Transmission & Driveshaft FAQ
Everyone has their own opinion regarding transmission selection for a Jaguar conversion. Most people feel the 3 best choices are the Chevy Turbo 350, Turbo 400, and Turbo 700-R4.
The Turbo 350 is very suitable; is abundant and most easily incorporated into the Jag/Chevy engine swap.
The (short shaft) Turbo 400 is the best choice for performance considerations. It is more robust than the T350 but is harder to find and more expensive. It makes driveshaft fabrication more difficult, but it is the way to go if one has the need for speed (but not MPG). Note: be aware that you need a "Chevy" style TH-400 with a short 4" tailpiece; they are getting rare.
The Turbo 700-R4 is the best choice for pre-1981 XJ vehicles-- due to the higher rear-end gear ratios on older cars. On a Jaguar with 3.31 rear end gears, the overdrive T700-R4 will drop engine speed from 2500 RPM to 1750 RPM at 60 MPH. Highway fuel economy will increase about 30% and general wear-and-tear on the engine components will be reduced. Avoid pre-1985 versions of these transmissions, as they have known reliability problems. Also, a switch is required to operate the lock-up feature of the torque converter in high gear-- failure to do so will cause damage to the transmission. B&M sells this "Power Switch" for about $40 and it includes wiring instructions. It is also possible to have a hydraulic version of this valve installed within the transmission.
Note: When searching for a 700-R4 for use in a conversion, remove the torque converter, and look on the front plate inside the bell-housing for the casting number. Get one with the last three digits being 732. This ensures a 87 or newer unit with the best of GMs updates.
This table list the most common GM automatic transmissions and thier gear ratios
This second table should also be useful-- It shows the most common GM transmissions as well as the overall gear ratios when they are used with the factory Jaguar rear-end ratios. This table should help greatly with transmission/rear-end ratio selection:
lists selected GM transmissions and their overall gear ratios
Torque converters and transmission coolers:
The transmissions from high performance GM cars generally have a higher stall speed torque converters and higher shift points than stock vehicles. After market performance torque converters like the B&M Torque Master 2000 can also be used to raise the lock up point of the converter by about 500 RPM over stock.
The benefits of these high performance torque converters-- is a better mating of the Chevy engines torque output to the Jags engine/vehicle matchup. It allows the engine to rev a little higher and to get into the camshafts "power-band" resulting in improved acceleration, smoother feel, and reduced "creeping" at idle. Disadvantages are reduced fuel economy and higher transmission oil temperatures.
Since heat is the number one reason for transmission failure; the Chevy/Jaguar conversion requires a transmission oil cooler due to many factors: Heavy car (4000 lbs), tall gearing (2.88 ratio rear end is typical), performance torque converter (if used), and Chevy powered Jags run hot in the first place. For these reasons, a heavy-duty cooler should be installed in the radiator when it is being made, and an additional external cooling radiator should be installed. The Hayden #403 is a good choice. Mount it in series with the internal Radiator cooler and in front of the A/C condenser.
Using the proper Chevy drive shaft and yoke will allow you to use U-joints that fit the drive shaft, transmission yoke, and Jaguar differential flange. New, the U-joints will cost only about $8 bucks each. Buy the "heavy-duty" variety if possible.
Drive shaft Yokes:
The GM Powerglide, TH-350, 200-4R, and 700-R4 transmissions all use the same style output shaft. But, only two of these yokes will work with the Jaguar conversion-- the Powerglide and the TH-350. The yokes from both the 200-4R and 700-R4 have U-joints that are larger (too large). If possible, obtain a Powerglide yoke (Spicer/Dana P/N# 2-3-4911X) because the U-Joint is about 3/4" closer to the tail of the transmission. This will reduce the amount of vibration by reducing the amount of play allowed between the U-joint and the tailshaft bushing.
The (short shaft) TH-400 yoke is entirely a different case. It is larger in diameter, and the shaft is only 2 ½" long. If you must purchase a new after-market yoke (very likely), you will need to have it cut down to 2 ½" from the flange to the end of the shaft. It is likely the drive shaft shop will argue that this is too short-- it IS correct. If it makes the shop feel better-- advise them that the drive shaft "telescopes" only slightly because the differential is in a "fixed" position.
Jaguars and certain Chevys use the same size U-joints. Therefore, the Jaguar differential flange will perfectly attach to a Chevy drive shaft of the proper length and diameter. Go to a wrecking yard and obtain a Chevy drive shaft with a diameter of 2.75" and external U-joint retaining clips. Measure the drive shaft length that is needed, from the centers of the U-joints at the yoke to the differential flange (center to center). Double-check your measurements. Although it is possible to find, and use, a used drive shaft at a wrecking yard-- it is advisable to have it taken to a drive shaft shop for balancing and checkout. Do not use a drive shaft that is dinged up. It is not overly expensive to have a new drive shaft tube welded to the old shaft ends.
A used drive shaft and yoke is about $20 at a wrecking yard, 2 new U-joints about $16, and a new tube and balancing around $85. Total cost is less than $125 for a first class drive shaft. Note: It is difficult to find 2.5" TH-400 yokes-- purchase a new one for about $45 from the drive shaft shop.
A good source of proper length drive shafts are 1970-78 Novas, Skylarks, Omegas, Venturas, and Apollos. You can also find 2.75" diameter drive shafts on Vegas, pickups, and Malibu's.
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