1985 GMC Jimmy Transmission Swap - B&M 700R4 Transmission

Before

B&M Helps Our Jimmy Get Off the Trailer It was a sad phone call. Our friend and freelance photographer Alisa "Bean" Morrow called us and said she needed a tow. After fighting a good fight, her '85 GMC Jimmy's high-mileage 700-R4 transmission decided that Third gear and Overdrive required too much effort, and it simply gave up. Rather than take our advice, she listened to another friend who used the most used and abused words in the automotive repair world, "Oh, I know a guy who can fix that." After six weeks and a Jimmy that still needed a transmission, she finally realized that she needed more help than "a guy who can fix that" could provide. Enter B&M Racing and a magazine guy eager to help.

After

B&M Racing knows transmissions-it's what they do-so the choice to unbolt our broken hunk of junk and install a tried-and-true transmission was a no-brainer. It also helps that B&M doesn't just sell you a rebuilt factory transmission with a shift kit with the pretense that it's a performance tranny. No, their transmissions are built with many brand-new performance parts and don't leave the factory until they're dyno tested to ensure optimum performance. Complete with Corvette 2-4 servo assembly, recalibrated valvebody, new bands and friction plates, and a shift kit designed to provide crisp 1-2 shifts, the new B&M transmissions are ready to rock right out of the box. All we needed was a new Tork Master torque converter, adjustable B&M throttle valve kick-down cable, and electronic torque converter lock-up controller, also from B&M.

For some of you, the thought of converting a 4WD fullsize Jimmy into a two-wheel-drive truck is heresy, and we understand that viewpoint. But, for this owner's mostly freeway driving and for better fuel mileage from the thirsty Quadrajet-equipped 350ci V-8, we opted to install a very street-friendly B&M 700-R4 with overdrive. If you've heard transmission horror stories in the past and those stories have scared you away from doing a swap yourself, this article will hopefully shed some light onto the truth about transmissions. With a little mechanical know-how and basic handtools, you too can resurrect your truck back onto the street and off the trailer.

It was a sad sight when we arrived at Bean's house, the broken-down Jimmy was parked in the driveway with no clue that B&M Racing had come to its rescue by way of a new 700-R4 transmission.
It was a sad sight when we arrived at Bean's house, the broken-down Jimmy was parked in th
Unfortunately, "a guy who can fix that" took the original tranny out of the truck, so we can't show you those steps, but here is a quick rundown: unbolt the exhaust crossover tubing, unbolt the starter and flexplate cover, along with the three torque converter bolts on the flexplate, remove the driveshaft, disconnect the fluid lines, remove the speedo cable, dipstick, T/V cable, and electronic connector on the driver side. Make sure you have the tranny supported with a large jack and a piece of wood to disperse the weight under the fluid pan and remove the transmission housing bolts from the block and slowly pull the transmission free.
Unfortunately, "a guy who can fix that" took the original tranny out of the truck, so we c
Opening the box from B&M immediately impressed us. Only a company who takes pride in their product goes to such an extent to ensure it gets to you undamaged. There's a 700-R4 under there, we promise.
Opening the box from B&M immediately impressed us. Only a company who takes pride in their

Our first step was to add a quart of B&M's Trick Shift performance transmission fluid to the B&M Tork Master torque converter (sold separately). We chose the Tork Master 2000 for its low cost, solid construction, and street friendly 1,900-2,100 rpm stall.
Our first step was to add a quart of B&M's Trick Shift performance transmission fluid to t
Moving to the transmission itself, we lubricated the torque converter pump drive with some Trick Shift fluid and then slid the Tork Master converter onto the pump drive. We made sure to slide the converter (while rotating) all the way onto the pump drive until we heard the second "click", indicating it was completely engaged.
Moving to the transmission itself, we lubricated the torque converter pump drive with some
An important step was to double-check the converter's engagement by measuring the distance of the torque converter's drive lug face from the edge of the bellhousing. To do this, we used a straight edge and tape measure to ensure there was at least 1-inch inside the front edge of the bellhousing.
An important step was to double-check the converter's engagement by measuring the distance

With the torque converter engaged, we placed the transmission on a large jack with a wide piece of wood on the jack cup to disperse the weight. A jack alone will crush the tranny pan.
With the torque converter engaged, we placed the transmission on a large jack with a wide
These alignment dowels do what they sound like, they help you align the tranny when bolting it in place. As you can see, there was orange paint on them from a rushed paint job and we made sure to scuff them down to ensure proper alignment.
These alignment dowels do what they sound like, they help you align the tranny when boltin
We also screwed in two double-ended 3/8-inch exhaust studs into the block to help us slide the transmission in place. Bean's brother Darren stepped in and maneuvered the jack while we lined the transmission up to the block.
We also screwed in two double-ended 3/8-inch exhaust studs into the block to help us slide

This wasn't a good sign. A rag-tag assortment of bolts were taken out of the transmission, so we took this time to go buy Grade 8 hardware for the new B&M trans.
This wasn't a good sign. A rag-tag assortment of bolts were taken out of the transmission,
Making sure the trans was flush against the engine block and not angled in any way, each bolt was tightened and torqued to 35 lb-ft from the inside out. The three M10x1.5 flexplate bolts were then installed to the torque converter and torqued to 35 lb-ft.
Making sure the trans was flush against the engine block and not angled in any way, each b
The next surprise we ran into was the transmission mount. Above, you can see the larger two-bolt mount that came on the Jimmy and below is the new mount we bought to work with the B&M 700-R4. This mount was for an '85 Camaro with a 305ci V-8.
The next surprise we ran into was the transmission mount. Above, you can see the larger tw

Because of the different trans mount, we had to drill one large hole in the factory crossmember and then we could bolt it in place. The entire crossmember had to be moved back a few inches too. After drilling a few holes, we bolted in back in place.
Because of the different trans mount, we had to drill one large hole in the factory crossm
One thing we should have checked before we started was the speedometer gear adapter. This goes in the back of the tailshaft housing and connects to the speedometer cable. Unfortunately, the original (right) was longer and smaller in diameter than the B&M 700-R4. We picked up a used one (also for an '85 Camaro) for around $30 at a trans shop.
One thing we should have checked before we started was the speedometer gear adapter. This
Next, we simply pushed it in place, made sure the O-ring was sealed and then bolted on the retaining C-clip.
Next, we simply pushed it in place, made sure the O-ring was sealed and then bolted on the

It was now time to slide in the speedometer cable adapter (included in the B&M lockup controller) and screw it onto the gear adapter.
It was now time to slide in the speedometer cable adapter (included in the B&M lockup cont
The B&M rpm signal adapter was then threaded in and the original speedo cable attached to it.
The B&M rpm signal adapter was then threaded in and the original speedo cable attached to
We opted to use B&M's electronic converter lockup controller, which will allow us to adjust the rpm shift range. The four-pin connector simply plugged into the transmission and the wires were routed inside the cab.
We opted to use B&M's electronic converter lockup controller, which will allow us to adjus

The shifter linkage was then installed and a cotter pin was used to secure it in place.
It was now time to replace the throttle kickdown (aka detent or T/V) cable. The cable is located on the driver side of the carb, connects to the carb linkage, and is held in by two barbed plastic clips. After we unclipped the linkage, the plastic barbs were depressed and the original cable pulled free.
It was now time to replace the throttle kickdown (aka detent or T/V) cable. The cable is l
The new detent (T/V) cable from B&M is adjustable and included several different linkage clips to fit different applications. We laid the cables next to each, marked the length and cut the new cable to the right length (with an inch or two of slack for adjustment) and then installed the cable.
The new detent (T/V) cable from B&M is adjustable and included several different linkage c

Once the other end of the cable was connected and bolted down to the tranny, Darren pressed the gas pedal to full throttle and we made the final tension adjustment to the cable. This step was very important, as the life of the tranny can be cut short if the adjustment wasn't right. Proper tension varies, but ours was a little looser than a guitar string.
Once the other end of the cable was connected and bolted down to the tranny, Darren presse
Here you can see the original line fittings that were removed from the old tranny and will be reused in the new B&M unit and the two new grommets, one for the dipstick and one for the other end of the new B&M detent cable.
Here you can see the original line fittings that were removed from the old tranny and will
With the line fittings in place, we used a flare nut wrench to tighten the tranny fluid lines to the B&M trans. The original dipstick was then routed down and pushed into the grommet.
With the line fittings in place, we used a flare nut wrench to tighten the tranny fluid li

Our final piece of the trans puzzle was a new driveshaft from the pros at Drivelines, Inc. in Mission Viejo, California. We took several key measurements (pinion U-joint cup to tailshaft with the truck on the ground) and in just a few days, we had the perfect-length driveshaft ready to go. It should also be noted the original trans slip yoke used the larger, heavy-duty unit and the B&M uses the smaller, car yoke, so a new yoke was added to the new driveshaft.
Our final piece of the trans puzzle was a new driveshaft from the pros at Drivelines, Inc.
Almost ready for a test drive, we wired up the electronic B&M converter lock-up control unit and mounted it underneath the dash. For the owner's driving style, we kept the lock-up point at the lowest setting. After adding a couple quarts of fluid and then starting the truck and letting it warm up, we shifted through all of the gears and checked the fluid. Our trans was thirsty, as we almost went through an entire case (12 quarts) of Trick Shift fluid. Once it was topped off, this Jimmy was ready for the road.
Almost ready for a test drive, we wired up the electronic B&M converter lock-up control un

FROM THE DRIVER SEAT
This was the first transmission I've installed and besides the 4WD to 2WD issues (like new tranny mount, crossmember relocation, the welded crossover exhaust tube, and buying a new driveshaft), it was a straightforward process. Thankfully, we didn't have a hard deadline, so working on it for a full weekend wasn't a big deal and like all wrenching, several trips to the parts and hardware stores were required, (but when aren't they required). Now the truck has a crisp 1-2 shift and strongly holds each gear, helping get the big Jimmy down the highway. The best parts of this install are seeing the Jimmy driving under its own power, keeping a cool truck on the road, and knowing we did the work ourselves.

YOUR QUESTIONS ANSWERED

Time Spent Working: A Weekend
Degree Of Difficulty: Moderate
(mechanical ability and ability to follow instructions are key)

Tools Needed:
Large hydraulic jack, jack stands, assorted wrenches and sockets, flare nut wrenches, screwdriver, torque wrench, rubber mallet, wide piece of wood for tranny support

Parts Used:
B&M 700-R4 transmission 117101 $1,686.81
B&M Tork Master 2000 rpm torque converter 70420 $244.65
B&M Lockup control 70244 $186.13
B&M T/V kickdown cable 70242 $39.95
B&M Trick Shift transmission fluid $59.99 (case of 12 quarts)
Used speedometer gear adapter $29.99
Miscellaneous Grade 8 bolts for tranny housing $11.00
Transmission mount from '85 Chevy Camaro $12.99
Driveline's Inc. custom one-piece driveshaft $300.00

Total: $2,571.51
(All B&M prices from Bmracing.com, all others vary by location and do not include tax, shipping, or installation)

SOURCE
B&M Racing 9142 Independence Avenue Chatsworth CA 91311 818-882-6422 www.bmracing.com	Drivelines, Inc. 25651 Taladro Circle Mission Viejo CA 92691 949-951-9673 www.drivelinesinc.com