Weakest
point in the Factory V8 drive train?
Jonathan
Moulds posted a note on the V8 Bulletin Board saying "a friend of mine has
had some special halfshafts made up in the USA for his Factory V8. The car in
question has a nitrous oxide injected, supercharged 4.6 Rover V8 and a Chevrolet
automatic gearbox. It will now pull away from the line with both front wheels
in the air for the first 6 feet or so.
I love my Factory V8, but I've
always wanted to drive it a little bit harder. The halfshafts are a known weakness
so I've always resisted full bore starts in the past. However, if I were to have
a pair of these bespoke drive shafts made and fitted them to the car, I suspect
it would then be the case that the gearbox is the next weakest link in the drive
chain. I suppose the questions I'm really asking are; what component in the
gearbox is the most likely to fail and would the gearbox be able to take repeated
full bore start in first gear?
I suspect the answer will be to either
have the box internals uprated or just bin the Factory box completely and fit
either an uprated Borg Warner 65 or a Chevrolet TH350 or possibly even a Powerglide?
I welcome your thoughts, ladies and gents?"
See
the V8BB thread
BCV8 Championship
The championship was
launched in 1974 by Victor Smith and Barry Sidery-Smith to provide an opportunity
for MG Car Club members to compete in their MGB, MGC and MGBGTV8 models. The launch
was at a time when the established and successful production sportscar championship
(BRSCC Prodsports) had become dominated by more modern sportscars and heavy sponsorship.
BCV8
- the early years
How to give your MGB V8 power
by Roger
Williams
Veloce Publishing
£29.99 UK US$59.95 USA pp 221
See our review of this useful book. More
Posted: 180711
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 | What
component in the gearbox is the most likely to fail and would the gearbox be able
to take repeated full bore starts in first gear?
Responses from Victor
Smith and Mike Breedon felt the gearbox will suffer from hard use so fitting an
uprated gearbox will be essential. That would be best done before before ruining
a good standard Factory gearbox - they are too valuable to break. |
Best
to think in terms of an uprated gearbox by replacing the Factory box with something
stronger
If you
want to drive an MGBGTV8 as hard as you suggest then I think the Factory gearbox
will sooner or later give out. Rather than damage a good Factory box, possibly
even the casing, I feel it would be best to think in terms of an uprated gearbox
by replacing the Factory box with something stronger and selling the Factory box
to a fellow V8 enthusiast who is in need of a good original gearbox.
A good starting point for considering uprated gearboxes would be to read the first
chapter of Roger Williams' excellent book "How to give your MGB V8 power".
The chapter "What car, engine and gearbox?" takes you through the considerations
depending on your choice of engine power - moderate up to 220bhp, medium (200
to about 250bhp) and high over 250bhp. "What gearbox?" is on page 19
and Roger covers alternative choices and getting the box to fit.
My second
suggestion is you could get a great deal of useful information from discussing
your ideas with Mike Breedon, a longstanding V8 member, who has been involved
in racing MGBGTV8s for over 20 years. He will probably be at the next MG Car Club
race meeting at Thruxton in Hampshire on Saturday 30th July. You could also give
Mike a call. You can look up his contacts on the V8 Grapevine. Look forward to
seeing you at Thruxton later this month.
Victor
Smith
What does an experienced MGBGTV8 racer feel on these
questions?
Looking at the comments and responses, I quite agree that
in general the Factory V8 gearbox is the weakest link in the drive train of a
V8. I have my own experience of stripping a tooth from third gear simply by hitting
a pot hole as I let the clutch out at the same time as I changed up from 2nd to
third even with “only” the power from the standard Factory built V8
engine. Later I did modifications to my 1973 Factory MGBGTV8 to match the BCV8
Championship Standard Class V8 race regulations so I could race in that championship
from 1984 to 1997. With a limited amount of work allowed on the engine, I swapped
the original Factory V8 for a Rover Vittesse 3.5 engine with a calmer cam and
simply went to straight cut gears in the standard gearbox casing and a rebuild
of the overdrive unit with special settings and valves to suit racing conditions.
In all races and road use, including 2,900 miles in 9 days on a MSA European Classic
Rally I never had a problem with the gearbox, overdrive or halfshafts. That rally
that took in race circuits along the way that included Spa Francorchamps, the
old Nuremburgring, foreign hill climb circuits, Saltzburgring, banked ovals and
various very quick runs across country lanes.
If however the engine is
taken to a much more powerful tune then this does introduce more power than the
original drive train was ever designed to withstand and people have had various
problems along the way depending on the power output being targeted. However,
even the MGCC BCV8 Class D full race cars are known to run with the Cosworth T5
gearbox which has proved both reliable and cost effective. Half shafts are occasionally
a problem with many seeking a heavier “beefed up” version but in general
until you hit a kerb or downshift at the wrong time they are very reliable.
I also agree with the comments above about a low mileage car being heavily
modified, I only hope the owner ensures he keeps all the original items especially
the gearbox as they are getting quite hard to find in serviceable condition.
I hope that helps but I have to admit that taking the V8 beyond the level
of Class D BCV8 standards is not something I have been involved in or know too
much about.
Mike Breedon |
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