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85 300D transmission gear vs engine RPM discrepancy
My 85 300D has a 722.315 4 spd automatic with the following gear ratios
At 60 mph, the tach read around 2800 RPM. I would think that at 60 it would be in 4th gear? If I plug in the numbers into this really useful online calculator Gear Up! In 4th gear (1.0 ratio) at 60 mph, 2.88 diff, 195 70R 14 tires, The engine should be doing 2347 RPM. This does not match what my tach is reading. If I use 3rd gear in the calculator (1.44 ratio), at 60 mph, engine should be at 3379 RPM, which does not match my tach either. I don't think the transmission was in 3rd since it did not sound like the engine was spinning that fast and it was quiet. Where do you think this discrepancy lies? My idle is set to 750 RPM at idle with a digital timing light so the tach is accurate (at least at idle). Could the tach be off at the higher RPM's? I counted 3 shifts starting from a standstill to 60 MPH. This transmission is supposed to start in 2nd so it did shift to 4th. Your thoughts?
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85 300D turbo pristine w 157k when purchased 161K now 83 300 D turbo 297K runs great. SOLD! 83 240D 4 spd manual- parted out then junked |
#2
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Quote:
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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar. 83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles 08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles 88 Jaguar XJS V12 94,xxx miles. Work in progress. |
#3
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OP, plug in 3.07 for the rear ratio and see where it lies. Keep in mind, the torque converter slips raising the rpms at speed about 200ish RPM
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 190D 2.5Turbo 1987 190D 2.5-5SPEED!!! 1987 300TD 1987 300TD 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere! |
#4
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If 3.07 works out, the speedo or the diff is not correct to the car. Have you verified the speedo to be accurate with a gps or mile markers?
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 190D 2.5Turbo 1987 190D 2.5-5SPEED!!! 1987 300TD 1987 300TD 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere! |
#5
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3.07 is 2501 RPM in 4th, 3602 in 3rd
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85 300D turbo pristine w 157k when purchased 161K now 83 300 D turbo 297K runs great. SOLD! 83 240D 4 spd manual- parted out then junked |
#6
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I have checked the speedo with GPS before and do not remember it being off. I will check it again as well as check the diff and transmission p/n's.
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85 300D turbo pristine w 157k when purchased 161K now 83 300 D turbo 297K runs great. SOLD! 83 240D 4 spd manual- parted out then junked |
#7
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I have fixed a number of tach amps like yours when the cig butt trick no longer works. Send it to me if you want it fixed.
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85 300D turbo pristine w 157k when purchased 161K now 83 300 D turbo 297K runs great. SOLD! 83 240D 4 spd manual- parted out then junked |
#8
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Keep in mind the TC slippage. Bumps the rpm 2-300
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 190D 2.5Turbo 1987 190D 2.5-5SPEED!!! 1987 300TD 1987 300TD 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere! |
#9
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Definitely take into account the torque converter slippage. I think it's like around 10% - 12% slippage.
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1983 123.133 California - GreaseCar Veg System |
#10
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Here are pics from my 85 300D taken this morning.
One pic with needle at 3000RPM The other was with the Speedo needle at 60MPH. |
#11
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also, the RPM's will vary depending on load, road angle, wind direction and acceleration/deceleration.
it looks like funola has close to average RPM at 60, with the 85. the car may have a slipping TC, or it may have been climbing a hill at the time of the pic...
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 190D 2.5Turbo 1987 190D 2.5-5SPEED!!! 1987 300TD 1987 300TD 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere! |
#12
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1. The transmission was not warmed up and torque converter slippage was higher. 2. The tach calibration is off by around 100 rpm (reading 100 rpm higher than actual). I rigged up my remote photo tach and took a video after driving the car for about 8 miles and got a freeze frame from it at 60 mph (my pic of the tach needle now nearly matches your pic with speedo at 60 mph). In this freeze frame, photo tach = 2530 RPM, cluster tach = 2625 RPM (95 RPM higher than actual). At 60 MPH in 4th, RPM should be 2347 with no torque converter slippage. 2530-2347= 183 183/2347 = 7.8% So my torque converter is slipping 7.8% at 60 MPH (level cruise)
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85 300D turbo pristine w 157k when purchased 161K now 83 300 D turbo 297K runs great. SOLD! 83 240D 4 spd manual- parted out then junked |
#13
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I would think the 7.8% slippage would be normal. Whole reason that auto trannys are not as efficient as a manual tranny. Some loss due to the extra work required to transfer energy and heat loss. On another note; I'm going to try to dial in my IP based on the suggestion you had for eaton9999. I have a borescope available and I'm gonna remove the cap on the side of the IP, set the crank to 15 atdc and align the notch. I was drip timed to about 25 degrees (slightly advanced) and noted some mild shudder at 3000 rpm; retarded back to original position (factory notch striked on side of IP). All seems ok.... for now. I got some new DN0SD240 nozzles that I want to pop test and install, before I tweak the timing again. Temps in the 50's today. Gonna wait til it warms up again before I brave the elements.... brrr. |
#14
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Make a funnel with a hose into a bucket when you remove the IP RIV port bolt = no mess. About a 1/4 qt of oil will come out. A small funnel that fits in there has too small of a spout and will spill over especially with cold oil so cut a bigger funnel to fit. Put the oil back in the IP when you're done. It fills very slowly and I don't know if that's a problem or not- better safe than sorry. How slow IDK. I had it idling for 10 min and no oil came out of the port and I didn't want to idle longer to find out.
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85 300D turbo pristine w 157k when purchased 161K now 83 300 D turbo 297K runs great. SOLD! 83 240D 4 spd manual- parted out then junked |
#15
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Average fillup is at around 415 miles and takes about 15 gallons. I've never seen below 27.4 and never above 27.6. Usually fill at the same station and stop at the first auto stop by the fuel pump dispenser. I'm about 60% at 65mph on the freeway and the rest at 40ish with some stop and go. All flat. Summer time with AC on in the afternoon, average might drop to 26.5. Next question would be are you pushing any white smoke, (unburned fuel)? I assume there are no leaks in the engine bay or at the tank feed and return? How does it run overall; Idle quality, rpm at idle? Does the governor have full control of the idle, or have you had to bump it with the external adjustment at the throttle linkage inboard of the IP? I put the new nozzles in this morning. Ran good but had a little knock; had the timing slightly retarded, edged it exactly back to the hashmark strike and all seems to have settled down. Seems to run quite a bit smoother than it did with the monarchs (261's) that I put in earlier this year. I know lots of folks like them, but i just wasn't happy with them. They spray different than the 240's and the car was just inconsistent in idle quality and general operation. One day an absolute pleasure to drive, the next would be uneven idle, occasional mild surging felt at 65 mph. Have 2 injectors that have a minor leak at the halves, gonna have to take em back out and do some more polishing. Don't have any shims, but all are popping between 1850 and 1925. Wrote the numbers down just in case I come across some shims on the cheap; will likely try to fine tune them another day. Might get lucky and find the leakers are the low ones and might get them to come up with more polishing. I've discovered that you'll never know if they are gonna leak until you run them. On your car, keep in mind that it's great to have the timing dead on per the fsm, but if your injectors are popping low, this will affect the actual injection timing at the cylinder. I'm thinking Low pop pressure will advance the timing for that particular cylinder, higher pop pressure will retard it. So the timing set to fsm is great, but it has to marry up with injectors that are spraying correctly and popping at 135. There is a check in the fsm that has you; (I have not done this test) 1. Cap off the main return line from #1 injector to the IP 2. Hook up a piece of tubing to each injector return. (Cap the other like on number 5) 3. capture the fuel from each return line and measure the quantity . Supposed to run it at 750 rpm for 2.5 minutes. Captured fuel should vary by less than 1.5cc You'll need 5 pieces of 4mm tubing cut to 24 inches. 5 pieces of 4mm tubing cut to 1.5 inches with a plug inserted to plug the unused return nipple. 5 containers to capture the fuel. Mike |
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