IndustrialDeere Posted July 10, 2006 Share Posted July 10, 2006 So I finally got my B-75 on the road this weekend. She's got a duplex tranny, 22" rears, 4.5 ratio, and her top speed at 1900-2000 rpms was 48mph. With a tail wind she hit 49mph. I checked the ratio by counting revolutions and by looking on the Mack spec sheet. She is a single axle with a 673 engine. We were in the Granny lane and being passed like we were standing still. I think the speedometer is correct. Thanks. Quote Link to comment https://www.bigmacktrucks.com/topic/1289-b-75-going-too-slow/ Share on other sites More sharing options...
Freightrain Posted July 10, 2006 Share Posted July 10, 2006 You need to check the numbers on the tranny to see if it's a DIRECT or OD Duplex. If it's a direct...I could see it not barely running low 50's. You need to confirm speed with another vehicle.My single OD Triplex, 4.62 gears, 22" rubber will run ~65mph. Take the OD off and you get about 52 mph. Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment https://www.bigmacktrucks.com/topic/1289-b-75-going-too-slow/#findComment-6501 Share on other sites More sharing options...
IndustrialDeere Posted July 12, 2006 Author Share Posted July 12, 2006 You need to check the numbers on the tranny to see if it's a DIRECT or OD Duplex. If it's a direct...I could see it not barely running low 50's. You need to confirm speed with another vehicle.My single OD Triplex, 4.62 gears, 22" rubber will run ~65mph. Take the OD off and you get about 52 mph.I don't think I have overdrive---I think it is direct.java script:emoticon('', 'smid_2') How tough is it to install OD? Thanks for the response.I don't think I have overdrive---I think it is direct.java script:emoticon('', 'smid_2') How tough is it to install OD? Thanks for the response. Quote Link to comment https://www.bigmacktrucks.com/topic/1289-b-75-going-too-slow/#findComment-6536 Share on other sites More sharing options...
terry Posted July 12, 2006 Share Posted July 12, 2006 I don't think I have overdrive---I think it is direct.java script:emoticon('', 'smid_2') How tough is it to install OD? Thanks for the response. Look i think on the left side of tranny ,behind fill plug should be a flat spot with numbers should be a trt or trtl 72 or 720, 72 is a single overdrive a 720 is a double overdrive. If yours is a single overdrive it would be easier to find a different trans. that is a double over. terry Quote Link to comment https://www.bigmacktrucks.com/topic/1289-b-75-going-too-slow/#findComment-6537 Share on other sites More sharing options...
HK Trucking Posted July 12, 2006 Share Posted July 12, 2006 Also the engine should be running at least 2100 rpm's when it's against the governor.I've turned up rpm's to 2300 on 673's, 711's E6's etc with no ill effects.Wont get you to 65 MPH, but will make a difference. Quote "If You Can't Shift It Smoothly, You Shouldn't Be Driving It" Link to comment https://www.bigmacktrucks.com/topic/1289-b-75-going-too-slow/#findComment-6538 Share on other sites More sharing options...
John Woge Posted July 12, 2006 Share Posted July 12, 2006 Our B-75 with Duplex direct, 22" rubber and 4.62 rear runs 57 MPH at 2100 RPM or 52MPH at 1900 rpm. If you have a 4.5 ratio it should run 53 MPH at 1900 or 59 at 2100 Rpm. John Quote Link to comment https://www.bigmacktrucks.com/topic/1289-b-75-going-too-slow/#findComment-6539 Share on other sites More sharing options...
Firemack Posted July 12, 2006 Share Posted July 12, 2006 Guys,While we are on the topic- you mentioned running up to 2100 on the governor- can you run on the governor and hold it without any damage to the engine? My B75 Gas firetruck has a 464 engine and has top speed of 64, I think at 2800 (no tach on the dash) can you run a gas engine on the governor like a diesel, or is that too much RPM to keep it at max?Thanks,Firemack Quote Link to comment https://www.bigmacktrucks.com/topic/1289-b-75-going-too-slow/#findComment-6547 Share on other sites More sharing options...
Freightrain Posted July 12, 2006 Share Posted July 12, 2006 I've run my ol 673 for 6-7 hrs on the floor!I would assume a gasser would be the same. They set it so that it can't hurt itself. Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment https://www.bigmacktrucks.com/topic/1289-b-75-going-too-slow/#findComment-6548 Share on other sites More sharing options...
HeyCharger Posted July 16, 2006 Share Posted July 16, 2006 So I finally got my B-75 on the road this weekend. ..... and her top speed at 1900-2000 rpms was 48mph. With a tail wind she hit 49mph. And you think you're Going Too Slow.Remember, some of us are flat out at 36mph.Rod. Quote Proud owner of;1961 Mack B61 prime mover.1981 International ACCO 1810C DualCab Fire Truck Link to comment https://www.bigmacktrucks.com/topic/1289-b-75-going-too-slow/#findComment-6610 Share on other sites More sharing options...
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