Olds Cutlass Jetaway Options
I really enjoy reading your responses every month; I find them all very interesting. I have a 1968 Oldsmobile Cutlass S with a 350-cu.in. V-8 and two-barrel carburetor, but that was changed out last year for a four-barrel unit. My car came with a two-speed Jetaway transmission, and it seems to leak fluid after sitting for a period of time. It has become very time-consuming cleaning up all the fluid from the drip pan and floor, not counting the cost of putting new fluid in all the time.
I would like to upgrade to a transmission that will give improved high-speed efficiency and performance. Various friends have offered opinions about which transmission to use. Some recommend the TH200-4R or the 700-R4, four-speed overdrives, while others have suggested a three-speed, like the TH400 or TH350.
My wife and I mainly use our Cutlass to go cruising and to go to car shows. I would greatly appreciate your advice and guidance as to what transmission to choose.
– Doug McCallister, via email.
In terms of ease of installation, a conversion to the TH350 would be the simplest, as some of the Jetaway components can be reused. The original flexplate should work and the overall length of the TH350 “short-tail” assembly and location of the transmission mount and crossmember are in the same place as the Jetaway, also known as the ST-300. This makes the TH350 the most logical choice. When sourcing, ensure the unit has the B-O-P bellhousing pattern and check the length of the TH350 extension housing. The B-O-P bolt pattern bellhousing has a valley between the two upper mounting bolts instead of having a peak between the bolts as was used in Chevrolets; GM also produced some TH350 units with a “multi-case” bellhousing that fits Chevy and B-O-P. The 6-inch tail extension housing is 27 11/16 inches overall, while the 9-inch extension unit is 30 11/16 inches, and the 12-inch extension housing is 33 7/8 inches overall – you should find the 6-inch version matches the overall length of your Jetaway, but measure what you have to be sure. The TH350 will require a kickdown cable and mounting bracket to finish the conversion. Lokar Performance Products sells a universal kickdown cable and bracket assembly for these transmissions, part# KD-235OU that is available from JEGS, Speedway, or Summit Racing.
You can also use the TH200-4R if you’d like to gain overdrive, though this is a more involved swap. The 200-4R should be the same overall length as your Jetaway and uses the same driveshaft yoke, but the transmission mount will be in the same position as a TH400; this shouldn’t be a problem in your case as your ’68 Cutlass should have the frame holes for mounting the crossmember in the position for that transmission. You would need to use a Chevrolet-type transmission crossmember or one from the aftermarket, however, as the B-O-P crossmember will likely interfere with the 200-4R pan. You will also need a way to control the lockup torque converter, but the aftermarket offers kits for this.
It would also be possible to adapt the TH700-R4 or 4L60E overdrive transmissions, if desired, but the conversion would be even more involved and the crossmember would have to be moved back about two inches to line up the rear mount. You would also have to have your driveshaft shortened, and if opting for the 4L60E, you would need a stand-alone electronic control unit.
Lokar Performance Products • 877-469-7440 • lokar.com
Summit Racing Equipment • 800-230-3030 • summitracing.com
MGB Five-Speed Conversion
I have a #2 condition 1975 MGB and I would like to convert the four-speed British manual transmission to a more economical five-speed unit. I recall that your Hemmings Sport and Exotics magazine mentioned in the December 2012 issue that this was possible and the article also listed several five-speeds that could be adapted. I believe they listed European Ford and Toyota options? I would appreciate any information as far as resources, degree of difficulty and any additional required parts to complete the installation. I don’t recall if a kit could be purchased or if the necessary items needed to be sourced separately.
Thomas Buntenbah, via Hemmings.com
Well, your MGB isn’t exactly a muscle car, though you could give it a dose of muscle power—more on that later.
Several donor options are offered for this four-speed to five-speed upgrade. Brittanicar in Canada sells a conversion kit used in conjunction with a donor Nissan FSW71C transmission, used in many 1998-2004 Nissan Frontiers. The transmission itself is not part of the kit, but the kit includes the proper flywheel, crossmember, clutch assembly, engine backing plate, clutch slave, driveshaft yoke, transmission mount, and gear reduction starter.
FAB-TEK makes an adapter kit that allows you to use a Tremec T-5 five-speed gearbox from a Fox-era Mustang or F-body GM car. The engine adapter plate is manufactured based on the transmission/bellhousing combination you source. The crossmember needs to be modified and FAB-TEK offers this service as well. All necessary parts are ordered a la carte, but the transmission must be sourced elsewhere. Contact FAB-TEK for further details or view their conversion pdf online at their fast-mg.com website.
One last alternative is a complete conversion kit offered by Moss Motors that uses a Mazda MX-5 five-speed transmission that has been adapted by Vitesse for easy installation in any 1962-’80 MGB, including those with V-8 conversions—there’s the muscle car part. The kit contains everything needed to install, including crossmember, adapter plate, driveshaft, clutch, shifter, and clutch slave. So maybe think about slipping a V-8 in there while you do that trans swap!
Brittanicar • 514-637-6661 • brittanicar.com
FAB-TEK • 970-564-5822 • fab-tek@live.com, Fast-mg.com
Moss Motors • 800-667-7872 • mossmotors.com
All discussions in this column regarding repairs, conversions, parts swaps, etc. are offered as suggestions. Performing any such work should be accompanied by thorough research to verify proper parts compatibility and procedures to achieve a safe, functional result. We welcome any and all questions related to suspension, brake, engine, differential and transmission upgrades. Email us at swapmeet@hemmings.com or submit inquiries to our Facebook page, www.facebook.com/HemmingsNews or our website where comments can be made at the bottom of dozens of previous Swap Meet articles posted there
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