I have an 87tr, the speedometer cable is two pieces. When I went to disconnect the lower portion of the cable from the upper portion I noticed that between the two cables is a black triangle looking thing. It looks like it slows down the upper portion of the speedometer cable. The reason I was messing around with the cables is because the speedometer wouldn't go over 45mph. I took that triangle looking thing out and now the speedometer seems to be working fine other then jumping a little. Does anyone know if this should be there, I'm thinking probably not but am not 100% sure. The way it looks to me is it was placed there to keep the odometer from racking up to many miles???? If anyone knows please let me know.
TIA
Ron K.
Is it possible your car had a 145 MPH speedometer face installed? Some of these units come with a device like you describe to make it read properly with the new face. However, it does make the odometer register incorrectly. (i.e. low)
There currently is a 145 MPH speedometer in the car now. With that piece installed on the cables the speedometer will not read past 45 MPH, when I take it off it seems to read correctly.
When I took that piece off I noticed that when the car shifts into overdrive it seems to bogg, meaning I'll hit the gas and nothing, the rpm's don't change, if I floor it the car does finally down shift and is OK until it goes back into overdrive. If I put that piece back on or disconnect the two cables all together the car is fine when it shifts into overdrive. I thought that maybe because I took that piece off that there was less slack in the speedometer cable and I was possible crushing a vacum line or something but that doesn't seem to be the case. Do you have any ideas why this would happen?
I appreciate your help, thanks.
Generally, I would think the piece should be in there, as the stock speedo only goes to 85. The reducer is usually in there to reduce the speed of the 'speedo' end of the cable so that full scale is 145, not 85. Otherwise, you would have to recalibrate the speedo. Which is probably the best option since that would let your odometer read correctly, too. Since yours does go to 145 (presumably) at full scale with it *out*, it doesn't appear to need the 'adapter'.
The 'bogging' you're getting is probably due to your torque converter clutch locking up early. (Not due to going into OD) The TCC makes the torque converter a 'direct drive' and elimiates the normal slippage. Most street chips set it to lock around 45 MPH at normal cruising throttle. When you hit the gas, it will unlock. With the adapter in the line, it appears that its causing this all to happen at a much lower speed. Probably because the VSS (Vehicle Speed Sensor - which is up in the speedo) thinks the car is going faster than it is. It tells the ECM that you're already at 45 (or whatever) MPH, and then your TCC locks, even though you're not going that fast.
My guess is that you have a combination of issues. The speedo may have indeed been recalibrated to full scale at 145, or perhaps a different gear was used in the transmission to make the speedo read properly with the new face. However, it looks like in the process no one thought about the VSS getting the proper information.
The next question is whether or not your odometer seems to read correctly when the adapter is *left out* of the cable. This should clarify if the speedo is modified or the tranny gear is.
My speedometer is jumping around on my 87 GN. I thought this would be a good time to fix the broken trip odometer and convert to a 145 speedometer face plate. Is it necessary to replace both sections of the cable to fix the bobbing needle? When I called the GM dealer for replacement cables, he asked for the cable length and transmission type. Was there more than one set of cables? He also asked if I needed the adapter? I was going to take the face plate and speedometer for recalibration, am I going to have the same problem as Ron? What else needs recalibrated? Thanks!
Thanks again for your help. I tested the odometer and it appears to be off. My friends car showed "1.2" miles on the tripometer and my car showed ".7". I put the reducer back in and drove back to where I started and the tripometer showed ".5". What next?
Thanks,
Ron K.
Ron: Let me qualify my response by mentioning that all of this ASSUMES you still have the stock 3.42 gear ratio AND 200-4R transmission. If that's not the case, there are other factors to consider.
I'm guessing you have a different speedometer gear in your transmision on the end of the speedo cable. One that more or less is set up to make your speedo read right without the adapter. Probably one for a car with a 2.41 rear end.
Note that 85 MPH / 145 MPH =0.59 and 1.2(miles) * 0.59 =0.708 miles. I hardly think this is a coincidence. I'm also guessing that somewhere around 27-30 MPH in second or third gear (without the 'adapter' in line) is where you feel the TCC kick in and bog the car down.
First, come to grips with the fact that your car probably has more miles than you thought. Perhaps 30% more.
Next, if you want EVERYTHING (speedo, odo, and VSS) to read right AND your TCC to work right, you'll probably need to get a stock ratio speedo gear, and have your speedo head unit recalibrated to read right with the 145 face.
Brian: The needle bouncing could be a speedo problem, cable problem, or cable lubrication problem. The TRs use a two-piece speedo cable. I don't believe any adapter should be required. You may be further ahead to buy a faceplate and go to a good speedo shop from the start for some help putting it all together properly.
Scott,
Thanks for your help, Is there an easy way to verify the gear ratio?
The car currently does not have posi so I'm assuming the gears are probably still stock. I'll check the tranny to make sure it's correct. When I bought the car I knew it had problems, you live and learn.L I just hope it doesn't have to many.
Follow up to my previous message, I read the article on the site referring to buying a TR and in the article it said that the RPM's should be around 2100 in overdrive when doing around 60 MPH if you have the 3:42:1 gear ratio in the car. On the way to work I kept an eye on my RPM's, though I can't be 100% sure on the speed I believe I was doing around 60 to 70 MPH. In overdrive the RPM's were steady at around 1500. So can I assume from this that the gear ratio probably is not stock?
Thanks.
Ron K.
Ron,
First off, I hope you aren't going by the stock tach. It lights up, and the more the rpms go up, the more lights you get. But, I don't ever remember anyone saying that they had an accurate one.
Anyone,
As for the speedo cable. When I needed one, they had 3 combos listed I believe(It was a while ago). Anyways, they asked me for the length. My car had a 2 piece cable, but the only combo they listed that was long enough was a single cable. The other two combos were two part cable setups. Well, I figured I needed the length, so I ordered the one piece, and it came as a two piece in the same package.
Brian
When I used to hunt junk yards in my earlier days for a rear end that was out of the car there is an easy way to determine gear ratio.In your case you would have to jack up the rear of the car and drop the drive shaft.Next turn the flange where the drive shaft was bolted on and have a helper count the tire revolution.If you turn the flange 3.4 turns for 1 turn of the tire you have the stock rear end.If for example you would turn the flange 2.7 turns you would have 2.73 ratio.Bruce
Not to be a pain in the butt, but isn't there an easier way. Isn't there a math calculation I could use depending on speed, rpm, and overdrive gear ratio??
Thanks.
Ron K.
Sure. But you will need an accurate tach and/or speedometer, which we've already determined you are lacking.
I installed and Autogage tach per your instructions and it seems to working correctly, I can get an accurate speed by following someone on the highway at a predetermined speed.
Thanks,
Ron K.
Just to keep things simple, 3rd gear is a 1:1 ratio. So, if you're in 3rd with the TCC locked, your motor should be turning just as fast as your driveshaft. And if you're running a 3.42 gear, your wheels should be spinning at )(Motor RPM)/3.42) RPM. A stock size tire should rotate about 776 times in a mile. (26" tire is about 82" in diameter) And at 60 MPH, it would rotate about 776 RPM. Which translates to (776 * 3.42)= 2654 RPM.
So at 60 MPH with the TCC locked and the car in *3rd* gear, you should be showing 2654 RPM with a stock height tire and 3.42 gears.
Finally got the speedometer problem fixed, sorta. I've got the wrong rear in the car. The rear that's in there is a 7 1/2 inch, 8 bolt rear with 2:56 gears. So I ended up getting the speedometer calibrated and a new speedo gear put in the trans.
Well...that sure explains the problem, doesn't it? Something just wasn't adding up, and now its clear why.
If I were you, I'd be putting the proper rear end on my shopping list. The car is probably a lot more a slug than it should be with that 2.56 rear, and its not as strong as the proper 8.5" piece. If I'm not mistaken, the driveshaft may be different as well.