Borg T5, behind a Merc Flathead, rattles if I put it into overdrive under 40 mph. Sounds almost like a really bad throwout bearing. However, if I go back to 4th, speed up over 40 mph, everything is fine. I'm clueless about the T5, so I'm wondering if this is normal, or I'm looking at a rebuild in the near future. I'm not absolutely positive, but I don't think it is a WC. The shift pattern is wide, which I like. When I had my close pattern in a '95 Corvette, I would go from 2nd to 5th fairly often. Go easy on me for that, as I'm an old guy who grew up with Borg T10 and Muncie 4 speeds...
Just my opinion but you shouldn't be putting that thing in overdrive below 40. I'd say you at least need to get it up to 60 miles an hour before put it in in overdrive. The rattling you here is could be pinging or just the engine bogging down really bad cuz of the low RPM
What is your engine RPM? Overdrive in most transmissions is not designed to be run at low engine speeds. I believe that you are lugging your engine - that is destructive to the engine, transmission and drive line. Suggest you wait until at least 50 MPH before going into 5th - and down shifting when slowing down below 50 MPH. UPDATE: What wheeltramp said... Russ
We don't know what your axle ratio is, but why use overdrive under 40 mph? My 88 Mustang 5.0 had an AOD and stock 2.73 gears. I left the shifter in 3rd below 45 mph. Cars that are computer-controlled are more forgiving, but I'm ***uming, considering your question is on this forum, that your car is not computer-controlled.
Yeah, stop doing that. Your 1995 Corvette had a much more powerful V8 than even a $10k blown flathead could ever hope to be. It also had something that your flathead does not have: a complete digital engine management system that included, but was not limited to, fuel delivery, spark curve, knock sensing, etc. The Wright Brother's plane and a F-35 are both airplanes. You are operating that flathead far too far under the torque peak at that speed, in that gear. 4th is 1:1. That is the same top gear as the original 3-speed that came behind the flathead. You should not be operating it in gears 1-4 any differently than the way that it was intended to be operated with the original gears 1-3. 5th gear is for ABOVE that operating range. It is for modern freeway speed (or marked equivalent road) capability.
I thought the flathead should be kept to a lower RPM, and I normally was putting it in 5th around 45mph, to keep RPM's down. A few times, I did it under 40, and it rattled. Sure sounded like the ******.Anyway, how high can I safely take the RPM's? And, what is top speed for a stock '50 Merc Flatty? I was just thinking that the modern cars seem to cruise just over 2 grand all the time....
Should also add, the rearend is Ford 8", and I was told gears were 3.50, however 1st is like a granny gear, and shift to 2nd is necessary just after getting her rolling...
I cruise down the highway in my flathead powered sedan at about 2500 RPM. It has a Merc crank, so I guess you could call it the same. I have tall rear tires, and a 3.78 rear gear.
Also, what is the fifth gear ratio? There are several, and I've got one that's 0.63:1. That puts even a 4.56 rear down to 2.87.
Install a tachometer and know what your engine speed is. Look up the horsepower and torque curves for your year of Merc flathead engine. You need to be cruising into the torque curve (the horsepower required approximately increases as the square of the vehicle speed - this is due to air resistance). I suspect that you are trying to run that poor flat head well down on the torque curve (i.e. too close to an idle) - the resulting strain will breaks something. Russ
Which one? I have never found one with a 0.75:1 5th. I have found: 0.72:1 0.73:1 0.76:1 0.78:1 0.86:1 I have swapped 5th sets for different derivative ratios, but never came up with that.
If he has an S10 T5 it is highly probable that it has the 4.03 1st and 0.86 5th In 1984-85 they had a 2.8 v6 S10 with a 0.76 5th gear [and the 4.03 1st] You are upshifting a little bit early. Lets compare with a stock 1989 Mustang. It would cruise at 65 mph in 5th [but you could change up earlier] The Mustang had a 3.08 rear and a 0.73 O/D 5th . This would cruise at 1925 rpm at 65 mph [with 25.5" diameter tyres] If you had 26.5" diameter tyres [and a 0.86 O/D 5th with 3.5 rear] you would be cruising at 50 mph at the same RPM as the Mustang. When you shift into 5th at 40 mph your engine is only pulling 1526 RPM If you shift into 5th at 45 mph [only 5 mph faster] your engine is now pulling 1717 RPM 5th is a cruising gear , not an accelerating / p***ing gear. But it still shouldn't rattle. First thing I would recommend is changing your driving style a bit [this is Free]. Also has somebody "Improved" your trans with a bronze shift cup or an aftermarket shifter? Put the delrin plastic cup back in....It takes away harshness. Stock shifters are also better ,regardless of what the aftermarket says [ The worst I've got out of an aftermarket shifter is 1 race meeting when all the springs break] Now if the noise / vibration progressively gets worse, the culprit is usually the little support bearing behind the 5th gear [into the tail housing] 5th gear places radial loads onto this bearing whereas 4th is direct drive.
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