimensions that might be needed later.(axle center lines, heights, distances to
stub axle flanges etc.) It appeared that the stock front frame diff. mounts
might be reusable but it was obvious the rears would not, so my (new) "sawsall"
removed them. I made an assortment of sketches of possible mounting adapters
and with consultations with my friend Dennis (who had helped with the engine
swap) I selected the approach. We then set the diff. in position supported by
the floor jack. Looking down on the frame over the diff. the frame tubes form
a triangle. We fabricated a quarter inch thick triangular plate that bolts to
the top of the diff. in its stock mounting holes and provides two corner
mounting points in the rear. We then added two gusset like horizontal plates in
each rear corner of the chassis and mounted a rubber doughnut from a Chevy
Chevette transmission mount that then attaches to each corner of the diff.
plate. (I knew there had to be some use for a Chevy Chevette) This assembly
supports the diff. side to side and up and down at the rear. Next was the front
mounts . The frame has a set of "pads" that were used to adapt the stock GT6
mounts which attach to a plate across the front of the GT6 diff. casting. This
feature is not available on the Jag. unit so we fabricated a pair of plates
that extend from the original inboard brake mounting holes forward to the
original mounts and use the original GT6 rubber biscuits in the metal cups
removed from the GT6 plate. (I`m sure all this would make more sense with
pictures or sketches.) All the plate adapters were designed by making card
board templates and then fabricating from steel plate. All of this has gotten
the differential nicely mounted but of course there is more! The input flange
is larger on the Jag. and since the new diff. is also longer the drive shaft is
to long. This has all been fixed by our local u-joint/shaft specialist and the
only thing left of the original drive shaft is a piece of tube in the middle!
Now the expensive part. With the larger diff. comes larger output flanges and
the need for shorter axles. I had thought that the original axles could be
shortened and larger flanges installed on the driven end but it was not to be.
The axles are solid splined forgings and the shop did not recommend cutting and
welding. But "no problem" the specialist shop could make up, from components by
Spicer, a new set of shorter splined axles with the proper flanges and larger
u-joints. The best guess was that the cost would be "hundreds of dollars", well
I like this shop and have had very good results with them in the past so I told
them to go ahead and order the parts. This was the week before Christmas and
yesterday I picked them up. Some machining was required on the inside of the
inner flange to clear the nut on the diff. output flange which they did and the
axles look great. They are much larger in diameter and are surely overrated
for the torque they will get. All of this for "only" $550 including some stub
axle seals and the drive shaft work. I had originally planned for the axle
adapting to cost about $250 for cutting rather that replacing. I do now have
a good GT-6 differential (one season under V8 torque) and a set of TVR axles
that I expect could be used to recover some of the parts cost. The new axles
are definitely first class! This is where the driveline redesign now stands,
you can see this project is not for the faint of heart but is within the
ability of experienced/amateur mechanics supported by a good
specialist/machine shop. If you plan on a driveline redesign make your estimate
and then double the cost and time you think is reasonable.
Yet to go is to complete the total suspension and stub axle rebuild, paint the
body and chassis, install new heat barrier padding, and reassemble the whole
thing. All must be done by The first week of April when the LBC season restarts
here in upstate New York.
PS: I agree with the moth ball approach to keep the critters out of your car
during storage. At my last home I had a large storage/modern barn that I could
store about 8 LBC`s over the winter. The first winter the mice moved into my
Lotus Elan and built a nest under the facia and filled the exhaust with wild
bird seed. The nest was a mess but I never did find any damage in the car and
in the spring the seed made some interesting small popcorn on the floor as the
car heated up for the first time. I tried cats and they were 100% effective but
tended to sleep on the convertible hoods leaving stretched centers and
occasionally there were cat "droppings" under the car during the worst snow
fall time. The use of moth balls worked with a couple inside the car (I don`t
like the smell either) and a lot of them under the car.
Here`s wishing you all a Happy New Year and a good winter (LBC upgrade) season.
John
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