Still haven't gotten my speedometer/cruise control working. Have replaced the VSS and ECM (for other reasons) so know they are OK. Does anyone know if you can purchase the buffer box for the VSS at Autozone? If so, what do you ask for? I've called and asked for a VSS Buffer box but they couldn't find anything on it. If they don't, anyone know where you can buy one and about how much they cost? Also, had a mechanic work on my car recently and he pulled the ECM out and didn't put it back up in the dash. Not sure how it fits back up in there? Can someone describe which end goes up first? Thanks for any help. 1991 Camaro 305 RS TBI.

I think I can help.

You can't get a VSS buffer from a regular auto parts store. You have to get them from a GM dealership or GM parts supplier. I had a very similar problem to yours (speedo wouldn't work at first, then randomly start working, and eventually quit working all together) and a new VSS buffer fixed it, although I did go through service manual info to test everything first.

Anyway, the cheapest place to get is GM Parts Direct, although it usually takes a week or two to get it. The part number for it is 25071437. If you need it immediately, than any GM dealership parts department can get it. The buffer is $30.57 at GM Parts Direct (not including shipping) while the dealership will charge $61.15, just for comparison.

http://www.gmpartsdirect.com/


As for the ECM, the end without the wiring goes up in the dash first. Once the ECM is all the way up, it should attach with some velcro and stay in the place. The wires will come out of the bottom of the ECM. I know that's not the best description, I'll see if I can't find a picture for you.

Ordered the buffer box. Finally got it today after about 3 weeks. Can anyone tell me where this goes? I looked up under the passenger side dash next to the ecm. There is a board inside a plastic box there but it looks nothing like this board. It has a number (25110819A) and has a lot more chips on it than this buffer box I ordered. Is the buffer box hard to find or should it be right up against the ECM?

Attached is a poor quality pic of the board inside the black plastic box next to the ECM with number 25110819a.

Can anyone tell me what this board is and where the buffer box is?

I responded to your e-mail with some pictures.

I have a similar problem...My Speedometer is not working (just bought a 91 RS V6).

I had a gauge cluster from my 91 (gutted for racing), so I swapped that, but the Speedo still didn't work...

I checked the VSS, the gears look good and the wiring look good.

I was going to try getting a new VSS, but from what you describe above, it sounds like possibly the buffer box is a better suspect?

If my VSS was dead, wouldn't I be seeing a "check engine soon" light? I'm not...

Assuming replacing the buffer box is the best option, can you tell me where it is...I've gutted out all the wiring from my other 91, but don't remember ever seeing something like that.

Also, did replacing the buffer box resolve your issue with the speedo??

In a perfect world, yes, you would see an SES light. But, I have seen many a VSS go bad without setting a code (other people on the boards, as well as myself).


Anyway, your 91 RS V6 doesn't have a buffer box. The only Camaros that got the VSS buffer box were the 88-92 305 TBI engine cars. The ECM controls the splitting of the VSS signal in all of the other engines, including yours.

What I would suggest in your situation, is to at least try a new VSS. Install the new VSS, and just see if your speedometer works again. If it works again, than you know the old VSS is bad, if it doesn't work, return the new VSS to the store, and start checking for other possible problems.

That makes sense...I'll try that. Glad to know I don't have a VSS buffer...it might have taken a while trying to find one that wasn't there!

When I called NAPA for a VSS, they told me that there are 3 different ones for that year Camaro... (ranging in price from $40-$90) I looked at the one I have and could not find any identifying part numbers or anything. They were talking about stampings that would identify it, but I didn't have anything close to what they were looking for.

Does it matter which one I get? And how do I figure out which on to try? I assume it's based mostly on rear-end ratio?

I may have to check with the dealer - but now I have to wait until Monday for that...

You can identify what type of VSS you have either 1 of 2 ways. The 1st is just from the part number on the old VSS. It's stamped on the VSS metal body right under the electrical connector (it's probably covered with dirt by now). The other way is by the RPO codes. The RPO code label is just a sticker on the inside of the rear locking storage compartment lid. Look for 1 of these 4 RPO codes on the sticker: D81, D8G, D8M, or D8N.

Depending on what store you go to, they will ask for 1 of those 2 things, usually the RPO code.


Something I forgot to mention earlier, is that if you happen to know someone, or have a friend with a scan tool or a laptop with WinALDL, you could have them hook it up to your car and see if the computer is reading MPH. This would just help you narrow down the possible problem. Just because, if the computer was reading/showing MPH, you would know that the problem is either the speedometer itself or the wiring to it. You don't have to do this, it's just something I forgot to mention.

I think I read elsewhere in this forum that WinALDL won't work on a 91 V6...because the 91 V6 uses 8192 baud and WinALDL expects 160 baud?

if true, that's too bad, because I was very interested in getting a cable and trying out WinALDL...

I honestly don't know, I don't really have much experience with WinALDL (yet, that is). Might be worth asking in the DIY PROM or V6 board, I'm sure someone will know for sure.

Do you have a picture of where the vss is connected to the transmission? My speedometer stopped working, and i've been trying to figure out where the vss is connected to the transmission. I've bought a manual for my 1991 camaro rs 305, but it doesn't show where the vss connects to the transmission. I know where the VSS is, but I don't know where it's connected to the transmission.

squierrel12000,

Get under the car on the drivers side, starting at the rear of the transmisson and going toward the engine the vss is the first thing that plugs into the side of the trans.

I got an email from you earlier today something about wanting a picture of the tailshaft. Did you email everyone on this site or was there a reason why you picked me? Just wondering cause I don't think I have ever posted in the electronice section or anywhere else about this. Besides, my car has a cable speedometer, not electronic.

I'll pile in with a question, or two of my own. The speedo in our 92 B4C is working intermittantly, slowly getting worse. When it works, it is usually rock-solid on the speed the car is going. If not, it is usually zero, or will spend some time bouncing around. One thing I have noticed is that the speedometer will occasionally bounce a bit even if the car is sitting at a light, with the trans in neutral, engine running. Does that help the problem diagnosis any?

I have checked the wiring, and it appears okay. It does not look like it has a break in either of the wires. I guess the next step is replacing the VSS, but does the above problem point to the 'buffer box', or could the speedometer moving while sitting still still be a sign the VSS is bad? Thanks, all,

Gene Beaird,
92 B4C 1LE, ex-Texas DPS
Pearland, Texas

My 91 RS 305 TBI speedo is out too. My check engine light comes on when I drive for about 5 mins. Cruise control does NOT work either. Does this mean that it's the VSS? I just ordered a new VSS from Autozone. Will be here in a week. If that doesn't fix it what do I check next? Thanks.

Got the VSS replaced in our B4C. All the parts guy needed was the engine code. Of course, I didn't know that but the other difference was the physical size of the unit; 55 mm dia or 23 mm dia. I got the 55 mm, because they didn't have the 23 mm unit in stock. Of course, it was the 23 mm unit. Waited a day and installed the new 23 mm VSS, and went for a test drive...... speedo is completely dead.

On the way to work this morning, on top of the speedo not working, the 'Service Engine Soon' light came on and shortly after that, the upshift light kept flashing on and off (I was in 5th). Not sure what the shift light means, but hopefully I now have a code saved so I can check. I guess I'll need to get a bufferbox next. Is the location well-described in the FSM? Thanks.

not to steal the spotlight BUT... my 89 (LO3 700r4) is setting off the 24/VSS code but the speedo is working all the time. it's not intermitten or anything. WTF? could still be the buffer box thing? Thanks.

If the car's not moving (according to my 85 manual), disregard.

JamesC

I'm looking to order a new buffer and I went to the link above, the gmpartsdirect link and put in the part number but it says no part can be found. Can anyone help?

Hello,

I was wondering if you could tell me/show me a picture where I could find the VSS buffer box on a 1991 chevy camaro rs 305?

Hello,

I have a 1991 chevy camaro rs 305. I was wondering if you could help me. I am trying to figure out where the vss buffer box is and what it looks like. Also, I would like to know if you know how to disengage the steering wheel airbag on.

I just want to turn off the airbag on the steering wheel so I can get behind the dash.

found mine, how I test if its the issue in my speedometer freaking out?

I am having the same problems with my speedo. I have a 85 IROC 305 TPI and the speedo either bounces around or does not work at all. I have another cluster out of a newer model (not sure what year) and it does the same thing. The VSS is new according to the PO and it looks new as well. I do have the buffer box that has been mentioned in previous post (mounted to the back of the cluster). I am getting the code 24 as well. What is confusing me is that I have a mechanical cable and the VSS/VSS bufferbox?? My next try would be the buffer box, but just looking for any additional input on my set up??

In addition to the speedo, my Tach is off also (reads higher than actual RPM). Have any of you had this problem too? If it's discussed in another thread please direct me to it.

Thanks!

The VSS, a yellow box located on the rear of your cluster, won't cause bouncing in your 85--and if the bounce occurs with both clusters, the problem probably lies in the cable itself. Check the following link for suggestions:

http://www.thirdgen.org/techboard/in...eedo-woes.html (Reasons for Mechanical Speedo Woes)

JamesC

The Tach doesn't bounce, just not accurate. would that still be in the cable??

Going to check out the link you sent as well.

Thanks

No.

JamesC

I have a 1990 Camaro RS and my speedo does not work. I put a 350 out of a 91 Z-28 and I still cant get the speedo working. question is could it be the VSS buffer box. I put a new VSS and gears on the Trans.

the 8th digit is a E. the car had a 305 TBI in it and I took that out for a 350 TPI

James C,

I will not get a chance to pull the cable and clean/grease it until later this week. But I have another question on the speedo, Now in addition to "bouning" it stopped working all together. I'm guessing I may need to replace the buffer in addition to the cleaning of the cable??

IIRC, your 85 isn't equipped with a buffer. Pull the cable and see what's what.

JamesC

OK, I'm confused. Is this the VSS buffer? This is mounted on the back of my cluster on my 85 IROC. It is actually behind the Tach, but runs to the speedo. I am pretty sure that it is the stock cluster, as it only has the 85mph speedo. If this is not the VSS buffer, then what is it and what is it's function to the speedo?

Oh, I see. The black piece near the speedo cable connection is the 'optic head.' The yellow box is the 'buffer' (the whole business is generally simply called the VSS). Here's the way it works from my 85 GM Shop Manual:

"This is the device that will supply the vehicle speed input to the controller. The optic head portion of the VSS is located in the speedometer frame. A reflective blade is attached to the speedometer cable/head assembly. The reflective blade spins like a propeller, with its blades passing through a light beam from a L.E.D. in the optic head. As each bade enters the L.E.D. light beam, light is reflected back to a photocell in the optic head causing a low power speed signal to be sent to a buffer for amplification and signal conditioning. This amplified signal is then sent to the controller."

In short, the VSS sends a signal to the ECM and to the cruise control module on your car (since your speedo is cable driven). It does not affect how the speedo reads.

JamesC

OK, It's starting to make a lot more sense now. Thanks for the clarification!!

So my speedo it self not working correctly has to be in the cable. I will examine and clean the cable later this week. I will let ya'll know the out come once I get it done.

I ordered my 92 RS 305 TBI & got it in March 92. It has 67,000 miles on it. Two days ago the Speedometer, odometer & tripometer quit & I got a check engine light. The light has gone out, the cruise control never quit & speedometer works some of the time, but not the tripometer & odometer. I do not think it is the sensor on the tail shaft housing due to speedometer works some and cruise works always. What is being called a VSS buffer on this page is what I have been told is a DRAC unit. I need to get this fixed as soon as possible & need to do as much of it myself as possible to save $$$$. Anyone have this problem? Anybody fixed it? Just need info. I really like my car and kept in the garage the 1st 11 years & only put 11,000 miles on the first ten years. It is my second favorite Camaro of my life. My favorite was a 76LT. This is my 3rd 3rd gen. My first was an 83 Crossfire Z28 & my second was a hotrod 84 with a 406, TH350, 3:73 posi, All my Camaros have been White with exception of a Red 02 SS SLP car. I prefered the 92 to 02. I have a 72, 73 RS & a 78 @ present have had 67,76 new,77, 79 new. I really like the 3rd gen the best but the 76 was neatest all around. Don't like the 5th gen & the 4th was dissapointing.

the board is for your Cruise control

Finally got a chance to pull the speedo cable. Cleaned it out with some brake cleaner and greased it as described (2/3 of the cable with white lithium grease, Don't have a NAPA close by for the grease you recommeded). The Speedo is working good now, just a slight bounce left at the lower speeds. Gonna check the cable routing and make sure there are no kinks or hard bends. Other than that it worked great!!

Thanks for the input!!

hey i am having the same problem. im wondering about this VSS box. I had a 92 305 TPI and went 350 CARBED with no ECM. i took the ecm out as well as the harness. only plugs i have left is the clear plug that i belive the ECM connected to under my pass dash.

- going through my factory harness i found the purple and yellow wire that went into the BIG connecter on me pass firewall(the connecter that hooks the engine harness to the internal harness that goes into 3 connecters that go into the ECM a green and 2 blacck connectors.)

- from what i researched my car dont have a buffer box it goes write into the ECM. i followed the wires and it seems to be correct.

i cut out the yellow/purple wire so i at least have the pigtail.

i have pics if needed im just wonding what i do from here and where do i connect the yellow and purple wire to.

http://www.thirdgen.org/techboard/tr...-problems.html (speedometer problems) - thats my thread that noone is responding too

I am having a similar problem with my 305 tpi when i bought the car the speedo did not work so i immediatly checked the vss and it was unplugged i plugged it in and started the car as soon as i put it ibto gear the car would stall. could this just be my vss failing? or maybe bad wiring?

also would the vss failing cause my car to shift funny?

does my 91 z28 305 tpi automatic with electronic vss have this buffer box mine doesnt work

Rptr. i would be guessing bad wiring, had a bad wire spot and my car would stall out. Now I am dealign with bad wirign againa nd she likes to stall in low rpms.

could the vss cause unusual shifting?

My speedo is jumping around in park and as I'm in park and rev the engine my speedo jumps between 0-100 mph. Could this be caused by a bad vss buffer?

Anyone have a vss wiring diagram for the entire speedo? My speedo is jumping all around in park.