What's a Seven?
Build page story
Build page pics
Zetec vs. X-Flow
Conversion to Zetec
Caterham 7 Gearbox Upgrade - Ford T9 to BGH-E7
|Gear ratio's in the Type 9 Ford
Sierra gearbox are good, except for 1st gear. The 3.36 ratio is
designed to work with the much heavier Ford Sierra car and is
unsuitable for a Seven: With engines with >
110..120ftlbs of torque, it's difficult to take off without spinning
the wheels. Second, the 1st to 2nd gap
is too large, which with a tuned engine causes it to drop off the
cam. BGH transmission
specialists, but also Quaife
ratio's for this Ford Type 9 box. Regarding horsepower, torque
rpm capacity of the T9.. it's fine up to 160..180ftlbs, and a taller
1st gear (lower ratio), will reduce internal stresses as well as the
load on the differential. Lubrication is a
critical point and Brian Hill and team have developed several
modifications to improve this. At a minimum I'd suggest to switch to
Redline MTL, which I've used now for some time with great result -
great synchromesh action (no more 2-3 crunching during track days).
Brian Hill's recommended E7 set includes a layshaft with a different input gear. This changes all the gears on the layshaft (not 4th) and in order to get practical ratio's both 1st and 5th on the output shaft are also changed to suit. 1st is intended to get to the 2.75 ratio, whereas 5th is intended to return to a ratio close to .85. If not, the resultant 5th would be .79, which is too tall for track work, but could be fine for long trips.
For my own car, the motivation for changing ratio's became clear when I put the 200HP Zetec in. Also, during spirited driving and track day running, 3rd gear shifts had become a bit crunchy, indicating wear on the 3rd gear baulk ring. These reasons provided ample justification to go ahead and open that gearbox!
|September 2005, my wife and I
a sightseeing tour to England and Scotland,
starting from Gatwick. I had spoken with the BGH team before over the
phone, but Wisconsin is just too far away, so I concluded an in-person
visit would be better and if anything more entertaining. Hence the
first stop on our tour was BGH Geartech in Cranbrook, Kent. The country
side in South Eastern England is always one of our
favorite areas for touring and we somehow have always been
lucky with the weather there, at least this is how I sold it to my
wife, who's a very good sport! The roads themselves are
absolutely fantastic. We had rented a Ford Focus, but I kept
Brian's shop is composed of several workspaces. Suspended off the ceiling of one of these, is the original prototype of the 6 speed Caterham gearbox, that he developed for them. During the tour through Brian's shop it became clear that his team can do anything with gears, from specifying and cutting special profiles to creating custom solutions. Their world wide reputation as gearbox experts is very much justified!
Andy, one of the BGH team members was kind enough to walk me through the disassembly process. For my own reference, I video taped the dismantling of a T9 box, which took him only 20 minutes, pointing out potential pitfalls. There are some differences between the older and newer Type 9 gearboxes, that require some attention, such as the layshaft stub shaft, vs. the full countershaft that is deployed in the older boxes. The shifter mechanism (half of which is housed in the tail), is different as well. E.g. there is no pin / spring under the 5th gear shifter location cover.
Later, back in Wisconsin when I disassembled my own box, I first thought this pin was missing, but it's absence it's one of those remnants of the earlier design.
We left BGH with a suit case full of parts, rings, layshaft, bearings etc. The return trip back to the US was interesting to say the least. We should have flown non-stop, but either way, the stop over in Philly was "special". One of the guards freaked out upon seeing the layshaft in my hand luggage. I had kept it there as I was concerned it'd work it's way through a checked suitcase, just because of it's mass. So, she was prancing it around claiming it to be a "blungeoning tool"... good grief... fortunately one of her more sane colleges was a carguy and recognized that it wasn't. An hour later we were let go with our stuff, but the delay forced us to take another flight to make it back to Wisconsin. The following week I started the swap, as the driving season was getting short and I wanted to at least experience the improved ratio's before parking it for the annual "Wisconsin ice-season".
|T9 (Scorpio) Gearbox disassembly and
mentioned above, the 3.36:1 1st gear ratio replacement was something I
had been wanting to do for a long time, esp. because of the 2.0ltr
torque. As far as a do-it-at-home
project, this is quite doable without major tools. Some key
items you'll need are a clean place to work (I use a small wooden
platform on wheels), and lots of trays for parts. Be careful of the
sychromesh assemblies and keep them "in-tact" if you can. If the
springs and keys do come out, clean and dry your hands otherwise on
keys may fly all over the place. Note they are gear specific.You will
be greatly helped by having
an air compressor and airwrench - 70..80psi / 1/2". Get the best
snap ring tool(s) you can get, the box is
designed around these, inside, outside, eyed, they are all there and
there are many of them.
For the friction fitted speedo gear removal, you'll need to modify a standard gear puller with some extensions - I used four strips to extend the puller arms. Make sure to note the exact gear location, as it's a friction fit, and it needs to go back exactly where you found it.
To get the bearing / sandwhich plate to come off, after removing the snapring (!), you will need two fabricated 3/16" rods, shaped as shown. Flatten the ends like blades as shown, as well as the small Z-bends. Dimensions are about 8..9 inches per side.
To replace the Torrington bearing (layshaft / output side), the outer ring just slips off, once the large nut has been removed from 5th gear. Engage 2 & 3th gear or 1st and 3rd and use a 1/2" air wrench for this, 70..80psi. Then a heavy duty puller will be needed to get 5th gear to come off. I used a little stub (see pic) under the puller to insert into the hollow layshaft with .780" diameter on the small end, but a 3/4" socket extension will work as well.
For lubrication, I've tried a number of different brands and viscosities, but settled on Redline MTL, which is a special blend of lightweight oil with synchromesh action promoting behaviour! This is critical, and really helps in a 7 where you'd be likely to shift quick. It stops the notorious 2-3 crunches when the box gets hot (Mobile 75/90 synthetic gear-oil lets go here) on the track. I also put this in my old '84 Esprit and it transformed that gearbox. It's well worth the added cost (about 2x that of regular synthetic gear oil).
Anything I'd do different: I'd certainly avoid machining past the end of the case like I did. In retrospect Brian Hill's notes were clear, but I misinterpreted his drawing. Of course after it's all done, it's all clear as always. No problem really, as my alternate solution with the oilite thrust washer has been working fine for thousands of miles and some track time. Meanwhile, it's winter of '06/'07 now and BGH was good enough to sell me another T9 Scorpio case and I'll be putting that in, as soon as it warms up here a bit. We've been below -15C for over a month now, and working in the non-heated garage is challenging. Once it get's warm here, like anything above -5C, I'll go back in there and replace the case, to make it all proper again. Nevertheless, the upgrade has been excellent and it's well worth the time and $ spent on it.
The pictorial log for my 2005 winter upgrade
gear, and 5th gear/synchro are located in the tail section
||5th gear pair & Shift mechanism.
- Top shaft left-of-center, the brass disc/disc-arm & coil spring arrangement provide the left-right location of the shift lever for the for-aft planes for Reverse / 1-2 / 3-4 / 5th. The brass arm straddles or forks a pin in the tail housing.
- The steel sleeve and disc on the top shaft, right-of-center allows for selection of 5th gear and provides lockout when other gears are engaged.
Left to Right:
- Far-left on-shaft - indentations for:
[2-4], [Neutral], [R-1-3-5]
- 4-3 shift fork, lockout disc
(disc is located by the cover plate)
- 2-1 shift fork, 5th shift fork
- 5th gear lockout disc
- L/R plane springload fork (far right)
(the spring reference is located by a pin in the tailhousing)
in the pie-tin: pin&spring
for locating shifter-shaft.
Center-right: speedo gear (194mm from gear back to sandwich plate face). Pull off with extended (fabricated) puller.
Low-center: get the best clip/snap ring pliers you can find!! This box has many external and internal snap rings.
Note: 5th gear shift cone engages by moving away from 5th gear, as it's plane is with gears 1/3/5. The cuff rides on an extension of 5th gear.
|Mainshaft ( = output shaft):
Left to Right:
- Synchro slider 3-4 gear
- baulk ring 3rd gear - 3rd gear
- 2nd gear - baulk ring 2nd
- 1-2 shift ring (accepts shift fork) / Rev. gear teeth
- baulk ring 1st - 1st gear
- Sandwich plate (holds bearings)
- cleaned off output shaft (5th & speedo removed)
layshaft stub shaft must be removed, by pounding it out through
hollow layshaft. I used a 10" 1/2" socket wrench extension.
To remove the layshaft (center / vertical), the outer race and rollers of the torrington bearing in the s.w. plate have to be pushed out. With two L-shaped 1/4" steel rods (Brian's suggestion), with the ends about 1" long and the "handles" about 9" long, the bearing outer race edge can be pushed out between the s.w. plate and the case. The s.w. plate can be moved out, about 1/2" inch. Then the layshaft can be lowered and the input shaft removed. Up to this point it's been caught behind the layshaft input gear.
Showing the input shaft, main bearing and input gear, and 4th gear synchro teeth & cone.
Note: the 4th gear synchro connects the input shaft with the output shaft, for a 1:1 ratio.
Also, in the left tray are synchro spring, blocker pins and a baulk ring.
In the right tray, some snap rings and the layshaft stub shaft. A roller bearing in the layshaft runs on that.
|Showing the old 3.36 1st gear and
layshaft meshed. Note the input shaft is on
then the common (input) gear pair drives the layshaft permanently, as
the output shaft is referenced via a pilot bearing right next to the
The 1st gear pair is on the right. Gears on layshaft:
Common - 3 - 2 - R - 1 (5th is removed).
Note round disc magnet at the bottom of the case.
The reverse idler gear has not been removed yet.
mates with the sandwich (bearing) plate, and requires some machining:
The larger 1st gear on the layshaft (bottom opening) interferes with
the edge of the lower opening, as well as with some ribs on the inside
just below the reverse gear stop.
I used a boring bar set to 2.5" diameter. as suggested by BGH, and then cut material side to side by .15"
view after machining. Note material removal at the bottom (low-center
Need to be careful with the small reverse gear stop, that can easily be nicked during the grinding process. The spring on the reverse idler gear fork, keeps the idler gear located towards the rear of the box, against the stop.
After washing the box, it's ready for test fitting and reassembly.
---- Ok, something went wrong here, as I machined out the thrust surface for the torrington bearing, the one that sits on the layshaft in the sandwhich plate. It is held captive by the snapring in the sandwhich plate and the case on the other side. But since I machined it out to the full thickness, no edge remains for the bearing to rest against - my solution is a new thrust surface made with a bronze washer and stainless shim at the other end of the layshaft - pics to follow below - yup, I screwed up, but it's fixed ....(see below)
|Test fit of
the layshaft. I used teflon tape to protect the inner race of the
Torrington bearing which was heat shrunk onto the layshaft (thanks to
John H. for calculating the correct temperature, and use of his oven!).
Note the rear side of the input shaft on top.
The layshaft stub shaft is used on the other side, to position the layshaft more or less in the correct location.
testfit view from the top, showing the input shaft more clearly.
Mainshaft shown in the top of the picture.
cluster, left to right:
3/4 shifter cuff hub then 3rd gear, 2nd gear
Reverse on top of 1/2 shift cuff
note: engaging R is accomplished by sliding the
Reverse idler gear, not this 2/3 cuff.
Next is the new 1st gear.
New brass baulk rings are in place for 1/2/3rd. The 4th and 5th showed no measurable wear and mated well.
new 1st and 5th gear, overall slightly closer ratio's for 2 and 3 as
well, due to the changed input gear on the layshaft.
New synchro rings (brass baulk rings) as well as fresh bearings. Turned out the bearings were like new. I wasn't sure what state they would be in as at the point of dissassembly I had put 60k miles on the box (and the car :-).
cover with top filler and oil level dipstick (see threaded entry top
right of the cover in this pic).
Note the slotted guide for the shift mechanism disc in the center of the top plate, which means test shifting without the cover in place, requires some care.
so now I'm making it right again - following a couple pics of the new thrust washer solution. Better would have probably been, not to machine out the whole opening, but this is certainly a lot more fun!
Also note that late(r) model T9 (Scorpio) gearboxes are very hard to come by in the US.
tried to find another gear case, but in the US no-one appears to have
The main difference between these boxes is that the older style has a support shaft running through the layshaft, which then runs on that. In the newer (Ford Scorpio style) box, the layshaft hangs on a small stub shaft (see below).
- 1/07 - Got another case - I'll swap it in sometime in the coming months. Right. Way way too busy. I really should retire sometime.
note: it's almost 2011 and that fresh case still sits under a desk. meanwhile the gearbox is still fine.
|The layshaft input side bearing in the older case is a set of roller pins, which have to be temporarily glued into the layshaft with some thick bearing grease. The newer vesion uses a caged roller bearing that is pressed into the end of the layshaft. I believe this bearing actually works both for the newer as well as the older boxes. Then, the other big difference is the 5th gear selector blocker which is much simplified in the newer box.||I would think (I need to test this some day) that a later style tail and sandwhich plate should fit with an older case. So, if my thrust bearing solution wears out prematurely, that's what I'll try do.|
|Left to Right:
a. Layshaft with inserted caged roller bearing
b. bronze oillite .062" washer
- with it's ID milled out to .950"
c. stainless shim washer .010"
d. stub shaft that bolts to the front of the case.
Note: the plate with the three holes will be shimmed on the outside, to allow for the slight laternal shift created by the washers. The longitudinal force is taken between the layshaft / washers / inside gearbox wall, instead of the torrington bearing, which resting-edge I accidentially machined away..
|Same as on the
showing the relative position of the washers. The .010" stainless shim
/ washer will
rest against the raised area on the case that exists where the stub
the front panel of the gearcase inside the box.
The gap is where the case wall will be (ok, that sounds confusing...). Note the three bolts will be outside on the front face of the gearbox.
Purpose of the .010" washer is to provide a smooth running surface for the bronze washer. The oil feed is from the opposite end of the hollow layshaft and thus these washers will run semi-submerged in oil.