after putting my a518 trans up to the 94 ctd i'm noticing that the rpms seem really high compared to when it was in my first gen. on the highway i'm running about 2400-2500 at 70 mph. after a little math work it seems really high. i know that its going into od, i've got that on a rocker switch. i've got 3.54 gears and 35 in tires. in my old first gen i had 3.07 and stock tires. i know its not going to be the same but i figure it should be closer than what it is now.the trans was rebuilt about 20,000 miles ago and it has a hughes converter. any help is greatly appriciated!

 

Are you sure your actually turning 70? My truck with 4.10's and 35's makes the speedometer off by 10mph. Just a thought

 

X2, try driving with a gps and see how it reads then...Mark

 

speed was checked with my gps. speedo in the truck isnt even connected.

 

does anyone have any ideas of have had a similar problem? i know its a little different set up with the 94 ctd. just looking for a direction to look or a test i haven't heard of before. anything would be extremely helpful!

 

Are you sure you are having a problem at all?

Road speed and engine speed will vary depending on load. For instance my bone stock 93 runs about 1800 rpm at light load and 60 mph. When pulling a heavy trailer and accelerating or climbing a grade, 2400-2500 rpm is common.

It isn't all slippage. When you put torque on a torque converter, the internal structure applies more than engine torque to the output shaft. It's like gearing down under load.

So just knowing your road speed and engine speed without knowing the loads (wind, tires, weight and grade, etc) doesn't allow a pat answer to your question.

A better indicator is transmission temp. It is possible for torque converter failure to cause a lot of slippage. In that case, the transmission would heat up more than normal.

I have learned to not mind mushy noises from under the hood as long as the speed meter is winding up at a good rate.

 

trans temp is the one gauge i do not own yet. i still need to hook up my pyro also. all the wires are ran just need to drill the manifold. ive got no idea what the wind speed was nor do i know exactly what grade i was on. but around chicago there isnt much issue with grade on the highway. i was running unloaded except the added weight of my flatbed which i'm not sure the difference in weight compared to a regular bed. [IMG][/IMG] so with the unknown variables i guess i'll have to wait to find out what my problem is...

 

hey-Hey!!!,
Simultaneously going from 3.07 to 3.54 and 35 from 31" tires looks like +2% faster engine speed to me( assuming the 235/85-16's are 31" tall ). That assumes you've actually engaged the .69:1 OD. Your rpm looks more like what I'd expect from a 3.07'd 727 truck to be doing.
cheers,
Douglas

 

i'm positive that od is engaging. i can see the rpms drop when shifted and feel the change. the overdrive is set up on a rocker switch also. no computer failure possible. this is why i'm lost on what the problem is.

 

Is it possible you're in second - overdrive?

Can't see that thing running much over 2100 at 70 on the flat.

 

unless i'm mistaken even if i was in second then flipped the switch for od i'd still shift to od? but i do feel it shift from first to second to third, flip switch to od.

 

I would note all the rpms that you have after each shift and if you see the correct progression, then a drop when it goes into OD, it would seem to be working. Then your left with different gears or a problem in the torque converter, my opinion of course...Mark