I didn't see hardly any info on this, so I thought I would do a writeup on this.
Many V8 swappers, myself included, want to use the econo-4 speed MY8 Muncie behind their V8 because of the really nice cruising gear, and the ratios match well with the broad torque curve of the V8. There were 7,099 of these made in ’84. However, the case is an ’84 case, and does not have the same strength as the ribbed V6 case, so many swap the gear set into the stronger case.
Many regard the V6 Muncie as the strongest of all of the Fiero manual transmissions. Due to the design of the Muncie, it is possible to keep the V6 1st and 2nd gear, and the econo 3rd, 4th, and final. I did this writeup to show how easy it is to keep the lower ratio and stronger V6 1st gear and the stronger V6 2nd gear to better handle the V8 torque. The V6 1st gear also is more useful as you can shift at a higher speed.
Reasons to build hybrid: a) The hybrid 1st gear has a 6% lower ratio over MY8, thus can shift at a higher speed (10.99 overall 1st ratio is the lowest possible ratio of all 4-speeds). b) The M17 1st gear is 5% thicker than the MY8, and thus stronger. c) The M17 2nd gear has fewer, but larger teeth than the MY8 gear, and is stronger.
Other than the gear ratios and thicknesses, there is one other difference between the MY8 and M17. The V6 Muncie uses a one piece 3rd and 4th gear, while the MY8 has a separate 3rd and 4th gear on the output shaft. As a result the spline configuration between the two shafts is different, and they are not interchangeable. In the hybrid transmission, the M17 input shaft and the MY8 output shaft and ring gear is used, the gears that are swapped are the ones that are not machined as part of the shaft or splined on.
First, the gear ratios, tooth counts, and gear thicknesses of each transmission, as well as the hybrid. Thicker gears and less, but larger teeth are generally stronger.
This writeup assumes all components of both transmissions are in good working order (bearings, synchronizers, etc.) and do not need replacing. These components should be replaced if they are worn. Both transmissions used in this writeup were low mileage transmissions.
Case, Disassembly
Remove shift brackets and speedo sensor (Figure 1.1 & 1.2). Leave the "z" shaped bracket on the shaft that goes into the transmission.
Figure 1.1, Shift Brackets
Figure 1.2, Speedo Sensor
Place the transaxle clutch side down (Figure 1.3), use shims to keep the input shaft and axle seals from touching the surface. Remove the (15) bolts securing the clutch cover to the transaxle case. Leave two bolts threaded, one on each side, to prevent the two halves from coming apart just yet.
Figure 1.3, Case Bolts
Flip the transmission over, and remove those last two bolts. Use a plastic hammer to carefully tap the clutch cover from the transaxle case. Anaerobic sealant is used between the case and cover, instead of a gasket. (Figure 1.4, 1.5, 1.6, & 1.7)
Figure 1.4, Clutch Side Up
Figure 1.5, Case Halves Separated
Figure 1.6, Gears
Figure 1.7, Clutch Cover Removed
Remove the ring gear/differential assembly shown in Figure 1.8 & 1.9. It just lifts out.
Figure 1.8, Removing Ring Gear/Differential
Figure 1.9, Ring Gear/Differential Assembly
[This message has been edited by NJD85GT (edited 04-14-2012).]
Removal of Internal Parts Position the shifter shaft in the neutral position so that the shifter shaft moves freely and is not engaged in any drive gear. Bend back tab on lock and remove bolt from shifter shaft (Figures 2.1 & 2.2) Remove the shifter shaft and the shift fork shaft from the synchronizer forks as shown in Figures 2.3, 2.4 & 2.5.
Figure 2.1, Shifter Shaft Bolt, Close Up
Figure 2.2, Shifter Shaft Bolt
Figure 2.3, Shift Fork Shaft Removal
Figure 2.4, Shifter Shaft Removal
Figure 2.5, Shifter and Shift Fork Shafts
Remove the reverse shift fork shown in Figures 2.6 & 2.7 by disengaging from the guide pin and interlock bracket.
Figure 2.6, Reverse Shift Fork Removal
Figure 2.7, Reverse Shift Fork Removal
Remove the lock bolt securing the reverse idler gear shaft. This bolt threads in from the outside of the case below the idler gear. Remove the gear/shaft/spacer assembly as shown in Figures 2.8 & 2.9.
Figure 2.8, Reverse Idler Gear Removal
Figure 2.9, Reverse Idler Gear Removal Remove the detent shift lever and interlock assembly (Figure 2.10). Leave shift forks engaged with the synchronizers as shown in Figure 2.11. Do not remove the detent spring.
Figure 2.10, Detent Shift Lever & Interlock Assembly Removal
Figure 2.11, Interlock Assembly
Grasp the input and output shafts and then lift them as an assembly from the case. Note the position of the shift forks, shown in Figure 2.13, for aid when reinstalling later. Remove the shift forks (Figures 2.12, 2.13, 2.14, & 2.15)
Figure 2.12, Shift Forks on Gear Shafts
Figure 2.13, Shafts/Shift Forks
Figure 2.14, Shift Forks Removed From Gear Shafts
Figure 2.15, Input and Output Shaft Assemblies. Left: Input Shaft, From Bottom: 4th, 3rd, 2nd, Reverse, 1st. Right, Output Shaft, From Bottom: 4th, 3rd, 2nd, 1st, Pinion to Ring Gear.
[This message has been edited by NJD85GT (edited 04-07-2012).]
Slide the left hand bearing and 4th gear from input shaft. They slide off very easily. (Figure 3.1)
Figure 3.1, Bearing and 4th Gear Removed
Remove brass blocker ring, Shown in Figure 3.2. Remove the snap ring from the 3-4 synchronizer (Figure 3.3).
Figure 3.2, Brass Blocker Ring Removed
Figure 3.3, Snap Ring (On Shaft Next To Synchronizer Behind Splines) Slide 3rd gear and 3-4 synchronizer from input shaft. They also should slide off easily, a press should not be needed as shown in the figure from the manual (Figures 3.4, 3.5, & 3.6).
Figure 3.4, From Right: Bearing, 4th Gear, Brass Blocker Ring, Synchronizer Sleeve With Snap Ring in the Middle (Do Not Need to Remove From Synch. Hub), Synchronizer Hub With 3rd Gear Underneath
Figure 3.5, Bare Input Shaft
Figure 3.6, Removing 3-4 Synch. and 3rd Gear (Input)
[This message has been edited by NJD85GT (edited 04-07-2012).]
Locate the M17 input shaft, and place the MY8 3rd gear onto the shaft, oriented toward the 3-4 synchronizer. Install the brass blocker ring onto the gear cone, then install the 3-4 synchronizer, using an appropriate cylinder to contact the hub, near the shaft. Do not press on the sleeve portion (Figure 4.1). Both synchronizer hubs are a press fit to the shafts. I just hand placed them on the shaft, no cylinder needed.
Figure 4.1, Installing 3rd Gear and 3-4 Synchronizer.
Install the snap ring to retain the 3-4 synchronizer. Be sure to position snap ring with beveled edges away from synchronizer for later access with snap ring pliers (Figure 4.2).
Figure 4.2, Installing Snap Ring.
Install brass blocker ring. Slide the MY8 4th speed gear onto shaft, oriented toward the 3-4 synchronizer and slide left hand bearing onto the shaft.
[This message has been edited by NJD85GT (edited 04-13-2012).]
Using support plates behind 4th gear, press on the end of the output shaft to remove 4th gear and the left hand bearing (Figures 5.1 - 5.3). I used a small 5-ton press.
Figure 5.1, MY8 Assembled Output Shaft. Notice the separate 3rd & 4th Gears.
Figure 5.2, 4th Gear and Bearing Removed.
Figure 5.3, Pressing 4th Gear Off.
Remove the snap ring retaining 3rd gear. Slide the 1-2 synchronizer assembly into first gear position to allow press plates to support 2nd gear. Press 2nd speed gear and 3rd gear from the output shaft. Remove the brass blocker ring (Figures 5.4 & 5.5).
Figure 5.4, Pressing 2nd & 3rd Gears Off.
Figure 5.5, Pressing 2nd & 3rd Gears Off.
Remove the snap ring retaining the 1-2 synchronizer. Using press plates behind 1st speed gear, press 1st gear and 1-2 synchronizer from the output shaft (Figures 5.6 & 5.7). I was able to do this without the press.
Figure 5.6, Pressing 1st Gear Off.
Figure 5.7, Disassembled MY8 Output Shaft.
[This message has been edited by NJD85GT (edited 04-13-2012).]
Remove the retainer from the left hand end of the shaft. The retainer and shaft are designed with LEFT HAND threads. This retainer uses a triple square bit, and is torqued to 45 ft•lb, and I was unable to remove it without starting to strip it. Because you do not need to use the M17 output shaft for this hybrid transmission, I used a grinder and cut the flange off the retainer. Using support plates behind 4th gear, press on the end of the output shaft to remove 3rd/4th gear and the left hand bearing (Figures 6.1 - 6.4). Third and fourth gear is a one piece gear on the M17 transaxle.
Figure 6.1, Assembled M17 Output Shaft
Figure 6.2, 3rd/4th Gear Removed.
Figure 6.3, 3rd/4th Gear.
Figure 6.4, Pressing Off 3rd/4th Gear.
Slide 2nd speed gear from the output shaft. Remove the brass blocker ring. Remove the snap ring retaining the 1-2 synchronizer. (Figure 6.5).
Figure 6.5, 2nd Gear Removed.
Using press plates behind 1st speed gear, press 1st gear and 1-2 synchronizer from the output shaft (Figure X). I was able to do this without the press.
Figure 6.6, Pressing Off 1st Gear.
Figure 6.7, M17 Output Shaft & Gears.
Figure 6.8, M17 Output Shaft.
[This message has been edited by NJD85GT (edited 04-14-2012).]
Locate the MY8 output shaft, and place the M17 1st speed gear onto the shaft, oriented toward the 1-2 synchronizer. Place the brass blocker ring onto the gear cone, then install the 1-2 synchronizer using an appropriate cylinder to press on the hub, near the shaft. Do not press on the sleeve portion (Figure 7.1). I just hand placed them on the shaft, no cylinder needed.
Figure 7.1, Installing 1st Speed Gear and 1-2 Synch.
Install the snap ring to retain the 1-2 synchronizer. Place the brass blocker ring into position. Place the M17 2nd speed gear onto the shaft, oriented toward the 1-2 synchronizer, then press the MY8 3rd gear onto the shaft, with its hub toward 4th gear. Use an appropriate cylinder to contact 3rd gear hub near the shaft (Figure 7.2). I inverted the shaft, placed 3rd gear on support plates, and pressed on the right hand end of the shaft with my press. When you can install the snap ring in the groove, you have pressed enough. (Figure 7.3).
Figure 7.2, Installing 2nd and 3rd Speed Gears.
Figure 7.3, Pressing 3rd Gear Into Place.
Install snap ring to retain 3rd gear. Press the MY8 4th gear onto the shaft, with its hub toward 3rd gear, using support plates. Install left hand bearing cone on the shaft. (Figure 7.4).
Figure 7.4, Installing 4th Gear and L.H. Bearing.
[This message has been edited by NJD85GT (edited 04-13-2012).]
The following section is optional, but highly recommended to set the correct pre-load on the bearings. This requires special shim selector tools, I bought mine off of Ebay for $17.
Shim Selection
Place the input and output shaft assemblies and the MY8 differential assembly into their installed positions. Remove the input, output, and differential bearing cups and shims from the clutch cover. Place the (3) right hand bearing races onto their respective bearings.
Position (3) gages; J-26935-2 on input bearing and J-26935-4 onto output bearing. Be sure the bearing races fit smoothly into the bores of the gauge tools (Figures 8.1 - 8.5).
Figure 8.1, Shim Selector Kit.
Figure 8.2, Shim Selector Kit Instructions.
Figure 8.3, Shim Selector Kit.
Figure 8.4, Gauges In Position.
Figure 8.5, Gauges In Position.
On J-26935-4, (output shaft), install oil shield retainer into bore on top of tool.
Carefully assemble the clutch cover over the (3) gages and onto the case, using (7) spacers placed evenly around the perimeter. Retain with bolts provided (Figure 8.6).
Figure 8.6, Compressing Gauges.
Draw the cover to the case by tightening alternately and gradually. Torque bolts to 10 ft•lb. This will compress all three gauge sleeves. Rotate each gage to seat the bearings. Rotate the differential case through three revolutions in each direction.
With the three gauges compresses, the gap between the outer sleeve and the base pad is larger than the correct preload shim at each location. Carefully compare the gap to the available shims. Determine the largest shim that can be placed into the gap and drawn through without binding. Then use the next shim size smaller on the output shaft and differential for reassembly. On the input shaft, use a shim 2 sizes smaller. If end play occurs, use the next larger shim sizes (Figure 8.7).
Figure 8.7, Measuring Gap.
When each of the three shim sized has been selected, remove the clutch cover, (7) spacers and (3) gauges. Place the selected shims into their respective bore in the clutch cover, add the metal shield and then install the bearing cups.
[This message has been edited by NJD85GT (edited 04-13-2012).]
Place the input shaft and output shaft together, on a bench. Install the two shift forks in the same configuration as when they were removed earlier.
Grasp the shafts as an assembly and carefully lower them into the transaxle case. Use care not to nick gears. Don’t forget the little plastic oil shield on the ends of the shafts.
Replace the detent shift lever and interlock assembly into the case. Install the shifter shaft through the interlock bracket and the detent shift lever. Do not extend further at this time.
Install reverse shift fork onto the guide pin. Be sure the reverse shift fork engages the interlock bracket.
Install the reverse idler gear and shaft into position. Be sure the long end of the shaft points upward, and the large chamfered ends of the gear teeth are facing up. Install the spacer onto the shaft. The flat on the reverse idler shaft faces the input gear (shaft).
Fully install the shifter shaft through the reverse shift fork, until it pilots into the inhibitor spring spacer. With the shaft in neutral position, install the bolt and lock through the detent shift lever. Bend tab of lock over bolt head.
Install fork shaft through the synchronizer forks and into the bore in the case.
Carefully install the MY8 ring gear and differential case assembly.
Apply a thin bead of anaerobic sealant (do not use RTV) to the clutch cover (Figures 9.1 & 9.2), then carefully install the cover onto the transaxle case, using the dowel pins to guide the cover into position. Tap the clutch cover gently with a plastic hammer to insure that the parts are seated.
Figure 9.1, Anaerobic Sealant.
Figure 9.2, Anaerobic Sealant.
Install the (15) attaching bolts. Torque to specifications.
Torque idler shaft retaining bolt in case.
Shift through the gear ranges to test for freedom of movement of all internal parts.
Replace shift brackets and speedo sensor.
Spend a week cleaning your trans case and then paint it. Enjoy!
Cleaning Case.
Primered.
Nice and Shiny.
Torque Specifications.
[This message has been edited by NJD85GT (edited 04-13-2012).]
Does anyone know if there is any provision for the later magnetic VSS available that will work with this trans?
Yes. AFAIK, it uses the same VSS and drive gear as the 282. This means you just pop the drive gear off the diff carrier, press the reluctor onto the diff carrier and install the magnetic VSS in place of the gear driven VSS.
Originally posted by NJD85GT: Output Shaft Disassembly, MY8
Using support plates behind 4th gear, press on the end of the output shaft to remove 4th gear and the left hand bearing (Figure X).
Remove the snap ring retaining 3rd gear.
quote
Originally posted by NJD85GT: Output Shaft Disassembly, M17
Using support plates behind 4th gear, press on the end of the output shaft to remove 3rd/4th gear and the left hand bearing (Figure X). Third and fourth gear is a one piece gear on the M17 transaxle.
As has been alluded here, the M17 uses a single cluster gear for the output sides of 3rd and 4th. The MY8 uses individual gears, pressed in place and retained with snap rings. The output shaft splines are DIFFERENT for the two configurations. Thus it is not physically possible to install the MY8 gears on the M17 shaft (or vice versa), even if you wanted to.
Not a drag racer anymore, if I were taking a 4.9 Fiero to the drag strip it would be my 4.9/4T60E Formula.
With the 3.33 final in the 4T60E. it pulls better than most 4.9 swaps, the PO claimed a 7.8 sec 1/8 mile on 225/50/15's at Nashville.
I've never had it to the track.
I've read RockCrawl saying the deeper final drive in the automatic didn't really do much for the car's 1/4 mile performance, but did affect gas mileage.
In Northstar cars, the stick cars are quicker because they're 200# lighter... The weight advantage of the Muncie vs. the 4T60 is only about 150#. I've read anecdotes describing the short gearing of the 282 hurting the 4.9's straight line performance due to it's high torque and low redline; I was guessing that taller gearing would benefit a car with that engine because it's a "puller" rather than a "revver".
The best gas mileage I've gotten on the interstate is 32 MPG on long runs.
Typical fuel mileage averages about 25 with mixed driving.
Maybe someday I'll take it to the strip, but it isn't a big priority.
Back to the topic of this thread, I was thinking the hybrid 4 speed would make for good autocrossing, track days and also keep the RPMs down when driving on the highway.
This is great timing as I think I might have spotted an MY8 in an old junkyard (RPO sticker ripped out ugh! but it is a definite base model coupe), and have been wondering what to do about my high RPM speed on the highway, AND have to split the case anyway to install an input shaft seal! Great write up and if I do end up going this route I'll let you know how easy it was to follow with the pieces in my hand.
Was the Fiero the only GM car of the era to receive the MY8, or did it also appear in some of the FWD models?
As far as I can tell, yes. Some other cars came with a 3.32 final but still had the 0.81 4th, which is better than nothing if you can't find an MY8, this writeup would still apply.
Nate
[This message has been edited by NJD85GT (edited 04-14-2012).]
so now that you have done all of this work, find me a car I can find another MY8 tranny from. I have been looking for one for a few years now.
And this is a great write up. thumbs up to you.
There is a local guy here that I'm pretty sure has one, and doesn't know what he has. I was trying to buy it from him but he dropped off of the face of the earth...I wanted to build myself a spare one. Shipped my first one from the east coast!
I know it calls for anaerobic sealant, but does anybody know why not RTV? I think I used that "RightStuff" to reassemble mine...
Hmmm..
Here is what someone else wrote about this, sounds reasonable:
Aside from the fact that it sets up better than RTV-type sealants and is less prone to leaking, I like anaerobic sealant because any excess that is not clamped in the mating surface does not set up (hence the name), and remains oil-soluble. This means that no little globs form on the inside of the transmission, like when RTV-type sealants are used. Those little globs can potentially cause issues.
Originally posted by NJD85GT: Spend a week cleaning your trans case and then paint it. Enjoy!
The dishwasher does a fantastic job of cleaning aluminum castings quickly with no fuss (except from the wife, unless you found a good one...). However, you either have to remove all the steel parts (bearing races, etc.) first or get the case out as quickly as possible when the dishwasher's done and WD-40 the steel parts.
I go over such parts thoroughly with the parts washer at the shop first to get the grime and scunge off. The dishwasher is only for the last bit of clean to get it looking nearly new.
[This message has been edited by Will (edited 04-15-2012).]
You get a HUGE PLUS and THANK YOU from me. This is sad for me to admit, but before I knew what an MY8 trans was, I blew up 2 in my Race built 2.9 Fiero. I thought they were just regular 3.65's and tossed them to scrap to be melted down, it was my 3rd trans that I put in, that was a 3.65 and I thought I had just F-D up and installed a 4.10 because the car oddly reved really high compared to my last 2 4spds. I found out that I installed a 3.65 and my previous were the 3.32's. I am now running a Getrag behind my 4.9 V8 and HATE IT. If it wasn't for the fact that I blew up 3 Isuzu's I would still be running the Isuzu Trans as the 5th in the Isuzu is really close to the 3.32's 4th gear revs.
If I can't find another 3.32 4spd, I am going to take an Isuzu apart, get it Cryo Treated and then install it. There was a woman on this forum running a Cryo Treated Isuzu behind a 383 SBC and had not blown it up. So I might be safe with the 4.9 and a little Nitrous.
Again Thank You Very Much for the Info.
------------------ 857GT Part 85GT Part 87GT Part Caddy, 93 Eldorado 4.9, 5spd Dual O2 Custom Chip, Custom Exhaust. MSD Everything Now with Nitrous. Capt Fiero --- My Over View Cadero Pics Yellow 88GT 5spd Full Poly Suspension, Lowered 1/2" in front, Corner Carver.
Just a little note I found out today after taking both of these transmissions apart, the shifter shafts and select levers are different between MY8 and M17, so you can not mix and match them. The M17 only has one piece on the side with a bigger "pin", while the MY8 has two smaller pins. I would think the M19 lever/shaft is the same as the MY8 as well, since they are both 84 4-speeds.
M17 on the left, MY8 on right.
EDIT: One thing I did forget to add, was that on both transmissions when I pulled the input and output shafts out at the same time, all of 4th gear and that bearing fell off the input shaft.
[This message has been edited by mattwa (edited 12-17-2012).]
Enjoy!
