Transmission 700r4 issues

[shamanie]

In overdrive the cruise control doesn't engage. It may engage from time to time but it cannot maintain speed so it down shifts to 3rd.

My blaze has real issues going 70+ and not downshifting when encountering the slightest grade.....WTF?

The tranny is brand new. Maybe 8000 highway miles.

[britannic]

Is this the 700R4 with a TV cable? If so, make sure it's correctly set, there's only one setting: http://www.tvmadeez.com/article/ (courtesy of BowTie transmissions).

I don't have a cruise control, so I'm not much help, although I did find out that the early systems used a special speedometer as part of the control system and that as they wear, they can cause problems. Is yours computer controlled?

[Dieselboy]

If it comes to replacing your entire cruise system, then you might consider an aftermarker electronic setup.

When I was having difficulty with my cruise control (I removed it :D ), Dr. Lee suggested a full electronic setup similar to the one he had installed. The engagement and disengagement speeds were entirely adjustable, and its total cost was equal to the cost of individual components on the GM system.

Edit: spelling

[ 08-13-2003, 10:14 AM: Message edited by: Dieselboy ]

[shamanie]

Thanks for the responses. Here is some clarification.

As I just did 700 miles from Las Vegas to Boise, I can elaborate a bit. The cruise control seemed to engage ok(strained, a little), the biggest problem came from not being able to hold speed. This was especially problematic up hill.

For instance, I can hold 75 no prob in third(burnin some diesel), but if I am in D, no way.
It cannot sustain that speed up even a slight grade.

Put a new k&n in before I left and that seemed to help her breathe a little. I cannot figure out what is wrong. Is this typical of a truck this age? Is turbo the answer?

Changin oil every 3000.

[britannic]

Can you hold OD when the cruise is disengaged?

[shamanie]

Originally posted by britannic:
Can you hold OD when the cruise is disengaged? Yes, as long as it is not a long grade. Although I will lose some speed.

[DmaxMaverick]

shamanie

Sounds like (possibly among other things) weak vacuum. If the pump is not providing sufficient vacuum, or there is a leak somewhere, it will not hold speed. On the flat, it doesn't require as much input force to throttle it, but when the demand comes up, the vacuum will fall off. If your vacuum pump is in good shape, lood for a cracked or loose fitting vacuum line. The HVAC could also be at fault, as it shares the vacuum supply. If it leaks, it will steal the vacuum from the rest of the system.

Good luck.

[mhagie]

You omited the year of the truck but as you have a 700R4 its safe to say you have an 80's style truck.
One issue not to overlook here is a basic lack of power from engine also the earlier 700's had a tendancy to downshift at the slightest hint of a grade.
A good look at engine timing might be in order here as the t/chain could be worn retarding timing.

[Cabasa]

I had the same problem in my 84 Suburban. When the 700R was rebuilt the guy added a heavier springed valved and it helped some. If I am on the flats and hit an overpass it will kick down. Very frustrating

[britannic]

From reading the original post I see two issues:

1. The cruise control intermittently engages

2. The engine isn't making enough power to pull OD on slight grades and so the accelerator is pushed down to the point that the transmission downshifts into 3rd.

I don't have any experience with the cruise control as I don't have one, so I'll tackle #2:

What diff ratio and tire sizes are you running, do you know the rpms at 70mph in OD and what power upgrades does the engine have if any?

[Cabasa]

Britannic,
You have a good point about the engine not making the power to where it has to kick down into Drive. I have purposely lightly held my foot on the pedal with cruise control on before hitting a hill to see what happens and yes you can feel the cruise control push the pedal down causing it to kick into drive. I feel that with a turbo the cruise control will not have to dig so deep in order to maintain speed on hills. Lack of power is my problem.

[britannic]

A turbo will help a lot, but first what diff ratio and tires do you have?

[shamanie]

The differential ratio is unknown to me at this time. Could you tell me how to find out what my blaze is running.

For reference purposes she is an '83 blazer 4wd. that my grand father gave to my fasmily. He had the tranny replaced not long ago(10,000 miles). I am fairly certain that the 700r4 replaced the th400 that was in there. I am just not sure how it's geared.

What is the best way to find out? Are there tell tale signs some where on the vehicle's tranny?

I'm sorry. I wish I was better at this stuff. I'm not affraid to get my hands dirty, just affraid to break something.

The tires are OEM. If not, they are not any bigger than stock. They look small. I will get exact specs. momentarily. It is in Idaho right now and I am in vegas.

However, I do not plan on running them much longer as I just found some Goodyear Wrangler MT/r's that I would like to throw on. I was thinking 33" tires. I would imagine it would need some suspension work to accomodate that size and am open to sugestions. The shocks need replacing.

I found a website called 4wheelparts.com has anyone had any experience with them.
http://www.4wheelparts.com/product2.asp?imseqn=468&occlass=PRO&cat=SUS


I realize that this is getting painfully off topic, however, I think I know where you might be headed with the gearing angle. How the vehicle is geared would dictate shift points right? So perhaps my gearing is not optimum?

[mhagie]

shamanie, The usual method for finding ratio is to jack up rear of vehicle rotate driveshaft keeping track of how many revolutions it takes shaft to complete 1 revolotion of rear tire.
I can tell you that you have about a 75% chance that you have a 3:08 ratio,most Blazers were geared for mileage rather than power.
With that ratio and a engine that is questionable on power you will REALLY have power issues with 33" tires. :(

[shamanie]

Originally posted by mhagie:
shamanie, The usual method for finding ratio is to jack up rear of vehicle rotate driveshaft keeping track of how many revolutions it takes shaft to complete 1 revolotion of rear tire.
I can tell you that you have about a 75% chance that you have a 3:08 ratio,most Blazers were geared for mileage rather than power.
With that ratio and a engine that is questionable on power you will REALLY have power issues with 33" tires. :( Mhagie,
I was totally trying to figure out how a larger tire would affect power but had trouble visualizing in my head. So does it not take as much output from the engine to turn a smaller diameter tire than a larger one?

I would imagine that the 3:08 gears are tall. I could take advantage of this though when the turbo goes on because I will have consistent power throughout a taller gear. I wouldn't want to have first end prematurely when there is still power pumping right?

[britannic]

Originally posted by shamanie:
I was totally trying to figure out how a larger tire would affect power but had trouble visualizing in my head. So does it not take as much output from the engine to turn a smaller diameter tire than a larger one?
Think of it this way:

If you had a choice of peddling a fixed gear bicycle with 1' dia. wheels and one with a 20' dia. wheel (ignore for a moment the practicalities ), which would you prefer?

The larger the diameter, the more circumference and therefore distance to be traveled before the wheel completes one revolution, therefore since horsepower is an arbitrary measure of how far a weight can be moved over time, it would take more power to move the larger wheel because it moves further per engine revolution.

[ 09-13-2003, 03:02 PM: Message edited by: britannic ]

[shamanie]

Originally posted by britannic:
</font><blockquote>quote:</font><hr />Originally posted by shamanie:
I was totally trying to figure out how a larger tire would affect power but had trouble visualizing in my head. So does it not take as much output from the engine to turn a smaller diameter tire than a larger one?
Think of it this way:

If you had a choice of peddling a fixed gear bicycle which 1' dia. wheels and one with a 20' dia. wheel (ignore for a moment the practicalities ), which would you prefer?

The larger the diameter, the more circumference and therefore distance to be traveled before the wheel completes one revolution, therefore since horsepower is an arbitrary measure of how far a weight can be moved over time, it would take more power to move the larger wheel because it moves further per engine revolution. </font>[/QUOTE]Just wondering if you guys just saw the light go on in my head?

Thanks....I'll get more info and get back to ya.

[britannic]

The 700R4's Drive gear ratio is 1:1 and OverDrive is .70, so once you have the diff figured out would multiply that by .70 to get the final actual drive ratio to the wheels.

So for example, I have 4.56 diffs, which when multiplied by my .70 OD ratio, gives me 3.192 turns of the driveshaft to rotate my rear wheels 1 revolution.

Use this formula to find the engine rpm for a given diff ratio and speed:

rpm=((mph x (diff ratio x final drive ratio)) x 336) / tyre diameter

Here's a great website with gear/speedo/tire etc. calculators to save you some time: www.4lo.com (http://www.4lo.com)

[Dieselboy]

Good call on 4lo.com, I've visited there many a time trying to figure out the "perfect gear ratio."

[Charlie Whitley]

When I first bought my 87 6.2 4x4 truck it had 3 different size tires on it 1 was a 31 inch and another was stock and 2 were 32s then I mounted 33s on it and never saw much of a change in the power and those were with the stock rally wheels on them then I bought a set of 15 x 10 chrome mods and that widen the tires out and shortened the hieght but never could tell any change in loss or gain of power. so going from stock to 33s shouldnt affect much that you really notice I now have 39 x 18 x 15 Mickey Thomsons on 15 x 14 Alcola wheels. Now that was a big drop in power but I added the Banks side winder kit so that helps alot. I have a higher than normal exhaust temp but had it before I put the lift and tires on. As far as the lift for your blazer you can go with 2 or 3 inch adaleafs thier easy to install and cheap and you can get shocks that go from stock to 3 inch and not be out a whole lot of money and have it all done in about a day 6 to 8 hrs tops. I also agree about checking your vacum line first I was having a simalar problem with mine and it was a cracked line simple fix had enough hose I cut it back and fixed the problem. then ifthat isnt it start checking other stuff that would possibly cuase it.

[Charlie Whitley]

The 4x4 company you listed is pretty good just make sure you let them know your blaser is a diesel or you could get the wrong parts like I did. if you send mee your e-mail I will send you some pictures of my truck I bought the intire lift through them.

[underpooch]

Maybe they installed a gas torque converter with that new tranny. It won't lock up at the lower
engine speed and when you hit the grade and lose
road speed it drops a gear ???