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View Full Version : 4th gear not 1:1??????Why??



fastsc92
08-17-2003, 09:35 PM
Ok i just got back from FFW at epping, NH. I live 30 min away so its a short drive. Anyways...i took the chance to get on the dyno there to make 3 pulls with a wideband 02 sensor. This dyno is a new style which doesn't use any drums. It is basically two boxes that bolt dirrectly to your rear wheels and the car rests right on them. They claim is the most accurate because there is no slipping. Anyways...they ask you what rear end ratio you have and what rpm you want to stop at. I told the guy 5500 to shut it down. The first pull he made, the rpm's were getting up there and it hit the rev limiter and he shut it right down. The dyno was supposed to tell him to shut it down at 5500. The car is run in 4th gear which is a 1:1 ratio. BUt, the machine said it was only at 5235rpms. For some reason the final drive in 4th gear is not 1:1. He asked me 3 times if i told him the correct rear end ratio, which is 3.27. I installed the gears myself and they are indeed 3.27's....the first thing when i opened the box was to count the teeth and divide and it came to 3.272727272727272727. The rear end ratio is correct..so something must be wrong with the tranny. He ended up tricking the computer and had to tell it that it had a 3.89 rear end ratio...which is bogus. I just rebuilt this tranny and there is no way that it could go together wrong. all the other gears are correct and shift smooth and fine. Why isn't 4th gear 1:1???? When i figured it out....the 4th gear is acttually 1.2 : 1. Why is this happening and how can i fix it? I am 100% sure that the rear end ratio is 3.27. Help me please. this also seemed strange because at the track...i am in 4th gear for almost half the track and pass the lights at 5100. Does anyone else have this problem with 3.27's in a speed???

XR7 Dave
08-17-2003, 09:51 PM
4th gear is 1:1. Something else is mixed up. I don't know anything about that dyno, so I can't help much.

MIKE 38sc
08-17-2003, 10:05 PM
Hehehehe:p

J57ltr
08-17-2003, 11:51 PM
Sounds like the clutch must be slipping. If you look in an exploded view of just about any 5 speed trans you will noitce that there isn't a fourth gear anywhere in there. This is because the input and output shaft are locked, hence 1:1 gear ratio.

Jeff

fastsc92
08-18-2003, 11:15 AM
i know...thats what i cant fiugre out. This has me sooo confused. I know his car inside and out and still...i cant figure it out. The clutch isn't slipping because there was a good size load on the engine and no slippage. Like i said...i dont see how the tranny could be messed up because it would't work right if it was together wrong. When i just rebuilt it i changed all the blocker rimgs and i also changed the 5th gear and 5th/reverse sleeve. Thats the only thing i've changed. All the gears work fine and each follows the one before it nicely. I dont know why......please help me fiugre out this huge headache.

David Neibert
08-18-2003, 11:30 AM
There is nothing to figure out...if there is any problem, it's with the dyno. BTW, I've never seen a dyno that used wheel speed to determine RPMS. They always use a plug wire or the negative side of the coil to pick up a tach signal.

David

fastsc92
08-18-2003, 12:08 PM
the kick who dynoed before me had a 90 sc....with a 5 speed and 3.27's also. His was right on the money. BEcause if 4th is 1:1.....then wheel speed should be rpm's. In my case it was way off.

DLF
08-18-2003, 02:10 PM
4th gear through the traps @ 5100 sounds like 3.73's to me.....

With your tire size and trap speed, I could tell you for sure.

J57ltr
08-18-2003, 02:19 PM
The clutch couls still be slipping. It's not like it's all or nothing (slipping), your brakes aren't all or nothing.

Like Dave said it could be the dyno or it HAS to be the clutch, since you say there cannot be slippige between the drive wheels and the dyno.

Jeff

fastsc92
08-18-2003, 02:41 PM
its a brand new clutch too...with about 1200 miles on it. I dont smell any clutch either. Usally it will stink, because i've had clutches slip before. my tire measures 26" in the back...and the mph is 101. I did the same thing and it says that i have a 3.89 rear end ratio. The dyno was suposed to be the most accurtate one on the market so i dont think its that. Like i said...there was an sc right before me and it worked flawlessly. It could be the clutch but i highly doubt it.

92strokedbird
08-18-2003, 02:46 PM
Do you have aftermarket wheels or a different tire size than stock!

fastsc92
08-18-2003, 02:51 PM
it has stock rims and a 225 60 16 tire. still....i'm baffled. I opened the inspection cover today and there was no clutch dust or any residue in there from slippage.

XR7 Dave
08-18-2003, 02:58 PM
Well, if you are sure about most all the stuff, it makes me think that you might have made a mistake on the gears. I know that stock and FMS gears have the ratio stamped right on them.

It should be really easy to verify gear ratio just by driving down the road and have someone pace you. Then just do the math to figure it out.

Clutch slippage would stink for sure, I don't think you'd miss that.

Also regarding the transmission, since the countershaft is solid, you can't mix anything up. It's not possible because it wouldn't go back together.

curse
08-18-2003, 03:07 PM
As far as I know Richmond does not make a 3.27:1 ratio for the 8.8, you might want check again. I wanted Richmond gear for my SC, when I called Summit to order them, they couldn't find them. I think they start at 3.55:1 for the 8.8, Good luck

fastsc92
08-18-2003, 06:41 PM
i ended up getting the gears from a local speed-shop. I too didn't see them in jegs, but he was able to get them and the first thing i did when i opend the box was to make sure that i counted the teeth on the ring gear and divided by the pinion teeth and it came to 3.27272727.......

MIKE 38sc
08-18-2003, 06:50 PM
There could only be 2 things causing that if theres no tire slipage involved.
1. The clutch is slightly slipping.
2. The guy running the dyno messed something up.

I dont have alot of faith in chassis dyno's and this kind of thing is why.
Its too easy to manipulate things in order to come up with #'s.
I will not use one unless I own it.

fastsc92
08-18-2003, 10:24 PM
i mean...it worked fine with the kid before me. also...does anyone else have 3.27's with a 5 speed. cause at the track i am holding 4th gear through the lights at about 5000rpms at 101mph. It seems like i'm in that gear forever, and i'm searching for another. anyone else have input on their gears?

MIKE 38sc
08-18-2003, 10:56 PM
Originally posted by fastsc92
i mean...it worked fine with the kid before me. also...does anyone else have 3.27's with a 5 speed. cause at the track i am holding 4th gear through the lights at about 5000rpms at 101mph. It seems like i'm in that gear forever, and i'm searching for another. anyone else have input on their gears?
I understand what youre saying but knowing what you know about your pull can you really say that 100% for sure the fella before you got any legitamite #'s either?
I've messed with dyno's for over 10 years and the only dyno I will use is a freestanding dyno that only has the engine bolted to the dyno pump.
Chasis dyno's could if used properly be usefull. Truth is I havent seen them used properly but a couple of times.
Most of these places offering dyno pulls are doing it for 1 reason to make money.
Alot of younger guy's put way too much faith in what gets printed out on a piece of paper after there pull like its some kind of trophy. Nothing could be further from the truth.
98% of the dyno printouts made today are only good for wiping your butt with.
Your experiance alone proves that.
I'm not trying to be a horses arse to you and I'm sorry and already appologised for our earlier misunderstanding. I really am sorry about that.
If you would like for me to further explain my stand on these dyno's let me know, I'd be happy to.

fastsc92
08-18-2003, 11:19 PM
oh i get what you're saying....but it jsut didn't make sense to me how it worked for the kid before me. and whe he said that it all kinda came together with how it was in 4th forever at the track. just making me think a lot.

DLF
08-18-2003, 11:23 PM
Originally posted by fastsc92
i mean...it worked fine with the kid before me. also...does anyone else have 3.27's with a 5 speed. cause at the track i am holding 4th gear through the lights at about 5000rpms at 101mph. It seems like i'm in that gear forever, and i'm searching for another. anyone else have input on their gears?

When I had 3.27's, I had to shift into fourth at about 1300 feet, just before the traps, and that's was with 275/40-17 DR's, about an inch shorter than the stock tires.

4th Gear 1:1 @ 5000 RPM with a 26" tire and 3.27's = 118MPH

4th Gear 1:1 @ 5000 RPM with a 26" tire and 3.73's = 104MPH

You don't have 3.27's.

DLF
08-18-2003, 11:32 PM
Here's a little gearing chart for the 89-93 M5R2 with 26" tires


RPM Ratio MPH

3.27's

5000 3.75 32
5000 2.32 51
5000 1.43 83
5000 1.00 118
5000 0.75 158

3.73's

5000 3.75 28
5000 2.32 45
5000 1.43 73
5000 1.00 104
5000 0.75 138

MIKE 38sc
08-18-2003, 11:32 PM
Its all in the comp runing the dyno. Theres an old saying I learned in electronics school about computers. "Garbage in---Garbage out"
I'm geussing he was having some problems with his programing but he didnt want to turn down making money from a couple of guys who wanted to do some pulls.
So he jerry riged it to give you a printout that came closer to sounding right. He knew what he was doing was bogus.
Save your money and quite worrying about what a dyno might say about your car. Its really not important anyway.;)

XR7 Dave
08-18-2003, 11:53 PM
Ya, DLF nailed it. You don't have 3.27's. Period. You have 3.73's and your tach is reading a little high. Most SC's do. End of story.

fastsc92
08-19-2003, 12:40 AM
ok....i dropped the rear end just a little while ago...i counted the teeth once again...and i DO have 3.27's. Now i have to wait for the silcone to dry before i put it back in the car. But i had to be sure. what gives? regardless of the dyno...my track mph shouldn't be what it is if i run through the lights at around 5000 in 4th.

DLF
08-19-2003, 01:47 AM
Originally posted by fastsc92
ok....i dropped the rear end just a little while ago...i counted the teeth once again...and i DO have 3.27's. Now i have to wait for the silcone to dry before i put it back in the car. But i had to be sure. what gives? regardless of the dyno...my track mph shouldn't be what it is if i run through the lights at around 5000 in 4th.

WOW! All you had to do was rotate the tire once and count the number of driveshaft revolutions......

2 3/4 = 2.73's
3 = 3.08's
3 1/4 = 3.27's
3 1/2 = 3.55's
3 3/4 = 3.73's

With a 26" tire and 3.27's 101 MPH is ~4250 RPM's in 4th. could be your tach is really messed up.

DLF
08-19-2003, 01:57 AM
Originally posted by fastsc92
ok....i dropped the rear end just a little while ago...i counted the teeth once again...and i DO have 3.27's. Now i have to wait for the silcone to dry before i put it back in the car. But i had to be sure. what gives? regardless of the dyno...my track mph shouldn't be what it is if i run through the lights at around 5000 in 4th.

BTW, What was your teeth count of the ring and pinion?

XR7 Dave
08-19-2003, 09:20 AM
Are you using the correct speedo gear? For 3.27's I believe it is the red gear. That wouldn't have anything to do with the dyno or the fact that you say you are running through the traps at 5100rpm in 4th.

Weird. That's all I can say.

Brianas
08-19-2003, 09:53 AM
I ran my car right b4 92 sc--what I know is that they had no other problems on the dyno for the 2 days they were there. I think they said they ran 12-13 cars. My 90 sc 5spd w 3.27 should be identical to what 92 sc had. Since your running a good shot of no2 I would bet on clutch slipping if ur gears are correct
Josh

fastsc92
08-19-2003, 02:07 PM
for my mph...i am going by what my trap speed is at the track..not my speedo. I also did change it to the red 21 tooth gear when i a did the gear swap. The ring gear teeth were 36 and the pinion was 11. equals 3.2727 if my math is right. AS for the clutch...i doubt it was slipping...like i said its brand new and i would have smelt something. The mystery goes on..................

racecougar
08-19-2003, 02:49 PM
Wow, a whole lot of debate over this. Your "problem" is very likely that your tach is just reading higher than the actual engine rpm. When your tach said 5500, the engine probably was turning 5235 rpm, just as the dyno said. If you're basing all of this off of a factory tach, you really can't expect it to be very accurate.

So they didn't even pop the hood when you got hooked up to the dyno? I also had never heard of a dyno calculating engine rpms from MPH, I've always seen them hook up to one of the plug wires.

-Rod

fastsc92
08-19-2003, 03:59 PM
the guy wsn't going by the tach though...he is going by what the computer tells him. Because if its in 4th gear.....it is 1:1....so every tire retation is one motor rotation....so he let the computer tell him when it was spinning at 5500 revs.

David Neibert
08-19-2003, 04:11 PM
Because if its in 4th gear.....it is 1:1....so every tire retation is one motor rotation..

You mean every driveshaft rotation...don't you.

David

fastsc92
08-19-2003, 05:52 PM
hey i got info for everyone. The guy at my local speed shop sold me the wrong gears. The serial number on the box matches the number in the summit book for 3.73's. What gives. I just counted and i could have sworn it was 36 teeth. I'll crack the case open again and see what i get. The gears have about 1000 miles on them, I dont think he'll take them back. What should i do? this is not funny at all.

racecougar
08-19-2003, 06:01 PM
Originally posted by fastsc92
the guy wsn't going by the tach though...he is going by what the computer tells him. Because if its in 4th gear.....it is 1:1....so every tire retation is one motor rotation....so he let the computer tell him when it was spinning at 5500 revs.

I must be misunderstanding. I thought your first post said that the car's rev limiter kicked in at 5500 rpms (according to the car), but the machine said that it was only at 5235 rpms.

-Rod

fastsc92
08-19-2003, 06:26 PM
the machine said it was at 5235...but the car hit the stock rev limiter...which is at 6300

GooeyGus2
08-20-2003, 01:42 AM
you should run a lot faster at the track when you switch back to some REAL 3.27's.

I would go in there and raise hell. he sold you the wrong gears, and it never hurts to try to get your money back or at least exchange for the right ones.

J57ltr
08-20-2003, 09:31 AM
So what you are saying is that you didn't actually count the teeth. I doubt you would have gotten them wrong twice.

Jeff

David Neibert
08-20-2003, 09:46 AM
I'll crack the case open again and see what i get.

You must be one hell of a mechanic, because the last time I pulled the pumkin and swapped it for another one, it took two experinced people with air tools about half a day.

We have to drop the exhaust, remove a wheel from one side, undo the upper link and pivot it to pull one of the half shafts, remove the ABS sensors, unbolt the drive shaft, unbolt the pumpkin supports and then lower while tilting the pumkin a little to remove the other halfshaft without dumping all that stinking gear oil on the floor. Seperating inspecting, cleaning and resealing/refilling the case takes at least another hour.

I'm starting to think your pulling our leg.

David

XxSlowpokexX
08-20-2003, 10:49 AM
counting teeth isnta problem..All yad have to do is take off th eback cover and mount..HJowever why count teeth when teh gears are alway sstamped with the ratio :O)

fastsc92
08-20-2003, 10:54 AM
no lie dude....when i did the gears before i got a bad set of motorsprt gears. I basically did the gear swap 4 times, becuase i thought i set it up wrong. turns out it was a bad set. Then i put the richmonds in from my speedshop that i ordered (3.27), but he got me the wrong set, becuase richmond doesn
t even make a 3.27. There were no markings on the box so i assumed it was right....anyways and i got a horible vibration....did the set-up two more times....turns out it was the u-joint. I can take that thing down in about an hour....doesn't take long if you've done it that many times. I un-bolt all the control arms from the knuckle, and put the axles out attatched to the knuckles. Take the rear exhuast off....unbolt the abs sensors and unbolt the pumpkin. I do it all myself and its about an hour to get it down. The first time i dropped it a little bit with the axles still attached....opened the cover and counted most of the teeth...i thought i got all of them. I put some stuff back on the cover and sealed it up. Then i got worried and opened it back up(didn't put it back in yet) and counted twice....and sure enough...there were 41 teeth on the ring and 11 on the pinion. which equals 3.7272727...or 3.73. now here's my problem....i dunno if the speed shop guy is going to get my another right for free. This was his screw up because i know this guy pretty well and he knows that i couldn't go anything over a 3.55 and that i only wanted a 3.27. Unless he heard me wrong, because i got 3.73 and the parts number match that. i'm going down there today to see what he says. I dont want my money back or anything..i just want the right set..and i still have to install them all over again which takes a good day to get the set-up right and press bearings on and off. luckly i have a press at my house and the tools to do the job right.
also..when i punched in my rear end ratio and a 3.27 ratio.....the two are almost the same acording to speed vs rpms. In gears 1-3...the mph is only 6mph difference at best. But when you hit 4th and 5th gears...this is where the numbers start to change a lot. And it makes sense because the speed at 5000rpm in 4th is suposed to be 104 with a 3.73 rear end and i was running 101 at the track. no wonder why my times were so bad this year.

fastsc92
08-20-2003, 10:57 AM
oh also...the richmond set wasn't stamped with the ratio on the ring gear side. I looked for that too. I know ford does it but its not on my set., all they have is their little logo.

David Neibert
08-20-2003, 11:20 AM
Okay..sounds like your getting pretty quick at pulling the pumpkin.

I would suggest selling the complete pumkin to one of the automatic guys or trading pumkins with one of them. You can easily get $100 and a 3.27 pumkin for yours.

I know Scott Long was looking for someone to trade 3.27s for 3.73s a couple days ago.

David

fastsc92
08-20-2003, 11:36 AM
ya but the thing is...when i had some noises that turned out to be a bad set...i changed every bearing and race in there. I did the axles bearings....carrier bearings, races...and both pinion bearings and races, plus all the seals and i rebuilt the posi and shimmed it up tight that sometimes it wants to lock all the time. It has since wore in so that it akways locks when going straight but stays loose in the corner. I would trade but i spent a lot of money and i know that its all brand new in there. If i trade with someone else then i'll be stuck with a rear end that could fail at any time.

MIKE 38sc
08-21-2003, 01:18 AM
I got a set of used but good 3.27's.
They werent noisy and theres nothing wrong with the gears.
I changed to a different ratio.
If interested PM me and make an offer.

fastsc92
08-21-2003, 10:26 AM
i rather stay away from used only because they wear in to the pattern for that car and when you switch to another car..they start to make noise because its not used to meshing a different way. I've done that before with other cars i've owned and it was a headache. The killer thing is....i'm stuck with these gears because the speed shop wont take them back and neither will richmond. So i'm out a little over 200 bucks. And...these gears only have about 800 miles on them..which is basically mint. what to do now. Only motorsport makes a 3.27 set, and richmond were very easy to set -up. anyone want a set of 3.73 richmonds?..lol

MIKE 38sc
08-21-2003, 05:47 PM
I'll trade dead even with you. Used good 3.27's for used good 3.73's. You pay shipping to me and I'll pay shipping to you.
Hows that?
If you install them and have a problem I'll swap back with you, no qeustions asked. If you set the backlash and mesh right you wont have any problems with these gears. They are well within spec and have NO problems.;)

fastsc92
08-21-2003, 05:54 PM
i just rather stay new. But you can take these if you want....$150....only 800 miles.

MIKE 38sc
08-21-2003, 06:01 PM
No thanks. No problem, another fella wants them. I just thought I would offer a fellow SCer first.:)