Topic: New Cluster Question Merged

[79 Rebel]

ok sounds great
tomorrow
i will do it

[OrigOwner77]

Just swap speedo's.  As for the wires, we'll tell you how to change the locations if necessary.  The white cluster has numbers on it if you look closely.  Just tell us the color of wire that corresponds with each number.  With that information and a picture of the back of the cluster, we can tell you exactly what you need to do.

Exactly...except for swapping speedometers. I believe the OP has an 85mph unit on the old cluster (80/81-style), and has purchased the correct 100 mph unit. Can the clip be removed from the old speedometer and placed on the new one? If I recall correctly, it can. I *believe* it just (pardon the term) clips to the speedometer.

[79 Rebel]

thats what im thinking
i think it will slip right on
because yes this is the correct cluster now 'i noticed the speedo works great but somethings when hits 20 it has to catch up
i think thats because the clip is not there to keep it secure

[OrigOwner77]

It could be jumpy if the cable isn't properly seated. The cable could also need lubrication. I believe white lithium grease has been suggested before - just spray some in each end of the cable (speedometer-end and transmission-end).

Not to scare you, but I have had a speedometer go bad mechanically and jump. However, I gather this is a rarity and would believe your issue to be related to the cable not being secured.

Try swapping the clip over and seeing if that helps first.

[79 Rebel]

ok
yes it works great
nice and steady
but sometimes when you floor it
it stops and 20 then catches up
i think it neeeds to be secured

[mattoree]

Hey guys. Just joined here on the forum. Happy to be here. Got a question for you all. On my 1978 trans am, my speedometer is incrementally off. As in the faster I go, the more its off. Around 70mph on my gps, and the speedo reads 65. And it obviously gets worse the faster I go. I have changed the cable as mine too was melted by the exhaust. Although it was off before the cable melted. After I replaced the cable, its still off but does at least work again. I actually used it as an excuse after getting pulled over for speeding. Ha. Any thoughts on what it could be? Anybody have this problem? Any help would be really appreciated. Thanks
Matt

[Wallington]

Nothing to do with cable or being melted or speedo fault, simply rear gear ratio does not match speedo gears in gearbox. Or by the sounds of it in your case, the tyre profile has been changed to something slightly taller than stock so it is going slightly faster than it thinks it is. Easy to fix if you want to, just depends on the combinations of above. Not sure they'd accept that excuse for speeding, more than likely they'd start to look around and find other faults.
Also, headers can be one thing with the speedo cable melting the sleeve, make sure the retainer is in place that holds it off as well, on inside of chassis rail.

[mattoree]

thanks! Yes, I have headers and no cats. At the time I had them installed, shortly after the cable melted. I replaced that but the speedo has been off since I bought the car in 2007. I thought the car was a ws6, but turns out someone just upgraded the wheels to 15x8 probably sometime ago. That being said, that's just a wider wheel. I'll have to check the tire size that's on it now to see how different it is than a stock size. How would I know what gear to change it to? Where is the gear located? According to the code on the rear, it has stock 2.56 gears unless they have been changed, but I don't think so.

[Wallington]

Assuming all the gears and diff ratio are standard, the speedo gears for 2:56 should be a Red 17-tooth Drive gear and a Light green 34-tooth driven gear. That was one of the common combos, based roughly around a 26-27" diameter tyre. Blue 18/White 35 tooth is also another combination used..

Here's some handy links, one to a calculator once you know your tyre diameter. The other is a handy shop of parts. Remember that the BOP TH350 does not use chev TH350 gears, but the TH700 type. This is not often made clear in shops and ads who only chev.

http://www.bgsoflex.com/speedo1.html

https://transmissioncenter.net/shop/700r4-driven-gear/

[mattoree]

oh super cool. Thanks for the info! Much appreciated. My trans is the 400 turbo. Just checked, my tires are eagle good year 255 60 R15. So the stock ones should of been 70 series. I guess that's where the problem is. So I'll have to change the gears then. How hard of a job is that?

[Wallington]

A 255/60 will be similar diameter to a 225/70. The fact you have a non-original th400 means it prob has anything for the speedo gears. Unplug the cable and shine a torch in can at least tell colour or housing type. That is If you have a th400 and not just a previous seller saying so.