FAB-TEK T5 transmission conversion for MGB (MGA too?) Introduction: I became interested in developing a 5-speed conversion for the MGB using an American Borg Warner T5 transmission after reading about some of the price and availability issues with the T9 trans from Europe being used in commercially available kits. I felt it would be worthwhile to be able to offer a 5 speed conversion kit with mostly over the counter (OTC) parts and no expensive specialty parts like a unique cast bellhousing. I think that the kit described in the following paragraphs achieves that goal with only the unique light weight aluminum engine backplate made by FAB-TEK.
The FAB-TEK T5 conversion kit for MGB’s uses T5 transmissions from 1983 thru 1992 Chevy Camaro both V6 and V8. It also is designed to use the 1985 thru 1993 Ford Mustang Transmission. The first running conversion was done in a 1972 MGB roadster using a 1985 Mustang World class transmission. The operating results with this first vehicle exceeded my expectations. The drive ratios in the lower gears are similar to the MGB transmission. The 0.80:1 5th gear achieves a nice reduction in road load engine noise yet drives the car with good throttle response. Clutch action is smooth with easy take-up and light pedal effort. There is a modest amount of gear noise but It’s noticeably less than the one T9 conversion I did on a customer’s car.
There are a wide variety of gear ratios available in these transmissions. First gears range from 4.03 down to 2.95. In my opinion (IMO) the 4.03 and 3.97 are a little bit too low. The 2.95 is probably OK but should be used with a well tuned good running engine. 5th gears range from .86:1 (why bother) down to .63:1. The .80:1 felt and sounded really good in a bone-stock ‘72 roadster at 6500’ elevation. IMO, anything taller than a .7:1 will drive like a “3 legged mule”. The best way to tell what the ratios are in any given transmission is via the tag bolted to the trans tail extension. The tag will read 13 52 xxx. These last 3 digits are the key to looking up the ratios. Vehicle application is not a reliable indicator as not all years used the same ratios and transmissions do get swapped in the field.
Mustang transmissions only bolt to a Mustang bellhousing. The Camaro transmissions, both V6 or V8 will bolt to either of the Camaro bell housings and probably to about any Chevy bell housing. A V8 bell housing (either Mustang or Camaro) is needed to fit over the larger MGB flywheel (12 7/8”) and both require a modest amount of hammer bumping at the left side front lower corner of the tunnel. The V6 Camaro bell housing should work in the early chrome bumper (’63-’65) cars but this bellhousing requires the small 3-main or early 5-main 11 7/8” flywheel.
BACKPLATE: The key element to bolting one of these T5 transmissions to the MGB engine is a fully machined 3/8” thick aluminum (6061T6) backplate which replaces the factory steel plate. These are made specifically for the transmission bellhousing being used. Both of the backplates for the V8 bellhousings rotate the transmission about 10 degrees counter clockwise (CCW) as viewed from the rear. This was done to provide a place for the locating dowels. This plate is the only part of the kit that must be purchased from FAB-TEK. It is supplied with a new Payen rear crank seal and is priced at $335.
FLYWHEELS. The conversion kit uses the original factory flywheel but it must be re-drilled for the 9” Chevy clutch. As noted above you will need the larger V8 bellhousings with the large MGB 12 7/8” FW (all MGB with 4-synchro transmissions have this). If you use a smaller 11 7/8” FW, either an early 5-main or a 3-main you can use the Camaro V6 bellhousing. Used flywheels should be resurfaced for the new clutch and if they are lightened (improves response) they should be balanced. Any of this work can be done at FAB-TEK ($125 for re-drilling) or re-drilling specs will be provided when the backplate is purchased to allow the work to be done by you.
CLUTCH: A 9” Chevy clutch is used with either of three different disc splines. The Camaro V6 and V8 and the Mustang use different input splines. Specific part numbers will be available for you to source or the parts can be provided by FAB-TEK. ($195-250)
HYDRAULIC THROW-OUT BEARING (HTOB). A Chevy HTOB is used which requires slight modification for mounting and hydraulic plumbing. This modified part can be provided by FAB-TEK. Clutch actuator piping and fittings can be sourced locally. Part numbers and descriptions will be made available with purchase. ($235)
BELLHOUSINGS: The two V8 bellhousings as well as the Camaro V6 require some amount of modification. One mod is to provide operating clearance for the starter drive pinion gear. These also require a bit of clearancing to match the backplate in the area which is tight at the front of the tunnel. This work can be done on your bellhousing by FAB-TEK ($75) or appropriate information with pictures will be provided with purchase of the backplate.
TRANSMISSION MOUNT: All three transmissions use a Camaro rear mount. The Camaro transmission bolts directly to the mount. The Mustang requires an adapter to attach the mount to the transmission. The Mustang mount is too tall to work with the MGB crossmember. The adaptor can be provided by FAB-TEK ($75) or specs will be provided to make your own.
TRANSMISSION CROSSMEMBER: The MGB transmission crossmember is used with modifications. This involves cutting out the MGB mounting bracketry and repositioning the crossmember rearward to clear the transmission tail extension. A mounting surface specific to the transmission used must be welded in place. Your crossmember can be reworked by FAB-TEK ($125) or specs will be provided for you to do this. A single nut secures the trans mount to the crossmember. This is a huge serviceability improvement over the factory MGB attachment.
SHIFTER: The Mustang has a short stub coming out of the shift block. On a ’72 (yours may vary) this stub interferes with the tunnel cover plate. What worked well for me is: I cut off the stub between the two bolt holes so it could move with out hitting this plate. Then I used the remaining threaded hole to bolt on an extension which placed the shifter in the correct location. (about 2” rearward). Specs and pictures for this will be made available with purchase. This work is best done on site by the installer. For the Camaro I was able to cut the shift lever off just below the rubber part, remove the rubber, shorten to “taste”, re-weld and bend as needed to best center for the OE rubber shift boot. Again this is best done on-site by the installer.
On the’72 roadster. I found it helpful to widen the tunnel hole about ¼” per side to help with putting the shift mechanism in and out during this process.
DRIVESHAFT:A custom made driveshaft is required to couple the T5 with the MGB rear end. Available from FAB-TEK ($295) or specs with component part numbers will be provided with purchase of the engine backplate. The Mustang and Camaro transmissions use different slip yokes (one spline tooth off). The driveshaft should be built by a competent shop that can build a true running shaft with no unbalance. Components for the shaft are available which maintain the stock tube size. However the MG shaft’s tube is not long enough to modify for the new front U-joint and slip yoke.
STARTER:A high torque gear-reduction lightweight starter is needed to fit the backplate. This can be supplied by FAB-TEK ($195) or ordered direct from Gustafson. If you have one of these already you can just re-clock the mount plate to match the picture provided.
MISCELLANEOUS: The transmission input pilot bushing is application specific and can be sourced from FAB-TEK ($65). If you do your own modification, fore-aft positioning must align with the input shaft. Specs are available with purchase.
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